Skull morphological evolution in Malagasy endemic Nesomyinae rodents.

Madagascar is a large island to the south-east of Africa and in many ways continental in size and ecological complexity. Here we aim to define how skull morphology of an endemic and monophyletic clade of rodents (sub-family Nesomyinae), that show considerable morphological variation, have evolved and how their disparity is characterized in context of the geographical and ecological complexity of the island. We performed a two-dimensional geometric morphometric analysis on 370 dorsal and 399 ventral skull images of 19 species (comprising all nine extant endemic genera) and tested the influence of three ecological parameters (climate, locomotor habitat and nychthemeral cycle) in a phylogenetic context on size and shape. The results indicate that skull shape appears to importantly reflect phylogeny, whereas skull size does not carry a significant phylogenetic signal. Skull shape is significantly influenced by climate while, skull size is not impacted by any of the ecological factors tested, which is controversial to expectations in an insular context. In conclusion, Nesomyinae must have evolved under unusual types of local constraints, preventing this radiation from demonstrating strong ecological release.