Data from: Facultative paedomorphosis as a mechanism promoting intraspecific niche differentiation

Organisms with complex life cycles are characterized by a metamorphosis that allows for a major habitat shift and the exploitation of alternative resources. However, metamorphosis can be bypassed in some species through a process called paedomorphosis, resulting in the retention of larval traits at the adult stage and is considered important at both micro- and macroevolutionary scales. In facultatively paedomorphic populations of newts, some individuals retain gills and a fully aquatic life at the adult stage (paedomorphs), while others undergo complete metamorphosis (metamorphs), allowing for a terrestrial life-stage. Because facultative paedomorphosis affects trophic structures and feeding mechanism of newts, one hypothesis is that it may be maintained as a trophic polymorphism, with the advantage to lessen intraspecific competition during the shared aquatic life-stage. Here, we tested this hypothesis combining stomach content data with stable isotope techniques, using carbon and nitrogen stable isotopes, in facultatively paedomorphic alpine newts (Ichthyosaura alpestris). Both stomach content and stable isotope analyses showed that paedomorphs had smaller trophic niches and were more reliant on pelagic resources, while metamorphs relied more on littoral resources, corresponding to a polyphenism along the littoral-pelagic axis and the extension of the population’s trophic niche to otherwise ‘underused’ pelagic resources by paedomorphs. Interestingly, stable isotopes revealed that the trophic polyphenism was less marked in males than in females and potentially linked to sexual activity. Although paedomorphosis and metamorphosis are primarily seen as results of trade-offs between the advantages of using aquatic versus terrestrial habitats, this study provides evidence that additional forces, such as intraspecific trophic niche differences between morphs and trophic niche expansion, may play an important role in the persistence of this dimorphism in heterogeneous environments. Moreover, the different patterns found in males and females show the importance of considering sex to understand the evolutionary ecology of trophic polymorphisms.具有复杂生活史的生物以变态为典型特征，该过程可使其实现生境的重大转换并开发替代性资源。然而，部分物种可通过幼态持续（paedomorphosis）过程绕过变态，最终在成虫阶段保留幼虫性状，该现象被认为在微观与宏观进化尺度上均具有重要意义。在蝾螈的兼性幼态持续（facultatively paedomorphic）种群中，部分个体在成虫阶段仍保留鳃并维持完全水生生活（幼态持续型个体），其余个体则完成完全变态（变态型个体），进而进入陆生生活阶段。由于兼性幼态持续会影响蝾螈的营养结构与取食机制，有假说提出，该现象可作为一种营养多态性（trophic polymorphism）得以维持，其优势在于能在共享的水生生活阶段缓解种内竞争。本研究以阿尔卑斯蝾螈（Ichthyosaura alpestris）的兼性幼态持续种群为研究对象，结合胃容物数据与碳、氮稳定同位素（stable isotope）技术对该假说进行了验证。胃容物与稳定同位素分析结果均显示，幼态持续型个体的营养生态位更小，且更依赖远洋水生资源（pelagic resources）；而变态型个体则更多利用沿岸资源（littoral resources），这对应了沿沿岸-远洋轴分布的表型多态性（polyphenism），且幼态持续型个体可将种群的营养生态位拓展至此前未被充分利用的远洋水生资源。值得注意的是，稳定同位素分析还揭示，雄性个体间的营养多态性较雌性个体更不显著，且这一差异可能与性活动相关。尽管幼态持续与变态通常被视为权衡水生与陆生生境利用优势的结果，但本研究证实，额外的驱动因素——例如不同形态个体间的种内营养生态位差异与营养生态位拓展——在异质环境中该二态性的维持中发挥了重要作用。此外，雌雄个体间的差异模式表明，在探究营养多态性的进化生态学时，考虑性别因素至关重要。