Abstract
Colonisation of new geographic regions and/or of new ecological resources can result in rapid species diversification into the new ecological niches available. Members of the subgenus Drosophila are distributed across the globe and show a large diversity of ecological niches. Furthermore, taxonomic classification of Drosophila includes the rank radiation, which refers to closely related species groups. Nevertheless, it has never been tested if these taxonomic radiations correspond to evolutionary radiations. Here we present a study of the patterns of diversification of Drosophila to test for increased diversification rates in relation to the geographic and ecological diversification processes. For this, we have estimated and dated a phylogeny of 218 species belonging to the major species groups of the subgenus. The obtained phylogenies are largely consistent with previous studies and indicate that the major groups appeared during the Oligocene/Miocene transition or early Miocene, characterized by a trend of climate warming with brief periods of glaciation. Ancestral reconstruction of geographic ranges and ecological resource use suggest at least two dispersals to the Neotropics from the ancestral Asiatic tropical disribution, and several transitions to specialized ecological resource use (mycophagous and cactophilic). Colonisation of new geographic regions and/or of new ecological resources can result in rapid species diversification into the new ecological niches available. However, diversification analyses show no significant support for adaptive radiations as a result of geographic dispersal or ecological resource shift. Also, cactophily has not resulted in an increase in the diversification rate of the repleta and related groups. It is thus concluded that the taxonomic radiations do not correspond to adaptive radiations.
Highlights
The large diversity of life forms that we see today is the result of different biological processes, one of which is adaptive radiation [1,2,3]
These results show that the presence of non-overlapping sequences is not a significant source of bias in the present study
The crown age of the subgenus Drosophila is placed in the Eocene/Oligocene transition around 34.33 Mya (30.24–38.30 Mya 95% HPD) when all 9 calibration points are used, while it is placed in the Oligocene/Miocene transition, 23.79 Mya (19.24– 28.83 Mya 95% HPD), when the calibration points used are reduced to 5 (Fig. 1 and 3)
Summary
The large diversity of life forms that we see today is the result of different biological processes, one of which is adaptive radiation [1,2,3]. A pattern that is generally considered to be the result of an adaptive radiation is when there is a rapid origin of species that adapt to a diversity of ecological niches followed by a slow down of the diversification rate through time as the new niches become occupied [2,6]. This is a common pattern observed in many taxonomic groups This is a common pattern observed in many taxonomic groups (e.g. [7,8,9,10])
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