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Is daar enige bewyse dat spermparameters verband hou met fiksheid van die nageslag wat deur daardie sperm geproduseer word?

Is daar enige bewyse dat spermparameters verband hou met fiksheid van die nageslag wat deur daardie sperm geproduseer word?



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In die meeste (indien nie alle) seksueel voortplantende spesies word die hoeveelheid nageslag wat 'n mannetjie kan produseer, nie beperk deur die hoeveelheid sperm wat hy kan produseer nie, maar deur die hoeveelheid eiers wat sy sperm kan bevrug (met seldsame individuele uitsonderings).

Daarom is die optimale strategie om eiers met die beste sperm te bevrug.

Daarom is dit redelik om te aanvaar dat daar aanpassings sal wees wat sperm met gebrekkige gene minder geneig sal maak om 'n eiersel te bevrug.

Maar is daar enige bewyse dat dit gebeur? Bv. sal bevrugting van eiers met minder beweeglike sperm (moontlik met IVF) 'n minder geneties fikse nageslag produseer of 'n miskraam tot gevolg hê?


Die enigste manier waarop natuurlike seleksie op gene kan inwerk, is wanneer hulle uitgedruk word, daar is geen meganisme om die "kwaliteit" van 'n geen in 'n sperm te lees en te assesseer nie. Natuurlik sal die gene wat die kwaliteit van die sperm beïnvloed, vir/teen geselekteer word.


Die sperm van verouderde manlike trafs vertraag hul nageslag se ontwikkeling

Om te verstaan ​​of die sperm van ouer mans 'n verminderde vermoë het om suksesvolle nageslag te produseer, is 'n sleuteluitdaging in evolusionêre biologie. Ons ondersoek hierdie kwessie deur gebruik te maak van 10 jaar se voortplantingsdata oor langlewende houbara-bustards (Chlamydotis undulata), waar die gebruik van kunsmatige inseminasietegnieke beteken dat ouers slegs die kwaliteit van die nageslag via hul gamete kan beïnvloed. Hier wys ons dat vaderlike veroudering beide die waarskynlikheid dat eiers uitbroei en die tempo waarteen kuikens groei verminder, met ouer mannetjies wat die ligste nageslag na die eerste maand produseer. Verbasend genoeg is hierdie koste van vaderlike veroudering op nageslagontwikkeling van 'n soortgelyke skaal as dié wat met moederveroudering geassosieer word. In ooreenstemming met voorspellings oor kiemlynveroudering, produseer die sperm van onvolwasse mannetjies die vinnigste groeiende nageslag. Ons bevindinge dui dus daarop dat enige goeie gene-voordeel wat deur ouer �wese' mannetjies gebied kan word, geërodeer sal word deur veroudering van hul kiemlyn-DNS.

Veroudering is die agteruitgang in fisiese toestand wat by verouderende diere voorkom1. In die natuur word veroudering toenemend erken as 'n wydverspreide beperking op lewenslange voortplantingsuitset2, wat verskeie fiksheidseienskappe afbreek en potensieel komplekse patrone van evolusionêre konflik tussen die geslagte genereer3,4,5. By manlike gewerwelde diere is gevind dat eienskappe wat met reproduktiewe mededingendheid geassosieer word, afneem by bejaarde mans (byvoorbeeld, sporingsaktiwiteit6, sosiale oorheersing7, seksuele seinering8), met die verwagting dat dit tot laer reproduktiewe uitset sal lei deur mededingende uitsluiting of vroulike paringsvooroordele. Veel minder oorweeg word die moontlike invloed wat manlike veroudering op hul sukses na inseminasie kan hê deur afname in die lewensvatbaarheid van hul gamete, en veral, die intrinsieke kwaliteit van nageslag wat hul gamete kan produseer.

Gamete van verouderde mans kan verouderende afname in kwaliteit ondergaan deur twee hoofmeganismes. Eerstens kan daar 'n progressiewe agteruitgang in die werkverrigting van mans se spermatogeniese masjinerie wees soos hulle ouer word, wat geassosieer word met afname in die vlakke van voortplantingshormone, en lei tot sperm wat minder in staat is om hul genetiese lading aan vroulike eierstokke te lewer9. Miskien belangriker egter, daar word ook verwag dat daar 'n toenemende waarskynlikheid van mutasie binne 'n man se kiemlyn oor tyd is, wat geassosieer word met die aantal stamseldelings tydens spermatogenese, en wat lei tot 'n degradasie van die DNS wat binne hul gamete gedra word10 ,11. Bewyse begin na vore kom uit longitudinale studies dat spermfunksie by verouderende gewerwelde mans kan afneem12, alhoewel die mate waarin verouderde afname in die funksionele prestasie of genetiese integriteit van gamete die algehele lewensvatbaarheid en kwaliteit van nageslag kan beïnvloed, is nie bekend nie.

Hier ondersoek ons ​​die sukses na inseminasie van langlewende manlike houbara-bustards (Chlamydotis undulata) wat deel was van 'n grootskaalse bewaringsprogram in Oos-Marokko. Dit is belangrik dat die doel van hierdie studie is dat die bewaringsprogram kunsmatige inseminasie en inkubasie gebruik, gevolg deur die hand grootmaak van uitgebroeide kuikens. Dus, krities, ouerlike invloed word slegs deur hul gamete bewerkstellig, met wyfies wat nie in staat is om voornemende vaars te kies of hul sorgtoekenning te verander op grond van verskillende assesserings van inseminerende mannetjies of die kwaliteit van nageslag wat geproduseer word nie5,13. Tien jaar se longitudinale rekords is versamel oor reproduktiewe parameters van ϡ 000 verskillende mans en wyfies wat wissel van 1 tot 23 jaar oud. Hierdie bewaringsprogram bied dus 'n unieke geleentheid vir grootskaalse longitudinale ontledings oor die reproduktiewe gevolge van gametiese veroudering in 'n wilde langlewende gewerwelde dier. In totaal is die lewensvatbaarheid van 58 977 eiers en ontwikkelingsdata van 31 404 kuikens gebruik in gemengde model-ontledings wat daarop gemik was om die invloed van manlike gametiese veroudering op beide die lewensvatbaarheid en kwaliteit van hul nageslag te toets. Enige bewyse van verminderde lewensvatbaarheid en/of kwaliteit van die nageslag wat deur ouer mans geproduseer word, sal 'n aanduiding wees van verouderende afname in die voortplantingsprestasie van hul gamete, maar die voorspellings vir die aard van die verhouding tydens adolessensie sal verskil afhangende van die dominante meganisme van spermveroudering, dit wil sê of dit te wyte is aan veroudering van die spermatogeniese masjinerie of van kiemlynintegriteit. 'n Vorige studie oor hierdie spesie het bevind dat maatstawwe van ejakulasiekwaliteit (die aantal, beweeglikheid en % afwykende morfologie van sperm) deur rypwording tot 4 jaar oud toeneem voordat dit senesente afname ondergaan12, dus verwag ons dat patrone van eierlewensvatbaarheid (soos bepaal deur uitbroeitempo) sal hierdie verwantskap weerspieël as veroudering van manlike spermatogeniese masjinerie𠅎n gevolglik die funksionele prestasie van hul sperm— hulle vermoë om lewensvatbare nageslag te produseer verhinder. As mutasie-gebaseerde veroudering van gametiese DNA egter die dominante meganisme van senesente afname is, sou ons eerder vermindering in beide nageslaglewensvatbaarheid en daaropvolgende ontwikkeling vanaf die aanvang van spermatogenese voorspel, aangesien dit die punt is waarop skadelike mutasies kan begin ophoop in die kiemlyn. Daar sal dus verwag word dat die sperm van jong mannetjies meer lewensvatbare sigote en die hoogste gehalte nageslag sal produseer. Benewens hierdie voorspelde verwantskappe, toets en kontroleer ons statisties vir 'n verwagte en moontlik verwarrende invloed van vroulike veroudering op die kwaliteit van eiers en nageslag14, terwyl ons ook beheer vir veranderinge wat voortspruit uit jaarlikse, seisoenale, lêorde-effekte en individuele lewensvatbaarheid15. Ons resultate toon dat vaderlike veroudering beide die lewensvatbaarheid van eiers en die groeitempo van nageslag beïnvloed, wat uiteindelik ligter kuikens op 30 dae ouderdom tot gevolg het. Hierdie bevindinge stem ooreen met die mutasie-gebaseerde veroudering van manlike kiemlyn-DNA, en dui daarop dat enige voordeel wat wyfies kan kry deur met ouer �wese mans te paring, verreken moet word teen die koste van die gebruik van die verouderende DNA wat hul sperm dra.


