Abstract
The relationship between rates of diversification and of body size change (a common proxy for phenotypic evolution) was investigated across Elapidae, the largest radiation of highly venomous snakes. Time-calibrated phylogenetic trees for 175 species of elapids (more than 50% of known taxa) were constructed using seven mitochondrial and nuclear genes. Analyses using these trees revealed no evidence for a link between speciation rates and changes in body size. Two clades (Hydrophis, Micrurus) show anomalously high rates of diversification within Elapidae, yet exhibit rates of body size evolution almost identical to the general elapid ‘background’ rate. Although correlations between speciation rates and rates of body size change exist in certain groups (e.g. ray-finned fishes, passerine birds), the two processes appear to be uncoupled in elapid snakes. There is also no detectable shift in diversification dynamics associated with the colonization of Australasia, which is surprising given that elapids appear to be the first clade of venomous snakes to reach the continent.
Highlights
Recent studies investigating the relationship between speciation rates and morphological evolution have produced contrasting results
Phylogenetic tests of this association have suggested a positive correlation between rates of speciation and phenotypic evolution in passerine birds [1] and ray-finned fishes [2], but no such association was found in mammals [3] and New World squamates [4], while both patterns have been proposed in plethodontid salamanders [5,6]
It has often been suggested that elevated speciation rates might be correlated with increased rates of morphological change, and broad-scale phylogenetic evidence for this hypothesis has been found in some instances (e.g. [1,2,6]), but not others (e.g. [3,4,5])
Summary
Recent studies investigating the relationship between speciation rates and morphological evolution have produced contrasting results. A link between elevated rates of speciation and morphological evolution would be reflected in highly speciose lineages exhibiting greater morphological disparity; groups with low species diversity should exhibit less disparity. Phylogenetic tests of this association have suggested a positive correlation between rates of speciation and phenotypic evolution in passerine birds [1] and ray-finned fishes [2], but no such association was found in mammals [3] and New World squamates [4], while both patterns have been proposed in plethodontid salamanders [5,6]. The potential confounding factor of extinction is likely to be less problematic in molecular phylogenies of young, rapidly radiating groups such as that presented here, due to the fast net diversification of these clades, and the potentially high fraction of total species diversity that still survives
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