Climate-driven diversification in two widespread Galerida larks.
BACKGROUND
The major impact of Plio-Pleistocene climatic oscillations on the current genetic structure of many species is widely recognised but their importance in driving speciation remains a matter of controversies. In addition, since most studies focused on Europe and North America, the influence of many other biogeographic barriers such as the Sahara remains poorly understood. In this paper, climate-driven diversification was investigated by using a comparative phylogeographic approach in combination with phenotypic data in two avian species groups distributed on both sides of the deserts belt of Africa and Asia. In particular, we tested whether: 1) vicariance diversification events are concomitant with past climatic events; and 2) current ecological factors (using climate and competition as proxies) contribute to phenotypic divergence between allopatric populations.


RESULTS
Mitochondrial and nuclear sequence data indicated that the crested and Thekla lark species groups diverged in the early Pliocene and that subsequent speciation events were congruent with major late Pliocene and Pleistocene climatic events. In particular, steep increase in aridity in Africa near 2.8 and 1.7 million years ago were coincident with two north-south vicariance speciation events mediated by the Sahara. Subsequent glacial cycles of the last million years seem to have shaped patterns of genetic variation within the two widespread species (G. cristata and G. theklae). The Sahara appears to have allowed dispersal from the tropical areas during climatic optima but to have isolated populations north and south of it during more arid phases. Phenotypic variation did not correlate with the history of populations, but was strongly influenced by current ecological conditions. In particular, our results suggested that (i) desert-adapted plumage evolved at least three times and (ii) variation in body size was mainly driven by interspecific competition, but the response to competition was stronger in more arid areas.


CONCLUSIONS
Climatic fluctuations of the Plio-Pleistocene strongly impacted diversification patterns in the Galerida larks. Firstly, we found that cladogenesis coincides with major climatic changes, and the Sahara appears to have played a key role in driving speciation events. Secondly, we found that morphology and plumage were strongly determined by ecological factors (interspecific competition, climate) following vicariance.
Guillaumet
Alban
A
Institut des Sciences de l'Evolution, C.C. 63, Université de Montpellier II, Place E. BATAILLON, 34095 Montpellier Cedex, France. alban.guillaumet@cefe.cnrs.fr
Crochet
Pierre-André
PA
Pons
Jean-Marc
JM
D000349:Africa; D000818:Animals; D001208:Asia; D002980:Climate; D004272:DNA, Mitochondrial / Q000737:chemistry / Q000235:genetics; D019143:Evolution, Molecular; D014644:Genetic Variation / Q000235:genetics; D005828:Genetics, Population; D005843:Geography; D046109:Passeriformes / Q000145:classification / Q000235:genetics* / Q000254:growth & development; D010802:Phylogeny; D017422:Sequence Analysis, DNA
D004272:DNA, Mitochondrial