Resumé

De plus en plus de données tendent à montrer que l'obésité paternelle a non seulement des effets néfastes sur la santé métabolique et reproductive de l'individu mais également sur celle de sa afstamming. Les mécanismes mis en jeu dans ce processus incluraient des altérations physiologiques en hormonales des fonctions reproductives de l'homme obèse ainsi que des altérations épigénétiques au niveau du génome spermatique. Les modifications hormonales associées à l'obésité et qui se caractérisent principalement par une réduction du taux d'androgènes et une augmentation du niveau d'estrogène induiraient une altération des paramètres spermatiques, une vermindering van die konsentrasie en die la numeration totale volume seminaal. Le stress oxydatif dans le testicule induirait une augmentation de la fragmentation de l'ADN spermatique et pourrait rendre compte de l'augmentation des risques de fausses-couches, des problèmes de développement embryonaire ainsi que de l'augmentation de mortalscendance , problèmes fréquemment rencontrés lorsque le père est. obèse. Les modifications épigénétiques (altérations des profils de méthylation de l'ADN, de la structure de la chromatine ou/et des profils d'expression des ARN spermatiques) induites par l'obésité sont, quant à elles, loin d'être omvat, même si elles sont, surement, les vecteurs clés de la transmissie épigénétique paternelle des maladies métaboliques. L'objet de cette revue est. de résumer puis de discuter les différentes études expérimentales et épidémiologiques publiés à ce jour sur les conséquences physiologiques et moléculaire de l'obésité paternelle sur la santé de l'individu de sacendance de sacendance.


Spermkompetisiespeletjies wanneer mans in vadersorg belê

Spermkompetisiespeletjies ondersoek hoe mans beperkte hulpbronne tussen voor- en nakopulatoriese kompetisie verdeel. Alhoewel uitgebreide navorsing ondersoek het hoe verskeie aspekte van paringstelsels hierdie toekenning beïnvloed, is die manlike toekenning tussen paring, bevrugting en ouerpoging nie voorheen oorweeg nie. Tog kan vaderlike sorg energiek duur wees en mans word oor die algemeen voorspel om hul ouerlike poging aan te pas in reaksie op verwagte vaderskap. Hier inkorporeer ons ouerpoging in spermkompetisiespeletjies, veral om te ondersoek hoe die verhouding tussen vaderlike sorg en nageslagoorlewing spermkompetisie en die verhouding tussen vaderskap en vaderlike sorg beïnvloed. Ons resultate ondersteun bestaande verwagtinge dat (i) bevrugtingspoging moet toeneem met vroulike promiskuïteit en (ii) vaderlike sorg moet toeneem met verwagte vaderskap. Ons ontledings toon egter ook dat die koste van manlike sorg die krag van hierdie patrone kan aandryf. Wanneer vaderlike gedrag energiek duur is, beperk verhoogde toewysing aan ouerlike inspanning toewysing aan bevrugtingspoging. Namate vaderlike sorg minder duur word, verswak die verband tussen vaderskap en vadersorg en kan dit selfs afwesig wees. Deur eksplisiet variasie in spermkompetisie en die koste van manlike sorg te oorweeg, bied ons model 'n integrerende raamwerk vir die voorspelling van die interaksie tussen vaderlike sorg en vaderskappatrone.

1. Inleiding

Oor die afgelope dekades het evolusionêre biologie 'n ontploffing van studies van spermkompetisie in verskeie taksonomiese groepe gesien, wat ons begrip verbeter het van hoe verskeie ekologiese en evolusionêre toestande manlike voortplantingstrategieë beïnvloed [1-3]. In teenstelling met wat tradisioneel aanvaar is, kan ejakulaatproduksie energiek veeleisend wees, wat hoë energiekoste op mans plaas [4-6]. Daarom sal mans waarskynlik 'n afweging ervaar tussen belegging in eienskappe wat ejakulasieproduksie verhoog en eienskappe wat hul paringsukses verhoog [7-10]. Evolusionêre modelle, veral spermkompetisiespeletjies, verteenwoordig 'n kragtige benadering om te voorspel hoe sulke afwykings die evolusie van manlike voortplantingstoewysingstrategieë onder spermkompetisie beïnvloed (gedefinieer as sperm van mededingende mans wat meeding om dieselfde koppel eierselle te bevrug [1, 2]). Sedert spermkompetisie-speletjies vir die eerste keer bekendgestel is [11], is verskeie uitbreidings in die veld geformuleer, wat byvoorbeeld die bykomende effekte van manlike alternatiewe voortplantingstaktieke [12], spermverplasing deur nuweling-ejakulate [13] en verskillende vorme van pre-kopulatoriese manlike kompetisie [14]. Hierdie modelle neem aan dat mans hul beperkte energiereserwes uitsluitlik tussen voor- en nakopulatoriese kompetisie verdeel. Spermkompetisiespeletjies het dus grootliks geïgnoreer hoe vaderlike sorg sal beïnvloed en beïnvloed word deur manlike ejakulasietoewysing.

Vaderlike sorg word in 'n groot verskeidenheid vorme in die natuur uitgedruk. Mannetjies kan eiers dra, die kleintjies voorsien, neste bou en verdedig, of net rondom bly [15–22]. Sulke gedrag verhoog die oorlewing van nageslag aansienlik as gevolg van hul rolle in beskerming teen natuurlike vyande en die verskaffing van hulpbronne wat nodig is vir behoorlike nageslagontwikkeling en groei [20-23]. Ouersorg kan ook 'n hoë fiksheidskoste op volwassenes oplê, in terme van verhoogde sterfterisiko's en energieke uitgawes en verminderde vrugbaarheid [20-22,24,25]. Die mate waartoe nageslagprestasie verbeter word deur addisionele vaderlike inspanning en die gevolglike koste wat aan mans opgelê word, sal waarskynlik tussen spesies verskil as gevolg van historiese en fisiologiese prosesse, en oor ekologiese toestande heen. Trouens, mans van verskeie spesies is bekend om die intensiteit van hul ouerlike gedrag te verander in reaksie op byvoorbeeld variasie in suurstof beskikbaarheid [26,27], voedsel beskikbaarheid [28,29], volwasse predasie risiko [30,31] en eierpredasierisiko [29,32]. Daarom beïnvloed variasie in die vlak van vaderlike inspanning wat nodig is vir voldoende nageslagoorlewing en instandhouding die gepaardgaande koste wat aan mans opgelê word, en sal gevolglik waarskynlik die afweging tussen manlike toekenning aan ander komponente van fiksheid versterk of verswak.

Daar word voorspel dat vaderlike pogings nie net afhang van die behoeftes van die nageslag nie, maar ook sal reageer op variasie in verwagte vaderskap, met mannetjies wat sorg verminder wanneer hulle minder geneig is om aan die kroos verwant te wees (bv. [33–36], maar sien [37,38] ). Binne spesies word gedragsaanpassings in vaderlike pogings verwag wanneer cuckoldry algemeen voorkom, vaderskap wissel tussen voortplantingsgebeure en die koste van vaderlike sorg hoog is [23,37]. Die positiewe assosiasie tussen vaderskap en vaderlike sorg onder spesies spruit egter nie uit sulke fyn aanpassings nie, maar eerder as die gevolg van manlike lewensgeskiedenis-afwegings wat spesie-spesifieke vlakke van vaderlike poging oor evolusionêre tyd beïnvloed. Alhoewel empiriese bewyse 'n mate van ondersteuning toon vir 'n positiewe verband tussen vaderskap en vaderlike poging, beide binne [23,35] en tussen spesies [17,39-42], bly uitgebreide onverklaarbare variasie [15,23,43-46].

Soos wyd erken, is vaderskap egter nie 'n statiese eienskap nie, maar is dit eerder die uitkoms van sosiale interaksies binne en tussen die geslagte [35,37,47]. Dit is dus noodsaaklik om eksplisiet te oorweeg hoe hierdie interaksies gelyktydig patrone van paring, bevrugting en ouerlike sorg beïnvloed, en dus die verhouding tussen vaderskap en vaderlike poging dryf [35,47]. In hierdie konteks bied spermkompetisiespeletjies 'n kragtige raamwerk waarbinne intra- en interseksuele interaksies verken kan word, aangesien dit die vlak van spermkompetisie bepaal, wat op sy beurt kies op manlike differensiële toekenning om ejakulasies ten koste van ander komponente van fiksheid [1,2]. Hier vra ons of gelyktydige toewysing tussen paring, bevrugting en ouerpoging in die teenwoordigheid van variasie in die koste van manlike sorg kan bydra tot ons begrip van sommige van die onverklaarbare variasie wat waargeneem word in die verband tussen vaderlike sorg en vaderskap.

