Speciation in little: the role of range and body size in the diversification of Malagasy mantellid frogs

Abstract

BackgroundThe rate and mode of lineage diversification might be shaped by clade-specific traits. In Madagascar, many groups of organisms are characterized by tiny distribution ranges and small body sizes, and this high degree of microendemism and miniaturization parallels a high species diversity in some of these groups. We here investigate the geographic patterns characterizing the radiation of the frog family Mantellidae that is virtually endemic to Madagascar. We integrate a newly reconstructed near-complete species-level timetree of the Mantellidae with georeferenced distribution records and maximum male body size data to infer the influence of these life-history traits on each other and on mantellid diversification.ResultsWe reconstructed a molecular phylogeny based on nuclear and mitochondrial DNA for 257 species and candidate species of the mantellid frog radiation. Based on this phylogeny we identified 53 well-supported pairs of sister species that we used for phylogenetic comparative analyses, along with whole tree-based phylogenetic comparative methods. Sister species within the Mantellidae diverged at 0.2-14.4 million years ago and more recently diverged sister species had geographical range centroids more proximate to each other, independently of their current sympatric or allopatric occurrence. The largest number of sister species pairs had non-overlapping ranges, but several examples of young microendemic sister species occurring in full sympatry suggest the possibility of non-allopatric speciation. Range sizes of species included in the sister species comparisons increased with evolutionary age, as did range size differences between sister species, which rejects peripatric speciation. For the majority of mantellid sister species and the whole mantellid radiation, range and body sizes were associated with each other and small body sizes were linked to higher mitochondrial nucleotide substitution rates and higher clade diversity. In contrast, small range sizes were unexpectedly associated with a slow-down of mitochondrial substitution rates.ConclusionsBased on these results we define a testable hypothesis under which small body sizes result in limited dispersal capabilities and low physiological tolerances, causing smaller and more strongly fragmented ranges. This can be thought to facilitate reproductive isolation and thus favor speciation. Contrary to the expectation of the faster speciation of such microendemic phenotype species, we only found small body sizes of mantellid frogs to be linked to higher diversification and substitution rates, but not small range sizes. A joint analysis of various species-rich regional anuran radiations might provide enough species with all combinations of range and body sizes for a more conclusive test of this hypothesis.

Genetic divergence in tropical anurans: deeper phylogeographic structure in forest specialists and in topographically complex regions

“…As a MCP spans the whole area between the sampled localities of a species, our topographic complexity measure is a simplified estimate that characterizes the entire region where dispersal events might have occurred in the past, regardless of range discontinuities and the current distribution of suitable habitats. However, considering the limited number of locality records available for most species, the calculations using MCPs may be more realistic than fine-scale mapping or ecological niche modeling (Wollenberg et al 2011) and from a biogeographic perspective still constitute an adequate estimate of habitat heterogeneity and potential barriers to gene flow.…”

Assessing the effects of climate change on distributions of Cape Floristic Region amphibians

“…We determined changes in area occupancy, rate of area change, the direction of range shifts (across both longitudes and latitudes) and fragmentation index (DI´) between climate periods. 57,58 We ran our results in two ways: first with a full suite of 37 species and second with 34 species (excluding those species with less than 10 species records, to avoid model over-fitting 59 ). We found that the results in both attempts were almost identical and that patterns remained largely similar and thus report results of the analysis considering a full suite of 37 species.…”

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

“…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.…”