Chameleon radiation by oceanic dispersal

Abstract

Historical biogeography is dominated by vicariance methods that search for a congruent pattern of fragmentation of ancestral distributions produced by shared Earth history. A focus of vicariant studies has been austral area relationships and the break-up of the supercontinent Gondwana. Chameleons are one of the few extant terrestrial vertebrates thought to have biogeographic patterns that are congruent with the Gondwanan break-up of Madagascar and Africa. Here we show, using molecular and morphological evidence for 52 chameleon taxa, support for a phylogeny and area cladogram that does not fit a simple vicariant history. Oceanic dispersal--not Gondwanan break-up--facilitated species radiation, and the most parsimonious biogeographic hypothesis supports a Madagascan origin for chameleons, with multiple 'out-of-Madagascar' dispersal events to Africa, the Seychelles, the Comoros archipelago, and possibly Reunion Island. Although dispersal is evident in other Indian Ocean terrestrial animal groups, our study finds substantial out-of-Madagascar species radiation, and further highlights the importance of oceanic dispersal as a potential precursor for speciation.

Large-scale phylogeny of chameleons suggests African origins and Eocene diversification

“…Molecular divergence estimates strongly support a role for oceanic dispersal in shaping historical biogeographic patterns of chameleons, as the earliest divergence events between African and Malagasy species are estimated ca 47-90 Myr ago [14,15]. This is substantially later than the fragmentation event of the Gondwanan supercontinent that has kept these landmasses separated by ca 400-1200 km of open ocean for the last 120 Myr (million years) [16][17][18].…”

“…Although it is therefore evident that oceanic dispersal has played a pivotal role in the current distribution pattern of chameleons, the geographical origin of the family and the direction of dispersal are still uncertain. The hypothesis that chameleons originated in Madagascar and later dispersed to Africa where they subsequently radiated [14] is oft-cited [18][19][20][21], despite some conspicuous inconsistencies in that scenario. Although multiple major chameleon clades are found on Madagascar, the chameleon sistergroup Agamidae does not occur there at present, nor is it in the Malagasy fossil record.…”

Geographical patterns of deep mitochondrial differentiation in widespread Malagasy reptiles

“…Each clade contains several species, spread over the diverse ecological habitats of east and west, without recurrent east-west vicariant patterns at shallower phylogeographic levels (Yoder and Heckman, 2006;Yoder et al, 2000). Deep interspecific north-south splits can also be found in the dwarf chameleons of the genus Brookesia (Raxworthy et al, 2002) and in the colubrid snake genus Madagascarophis (Nagy et al, in press); a vicariant north-south pattern of sister species pairs occurs in several reptile groups, e.g., the boids Acrantophis madagascariensis (north) and Acrantophis dumerili (south), the geckos Uroplatus alluaudi (north) and Uroplatus malahelo (south), and the chameleons Brookesia lolontany (north) and Brookesia nasus (south) (Nussbaum and Raxworthy, 1994;Raxworthy and Nussbaum, 1995;Vences and Glaw, 2003). Interestingly, there is no obvious biogeographic barrier which would explain this primary biogeographic division between north and south.…”

Phylogeographic inferences from the mtDNA variation of the three‐toed skink, Chalcides chalcides (Reptilia: Scincidae)

“…In fact, this type of colonization seems to be quite common in reptiles like skinks of the genus Mabuya (Arnold, '76;Mausfeld et al, 2000;Carranza et al, 2001;Carranza and Arnold, 2003), chameleons (Raxworthy et al, 2002) and geckos (Carranza et al, 2000), even across long distances. This type of colonization might have been relatively easy for C. chalcides, considering the narrowness of the Sicily channel (about 60 km vs. the present 160 km) due to the decreases in the sea level during the Pleistocene glaciations (Antonioli et al, 2004).…”