In hierdie vraestel brei ons spermkompetisiespeletjies uit deur manlike toekenning te modelleer tussen eienskappe wat paringsukses, ejakulasieproduksie en ouerlike sorg beïnvloed. Deur voort te bou op bestaande teorie [1,2], oorweeg ons hoe die effek van manlike toewysing aan ouerpoging op nageslagoorlewing voorspel word om die verhouding tussen paringstempo, bevrugtingsukses en vaderlike sorg te beïnvloed. In die besonder ondersoek ons ​​die variasie tussen spesies in die koste van manlike sorg, van scenario's waar ouergedrag energiek goedkoop is (dws lae toewysing aan ouerlike inspanning lei tot relatief hoë nageslagoorlewing) tot situasies waar sorg baie duur is (dws ekwivalente nageslagoorlewing) vereis hoë manlike toewysing om te sorg sien elektroniese aanvullende materiaal, S1). Die hoofdoelwitte van hierdie studie is om te evalueer hoe variasie tussen spesies in vroulike losbandigheid en die koste van manlike sorg beïnvloed (i) manlike toekenning tussen die verkryging van parings, die vervaardiging van ejakulate en die verskaffing van ouerlike sorg en (ii) die verband tussen vaderlike sorg en vaderskap wat ontstaan ​​as die resultaat van manlike toewysing tussen hierdie drie verskillende komponente van fiksheid. Ons bevindinge toon dat die koste van vaderlike sorg kan aandryf hoe mans reageer op spermkompetisie en of 'n waarneembare empiriese assosiasie tussen vaderskap en vaderlike sorg voorspel word.

2. Modelbeskrywing

Om vaderlike sorg in spermkompetisiespeletjies in te sluit en direkte vergelykings tussen ons model en vroeëre teorie te tref, neem ons 'n paar sleutelaannames aan wat deur vorige modelle gemaak is. Ons neem byvoorbeeld aan dat individue voortplant in 'n groot populasie (met 1 : 1 geslagsverhouding en weglaatbare kanse op dubbelparing tussen enige twee individue), waar wyfies hul eie paringstempo bepaal en, gevolglik, die intensiteit van spermkompetisie (sien resensies) in [1,2]). Boonop het mans dieselfde totale energiebegroting beskikbaar vir voortplanting wat tussen verdeel word n voortplantingsgebeure, soos 'n mannetjie toeken C eenhede om elke paring te verkry en s eenhede na die een ejakulasie oorgedra tydens elke inseminasie gebeurtenis. 'n Sleutelverskil in ons model is dat mannetjies ook moet allokeer P eenhede van hul totale energiebegroting vir vaderlike sorg vir een koppelaar wat deur enige spesifieke wyfie gedurende die broeiseisoen geproduseer word (sien tabel 1 vir die volledige lys van veranderlikes). Die algemene voortplantingsdinamiek wat deur hierdie modelleringstruktuur voorgestel word, is dat mannetjies en wyfies gedurende die broeiseisoen kan vermeerder, maar dat wyfies 'n enkele kloutjie eiers met een mannetjie na hierdie periode van paring lê (bevrug deur die sperm van hulle f maats) en dat mannetjies net vir een koppie eiers per reproduktiewe aanval omgee. Alhoewel dit nie alle spesies vang nie, stem hierdie paringspatroon ooreen met spesies met vaderlike sorg (i) waarin mannetjies en wyfies sosiale monogamie toon, maar kan vermenigvuldig (soos algemeen by baie voëls [17] en soogdiere [18]), (ii) waarin wyfies met veelvuldige mannetjies paar, maar hul koppelaar in die nes of gebied van hul finale maat lê (soos waargeneem by sommige geleedpotiges [23]) of (iii) waarin bevrugting ekstern is en veelvuldige mannetjies hul gamete gelyktydig vrystel oor een koppie eiers (soos algemeen by baie visse [15,48] en amfibieë [22]).

Tabel 1. Definisie van parameters en veranderlikes wat in die model gebruik word.

’n Mannetjie wat meer aan ouerlike sorg toeken, verhoog die oorlewing van sy nageslag ten koste van die vermindering van sy paringsgeleenthede en/of sy spermmededingendheid. In hierdie sin, terwyl C verteenwoordig die energieke koste van die verkryging van elke paringsgebeurtenis (wat betrokke is, byvoorbeeld by maatsoektog, gebiedsverdediging of man-man-kompetisie) wat ewe veel deur alle mans binne 'n populasie ervaar word, manlike toekenningstrategieë verskil in hul uitgawes in s en P, en, gevolglik, hul paringstempo n. Deur die totale energiebegroting na 1 (na [1]) te skaal, kan die parameters wat manlike toekenningstrategieë verteenwoordig, geredelik geïnterpreteer word as relatiewe toekenning aan verskillende komponente van fiksheid, soos

Behalwe om die bykomende toewysing aan ouerlike pogings in te sluit, moet ons ook die bydrae van vaderlike sorg tot mans se fiksheid in ons model uitdruklik vasstel. Na aanleiding van vorige modelle van ouerbelegging [33,36,49-51], modelleer ons die verhouding tussen ouerlike poging en nageslagoorlewing as 'n nie-lineêre funksie met dalende opbrengste. Hier neem ons aan dat nageslagoorlewing afhang van manlike toewysing aan sorg, sodat die waarskynlikheid van nageslagoorlewing 1 benader as P verhogings. Nageslagoorlewing word egter ook bepaal deur biotiese en abiotiese toestande wat nageslagontwikkeling en -groei beïnvloed, soos suurstof- en temperatuurvlakke, voedselbeskikbaarheid, predasierisiko en moedersorg. Alhoewel dit nuttig kan wees om die presiese bron van hoe nageslag se oorlewing verander met ouerlike inspanning te onderskei, vir die doel van ons model, verteenwoordig ons dit saam as die koste van manlike sorg. Daarom modelleer ons nageslagoorlewing volgens die eksponensiële funksie:

In ons model is die fiksheid van enige mannetjie direk eweredig aan die aantal nageslag wat geproduseer word wat die versorgingstydperk oorleef. Soos vroeër in meer besonderhede beskryf, vang ons model die situasie vas waar mannetjies en wyfies paar gedurende die broeiseisoen vermeerder en elke mannetjie voorsien ouerlike sorg aan een potensieel gemengde vaderskap-broedsel wat deur sy sosiale of finale maat gelê word. Daarom hang 'n mutante mannetjie se fiksheid af van (i) sy paringstempo, (ii) sy bevrugtingsukses na elke paring (d.w.s. eweredig aan die hoeveelheid van sy ejakulasie relatief tot die hoeveelheid wat deur die ander vrygestel word) f − 1 mannetjie wat met die fokuswyfie kopuleer—na 'n 'regverdige tombola' sensu [11]), (iii) die oorlewing van sy genetiese nageslag teenwoordig in die enkele koppelaar wat onder sy sorg gelaat is, wat afhang van sy eie toewysing P om te sorg (d.w.s. binne-paar) en (iv) die oorlewing van sy genetiese nageslag teenwoordig in die kloue wat deur die ander wyfies geproduseer word en by ander mannetjies gelaat word, wat afhang van hul toewysing aan sorg (m.a.w. ekstra-paar). Vir eenvoud neem ons nie variasie in die aantal eiers per koppelaar onder wyfies of wyfies se voortplantingsgebeure in nie. Dan, die verwagte fiksheid van 'n mutante mannetjie wat die toekenningstrategieë aanneem s en P, in 'n populasie van mans met die gemiddelde toekenning strategieë en , word gegee deur

3. Analitiese oplossing

Deur standaardmetodes [52] te gebruik, kan ons die analitiese oplossing vir die evolusionêr stabiele toekenning (ESA) strategieë in vier stappe vind. Eerstens verkry ons die volgende ESA om te ejakuleer deur op te los by en:

