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 371 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.