The evolution of male-biased sexual size dimorphism is associated with increased body size plasticity in males

1.Sexual size dimorphism (SSD) can vary drastically across environments, demonstrating pronounced sex-specific plasticity. In insects, females are usually the larger and more plastic sex. However, the shortage of taxa with male-biased SSD hampers the assessment of whether the greater plasticity in females is driven by selection on size or represents an effect of the female reproductive role. Here we specifically address the role of sex-specific plasticity of body size in the evolution of SSD reversals to disentangle sex and size effects.

2.We first investigate sex-specific body size plasticity in Sepsis punctum and S. neocynipsea as two independent cases of intraspecific SSD reversals in sepsid flies. In both species, directional variation in SSD between populations is driven by stronger sexual selection on male size. Using controlled laboratory breeding, we find evidence for sex-specific plasticity and increased condition dependence of male size in populations with male-biased SSD, ...

1. 性大小二态性（Sexual size dimorphism, SSD）可随环境发生剧烈变化，呈现出显著的性别特异性可塑性。在昆虫类群中，雌性通常体型更大且可塑性更强。然而，具有雄性偏向性大小二态性的类群较为稀缺，这制约了学界对雌性更高可塑性成因的评估：其究竟是由体型选择驱动，还是源于雌性生殖角色的影响。本研究聚焦于体型的性别特异性可塑性在性大小二态性逆转演化中的作用，以厘清性别与体型各自的效应。
2. 本研究以尖眼粪蝇科（Sepsidae）的两个独立物种——斑眼粪蝇（Sepsis punctum）与新胞粪蝇（S. neocynipsea）的种内性大小二态性逆转作为独立研究案例，率先探究二者体型的性别特异性可塑性。在这两个物种中，种群间性大小二态性的方向性差异，由对雄性体型的更强性选择所驱动。通过可控实验室繁育实验，我们在具有雄性偏向性大小二态性的种群中，观测到性别特异性可塑性以及雄性体型条件依赖性增强的相关证据……