Dan, stel en oplos by , verkry ons die ESA tot vaderlike sorg as

Die volgende stap is om nie net te verseker dat die model intern konsekwent is nie (wat sy wiskundige en logiese eienskappe betref), maar ook dat dit biologies konsekwent is [37,53]. Die model moet veral die 'Visser-toestand' respekteer: in 'n diploïede spesie met seksuele voortplanting moet elke nageslag noodwendig die gevolg wees van die bevrugting van een vroulike gameet deur een manlike gameet en elke paringsgebeurtenis moet plaasvind tussen 'n manlike en 'n vroulik [37,53]. Om dus selfkonsekwentheid in 'n reproduserende populasie met 1 : 1 geslagsverhouding te verseker, moet vroulike en manlike paringtempo's dieselfde wees by ewewig. Wanneer wyfies hul eie paringstempo bepaal, is die parameter wat sulke selfkonsekwentheid verseker die koste C van mannetjies wat elke paring verkry. Om die 'Fisher-voorwaarde' te bevredig, los ons die gelykheid op f = n* vir C. Alhoewel die koste C kan onafhanklik van die vroulike paringstempo en die koste van manlike sorg behandel word (parameters α en B), moet dit 'n funksie van al hierdie drie parameters wees sodat:

Die vierde stap kontroleer of die ewewigsoplossings (d.i. en ) fiksheidsmaksima verteenwoordig. Hierdie voorwaarde word bevredig vir funksies met veelvuldige veranderlikes as die Hessiese matriks geen positiewe eiewaardes het nie [52]. In ons model, vergelykings (3.1ac) verteenwoordig fiksheidsmaksima wanneer f > 2, B ≥ 0 en α ≥ 10 (sien elektroniese aanvullende materiaal, S3). Ons verken die parametriese ruimte afgebaken deur 2 ≤ f ≤ 15 (waar wyfies paar vermeerder, wat 'n 'intensiteit' spermkompetisie-speletjie verteenwoordig [1,2]), 0 ≤ B ≤ 0,8 (wat scenario's insluit waar die gebrek aan manlike sorg die hele koppelaar tot die dood veroordeel tot scenario's waar slegs 'n klein subset van die nageslag nie oorleef nie, sien elektroniese aanvullende materiaal, S1) en 10 ≤ α ≤ 80, en daarom is ons interpretasie beperk tot hierdie parameterruimte. Die voorspelde ESA tot paring, bevrugting en ouerpoging word gegee deur

Laastens, omdat daar voorspel word dat manlike ESA-strategieë by ewewig oor tyd tot fiksasie in die populasie gaan, word die vaderskap wat deur elke man in hul kloue behaal word (d.w.s. binne-paar vaderskap) gegee deur 1/f = 1/n*.

4. Teoretiese voorspellings

(a) Geval 1: oorlewing van die nageslag hang geheel en al af van vaderlike sorg

Ons kyk eers na die geval waar nageslag nie sonder vaderlike sorg kan oorleef nie (d.w.s. verpligte manlike sorg - die basislyn-nageslagoorlewing B gelyk aan 0). Dit kan voorkom in spesies wat strawwe ekologiese toestande ervaar vir nageslagprestasie (oorlewing en/of ontwikkeling) en/of waar moedersorg afwesig is (d.w.s. vaderlike toekenning P > 0 is nodig vir nageslagoorlewing vir verdere besonderhede sien elektroniese aanvullende materiaal, S1). In hierdie scenario bevoordeel toenemende vroulike losbandigheid manlike strategieë wat die toewysing van energie aan bevrugtingspogings verhoog, en as gevolg daarvan word minder energie oorgelaat vir toewysing aan paring en ouerpoging (figuur 1)a–c). Hierdie voorspelde patroon word egter beïnvloed deur die omvang van die moeilikheid om sorg te verskaf. Wanneer ekologiese en fisiologiese toestande nie 'n hoë energiekoste van vaderlike sorg oplê nie (d.w.s. hoog α-waardes), is lae toewysing aan ouerpoging voldoende om hoë nageslagoorlewing te verseker (sien elektroniese aanvullende materiaal, S1 en S4). Vir hierdie biologiese scenario bevoordeel 'n lae sorgkoste dus 'n laer manlike toewysing aan ouerlike pogings (figuur 1)c), wat mannetjies toelaat om meer energie toe te wys om parings te verkry (figuur 1a) en ejakulate produseer (figuur 1b). Aangesien ekologiese en fisiologiese toestande veroorsaak dat die koste van vaderlike sorg toeneem (d.w.s. afneem in α-waardes), sal hoër toewysing aan sorg vereis word vir die nageslag om te oorleef (sien elektroniese aanvullende materiaal, S1 en S4), wat toenemende toewysing aan ouerpoging bevoordeel (figuur 1c) en verminder gevolglik toewysing aan paring en bevrugtingspoging (figuur 1a,b).

Figuur 1. Evolusionêre stabiele toekenningstrategieë vir paring, bevrugting en ouerpoging in reaksie op spermkompetisie-intensiteit (bepaal deur vroulike paringstempo) en twee komponente van die koste van manlike sorg. (ac) Voorspellings vir geval 1, waar die basislyn nageslag oorlewing sonder manlike sorg B gelyk aan nul. (d-f) Voorspellings vir geval 2, veral wanneer B = 0.25. (gek) Voorspellings vir geval 2, in die besonder, wanneer die vorm parameter α van die eksponensiële funksie van nageslagoorlewing in reaksie op vaderlike poging is gelyk aan 20. Hoë waardes van α (af) of B (gek) verteenwoordig scenario's waar manlike sorg energiek goedkoop is. Die kleurkode vir die voorspelde relatiewe toekenning aan elke komponent van fiksheid word in die ooreenstemmende balk aan die regterkant van elke grafiek getoon.

Ons model voorspel ook 'n positiewe assosiasie tussen die ESA tot ouerpoging en die verwagte gemiddelde binne-paar vaderskap (figuur 2a). Hierdie patroon word egter nie voorspel uit 'n eksplisiete of veronderstelde effek van verwantskap op manlike toewysing aan sorg nie, maar kom eerder uit hoe mans aanpasbaar toewys aan verskillende komponente van fiksheid in reaksie op die interaktiewe effek tussen spermkompetisie-intensiteit en die koste van manlike sorg oor spesies heen. Hierdie teorie voorspel dus dieselfde positiewe assosiasie tussen vaderskap en vaderlike sorg, maar om 'n ander onderliggende rede as die effek van verwantskap op die voordele van sorg. Daarbenewens is die verskil tussen die ESA tot ouerpoging in spesies waarin wyfies net 'n paar keer paar (dws hoë verwagte gemiddelde binne-paar vaderskap) en die ESA tot ouerpoging in hoogs polyandriese spesies (dws lae verwagte gemiddelde binne-paar vaderskap) ) word gewysig deur die koste van sorg (figuur 2a). Wanneer ekologiese en fisiologiese toestande 'n hoë energiekoste van manlike sorg oplê (d.w.s. lae α-waardes), is die verskil tussen spesies met 'n lae versus hoë wyfies se promiskuïteit groot, met mannetjies wat baie meer energie aan ouerpoging toeken in spesies met 'n lae as hoë paringtempo (swart lyn in figuur 2)a). Aangesien ekologiese en fisiologiese toestande 'n dalende koste van manlike sorg meebring (d.w.s. toenames in α-waardes), verminder die verskil in die ESA tot ouerlike pogings onder spesies, met mans wat soortgelyk aan sorg belê ongeag vroulike losbandigheid, wat dus die assosiasie tussen vaderlike sorg en binne-paar vaderskap verswak (ander lyne in figuur 2)a).

Figuur 2. Die opkomende assosiasie tussen die evolusionêre stabiele toewysing aan ouerpoging en die verwagte gemiddelde binne-paar vaderskap oor spesies hang af van die koste van manlike sorg. (a) Geval 1, waar die basislyn nageslag oorlewing sonder manlike sorg B is gelyk aan nul, (b) geval 2, veral wanneer B = 0.25 en (c) geval 2, in die besonder, wanneer die vorm parameter α van die eksponensiële funksie van nageslag-oorlewing in reaksie op vaderlike poging is gelyk aan 20. Vir (a) en (b), die kleur van die punte en die lyne beeld scenario's uit met verskillende waardes vir die parameter α: swart punte en soliede lyn wanneer α = 10, donkergrys punte en soliede lyn wanneer α = 20, liggrys punte en soliede lyn wanneer α = 40, en wit punte en stippellyn wanneer α = 60. Vir (c), verskillende kleure beeld scenario's uit met verskillende waardes vir die parameter B: swart punte en soliede lyn wanneer B = 0.10, donkergrys punte en soliede lyn wanneer B = 0.20, liggrys punte en soliede lyn wanneer B = 0.40, en wit punte en stippellyn wanneer B = 0.60.

