Data from: 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, but not of female size in populations with female-biased SSD, indicating no adaptive canalization of female size. 3.To extend the comparative scope, we next estimate sex-specific body size plasticity in eight additional fly species that differ in the direction of SSD under laboratory conditions. In all species with male-biased SSD we find males to be the more plastic sex, while this was only rarely the case in species with female-biased SSD, thus suggesting a more general trend in Diptera. 4.To examine the generality of this pattern in holometabolous insects, we combine our data with data from the literature in a meta-analysis. Again, male body size tends to be more plastic than female size when males are the larger sex, though female size is now also generally more plastic when females are larger. 5.Our findings indicate that primarily selection on size, rather than the reproductive role per se, drives the evolution of sex-specific body size plasticity. However, sepsid flies, and possibly Diptera in general, show a clear sexual asymmetry with greater male than female plasticity related to SSD, likely driven by strong sexual selection on males. Although further research controlling for phylogenetic and ecological confounding effects is needed, our findings are congruent with theory in suggesting that condition dependence plays a pivotal role in the evolution of sexual size dimorphism.1. 性体型二态性（Sexual size dimorphism, SSD）可随环境发生剧烈变化，表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，目前具备雄性偏向型性体型二态性的类群较为匮乏，这阻碍了我们评估雌性更强的可塑性究竟是由体型选择驱动，还是源于雌性生殖角色的影响。本研究聚焦于体型性别特异性可塑性在性体型二态性反转演化中的作用，以厘清性别与体型效应各自的贡献。 2. 本研究首先以两种具有种内性体型二态性反转的扁脚蝇（Sepsid flies）类群——斑眼扁脚蝇（Sepsis punctum）和新尖眼扁脚蝇（S. neocynipsea）——为独立研究对象，探究其体型的性别特异性可塑性。两个物种种群间的性体型二态性方向性差异，均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，我们发现：在雄性偏向型性体型二态性的种群中，雄性体型存在性别特异性可塑性且条件依赖性增强；而在雌性偏向型性体型二态性的种群中，雌性体型并无此类特征，表明雌性体型未出现适应性稳态。 3. 为拓展比较研究的范围，本研究接下来在实验室条件下，对另外8种性体型二态性方向各异的蝇类的体型性别特异性可塑性进行了评估。在所有雄性偏向型性体型二态性的物种中，雄性均为可塑性更强的性别；而在雌性偏向型的物种中，这一现象极少出现，这提示双翅目（Diptera）中存在这一更为普遍的演化趋势。 4. 为验证这一模式在全变态昆虫（holometabolous insects）中的普遍性，我们将本研究数据与文献数据相结合，开展了元分析（meta-analysis）。分析结果再次显示：当雄性体型更大时，雄性体型的可塑性通常高于雌性；不过当雌性体型更大时，雌性体型的可塑性如今也普遍更高。 5. 本研究结果表明，驱动体型性别特异性可塑性演化的主要因素是体型选择，而非生殖角色本身。不过，扁脚蝇科昆虫乃至整体双翅目，均呈现出清晰的性别不对称性：与性体型二态性相关的雄性可塑性高于雌性，这一现象可能由对雄性的强性选择所驱动。尽管未来仍需开展控制了系统发育与生态混淆因素的进一步研究，但本研究结果与相关理论相符，即条件依赖性在性体型二态性的演化中发挥着关键作用。