Multilocus phylogenetic and geospatial analyses illuminate diversification patterns and the biogeographic history of Malagasy endemic plated lizards (Gerrhosauridae: Zonosaurinae).

Although numerous studies have attempted to find single unifying mechanisms for generating Madagascar's unique flora and fauna, little consensus has been reached regarding the relative importance of climatic, geologic and ecological processes as catalysts of diversification of the region's unique biota. Rather, recent work has shown that both biological and physical drivers of diversification are best analysed in a case-by-case setting with attention focused on the ecological and life-history requirements of the specific phylogenetic lineage under investigation. Here, we utilize a comprehensive analytical approach to examine evolutionary drivers and elucidate the biogeographic history of Malagasy plated lizards (Zonosaurinae). Data from three genes are combined with fossil information to construct time-calibrated species trees for zonosaurines and their African relatives, which are used to test alternative diversification hypotheses. Methods are utilized for explicitly incorporating phylogenetic uncertainty into downstream analyses. Species distribution models are created for 14 of 19 currently recognized species, which are then used to estimate spatial patterns of species richness and endemicity. Spatially explicit analyses are employed to correlate patterns of diversity with both topographic heterogeneity and climatic stability through geologic time. We then use inferred geographic ranges to estimate the biogeographic history of zonosaurines within each of Madagascar's major biomes. Results suggest constant Neogene and Quaternary speciation with divergence from the African most recent common ancestor ~30 million years ago when oceanic currents and African rivers facilitated dispersal. Spatial patterns of diversity appear concentrated along coastal regions of northern and southern Madagascar. We find no relationship between either topographic heterogeneity or climatic stability and patterns of diversity. Ancestral state reconstructions suggest that western dry forests were important centres of origin with recent invasion into spiny and rain forest. These data highlight the power of combining multilocus phylogenetic and spatially explicit analyses for testing alternative diversification hypotheses within Madagascar's unique biota and more generally, particularly as applied to phylogenetically and biologically constrained systems.

Spatial variation in the fitness of divergent aposematic phenotypes of the poison frog, Dendrobates tinctorius.

Aposematic species use brightly coloured signals to warn potential predators of their unpalatability. The function of these signals is largely believed to be frequency-dependent. All else being equal, stabilizing selection is expected to constrain the evolution of novel signals. However, despite the expected frequency-dependent function of aposematic signals, interpopulation variation in aposematic signals is ubiquitous in nature. Here, we used clay models of the poison frog Dendrobates tinctorius to test the nature of selection in regions containing varying frequencies of frogs possessing the local aposematic signal. Our findings support a role for stabilizing selection in maintaining the local signal type in a region of high signal frequency; however, we observe a lack of stabilizing selection at one site coincident with a decrease in the density of frogs possessing the local signal. Spatial variation in local aposematic signal frequencies may facilitate the evolution of novel signal types by altering the adaptive landscape for divergent aposematic phenotypes. Our results provide evidence for spatial variation in the selective regime acting on aposematic signals within an established aposematic system and highlight the need for further study of the nature of selection acting across different spatial scales in diverse aposematic systems.

A new species of Osteocephalus (Anura: Hylidae) from Guyana.

A new member of the genus Osteocephalus is described from the Pakaraima mountains of western Guyana. This species is the smallest known member of the genus and is probably closely related to O. subtilis. Both share a small size (less than 40 mm snout-vent length), large and bulgy eyes directed somewhat rostrally, green bones, smooth and brownish dorsal skin, relatively short and truncate snout, small tympanum, subgular and laterally expanded vocal sac, poorly developed subarticular and supernumerary tubercles, a supra-anal glandular ridge, and cream-white venter and subocular region. The new species can be distinguished from O. subtilis by the Buff iris (vs black), smaller overall size (32.7 vs 35.8-38.8 mm snout-vent length), relatively larger toe disks, and less developed foot webbing. The cranium of the new species is well ossified, relatively reduced in width between the orbits, without an exposed frontoparietal fontanelle and with the anterior arm of the squamosal extending to about half the distance to the maxillary. The vocal sac is subgularly poorly developed and possess lateral extensions to the area behind the jaw angles. Well developed supraocular and suprasquamosal cartilages give support to the enlarged eyes of this species.