(b) Geval 2: nageslag-oorlewing hang gedeeltelik af van vaderlike sorg

Ons kyk nou na die situasie wanneer nageslag sonder vaderlike sorg kan oorleef (d.w.s. die basislyn B > 0, sien elektroniese aanvullende materiaal, S1). Dit kan voorkom by spesies met slegs manlike sorg, waar byvoorbeeld ekologiese toestande vir nageslagprestasie (oorlewing en/of ontwikkeling) nie so beperkend is nie, of in spesies met tweeouerlike sorg, waar wyfies sorg verskaf onafhanklik van vaderlike gedrag. Die kwalitatiewe voorspellings vir hierdie geval is soortgelyk aan dié van geval 1. Eerstens, hoewel toenames in vroulike promiskuïteit ook manlike strategieë bevoordeel wat verkieslik energie aan bevrugtingspogings toeken (figuur 1)d–i), word hierdie patroon gewysig deur die omvang van die koste van manlike sorg, verteenwoordig in geval 2 deur die kombinasie van twee komponente: die moeilikheid om sorg te verskaf (d.i. deur die vorm parameter α van die nageslag-oorlewingsfunksie figuur 1d-f) en die basislyn-nageslagoorlewing (d.w.s. deur die intercept parameter B van die nageslag-oorlewingsfunksie figuur 1g-i). Wanneer ekologiese en fisiologiese toestande nie 'n hoë energiekoste van sorg op mans oplê nie (d.w.s. hoog α- of B-waardes), word minder toewysing aan ouerlike inspanning bevoordeel, terwyl toenames in die energieke koste van manlike sorg (d.w.s. afnames in enige van die twee) α- of B-waardes) bevorder toenemende toewysing aan ouerpoging.

Tweedens voorspel geval 2 ook 'n opkomende positiewe assosiasie tussen ouerpoging en verwagte binne-paar vaderskap, met die koste van manlike sorg wat hierdie assosiasie moduleer (figuur 2)b, c). The strength of this modification effect, however, depends on which of the two parameters that capture the different aspects of the cost of paternal care one considers. For the shape parameter α, when ecological and physiological conditions lead to care being difficult (i.e. costly) for males to provide (i.e. low α-values), the difference in parental effort between species where females mate just a few times and species where females are highly polyandrous is large (black line in figure 2b). In species where paternal care is less costly to provide (i.e. increases in α-values), the association between paternal care and within-pair paternity is predicted to be present but weaker (other lines in figure 2b) and thus may be harder to detect empirically. Finally, the baseline offspring survival B does not affect how parental effort is predicted to vary among species as a function of whether females mate just a few times or are highly polyandrous (figure 2c). Instead, variation across species in baseline offspring survival in the absence of male care, B, has only a small quantitative effect on parental effort (different lines in figure 2c).

The overall results from both cases explored here show that variation among species in ecological, physiological or maternal conditions that affect the cost of male parental behaviour in terms of the difficulty of providing care (i.e. the parameter α), but not the baseline offspring survival without care (i.e. the parameter B), is predicted to alter the strength of the association between parental effort and expected within-pair paternity. From an empirical perspective, all else being equal, an association between paternity and paternal effort will be more likely detected when focusing on species in which male care is consistently very difficult to provide. In species where the costs of care vary or male care is not difficult to provide, other aspects of the breeding system and the reproductive biology of species are more likely to explain patterns of parental effort across species than variation in female promiscuity and, ultimately, variation in paternity.

5. Discussion

Our model predicts how male allocation between mating, fertilization and parental effort is expected to evolve in response to among-species variation in the intensity of sperm competition and the cost of male care, both of which are likely to be shaped evolutionarily by even small changes in ecological conditions among species [26–32]. Consistent with ubiquitous theoretical predictions [1,2] and patterns observed in nature (e.g. insects: [9,54] vertebrates: [7,8,10,54–56]), our model predicts that increases in sperm competition intensity favour male allocation to fertilization effort over other components of reproduction. Though sperm competition games have not previously been used to consider the situation where males must also allocate limited energy to parental effort, our results reveal that existing sperm competition expectations are generally robust, even for species in which males benefit from allocating a large amount of energy to paternal care. Moreover, our model predicts the positive association between parental effort and the expected average within-pair paternity that is predicted by parental investment theory [25,33], simply by considering that male allocation to paternity assurance (i.e. ejaculate production) and paternal care trade-off with each other (see similar arguments in [37,38]). Although previous work modelled the benefit function of parental care on offspring survival explicitly [36,50,51], little attention has been given to exploring variation in this function (but see [33,49]), despite the recognition that such variation may drive an association between parental effort and paternity that does not necessarily represent a causal relationship between these two variables [23,34,37,38]. Therefore, our theory not only shows that the core predictions of sperm competition theory also apply to species with paternal care, but also reveals an important role for the cost of male care in modulating both the evolution of male allocation to parental effort, the association between parental effort and paternity and our ability to detect and understand these patterns empirically.

Our model shows that the cost of paternal care can affect the resolution of life-history trade-offs between mating, fertilization and care. Conditions that increase this cost (due to either changes in the baseline offspring survival or in the difficulty of providing care) are predicted to favour strategies that divert energy from fertilization to parental effort, even at moderately high levels of sperm competition. To our knowledge, only a few empirical studies have addressed this question. In the black redstart Phoenicurus ochruros, increases in food availability (which likely represents decreases in the cost of paternal care) are indeed associated with decreases in male attendance and increases in male mating success [28], as expected by our model. In cuckoos with paternal care (which are likely to represent species where the cost of male assistance are stronger than species without care), male fertilization effort represented by testes size is higher (instead of lower) than in cuckoos without parental assistance [57], contrary to our model's prediction. A possible explanation for this latter case could be that the particular biotic or abiotic conditions that affect the cost of male care across species simultaneously affect other aspects of the mating system, such as, female promiscuity. In this sense, future empirical and theoretical work may contribute to our understanding on how and when the cost of male care should be expected to covary with sperm competition intensity. Nevertheless, there is still insufficient empirical data at present on how the cost of paternal care affects male behaviour and the relationship between mating, sperm allocation and care to test whether our predictions generally hold in nature.

As described above, our model also highlights the importance of the difficulty of providing care to alter the emergent association between paternal care and paternity: the easier paternal care is to provide, the weaker the association between paternity and parental effort. In fact, a recent and very comprehensive study of birds [17] found that, while male share of care decreases with extra-pair paternity in species where nestlings demand extensive care (i.e. altricial species), this association disappears when offspring require little care (i.e. precocial species). One could also test our model's predictions by exploring paternity patterns at different stages of parental care, which are likely to vary in the cost and benefit of care. In birds, provisioning is the most energetically expensive stage [58] and the common attendance by both parents suggests an essential role of male contribution. Conversely, although incubation greatly affects offspring development [59], females are generally able to compensate for decreases in male contribution during this stage [60], suggesting paternal care may not be very difficult for males to provide. Nest construction plays an important role not only in protecting the offspring but also in sexual signalling [61], so female compensation for a male's failure at this stage is unlikely. Therefore, the difficulty of providing paternal care in birds with biparental care seems to be low during incubation, increasing in importance during nest construction (when females cannot compensate for a male's failure to provide care) and is the highest during provisioning. In fact, extra-pair paternity and male share of feeding are strongly and negatively associated across 122 bird species (based on standardized regression coefficients), followed by the association with nest construction and, then, with incubation ([41] for qualitatively similar results [39], but see [40]). Therefore, although empirical evidence is still scarce, results from the most comprehensive dataset in birds so far are consistent with our predictions for how the difficulty of providing male care affects the association between paternity and paternal care in two scales: among species with different development modes and within species between different stages of care.

In order to compare our results more directly to existing theory, we used a set of assumptions common to most sperm competition games (reviews in [1,2]) and parental investment theory [34–37]. Particularly, we assumed a priori the existence of energetic and temporal trade-offs between paternal care and other components of fitness. In numerous species with male-only care, however, parental males are able to attend several clutches simultaneously [16,22,48], reducing the extent of such trade-offs. Our predictions for situations with little energetic cost of male care may be similar to scenarios with weak trade-offs, although the mechanisms leading to little male allocation to parental effort are substantially different in each case. Moreover, males in some species are more attractive when attending the offspring than when at a non-parental state [22,27,62–64], resulting in a synergistic relationship between paternal care and mating and/or fertilization effort. This situation, however, must dramatically change the outcome of intra- and inter-sexual interactions and, consequently, the expected patterns of paternal care [25,65]. Therefore, the assumptions of existing theory do not capture the entire diversity of forms of paternal care and its relationship with sexual selection. We suggest not only that the extent but also the existence of trade-offs between different components of fitness deserve further attention. Particularly, future theoretical work could explore ‘loading factors’ in sperm competition games (i.e. parameters that scale the relative effect of energy expenditure on male traits and their corresponding component of fitness, which have been used in the context of pre- [14] and post-copulatory [11] male competition). In this sense, our model provides a strong starting point from which to study the evolution of paternal care, using a framework that explicitly considers how allocation strategies and social interactions affect patterns of mating, fertilization and care, where the extent of trade-offs between different components of fitness can easily be explored and evaluated.

