Aim: The expansion of open habitats during the mid‐Miocene has been hypothesized
as a driver of allopatric speciation for many African taxa. This habitat‐dependent
mode of diversification has been implicated in the shift from C3 (e.g. forest/woodland)
to C4 dominated systems (i.e. open savanna, grasslands) in a number of African
squamates. We examined this hypothesis using a genus of African viperid snakes
(Bitis) with both open habitat and forest‐dwelling representatives.
Methods: A comprehensive multilocus dataset was used to generate a calibrated
species tree using a multispecies coalescent model. Individual gene trees and patterns
of nuclear allele sharing were used to assess species monophyly and isolation.
To test the habitat‐dependent evolution hypothesis, we generated an ancestral character
state reconstruction for open and closed habitats using the dated phylogeny.
This was related to the timing of open habitat expansion and forest/woodland contraction
Results: The genus Bitis originated in the Oligocene, with species level diversification
in the late Miocene/Pliocene. Four well‐supported clades correspond to the recognized
subgenera Bitis, Keniabitis, Macrocerastes and Calechidna. Several previously
unrecognized lineages potentially represent cryptic species.
Main conclusions: Habitat‐dependent evolution does not appear to have been a
main driver for generic level viperine diversification: the ancestral state for Bitis
was open habitat and at least one clade moved into forest in the Miocene, long after
forest had contracted and fragmented. Forest‐dependent species diversified only
in the late Miocene, presumably as forest became further reduced in extent, fitting
an allopatric model of speciation. Although our results do not favour a general pattern
of habitat‐dependent diversification in Bitis, cladogenesis within the subgenus
Calechidna for “arenicolous” species (Bitis caudalis complex) and “rupicolous” species
(B. atropos‐cornuta complex), corresponds to the aridification of southwest Africa.