Identifying the evolutionary processes that underlie morphological variation at the intraspecific level is cornerstone for understanding the drivers of phenotypic diversity at higher macro-evolutionary scales. The fire salamander, Salamandra salamandra, exhibits exceptional intraspecific variation in multiple phenotypic traits (i.e. body size, head shape, coloration, reproductive modes). Pueriparity (females laying fully metamorphosed juveniles) in S. salamandra entails modifications during embryonic development in comparison to larviparity (females laying aquatic larvae), which is the ancestral reproductive mode. These heterochronic modifications involve a general acceleration of development and mainly focus on cephalic structures to facilitate intrauterine active feeding, which might impact head shape in the adult stage. In the present study, we (i) describe the main features of head shape variation in adults of the two distinct subspecies of Salamandra salamandra that independently evolved to pueriparity, and (ii) explore the morphological consequences of developmental and functional changes related to this major evolutionary shift. Our results show that evolutionary history, and not reproductive mode, is the main driver of head shape variation in S. salamandra. These results suggest different evolutionary processes acting differentially on each subspecies, at least at the adult stage. The present study highlights the importance of comparative studies integrating evolutionary histories and ontogenetic trajectories to explore the different sources of observed morphological diversification.

中文翻译：

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进化史，而不是与异时变体修饰相关联的繁殖多态性物种，Salamandra salamandra的胎盘驱动头形状分化。

在种内水平鉴定出形态学变异基础的进化过程，是理解更高宏观进化尺度上表型多样性驱动因素的基石。火sal Salamandra salamandra在多种表型特征（即体型，头部形状，着色，生殖方式）上表现出出众的种内变异。Pueriparity（女铺设完全变质少年）在S.蝾螈与幼体（雌性产水生幼虫）相比，它在胚胎发育过程中需要进行修饰，这是祖先的繁殖方式。这些异时的修饰涉及发育的总体加速，并且主要集中在有助于子宫内主动喂养的头状结构上，这可能会影响成年期的头部形状。在本研究中，我们（i）描述了独立地发展为产卵的Salamandra salamandra的两个不同亚种的成年人头部形状变化的主要特征，以及（ii）探索了与该主要物种相关的发育和功能变化的形态学后果进化的转变。我们的结果表明，进化史而非生殖方式是导致头部形状变化的主要因素。S. salamandra。这些结果表明至少在成年阶段，不同的进化过程对每个亚种的作用不同。本研究强调了将进化史和个体发生轨迹相结合的比较研究的重要性，以探索观察到的形态多样性的不同来源。