Data from: The heritability of mating behaviour in a fly and its plasticity in response to the threat of sperm competition

Phenotypic plasticity is a key mechanism by which animals can cope with rapidly changeable environments, but the evolutionary lability of such plasticity remains unclear. The socio-sexual environment can fluctuate very rapidly, affecting both the frequency of mating opportunities and the level of competition males may face. Males of many species show plastic behavioural responses to changes in social environment, in particular the presence of rival males. For example, Drosophila pseudoobscura males respond to rivals by extending mating duration and increasing ejaculate size. Whilst such responses are predicted to be adaptive, the extent to which the magnitude of response is heritable, and hence selectable, is unknown. We investigated this using isofemale lines of the fruit fly D. pseudoobscura, estimating heritability of mating duration in males exposed or not to a rival, and any genetic basis to the change in this trait between these environments (i.e. degree of plasticity). The two populations differed in population sex ratio, and the presence of a sex ratio distorting selfish chromosome. We find that mating duration is heritable, but no evidence of population differences. We find no significant heritability of plasticity in mating duration in one population, but borderline significant heritability of plasticity in the second. This difference between populations might be related to the presence of the sex ratio distorting selfish gene in the latter population, but this will require investigation in additional populations to draw any conclusions. We suggest that there is scope for selection to produce an evolutionary response in the plasticity of mating duration in response to rivals in D. pseudoobscura, at least in some populations.表型可塑性（phenotypic plasticity）是动物应对快速变化环境的关键机制，但此类可塑性的进化易变性仍未明确。社会-性环境波动极为迅速，既会影响交配机会的出现频率，也会改变雄性可能面临的竞争强度。诸多物种的雄性会对社会环境变化，尤其是竞争对手的存在，表现出可塑性行为响应。例如，拟暗果蝇（Drosophila pseudoobscura）的雄性会通过延长交配时长、增加射精量来响应竞争对手。尽管此类响应被认为具有适应性，但响应幅度的遗传力及其可被选择的程度，目前仍属未知。本研究以拟暗果蝇的单雌系（isofemale lines）为实验材料，对暴露于竞争对手环境与未暴露环境下的雄性交配时长遗传力，以及该性状在两种环境间的变化（即可塑性程度）的遗传基础进行了估算。两个种群在种群性比以及是否携带性比扭曲型自私染色体（sex ratio distorting selfish chromosome）方面存在差异。研究结果显示，雄性交配时长具有遗传力，但未发现种群间存在显著差异。其中一个种群的交配时长可塑性未检测到显著遗传力，而另一个种群的该可塑性则呈现边缘显著的遗传力水平。两个种群间的这一差异或许与后者携带性比扭曲型自私基因有关，但该推论仍需在更多种群中开展研究方能得出确切结论。本研究表明，至少在部分拟暗果蝇种群中，针对竞争对手的交配时长可塑性存在被选择并产生进化响应的潜力。