Exposure to rivals does not affect male mate choice in <em>Drosophila melanogaster</em>

Male-male competition can affect male mate choice in different ways, potentially leading to stronger preferences when males benefit from investing more resources in fewer, but higher-quality matings, or weaker preferences if choosiness could lead to missed mating opportunities. As in many insects, Drosophila melanogaster males show both pre- and postcopulatory preferences for larger, higher-fecundity females. Exposure to rivals alters some aspects of male courtship and mating behavior in this species, but it is unknown whether male mate choice is similarly affected by increased competition. We tested whether perceived competition influenced the strength of male precopulatory and postcopulatory preferences for large females by housing D. melanogaster males with or without rivals before they encountered females that differed in size. Males from both treatments exhibited equally strong courtship preferences for large females and extended matings to a similar degree with large versus small females, indicating that exposure to rivals did not affect these components of male mate choice. There was also no difference in offspring production between males from the two treatments. Our findings suggest that male preferences for large females are relatively stable across social environments in D. melanogaster, supporting the hypothesis that strong, consistent preferences for high-quality mates can be maintained despite variation in competitive contexts.雄性间竞争可通过多种途径影响雄性配偶选择：当雄性通过将更多资源投入到少量但更高质量的交配中以获得适配收益时，会产生更强的配偶偏好；但若择偶行为可能导致错失交配机会，则偏好强度会有所减弱。与多数昆虫类群一致，黑腹果蝇（Drosophila melanogaster）的雄性同时表现出对体型更大、繁殖力更强雌性的交配前及交配后配偶偏好。已有研究显示，暴露于竞争者环境会改变该物种雄性求偶与交配行为的部分特征，但尚不清楚雄性配偶选择是否同样会因竞争加剧而受到影响。本研究通过在黑腹果蝇雄性接触体型各异的雌性之前，将其分别饲养于有竞争者或无竞争者的环境中，以此检验感知到的竞争是否会影响雄性对大体型雌性的交配前及交配后偏好强度。结果显示，两组处理下的雄性均表现出对大体型雌性同等强度的求偶偏好，且与大体型雌性和小体型雌性的交配时长无显著差异，表明暴露于竞争者环境并未影响雄性配偶选择的这些组分。两组处理雄性的子代繁殖量亦无显著差异。本研究结果表明，黑腹果蝇雄性对大体型雌性的配偶偏好会在不同社会环境中保持相对稳定，这支持了以下假说：尽管竞争背景存在差异，对高质量配偶的强烈且稳定的偏好仍可得以维持。