The Malagassy Giant & Warty Chameleons: Furcifer oustaleti & Furcifer verrucosus

Abstract

The Malagasy giant chameleons (Furcifer oustaleti and Furcifer verrucosus) are sister species that are both broadly distributed in Madagascar, and also endemic to the island. These species are also morphologically similar and, because of this, have been frequently misidentified in the field. Previous studies have suggested that cryptic species are nested within this chameleon group, and two subspecies have been described in F. verrucosus. In this study, we utilized a phylogeographic approach to assess genetic diversification within these chameleons. This was accomplished by (1) identifying clades within each species supported by both mitochondrial and nuclear DNA, (2) assessing divergence times between clades, and (3) testing for niche divergence or conservatism. We found that both F. oustaleti and F. verrucosus could be readily identified based on genetic data, and within each species, there are two well-supported clades. However, divergence times are not contemporary and spatial patterns are not congruent. Diversification within F. verrucosus occurred during the Plio-Pleistocene, and there is evidence for niche divergence between a southwestern and southeastern clade, in a region of Madagascar that shows no obvious landscape barriers to dispersal. Diversification in F. oustaletioccurred earlier in the Pliocene or Miocene, and niche conservatism is supported with two genetically distinct clades separated at the Sofia River in northwestern Madagascar. Divergence within F. verrucosus is most consistent with patterns expected from ecologically mediated speciation, whereas divergence in F. oustaleti most strongly matches the patterns expected from the riverine barrier hypothesis.

Conclusions

We found that there are two well-supported clades within both Furcifer oustaleti and F. verrucosus, using both mitochondrial and nuclear data. However, there are no clear morphological distinctions between the genetic clades found within each species. We thus hesitate in describing new species at this time, especially since nuclear and morphological support for each clade is low, but note that additional genetic data may strengthen the case for dividing these taxa into additional species.
This study has also clarified the range of the Malagasy giant chameleons. The range of the F. verrucosus complex is restricted to southern and southwestern Madagascar, and the species complex is found only as far north as the Mangoky River in the southwest. However, the F. oustaleti complex has a large distribution, ranging as far south as Marolinta and throughout central and northern Madagascar. Additionally, clades within F. verrucosus have a parapatric distribution, whereas clades within F. oustlaeti are allopatrically distributed across the Sofia river. Diversification in the F. verrucosus complex occurred during the Plio-Pleistocene, niche divergence is supported, and the sister clades are parapatrically distributed. In contrast, diversification within F. oustaleti occurred earlier, either in the Pliocene or Miocene, clades are allopatrically distributed across the Sofia River in Madagascar, and niches between the sister clades are conserved. Divergence within F. verrucosus is most consistent with patterns expected from ecologically mediated speciation, whereas divergence in F. oustaleti most strongly matches the patterns expected from the riverine barrier hypothesis.