Data from: Experimental evidence for sexual selection against inbred males

The detrimental effects of matings between relatives are well known. However, few studies determine the extent to which inbreeding depression in males is due to natural or sexual selection. Importantly, measuring fitness or key fitness components, rather than phenotypic traits allows more accurate estimation of inbreeding depression. We investigate how differences in inbreeding and juvenile diet (i.e. early stressful environment) influence a key component of male fitness, namely their reproductive success. We experimentally created inbred and outbred male mosquitofish (Gambusia holbrooki) by mating full-sibs (f = 0·25). We show that this led to a 23% reduction in genome-wide heterozygosity based on SNPs. Males were raised on different diets early in life to create high-stress and low-stress rearing environments. We then allowed adult males to compete freely for females to test if inbreeding, early diet and their interaction affect a male's share of paternity. Early diet had no effect on paternity, but outbred males sired almost twice as many offspring as inbred males (n = 628 offspring from 122 potential sires). Using artificial insemination methods we determined that this was unlikely to be due to early embryo mortality of eggs fertilised by inbred males: there was no evidence that male inbreeding status affects the realised fecundity of females (n = 288). Given there was no difference in male mortality in our competitive mating experiment, the lower reproductive success of inbred males can most parsimoniously be attributed to inbreeding negatively affecting sexually selected traits that affect male mating success and/or sperm competitiveness. We discuss which sexually selected traits might be involved.亲属间交配的有害效应早已得到广泛认知。然而，鲜有研究明确雄性近交衰退（inbreeding depression）在多大程度上源于自然选择或性选择。尤为重要的是，相较于表型性状（phenotypic traits），测量适合度（fitness）或关键适合度组分，能够更精准地估算近交衰退。 本研究旨在探究近交程度与幼体日粮（juvenile diet，即早期应激环境）的差异，如何影响雄性适合度的关键组分——即其繁殖成功率（reproductive success）。 我们通过同胞（full-sibs）交配，实验构建了近交与远交的雄性食蚊鱼（Gambusia holbrooki），其近交系数f=0.25。结果显示，基于单核苷酸多态性（Single Nucleotide Polymorphisms, SNPs）检测表明，这一操作使得全基因组杂合度（genome-wide heterozygosity）降低了23%。研究人员在雄性幼体阶段设置不同日粮，以构建高应激与低应激的饲养环境。随后让成年雄性自由竞争配偶，以此检验近交、早期日粮及其交互作用是否会影响雄性的父权份额（paternity share）。 早期日粮对父权份额无显著影响，但远交雄性的子代数量几乎是近交雄性的两倍（本研究纳入122头潜在父本，共计628个子代）。通过人工授精（artificial insemination）方法，我们发现这一现象不太可能源于近交雄性所授精的卵的早期胚胎死亡（early embryo mortality）：并无证据表明雄性近交状态会影响雌性的实际繁殖力（realised fecundity）（本研究共纳入288头雌性个体）。 鉴于竞争性交配实验中雄性死亡率无显著差异，近交雄性繁殖成功率较低这一现象，最简约的解释为：近交对影响雄性交配成功率和/或精子竞争力（sperm competitiveness）的性选择（sexual selection）性状产生了负面影响。我们还就可能参与其中的性选择性状展开了讨论。