Data from: Genotype-by-environment interactions underlie the expression of pre- and postcopulatory sexually selected traits in guppies

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 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 postcopulatory sexual traits. In accordance with previous work, we found that dietary limitation had strong phenotypic effects on numerous pre- and postcopulatory 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 colouration 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-环境互作（genotype-by-environment interactions, GEIs）在性选择中所扮演的角色，直至近期才受到进化生物学家的关注。然而，GEIs可通过削弱性信号的诚实性、维持其表达背后的高水平遗传方差，以及改变适合度性状（fitness traits）间的遗传协变（genetic covariance）模式，产生深远的进化影响。 本研究以高度性二态的淡水鱼类——孔雀鱼（Poecilia reticulata）为研究对象，开展基因型-环境互作的检测。我们采用父本半同胞育种设计（paternal half-sibling breeding design）获得雄性后代，并将其分配至不同的营养“环境”（高投喂量或低投喂量组）。随后我们探究了日粮数量的操控是否会影响若干高变异、依赖于身体状况（condition-dependent）的交配前（precopulatory）与交配后（postcopulatory）性性状的加性遗传方差（additive genetic variance）与协变水平。 与既往研究结果一致，我们发现日粮限制对诸多交配前、交配后性性状具有显著的表型效应（phenotypic effects）。我们还报告了若干此类性状存在显著GEI的证据，其中部分性状（虹彩面积与精子速度）表现为不同营养环境下基因型的排序发生改变（即生态交叉（ecological crossover））。此外，我们证实遗传相关性（genetic correlations）在不同营养环境间存在显著差异。值得注意的是，高投喂组中虹彩体色与精子活力间显著的负遗传相关性，在日粮限制条件下不复存在。 综上，这些发现很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，并促成该物种中通常报道的性性状极端多态性水平。此外，环境特异性遗传协变的存在表明，在某一环境中测得的权衡（trade-offs）关系，或许无法反映另一环境中的遗传约束（genetic constraints）。