Climate-driven diversification in two widespread Galerida larks

Abstract

BackgroundThe 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.ResultsMitochondrial 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.ConclusionClimatic 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.

Multilocus phylogeny of the avian family Alaudidae (larks) reveals complex morphological evolution, non-monophyletic genera and hidden species diversity

“…2). The most recent split between marginally sympatric, reproductively isolated species (Galerida cristata and G. macrorhyncha; Guillaumet et al, 2005Guillaumet et al, , 2006Guillaumet et al, , 2008 was estimated to 1.9 MYA (95% HPD 1.3-2.7 MYA; indicated by orange line in Fig. 2).…”

“…García-Moreno, 2004;Lovette, 2004;Penny, 2005; but see Weir and Schluter, 2008, whose average rate we have adopted), we emphasize the relative ages of different clades more than the actual ages inferred. Guillaumet et al (2005Guillaumet et al ( , 2006Guillaumet et al ( , 2008 discovered two primary clades within Galerida cristata, which had reached reciprocal monophyly in mtDNA and showed evidence of strong reproductive isolation in their narrow contact zone in Morocco. These were later recognised as separate species, Galerida cristata sensu stricto and G. macrorhyncha (Gill and Donsker, 2012).…”

“…As all available G. macrorhyncha sequences are from Morocco, at the western edge of the purported range of the taxon randoni (Cramp, 1988;de Juana, 2004), and as there are no samples from or close to the Algerian type localities of randoni and macrorhyncha, more research is needed on the circumscription and nomenclature of these taxa. Guillaumet et al (2008) showed using cytb sequences that the subspecies Galerida theklae praetermissa (Ethiopia) and G. t. ellioti (Somalia) are deeply diverged from the northwest African subspecies, and also fairly distinct from each other. Using mainly the same data, the present study infers the split between the populations from northwest Africa and the Horn of Africa to be approximately the same as that between the youngest widely sympatric reproductively isolated species pair.…”

“…This pattern provides camouflage in the open, grassy or arid habitats where larks occur, and several authors have noted a positive correlation between the coloration of the upperparts of a species and the colour of the soil on which it lives (Bannerman, 1927;Guillaumet et al, 2008;Kleinschmidt, 1907Kleinschmidt, , 1912Meinertzhagen, 1951;Niethammer, 1940;Vaurie, 1951). In most species, there is no sexual dimorphism in plumage, although males average larger than females.…”

“…Recent studies based on molecular and/or vocal data have revealed considerable hidden diversity and taxonomic confusion in some taxa (Alström, 1998;Ryan et al, 1998;Ryan and Bloomer, 1999;Guillaumet et al, 2005Guillaumet et al, , 2006Guillaumet et al, , 2008, and it seems likely that the total number of recognised lark species is underestimated.…”