Here, we demonstrate the importance of considering explicitly the cost of paternal care on the evolution of male allocation strategies, which in turn mediates expected paternity. Our main results show that the core predictions of sperm competition games [1,2] and parental investment theory [34–37] can be modified by the cost of paternal care. Although existing empirical evidence supports the expected association between paternity and male care across species [17,39–42]), extensive unexplained variation remains [23], particularly in species where males are exclusively responsible for offspring survival and high levels of paternity are expected [15,43–46]. The cost of paternal care varies widely among natural populations, and we argue that investigating how this variation affects patterns of mating, fertilization and care has the potential to improve our understanding of the coevolution between parental investment and reproduction.

Etiek

The authors declare that this research (i) has not been published previously elsewhere, (ii) was not misconducted, (iii) did not involved animal treatment or (iv) involved plagiarism in any form.


Old male sex: large ejaculate, many sperm, but few offspring

Reproduction induces non-trivial costs, such that both males and females should choose their mates carefully and invest their resources prudently. Male performance and thus their investment into ejaculates are often predicted to decrease with age and mating frequency, which may in turn negatively affect female fitness and thus feedback on the attractiveness of old males. Such reproductive senescence may be mediated by changes in the males’ oxidative status. Here, we investigated the effects of male mating frequency and age on male reproduction and oxidative status, and the respective consequences for female reproduction. We used the tropical butterfly Bicyclus anynana, in which counterintuitively older males have a higher mating success than younger ones. In once-mated males, spermatophore mass and sperm numbers strongly increased with age, while antioxidant defences and oxidative damage declined with age. In repeatedly mated males, spermatophore mass and sperm number showed little variation being similar to young once-mated males, while antioxidant defences increased and oxidative damage decreased with mating frequency. Female reproductive success was highest when mating with young once-mated males, although these produced small spermatophores with low sperm numbers. Our findings suggest that in B. anynana, (1) ejaculate size and sperm number are not reliable proxies of male quality, (2) ejaculate quality diminishes with age and mating number, and that (3) old male mating advantage likely results from sexual conflict owing negative effects on female fitness.

Dit is 'n voorsmakie van intekeninginhoud, toegang via u instelling.


Bespreking

One proposed explanation of polyandry is its potential to increase the reproductive success of females via expansion of offspring genetic diversity (Yasui 1998 Jennions and Petrie 2000 Parker and Birkhead 2013 ). However, the widespread phenomenon of LMSP, strongly biasing paternity in favor of the last male, limits the scope for such genetic benefits. In response to this, sexual conflict theory predicts that selection should favor female mechanisms that reduce males’ ability to manipulate paternity. Here, we show that D. melanogaster females who remate in quick succession with three males counteract LMSP, maintaining a more evenly distributed paternity and thereby increasing the genetic diversity of their offspring. Thus, modulation of paternity via remating behavior may have evolved as a counteradaptation to male traits that promote LMSP.

Most research on LMSP in this species has focused on a two-male competitive assay with at least one 24-h interval of isolation between matings. Want D. melanogaster females are documented to mate with several males in the wild, we investigated whether lessons learnt from the two-male scenario extend to a perhaps more natural situation when females mate with more males, more frequently. Despite the modifications to the paradigm, we still observed LMSP in thrice-mated females, but it was less strong than in twice-mated females. We also observed next to no sperm displacement in the Sp in comparison to the SR as detected with the previous experimental design (Manier et al. 2010 ). Together, these results suggest that the mechanism of sperm displacement in the Sps is biased by neither mating latency nor mating order, allowing for Sps to provide equal storage for all mates. Most of LMSP therefore happens in the SR. In addition to supporting previous findings, we were also able to highlight the importance of variability of female reproductive behavior. By regulating mating rate, previous research has identified important female-derived factors of postcopulatory sexual selection. However, by standardizing female mating behavior, previous paradigms have also simultaneously abolished meaningful consequences of plasticity in this trait. In contrast to the previous paradigm, we accommodated for variation in female mating rate and extended our understanding of the impact of female mating behavior on offspring production. By utilizing this new approach, we revealed that the duration between matings is a critical element in the outcome of paternity.

Uncovering the factors that influence female mating behavior will allow researchers to address such fundamental questions about the extent of female control over reproduction. More specifically, the relationship between remating rate and LMSP in D. melanogaster uncovered here demonstrates a key entry point into the cellular and molecular underpinning of postcopulatory sexual selection. As both mating and sperm storage are active processes (Arthur et al. 1998 Zhou et al. 2014 Aranha et al. 2017 ), there is much potential to use this genetic model to gain access into the neuronal architecture of female control over paternity. Moreover, the propensity of D. melanogaster females to remate is not only influenced by food availability (Gorter et al. 2016 ), current nutritional status (Fricke et al. 2010 ), and developmental conditions (Amitin and Pitnick 2007 ), but it has also been linked to natural female genetic variation (Arthur et al. 1998 Giardina et al. 2011 Billeter et al. 2012 ). Remating rate also increases with group size (Gorter et al. 2016 ) and group genetic diversity (Krupp et al. 2008 Billeter et al. 2012 ), suggesting that females can detect variation in her social group and adapt her mating rate to maximize her reproductive success. We acknowledge that male–male competition likely also has an impact on LMSP in thrice-mated females as male-derived seminal fluid peptides within the male ejaculate can affect sperm storage, female sexual receptivity, and fecundity. Moreover, the transfer of these peptides can be modulated based on the perception of the female mating status (Wigby et al., 2009 Sirot et al. 2011 Wigby et al., 2016 ). These factors were not explored in our study, but their impact was mitigated by the usage of genetically similar males. Moreover, the fact that the female, and not male, genotype is the main factor influencing remating intervals in the mating assay used here (Billeter et al. 2012 ) indicates that females are in control of their remating rate, perhaps as a means of protecting genetic diversity in their clutches, as demonstrated here.

The correlation between the timing of remating and paternity patterns uncovered here allows us to speculate on the potential mechanisms that achieve the modulation of LMSP. Because we observe reduced LMSP associated with short remating latencies, it is possible that resident sperm's defensive ability decreases over time. Therefore, the timing of the exposure of the resident sperm to the newly acquired ejaculate may influence sperm competition outcomes. Additionally, other postcopulatory events independent of remating latency may also influence the displacement process such as the timing of sperm ejection (Lüpold et al. 2013 ). Following remating, recently acquired sperm displaces the resident sperm from the sperm storage organs until the female removes the unstored ejaculate via ejection (Manier et al. 2010 ). The longer the process continues, the more exchange can occur, resulting in increased LMSP (Lüpold et al. 2013 ). Moreover, we have shown that females remate shortly after sperm ejection (Laturney et al. 2016 ), which suggests that females who are quick to remate are also likely quick to eject, offering prospective support for ejection as the potential mechanism governing the magnitude of the displacement process. Although previous reports on the effect of sperm ejection on LMSP focused on twice-mated females, isolated between matings, with remating latencies between two and four days, it is likely that a similar mechanism may also influence the outcome of sperm competition within the experiment context employed in this present investigation.

Polyandry has been observed in females of various species ranging from insects to marsupials (Kraaijeveld-Smit et al. 2002 Friesen et al. 2014 Rovelli et al. 2015 ). More intriguing, the relationship between female mating latency and paternity allocation has been observed in multiple species (Zeh and Zeh 1994 Arnaud et al. 2001 Blyth and Gilburn 2005 Drnevich 2003 , for a review see Simmons 2001 ). This demonstrates that across taxa irrespective of the species-specific biochemistry, genetic architecture, and physiology, females who remate more often produce more equal paternity shares, suggesting that not only is female remating behavior plastic, but also that females of various species may have evolved the same adaptation to combat paternity manipulation.

As new technologies allow for greater inspection into the principles governing sexual reproduction, we gain greater insight into how the genetic makeup of the next generation is determined and the explicit role that a force such as conflict theory plays. This present study highlights that offspring genetic diversity depends on the number of mates a female acquires as well as the timing of those matings. If paternity confers drastically different chances of survival and/or reproduction to the offspring, then not only the “who,” but also the “when” of female mating behavior have important evolutionary consequences.


