Data from: Convergent morphological responses to loss of flight in rails (Aves: Rallidae)

The physiological demands of flight exert strong selection pressure on
avian morphology and so it is to be expected that the evolutionary loss of
flight capacity would involve profound changes in traits. Here we
investigate morphological consequences of flightlessness in a bird family
where the condition has evolved repeatedly. The Rallidae include more than
130 recognised species of which over 30 are flightless. Morphological and
molecular phylogenetic data were used here to compare species with and
without the ability to fly in order to determine major phenotypic effects
of the transition from flighted to flightless. We find statistical support
for similar morphological response among unrelated flightless lineages,
characterised by a shift in energy allocation from the forelimbs to the
hindlimbs. Indeed flightless birds exhibit smaller sterna and wings than
flighted taxa in the same family along with wider pelves and more robust
femora. Phylogenetic signal tests demonstrate that those differences are
independent of phylogeny and instead demonstrate convergent morphological
adaptation associated with a walking ecology. We found too that
morphological variation was greater among flightless rails than flighted
ones, suggesting that relaxation of physiological demands during the
transition to flightlessness frees morphological traits to evolve in
response to more varied ecological opportunities.