Data from: Coevolution of female and male genital components to avoid genital size mismatches in sexually dimorphic spiders

Background: In most animal groups, it is unclear how body size variation relates to genital size differences between the sexes. While most morphological features tend to scale with total somatic size, this does not necessarily hold for genitalia because divergent evolution in somatic size between the sexes would cause genital size mismatches. Theory predicts that the interplay of female-biased sexual size dimorphism (SSD) and sexual genital size dimorphism (SGD) should adhere to the ‘positive genital divergence’, the ‘constant genital divergence’, or the ‘negative genital divergence’ model, but these models remain largely untested. We test their validity in the spider family Nephilidae known for the highest degrees of SSD among terrestrial animals. Results: Through comparative analyses of sex-specific somatic and genital sizes, we first demonstrate that 99 of the 351 pairs of traits are phylogenetically correlated. Through factor analyses we then group these traits for MCMCglmm analyses that test broader correlation patterns, and these reveal significant correlations in 10 out of the 36 pairwise comparisons. Both types of analyses agree that female somatic and internal genital sizes evolve independently. While sizes of non-intromittent male genital parts coevolve with male body size, the size of the intromittent male genital parts is independent of the male somatic size. Instead, male intromittent genital size coevolves with female (external and, in part, internal) genital size. All analyses also agree that SGD and SSD evolve independently. Conclusions: Internal dimensions of female genitalia evolve independently of female body size in nephilid spiders, and similarly, male intromittent genital size evolves independently of the male body size. The size of the male intromittent organ (the embolus) and the sizes of female internal and external genital components thus seem to respond to selection against genital size mismatches. In accord with these interpretations, we reject the validity of the existing theoretical models of genital and somatic size dimorphism in spiders.背景：在绝大多数动物类群中，躯体尺寸的变异与两性间生殖器大小差异的关联机制仍不明确。尽管多数形态特征通常会随整体躯体尺寸呈比例变化，但生殖器未必遵循这一规律——因为两性躯体尺寸的分化演化可能会引发生殖器大小匹配失衡。理论研究预测，雌性偏倚的性别体型二态性（sexual size dimorphism, SSD）与性别生殖器大小二态性（sexual genital size dimorphism, SGD）之间的相互作用，应符合“正向生殖器分化”“恒定生殖器分化”或“负向生殖器分化”模型，但目前这些模型尚未得到充分验证。本研究以陆生动物中性别体型二态性程度最高的络新妇科（Nephilidae）蜘蛛为研究对象，对上述模型的有效性进行检验。 结果：通过对两性躯体尺寸与生殖器尺寸的比较分析，我们首先证实351个性状对中有99对存在系统发育相关性。随后通过因子分析对这些性状进行分组，用于开展马尔可夫链蒙特卡洛广义混合模型（MCMCglmm）分析以检验更广泛的相关模式，结果显示36组两两比较中有10组存在显著相关性。两类分析均一致表明：雌性躯体尺寸与内生殖器尺寸的演化相互独立。雄性非插入式生殖器部件的尺寸会随雄性躯体尺寸协同演化，而雄性插入式生殖器部件的尺寸则与雄性躯体尺寸无关；与之相反，雄性插入式生殖器的尺寸会与雌性（外生殖器及部分内生殖器）的尺寸协同演化。所有分析还一致证实，性别生殖器大小二态性与性别体型二态性的演化相互独立。 结论：络新妇科蜘蛛雌性生殖器的内部尺寸演化与雌性躯体尺寸无关，同理雄性插入式生殖器尺寸的演化也与雄性躯体尺寸无关。因此，雄性插入式生殖器（引导器embolus）的尺寸，以及雌性内外生殖器各组分的尺寸，似乎均受到了对抗生殖器大小匹配失衡的选择压力作用。与上述结论相符，我们的研究结果不支持现有的蜘蛛躯体与生殖器尺寸二态性理论模型。