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...