Data from: Thorson’s rule, life history evolution and diversification of benthic octopuses (Cephalopoda: Octopodoidea)

Here we evaluate the so-called Thorson’s rule, which posits that direct-development and larger eggs are favored towards the poles in marine organisms and whose validity been the subject of considerable debate in the literature, combining an expanded phenotypic dataset encompassing 60 species of benthic octopuses with a new molecular phylogeny. Phylogenetic reconstruction shows two clades: clade 1 including species of the families Eledonidae, Megaleledonidae, Bathypolypodidae and Enteroctopodidae, and clade 2 including species of Octopodidae. Egg size, development mode and all environmental variables exhibited phylogenetic signal, partly due to differences between the two clades: whereas most species in clade 1 inhabit cold and deep waters, exhibit large eggs and hatchling with holobenthic development, species from clade 2 inhabit tropical-temperate and shallow waters, evolved small eggs and generally exhibit merobenthic development. Phylogenetic regressions show that egg size exhibits a conspicuous latitudinal cline, and that both egg size and development mode vary with water temperature. Additionally, analyses suggest that egg size is constrained by body size in lineages with holobenthic development. Taken together, results suggest that the variation in egg size and development mode across benthic octopuses is adaptive and associated with water temperature, supporting Thorson’s rule in these organisms.

本研究结合涵盖60种底栖章鱼的扩展表型数据集与全新的分子系统发育（molecular phylogeny）分析，对索恩法则（Thorson’s rule）展开评估。该法则提出，海洋生物的直接发育与大型卵在极地环境中更受青睐，其有效性在学界曾引发广泛争议。系统发育重建结果显示存在两个演化支：演化支1包含电蛸科（Eledonidae）、巨鳍蛸科（Megaleledonidae）、深居蛸科（Bathypolypodidae）和肠蛸科（Enteroctopodidae）的物种，演化支2则涵盖蛸科（Octopodidae）的物种。卵大小、发育模式与所有环境变量均表现出系统发育信号，这在一定程度上源于两个演化支间的差异：演化支1的多数物种栖息于寒冷深水环境，产下大型卵且幼体为全底栖发育（holobenthic development）；而演化支2的物种则栖息于热带-温带浅水环境，产下小型卵，幼体通常为半底栖发育（merobenthic development）。系统发育回归分析结果显示，卵大小呈现出显著的纬度梯度格局，且卵大小与发育模式均随水温发生变化。此外，分析结果表明，在实行全底栖发育的演化支中，卵大小受个体体型的制约。综合来看，研究结果表明，底栖章鱼的卵大小与发育模式变异具有适应性，且与水温密切相关，从而支持了该类群中索恩法则的合理性。