Data from: Evolution of alternative male morphotypes in oxyurid nematodes: a case of convergence?

Male dimorphism has been reported across different taxa, and is usually expressed as the coexistence of a larger morph with exaggerated male traits and a smaller one with reduced traits. The evolution and maintenance of male dimorphism are still poorly understood for several of the species in which it has been observed. Here, we analyse male dimorphism in several species of reptile parasitic nematodes of the genus Spauligodon, in which a major male morph (exaggerated morph), which presents the traditional male morphological traits reported for this taxon, coexists with a minor morph with reduced morphological traits (i.e. reduced genital papillae) resembling more closely the males of the sister genus Skrjabinodon than Spauligodon major males. Because of the level of uncertainty in the results of ancestral state reconstruction, it is unclear if the existence of male dimorphism in this group represents independent instances of convergent evolution or an ancestral trait lost multiple times. Also, although the number of major males per host was positively correlated with the number of females, the same did not hold true for minor males, whose presence was not associated with any other ecological factor. Nevertheless, the existence of male dimorphism in Spauligodon nematodes is tentatively interpreted as resulting from alternative reproductive tactics, with differences in presence and number of individuals as indicators of differences in fitness, with the lower numbers of minor males per host likely maintained by negative frequency-dependent selection.跨多个分类群均已报道存在雄性二态性，其通常表现为两种雄性形态共存：一种为体型更大且具夸张雄性特征的形态，另一种为体型更小且特征弱化的形态。截至目前，对于已观测到雄性二态性的多个物种，其演化与维持机制仍未被充分阐明。本研究针对多个隶属于Spauligodon属的爬行动物寄生线虫物种的雄性二态性展开分析：该类群中，一种为主导雄性形态（夸张型形态），具备该分类群已报道的典型雄性形态特征；另一种为次要雄性形态，其形态特征弱化（如生殖乳突缩减），相较于Spauligodon属的主导雄性个体，该形态与姊妹属Skrjabinodon的雄性更为相似。由于祖先状态重建的结果存在较高不确定性，目前尚无法明确该类群的雄性二态性究竟是多次独立演化产生的趋同进化结果，还是源自某一祖先性状的多次独立丢失事件。此外，尽管单宿主体内的主导雄性个体数量与雌性个体数量呈正相关，但这一规律并不适用于次要雄性个体——次要雄性的存在与其他任何生态因子均无关联。尽管如此，我们暂将Spauligodon属线虫的雄性二态性解读为替代生殖策略的产物：个体存在与否及种群数量差异可作为适合度差异的指示指标，而单宿主体内次要雄性个体数量较低的现象，大概率由负频率依赖选择所维持。