2. Material and Methods

(a) Beetle and line management

Beetles were maintained under 16 L : 8 D photoperiod at 30ଌ and 65 per cent relative humidity, in food containing plain white organic flour and powdered organic brewer's yeast (9 : 1) with some large organic rolled oats to aid traction and food aeration. Pairs were formed by placing single virgin females with single virgin males for 7 days in an 8 ml vial filled with 3 g of food topped with rolled oats and secured with a perforated cap. Under these conditions beetles were able to mate freely and the females were able to lay eggs. Subsequent to egg laying, adults were removed and food with eggs and larvae was transferred to a 5 cm diameter Petri dish (35 ml). After pupae developed, they were sexed and isolated. At approximately 14 days after eclosion into adults, new pairs were created.

Inbred and non-inbred lines were created using male�male pairs of randomly selected virgin beetles from the ‘Georgia 1’ (GA1) strain (originally derived from stored corn in 1980, cultured since in the Beeman Laboratory, US Department of Agriculture, Biological Research Unit, Grain Marketing and Production Research Center, 1515 College Avenue, Manhattan, KS, USA). To create inbred lines, we first generated 50 families from random pairings of single virgin male and female GA1 adults. Inbreeding was then initiated in each family through reproducing offspring from a single male and female virgin adult sibling. The resulting offspring were then grown up to adult emergence, and again a randomly selected male × female sibling pair in each family was used to produce the next generation. These sib × sib crosses were repeated for four generations of inbreeding. We anticipated extinctions throughout the inbreeding protocol, and almost half of the original families went extinct over these first four generations of inbreeding. Beyond generation 4, we initiated the generation of separate inbreeding lines by splitting the surviving families. Again, monogamous sib × sib pairings were used to generate each new inbred line, and again some of these lines were terminated through extinction. Thus, each remaining family potentially gave origin to two lines in the fifth generation, four lines in the sixth generation, eight lines in the seventh generation and potentially 16 lines in the eighth generation. Because of extinctions, the eighth generation gave rise to 77 lines from 16 of the original surviving families, and in the ninth and final generation, we split only those lines with five or less lines from the original families (to avoid the over-representation of individual original families across the different final lines). After eight generations of these sib × sib pairings, and some families being split into separate lines and other families going extinct, we finally retained 98 extant lines producing inbred males for experimentation. Only one inbred male per line was used and replicated within any experimental treatment to minimize pseudo-replication within statistical comparisons.

Such relatively intense inbreeding was conducted because (i) pilot tests after one generation of full sib × sib inbreeding did not show depression of reproductive output compared with non-inbred crosses (n = 29 inbred and 27 non-inbred crosses, t54 = 𢄠.851, r = 0.12, bl = 0.398) and (ii) we expected our GA1 laboratory stock to have already passed through previous population genetic bottlenecks, potentially purging the population of some deleterious recessive alleles (e.g. Barrett & Charlesworth 1991 Hedrick 1994).

Alongside the inbred lines, we created non-inbred controls that were maintained identically and mated in monogamous pairings as for the inbred lines, except that we randomly mixed mating individuals between familial lines, so that chances for sib × sib pairings were very low. Three lines were established, each perpetuated by 20 monogamous pairings of single male and female virgin adults (maximal effective population size in each line Ne = 40), as for the inbred lines. Beetles were able to mate and lay eggs for a week and then adults were removed. All eggs and larvae within each of the three groups were then pooled and provided with ad libitum food as for the inbred lines. At pupation, male and female virgins were randomly paired (thus maintaining random genetic mixing) to create offspring for the next generation. As a consequence, the degree of inbreeding was (statistically) up to 20 times lower than in the inbred lines. Throughout, we present arithmetic means ± standard errors.

(b) Male fertility

To compare male fertility in detail over time between inbred and non-inbred males, we crossed control virgin females (from the GA1 stock) with either inbred (n = 30, each individual from a different line) or non-inbred control males (n = 11, chosen randomly from the GA1 stock). After 10 days of mating interaction, males were removed and females moved to new Petri dishes with fresh food for another 10 days, and then repeatedly transferred to new dishes with new food every 10 days across 140 days of oviposition. When all females had stopped producing offspring, they were placed with new virgin control males for an additional 10 days in order to establish whether the decrease in female fertility was a female or a male effect. The number of adults emerging within each Petri dish gave a measure of fertility for each cross, and by comparing offspring productivity between inbreeding treatments under sperm competition, were able to confirm that differential offspring viability was not a confound (see ੳ). A mixed repeated-measures ANOVA was used to analyse male fertility through time: male origin (inbred or non-inbred) was entered as a fixed independent factor, 10-day time period as a repeated-measures variable and number of offspring as the dependent variable. A separate, Gosset's paired t-test for females mated with inbred and control males was run to compare offspring production in the first 10-day block and the 15th 10-day block when females were mated with new control males. The proportion of females that survived to the 15th 10-day block was compared between the treatments using a χ 2 -test.

(c) Sperm competitiveness

Sperm competition experiments were conducted between the experimental males (inbred or non-inbred) and control males carrying the Reindeer (Rd) phenotypic marker, using control GA1 females. Reindeer males are dominant homozygotes at the Rd allele, so all offspring sired by an Rd male express the Rd phenotype with antler-shaped antennae. All individuals were virgins and ca. 14 days since emergence. A female was provided with the first male for 24 h, and then this male was replaced with the second male for 24 h. After this 48 h mating period, females were allowed to oviposit into fresh medium for one week and then removed. Although females can oviposit fertile eggs for up to 20 weeks after such mating treatments (e.g. figureਂ ), and high (greater than 70%) last-male sperm precedence persists in T. castaneum for at least 30 days of oviposition without re-mating (Arnaud et al. 2001a,b), under normal circumstances, the females will re-mate repeatedly during adulthood with new males (Fedina & Lewis 2008). Therefore, the most informative representation of sperm competition success for an individual male exists over the initial period after any bout of multiple mating, and before the female re-mates with a new male who will then go on to achieve high last-male precedence.

Offspring production by control GA1 females mated to either inbred (closed squares and solid lines) or control non-inbred (open squares and dashed lines) males shows no difference over 140 days of oviposition (in 10-day blocks). The initial numbers of females mated with inbred and control males were 30 and 11, respectively. Re-mating females after inbred or non-inbred male treatments restores female fertility (means at block 15), thus proving that the offspring production decline is due to male or sperm effects, not female senescence.

After 40 days when all adults had emerged, sperm competition success was scored as the relative number of wild-type (GA1) and Rd phenotypes (employing a balanced experimental design to control for potential differences between marker and GA1 offspring).

We assessed sperm precedence for both first-mated (P1) and second-mated (P2) experimental males, comparing the fertilization success of inbred males with non-inbred males, when they were in competition with Rd marker males for GA1 control females ( figureਁ ). Seventy-four to 90 sperm competition replicates were performed across the four possible treatments (=either inbred or non-inbred, and either P1 of P2 see figureਁ ), generating a total of 330 separate sperm competition trials. Within these trials, an average of 47 offspring per female/cross were produced and scored. Only two males from each inbred line were used for each set of matings, i.e. one male as the first to mate and the other one as the second to mate ( figureਁ a,c). Non-inbred males were chosen randomly from all available lines.

Crossing design for the two-male sperm competition experiments to measure influence of inbreeding on relative fertilization success of the first- and second-male-to-mate. Paternity can be assigned for the phenotypic marker male (M) using the Reindeer strain, and therefore sperm competition success for the inbred (I) versus non-inbred (N) experimental males, and P1 versus P2 females are non-inbred virgin controls (C) from the GA1 stock (see ੲc for details, (a)–(d) correspond with the same denotations in figure 3 ).

The sperm competition data were distributed binomially. Thus, in order to obtain statistical information equivalent to a full factorial two-way ANOVA with two fixed independent variables, we used the generalized linear model with a quasi-binomial error distribution (the quasi-extension was used to account for overdispersion of the data, dispersion parameter = 26.72) and a logit-link function (Crawley 2005). The analysis was performed in R v. 2.6.2 (The R Development Core Team 2005). The significance of variables was assessed through the analysis of deviance, where a variable was removed from the full model and the reduced model was compared with the full model. The deviance (G 2 ) is defined as 𢄢 × the difference between the log likelihood of the reduced model, and the log likelihood of the full model and the resulting statistic was compared with the F-distribution (Crawley 2005).

