Phylogenomic evidence for multiple losses of flight in ratite birds.
Ratites (ostriches, emus, rheas, cassowaries, and kiwis) are large, flightless birds that have long fascinated biologists. Their current distribution on isolated southern land masses is believed to reflect the breakup of the paleocontinent of Gondwana. The prevailing view is that ratites are monophyletic, with the flighted tinamous as their sister group, suggesting a single loss of flight in the common ancestry of ratites. However, phylogenetic analyses of 20 unlinked nuclear genes reveal a genome-wide signal that unequivocally places tinamous within ratites, making ratites polyphyletic and suggesting multiple losses of flight. Phenomena that can mislead phylogenetic analyses, including long branch attraction, base compositional bias, discordance between gene trees and species trees, and sequence alignment errors, have been eliminated as explanations for this result. The most plausible hypothesis requires at least three losses of flight and explains the many morphological and behavioral similarities among ratites by parallel or convergent evolution. Finally, this phylogeny demands fundamental reconsideration of proposals that relate ratite evolution to continental drift.
Harshman
John
J
Zoology Department, Field Museum of Natural History, 1400 South Lakeshore Drive, Chicago, IL 60605, USA.
Braun
Edward L
EL
Braun
Michael J
MJ
Huddleston
Christopher J
CJ
Bowie
Rauri C K
RC
Chojnowski
Jena L
JL
Hackett
Shannon J
SJ
Han
Kin-Lan
KL
Kimball
Rebecca T
RT
Marks
Ben D
BD
Miglia
Kathleen J
KJ
Moore
William S
WS
Reddy
Sushma
S
Sheldon
Frederick H
FH
Steadman
David W
DW
Steppan
Scott J
SJ
Witt
Christopher C
CC
Yuri
Tamaki
T