Data from: The effects of sexual selection on life history traits: an experimental study on guppies

Sexual selection is often prevented during captive breeding in order to maximize effective population size and retain genetic diversity. However, enforcing monogamy and thereby preventing sexual selection may affect population fitness either negatively by preventing the purging of deleterious mutations or positively by reducing sexual conflicts. To better understand the effect of sexual selection on the fitness of small populations, we compared components of female fitness and the expression of male secondary sexual characters in 19 experimental populations of guppies (Poecilia reticulata) maintained under polygamous or monogamous mating regimes over nine generations. In order to generate treatments that solely differed by their level of sexual selection, the middle-class neighbourhood breeding design was enforced in the monogamous populations, while in the polygamous populations, all females contributed similarly to the next generation with one male and one female offspring. This experimental design allowed potential sexual conflicts to increase in the polygamous populations because selection could not operate on adult-female traits. Clutch size and offspring survival showed a weak decline from generation to generation but did not differ among treatments. Offspring size, however, declined across generations, but more in monogamous than polygamous populations. By generation eight, orange- and black-spot areas were larger in males from the polygamous treatment, but these differences were not statistically significant. Overall, these results suggest that neither sexual conflict nor the purging of deleterious mutation had important effects on the fitness of our experimental populations. However, only few generations of enforced monogamy in a benign environment were sufficient to negatively affect offspring size, a trait potentially crucial for survival in the wild. Sexual selection may therefore, under certain circumstances, be beneficial over enforced monogamy during captive breeding.圈养繁育过程中，为最大化有效种群规模并保留遗传多样性，研究者通常会规避性选择（sexual selection）。然而，强制实行单配制（monogamy）并以此规避性选择，可能会通过两种途径影响种群适合度：一是因阻止有害突变（deleterious mutations）的清除而产生负面影响，二是通过减少性冲突（sexual conflicts）带来积极影响。为更深入理解性选择对小型种群适合度的影响，本研究针对19个孔雀鱼（Poecilia reticulata）实验种群展开了为期9代的繁育实验，对比了不同交配制度（多配制（polygamy）与单配制）下的雌性适合度组分以及雄性第二性征（secondary sexual characters）的表达情况。 为确保各组仅在性选择强度上存在差异，单配制种群采用了中邻里繁育设计（middle-class neighbourhood breeding design），而多配制种群中，所有雌性个体均通过产出1尾雄性和1尾雌性后代的方式，为下一代种群贡献等量的遗传资源。该实验设计使得多配制种群中的潜在性冲突得以加剧，因为选择无法作用于成年雌性的性状。 每代的窝仔数与后代存活率均呈现微弱的世代下降趋势，但各组间并无显著差异。然而后代体型则随世代推移逐渐减小，且单配制种群的下降幅度显著大于多配制种群。至第8代时，多配制组雄性个体的橙色与黑色斑点面积更大，但该差异未达到统计学显著性水平。 综合来看，本研究结果表明，性冲突与有害突变清除过程均未对实验种群的适合度产生显著影响。然而，在适宜环境中仅经数代强制单配制繁育，便足以对后代体型产生负面影响——而该性状对野生个体的存活可能至关重要。因此，在特定情境下，圈养繁育过程中保留性选择或许比强制实行单配制更具优势。