It is important to note that any differences in male reproductive success under competition may theoretically be due to sperm competitiveness as well as to the viability of offspring. If the latter explains some of the variance, we would expect differences in total offspring number produced between trials, especially when the inbred and non-inbred males were the second male to mate (because of the high second-male precedence). To check for this potential effect, we ran a two-way ANOVA with the origin of the experimental male (inbred or non-inbred) and the order in which he was mated relative to the marker male (first or second) entered as independent fixed factors and the total number of offspring (=offspring viability) as the dependent variable. If inbred males fertilized the same number of eggs as non-inbred males, but offspring of inbred males had lower survival, there should be a significant effect of the origin of the experimental male on the total number of offspring produced by females. If, however, offspring sired by inbred males are not less viable than offspring sired by non-inbred males, we should expect no significant differences in female total offspring production.

(d) Male mating behaviour

To compare effects of inbreeding on male mating behaviour, and to estimate the potential effect of the number of matings on the results of the sperm competition experiments, we assayed male mating competence. Thirty-six control virgin GA1 females were randomly assigned to two groups in which they were maintained with either an inbred or a non-inbred male for 1 h. Within this time, the number of mounts (a male attempting to mate with a female or pairs in copula for less than 45 s), copulation latency and duration (copulation = a pair remaining in copula for 45 s or more see also Attia & Tregenza 2004) were recorded. In the second hour, females that had previously been given inbred males were provided with non-inbred males (and vice versa). Again, the same behaviours were recorded. These mating behaviour assays followed the protocols of the sperm competition experiments (see above), thus allowing us a measure of the potential contribution of behavioural variability to sperm competition success. Moreover, the relative number of mounts and latency to mate will represent the male's mating success under inter-sexual competition from female choice (Fedina & Lewis 2008). Given that the χ 2 -test expected counts in the proportions of females that mated with inbred and non-inbred males were less than 5, we conducted a two-tailed Fisher's exact test instead. All other variables (number of mounts, copulation latency and duration) were analysed with separate independent samples two-tailed Mann–Whitney's U-toetse. This was because for some variables the distribution was not normal, whereas for others the number of observations was insufficient to assess the distribution for normality. One male from a given inbred line was used in the experiment and non-inbred males were chosen randomly from all available lines.

(e) Sperm morphometry

Mature spermatozoa were recovered from the vesicula seminalis of 15 inbred and 15 non-inbred males (each from a different family line) and suspended in a drop of water on a microscope slide under a square coverslip. Previous work established that mature spermatozoa from the vesicula seminalis do not differ in length from those ejaculated and stored in female spermathecae (Michalczyk 2008). The lengths of five spermatozoa per male were measured under phase contrast light microscope at 흀 using Synoptics image analysis exact to 0.01 µm. Differences in both the total sperm lengths and their coefficients of variation (CV) were analysed with separate Gosset's independent samples t-toetse.


Sperm Selection Based on Sperm Morphology – Intracytoplasmic Morphologically Selected Sperm Injection (IMSI)

The morphometric evaluation of spermatozoa is widely applied to analyze sperm quality due to its correlation to fertility (Yániz et al., 2015 Soler et al., 2016). Furthermore, the introduction of computer-enhanced digital microscopy has enabled the analysis and quantification of detailed features of the cell that applied to motile spermatozoa configure the “Motile Sperm Organelle Morphology Examination” (MSOME) (Bartoov et al., 2002). The use of MSOME for selecting spermatozoa for ICSI is known as IMSI. This technique consists in the selection and direct capture of those spermatozoa with a low number of vacuoles and a nucleus of normal morphology under a microscope equipped with a micromanipulation system and a magnification system of 6300x (Bartoov et al., 2002) (Figure 3). The power of selecting spermatozoa with higher DNA integrity has been proved by different authors, although contradictory results are also present in the literature (Table 6). Using this methodology, Franco et al. (2008) revealed that the presence of large vacuoles in the sperm nucleus is associated with a higher DNA fragmentation compared to those spermatozoa with normal nucleus. The correlation between the presence of vacuoles, as detected by MSOME, and DNA fragmentation was later confirmed by Wilding et al. (2011). However, Leandri et al. (2013) did not find significant differences in this respect between the spermatozoa selected by IMSI and those selected as conventionally done during regular ICSI. Other authors have suggested that IMSI could be useful only in specific cases of male infertility. Accordingly, when spermatozoa from infertile donors showing more than 13% of DNA fragmentation were selected by IMSI, those showing normal morphology under high magnification delivered less DNA fragmentation than those classified as motile and normal using conventional magnification of 200x (Hammoud et al., 2013). Moreover, the authors reported in the same work that those selected under lower magnification showed the same DNA fragmentation than the unsorted spermatozoa. Results reported by Lavolpe et al. (2015) suggest that in patients whose semen scored ≤ 4% according to the strict morphology index, the presence of vacuoles in the nucleus of the spermatozoa was less related to DNA fragmentation and chromatin compaction than in those patients with strict morphology index ≥ 14%.

Figuur 3. Intracytoplasmic morphologically selected sperm injection (IMSI). Spermatozoa are examined under a magnification system of 6300x in order to discriminate those spermatozoa lacking vacuoles (arrow) and showing normal morphology. These spermatozoa are collected with the micromanipulation system for their use in ICSI.


Etiologie

There are multiple causes for male infertility, which can be broadly classified due to their general underlying etiology.  These include endocrine disorders (usually due to hypogonadism) at an estimated 2% to 5%, sperm transport disorders (such as vasectomy) at 5%, primary testicular defects (which includes abnormal sperm parameters without any identifiable cause) at 65% to 80% and idiopathic (where an infertile male has normal sperm and semen parameters) at 10% to 20%.[6]  These are broad estimates only as accurate statistics are unavailable due to general underreporting, cultural factors, and regional variations.  Patients sent to a tertiary referral center are more likely to have their condition reported, while private patients may never have their data collected.[6]ਊ partial summary of specific etiologies is listed below: 

Male infertility can also be classified based upon the medical interventions that can potentially assist conception.[7]


Infidelity Produces Faster Sperm, Swedish Fish Study Finds

Until now, it has been difficult to prove that fast-swimming sperm have an advantage when it comes to fertilizing an egg. But now a research team at Uppsala University can demonstrate that unfaithful females of the cichlid fish species influence the males&rsquo sperm. Increased competition leads to both faster and larger sperm, and the research findings now being published in the scientific journal PNAS, Proceedings of the National Academy of Sciences, thus show that the much mythologized size factor does indeed count.

&ldquoThe competition among sperms to fertilize a female&rsquos eggs is an extremely powerful evolutionary force that influences various characteristics of sperms, such as size and speed,&rdquo says Niclas Kolm, a researcher at Uppsala University, who, in collaboration with scientists from several other universities, has studied the mating system of 29 species of Tanganyika cichlids. &ldquoFor the first time, we can show a strong link between the degree of sperm competition and the size and speed of the sperms. Males with promiscuous females develop faster and larger sperms than the monogamous species,&rdquo says Niclas.

"In promiscuous species we found that males produced larger and faster sperm than in closely related species that were monogamous," says Sigal Balshine, associate professor in the department of Psychology, Neuroscience & Behaviour at McMaster University, and senior author on the study. "This research offers some of the first evidence that sperm has evolved to become more competitive in response to females mating with multiple males."

Female promiscuity is a major problem for males because the sperm from rival suitors will compete in the race to procreate, explains Balshine. While the idea that sperm would evolve to become more competitive when males compete for fertilization seems obvious, to date there has been little evidence to support this theory.

&ldquo[One] unique aspect of the study is that we based our study on an unusually large base, with many fish from many different species. The fish were caught in lakes in Africa, and a special characteristic of this group of fishes is that there are incredible numbers of species,&rdquo says Niclas. &ldquoThere&rsquos an unbelievable variety of species and different kinds of mating behaviors. There&rsquos the whole spectrum of mating systems, from monogamous males to females that mate with many many males.&rdquo

The findings also show that the speed and the size of sperm are closely related: larger sperms are faster. These sperm swim faster thanks to the greater power of a larger flagellum, but faster sperm also need to have a larger store of energy, which in turn results in larger sperm.

Thanks to new analytical methods, they have also managed to demonstrate the order of this development. The sperm first become faster, then larger, following increased female promiscuity in a species.

&ldquoNo one has previously been able to show what causes what. Here we can clearly see that female promiscuity determines the character of sperms,&rdquo says Niclas.

Storiebron:

Materiaal verskaf deur Uppsala University. Let wel: Inhoud kan geredigeer word vir styl en lengte.