Evans J P, Rahman M M, Gasparini C
Centre for Evolutionary Biology, School of Animal Biology (M092), Crawley, WA, Australia.
J Evol Biol. 2015 Apr;28(4):959-72. doi: 10.1111/jeb.12627. Epub 2015 Apr 17.
The role that genotype-by-environment interactions (GEIs) play in sexual selection has only recently attracted the attention of evolutionary biologists. Yet GEIs can have profound evolutionary implications by compromising the honesty of sexual signals, maintaining high levels of genetic variance underlying their expression and altering the patterns of genetic covariance among fitness traits. In this study, we test for GEIs in a highly sexually dimorphic freshwater fish, the guppy Poecilia reticulata. We conducted an experimental quantitative genetic study in which male offspring arising from a paternal half-sibling breeding design were assigned to differing nutritional 'environments' (either high or low feed levels). We then determined whether the manipulation of diet quantity influenced levels of additive genetic variance and covariance for several highly variable and condition-dependent pre- and post-copulatory sexual traits. In accordance with previous work, we found that dietary limitation had strong phenotypic effects on numerous pre- and post-copulatory sexual traits. We also report evidence for significant GEI for several of these traits, which in some cases (area of iridescence and sperm velocity) reflected a change in the rank order of genotypes across different nutritional environments (i.e. ecological crossover). Furthermore, we show that genetic correlations vary significantly between nutritional environments. Notably, a highly significant negative genetic correlation between iridescent coloration and sperm viability in the high food treatment broke down under dietary restriction. Taken together, these findings are likely to have important evolutionary implications for guppies; ecological crossover may influence sexual signal reliability in unstable (nutritional) environments and contribute towards the extreme levels of polymorphism in sexual traits typically reported for this species. Furthermore, the presence of environment-specific genetic covariance suggests that trade-offs measured in one environment may not be indicative of genetic constraints in others.
基因型与环境的相互作用（GEIs）在性选择中所起的作用直到最近才引起进化生物学家的关注。然而，GEIs可能具有深远的进化意义，因为它会损害性信号的诚实性，维持其表达背后的高遗传变异水平，并改变适合度性状之间的遗传协方差模式。在本研究中，我们在一种具有高度两性异形的淡水鱼——孔雀鱼（Poecilia reticulata）中测试了GEIs。我们进行了一项实验性定量遗传学研究，在该研究中，将来自父本半同胞育种设计的雄性后代分配到不同的营养“环境”（高饲料水平或低饲料水平）中。然后，我们确定饮食量的操纵是否会影响几种高度可变且依赖于条件的交配前和交配后性性状的加性遗传方差和协方差水平。与之前的研究一致，我们发现饮食限制对许多交配前和交配后性性状具有强烈的表型效应。我们还报告了其中一些性状存在显著GEI的证据，在某些情况下（虹彩面积和精子速度），这反映了不同营养环境下基因型排名顺序的变化（即生态交叉）。此外，我们表明营养环境之间的遗传相关性差异显著。值得注意的是，在高食物处理中，虹彩颜色与精子活力之间高度显著的负遗传相关性在饮食限制下消失了。综上所述，这些发现可能对孔雀鱼具有重要的进化意义；生态交叉可能会在不稳定（营养）环境中影响性信号的可靠性，并导致该物种通常报道的性性状极端多态性水平。此外，特定环境的遗传协方差的存在表明，在一种环境中测得的权衡可能并不代表其他环境中的遗传限制。
