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.

We assembled a matrix of morphological character data from measurements made by Livezey (2003). These data were supplemented by the standard body lengths of rails reported in the Handbook of the Birds of the World Alive Online (del Hoyo et al. 2015).

Molecular data are available for 88 rail species and 7 outgroups species. Five genetic markers were used including 3 mitochondrial genes (COI, cyt-b, 16S) and 2 nuclear genes (FGB, RAG-1) from Garcia-R et. al (2014a).

Convergent morphological responses to loss of flight in rails (Aves: Rallidae)
Julien Gaspar*, Gillian C. Gibb1, Steve A. Trewick2

*,1,2Ecology Group, Institute of Agriculture and Environment, Massey University, Private Bag 11-222, Palmerston North, New Zealand
*j.gaspar@massey.ac.nz
* https://orcid.org/0000-0003-3985-4436
1 https://orcid.org/0000-0002-4283-9790
2 https://orcid.org/0000-0002-4680-8457

Alignment.phy : alignment used for phylogenetic analysis 
RAxML_tree.nex : Phylogenetic tree from Appendix 1 Figure A1
Tree_52.nex : Phylogenetic tree used for Figure 4 

Script.R : Script used to make the statistical analysis and create the graphs 
Data_52_ratios: R input file 
Data_52_S: R input file
Data_52_S_tips: R input file
Data_75_S: R input file
Data_90: R input file
Datasets_morphological_data.xlsx: Excel file including the matrix of morphological character