Gasparini Clelia, Congiu Leonardo, Pilastro Andrea
Department of Biology, University of Padova, Padova, 35100, Italy.
Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, Crawley, WA, 6009, Australia.
Mol Ecol. 2015 Aug;24(16):4286-95. doi: 10.1111/mec.13222. Epub 2015 Jun 15.
Females that mate multiply have the possibility to exert postcopulatory choice and select more compatible sperm to fertilize eggs. Prior work suggests that dissimilarity in major histocompatibility complex (MHC) plays an important role in determining genetic compatibility between partners. Favouring a partner with dissimilar MHC alleles would result in offspring with high MHC diversity and therefore with enhanced survival thanks to increased resistance to pathogens and parasites. The high variability of MHC genes may further allow discrimination against the sperm from related males, reducing offspring homozygosity and inbreeding risk. Despite the large body of work conducted at precopulatory level, the role of MHC similarity between partners at postcopulatory level has been rarely investigated. We used an internal fertilizing fish with high level of multiple matings (Poecilia reticulata) to study whether MHC similarity plays a role in determining the outcome of fertilization when sperm from two males compete for the same set of eggs. We also controlled for genomewide similarity by determining similarity at 10 microsatellite loci. Contrary to prediction, we found that the more MHC-similar male sired more offspring while similarity at the microsatellite loci did not predict the outcome of sperm competition. Our results suggest that MHC discrimination may be involved in avoidance of hybridization or outbreeding rather than inbreeding avoidance. This, coupled with similar findings in salmon, suggests that the preference for MHC-dissimilar mates is far from being unanimous and that pre- and postcopulatory episodes of sexual selection can indeed act in opposite directions.
多次交配的雌性有机会进行交配后选择，挑选更匹配的精子使卵子受精。先前的研究表明，主要组织相容性复合体（MHC）的差异在决定配偶间的遗传相容性方面起着重要作用。选择具有不同MHC等位基因的配偶会产生具有高MHC多样性的后代，因此由于对病原体和寄生虫的抵抗力增强，后代的存活率也会提高。MHC基因的高变异性可能还会使雌性能够区分来自近亲雄性的精子，从而降低后代的纯合性和近亲繁殖风险。尽管在交配前水平上已经进行了大量研究，但配偶间MHC相似性在交配后水平上的作用却很少被研究。我们使用一种多次交配水平较高的体内受精鱼类（孔雀鱼）来研究当来自两个雄性的精子竞争同一组卵子时，MHC相似性是否在决定受精结果中发挥作用。我们还通过确定10个微卫星位点的相似性来控制全基因组相似性。与预测相反，我们发现MHC相似度越高的雄性产生的后代越多，而微卫星位点的相似性并不能预测精子竞争的结果。我们的结果表明，MHC识别可能与避免杂交或远交有关，而不是与避免近亲繁殖有关。这一点，再加上在鲑鱼中得到的类似发现，表明对MHC不同配偶的偏好远非一致，而且交配前和交配后的性选择过程确实可能朝着相反的方向起作用。
