Patterns of Endemism and Species Richness in Malagasy Cophyline Frogs Support a Key Role of Mountainous Areas for Speciation

Abstract

Cophyline narrow-mouthed frogs (Anura: Microhylidae) are a diverse endemic radiation of Madagascar. Cophylines contain a high proportion of range restricted species and constitute a good model system to understand patterns of evolutionary diversification in tropical ecosystems. We combine spatial and phylogenetic analyses for a near-complete taxon sample to test competing explanations for patterns of species richness (SR) and endemism. Our reconstruction of the phylogeny of cophylines indicates the presence of 22 new species and several instances of nonmonophyly. We found a strong historical signal in current cophyline ranges indicating a high degree of spatial niche conservatism in clade diversification, with clades occurring in the North of Madagascar constituting the most derived in the phylogeny. We identified six positively correlated centers of SR and endemism that can neither be explained by stochastic models such as elevational or latitudinal mid-domain effect, nor by low-elevation river catchments.Instead, the locations of these centers in areas spanning a high altitudinal range in combination with specific climatic parameters support a key role of mountainous areas for speciation of these anurans, although we cannot exclude an influence of habitat loss due to human impact. High conservation priority is ascribed to these areas.

A necessarily complex model to explain the biogeography of the amphibians and reptiles of Madagascar

“…Our approach accounts for biological complexity in searches for prevalent factors influencing the distribution of biodiversity, both in Madagascar and elsewhere. It considerably extends univariate and sometimes narrative approaches that examine the fit of the observed patterns to only single explanatory models or mechanisms (for example, in Madagascar 27,29,38 ) or compare a limited number of competing variables in univariate approaches 32 . Such analyses might be hampered by spatial autocorrelation of biodiversity patterns and predictor variables thereby inflating type-I errors in traditional statistical tests 39,40 .…”

“…While patterns of richness and endemism of the Malagasy herpetofauna have been analysed several times for various purposes based on partial data sets 8,29,32,38,45 , the analysis of turnover of species composition and the definition of biogeographic regions following from such explicit analyses are still in their infancy. For reptiles, Angel's 47 proposal of biogeographic regions based on classical phytogeography (regions based on plant community composition 48 ) has usually been adopted 49 .…”

“…Measures of endemism are inherently dependent on spatial scale. We chose a grid scale of 82 Â 63 km, separating Madagascar into 24 latitudinal and eight longitudinal rows, to reduce problems associated with estimating endemism over too small or large areas 11,29 . Specifically, this spatial scale was chosen so that we calculated a landscape-level measure of endemism (versus fine-scale regional differences).…”

“…The extraordinary proportion of family-level endemism in Madagascar, and the long isolation from non-Malagasy sister lineages, provide a unique opportunity to study the mechanisms driving divergence and diversification in situ 22 . Over the past decade, numerous mechanisms and models have been formulated to explain biodiversity distribution patterns and species diversification in Madagascar, pertaining to environmental stability (or instability), solar energy input, geographic vicariance triggered by topographic or habitat complexity, intrinsic traits of organisms or stochastic effects [23][24][25][26][27][28][29][30][31] . Evidence has supported numerous hypotheses, though this evidence has typically been marshalled from limited taxa or groups of taxa with restricted phylogenetic diversity.…”

Systematic relationships of Oriental tiny frogs of the family Microhylidae (Amphibia, Anura) as revealed by mtDNA genealogy

“…Thus, the available common region is very limited as exemplified in Fig. 2, which could be constructed using only 309 bp of 16S rRNA partial sequences that were comparable among GenBank data (Darst and Cannatella, 2004;Frost et al, 2006;Blackburn, 2008;Wollenberg et al, 2008;Köhler and Günther, 2008;Funk and Cannatella, 2009;Vences et al, 2010). As shown in the figure, basal resolution was chaotic and supports for terminal branches were also very weak.…”