Data from: Evolution of extreme ontogenetic allometric diversity and heterochrony in pythons, a clade of giant and dwarf snakes

Ontogenetic allometry, how species change with size through their lives, and heterochony, a decoupling between shape, size and age, are major contributors to biological diversity. However, macro-evolutionary allometric and heterochronic trends remain poorly understood because previous studies have focused on small groups of closely related species. Here we focus on testing hypotheses about the evolution of allometry and how allometry and heterochrony drive morphological diversification at the level of an entire species-rich and diverse clade. Pythons are a useful system due to their remarkably diverse and well-adapted phenotypes and extreme size disparity. We collected detailed phenotype data on 40 of the 44 species of python from 1,191 specimens. We used a suite of analyses to test for shifts in trajectories that modify morphological diversity. Heterochrony is the main driver of initial divergence within python clades, and shifts in the slopes of allometric trajectories make exploration of novel phenotypes possible later in divergence history. We found that allometric coefficients are highly evolvable and there is an association between ontogenetic allometry and ecology, suggesting that allometry is both labile and adaptive rather than a constraint on possible phenotypes.

个体发育异速生长（ontogenetic allometry）指物种一生中随体型变化的规律，而异时性（heterochrony，原文此处笔误为heterochony）则指形态、体型与年龄之间的解耦现象，二者均为生物多样性形成的核心驱动因素。然而，宏观进化层面的异速生长与异时性演化趋势仍有待深入阐释，因既往相关研究多聚焦于近缘物种的狭小类群。本研究旨在检验两类假说：一是异速生长的演化模式，二是异速生长与异时性如何驱动整个物种丰富、多样的演化支的形态多样性分化。蟒蛇类是极佳的研究体系，因其表型极为多样且适应性极强，同时体型差异悬殊。我们采集了1191号标本的详细表型数据，涵盖44个已知蟒蛇物种中的40种。我们运用一系列分析方法，对能够改变形态多样性的演化轨迹偏移展开检验。研究结果显示，异时性是蟒科类群初始分化的核心驱动因素，而异速生长轨迹的斜率偏移则为分化后期探索全新表型提供了可能。我们发现异速生长系数具有极高的演化可塑性，且个体发育异速生长与生态习性存在显著关联，这表明异速生长兼具易变性与适应性，而非制约表型演化的硬性束缚。