Testing recurrent ecological speciation processes in microendemic Madagascan reptiles and amphibians of the isolated Amber Mountain

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The processes by which new species arise have long been an active field of debate Current research on speciation focuses the mechanisms driving the divergence. Ecological Speciation (ES) occurs if natural selection strongly favours different ecotypes, and reproductive isolation evolves as a consequence of adaptive divergence due to differing ecology. However, suitable settings to study ES are rare. Our long-term research program on the evolution of the vertebrate fauna of Madagascar has yielded preliminary indicated that the isolated Amber Mountain Massif in northern Madagascar harbours distinct locally endemic sister clades of various amphibians and reptiles, and some of these appear to be restricted to distinct elevational ranges. This suggests that these lineages might have originated in the Massif by ES, and points to Amber Mountain as a suitable model system for studying diversification across ecological (elevational) gradients. The research project proposed here will combine cutting-edge methods in metabarcoding and population genetics, to explore ES processes in the microendemic herpetofauna of this massif. It applies a strict hypothesis-testing framework to assess whether an ecological gradient is the predominant driver of past and ongoing ES. Our approach will use metabarcoding data for the entire herpetofaunal community of Amber Mountain, and population genetic in-depth study of three target taxa (likely including one or several of the genera Brookesia, Stumpffia, Phelsuma, or Uroplatus). Dense sampling will be carried out along pre-defined transects that will be characterized ecologically, and furthermore, rapid surveys will be done using a grid approach in order to characterize the distribution and phylogeography of the entire herpetofauna in the massif. The large number of samples collected during fieldwork will be analyzed using high-throughput amplicon metabarcoding of pooled samples with Illumina sequencing. For the target taxa, microsatellites and RADseq-derived SNPs will be used to characterize small-scale population differentiation. If ES triggered the diversification of amphibians and reptiles of Amber Mountain, then we predict that (i) endemic sister lineages that differentiated on Amber Mountain will be distributed at distinct elevational ranges, (ii) their contact zones coincide with ecotones and with turnover of the entire herpetofaunal community, (iii) target lineages distributed across these ecotones will show reduction of gene flow related to the ecological gradient rather than to distance or physical barriers. Given the scarcity of research that tests ES in Madagascar, the endeavour to establish the Amber Mountain as study region for such research would be ground-breaking, and stimulate process-based speciation research in this unique biota.