Amphibians and reptiles of Madagascar: Adaptive radiation and patterns of diversity
Madagascar harbours a fascinating amphibian and reptile fauna. The main interest lies in the extraordinary degree of endemism: 100% of the native amphibians and 92% of the reptiles are endemic to the Malagasy region at the species level. The herpetofauna is also very diverse, with currently more than 235 species of amphibians and 360 species of reptiles known.
Own taxonomic studies, carried out in close cooperation with Frank Glaw (Zoologische Staatssammlung München), have so far led to the description of more than 100 new species of Malagasy frogs and various new snakes, geckos and chameleons. The lack of a comprehensive work on their distribution, biology, and identification led us to the publication, in 1992, of a "Fieldguide to the amphibians and reptiles of Madagascar" which, in 1994, was published in a second edition and in 2007 in a much expanded third edition. Unpublished data show that the species inventory is still far from being complete, and intensive descriptive work will still be necessary during at least the next decade to fully understand the herpetofaunal biodiversity of Madagascar. By now, we have identified at least 150 additional, new species of Malagasy frogs that attend being described in the next years. Field trips into poorly surveyed areas of Madagascar are continuously yielding further new species. We have furthermore largely revised the genus-level systematics of various groups, in particular mantellid frogs, but also of colubrid snakes.
Glaw, F., S. Hoegg & M. Vences (2006): Discovery of a new basal relict lineage of Madagascan frogs and its implications for mantellid evolution. Zootaxa 1334: 27-43.
Glaw, F. & M. Vences (2006). Phylogeny and genus-level classification of mantellid frogs. Organisms Diversity and Evolution 6: 236-253.
Glaw, F., Z. T. Nagy, M. Franzen & M. Vences (2007): Molecular phylogeny and systematics of the pseudoxyrhophiine snake genus Liopholidophis (Reptilia, Colubridae): evolution of its exceptional sexual dimorphism and descriptions of new taxa. Zoologica Scripta 36: 291-300.
The improvements in understanding of taxonomy of Malagasy amphibians is mainly based on an integrative approach: as argued in Vences et al. (2005) it is currently most efficient to base the first identification of specimens on DNA barcoding, for which we established a fragment of the mitochondrial 16S rRNA gene in almost all species of Malagasy amphibians. Specimens with divergent DNA sequences are subjected to detailed morphological and bioacoustic studies to understand if the molecular divergence is indicative of a species-level differentiation or is best interpreted as intraspecific variation.
A major current focus is to identify patterns of biogeography and speciation within Madagascar. We integrate data from mitochondrial DNA sequences and nuclear markers with those from pattern analysis with Geographic Information Systems (GIS).
• to study ongoing and past speciation in Malagasy amphibians: is speciation initially mainly triggered by (a) sympatric bioacoustic differentiation of populations, (b) allopatric vicariance by geographical isolation of populations, e.g. due to past climatic shifts, or (c) differentiation along an altitude gradient?
• to understand historical processes as well as present and past natural barriers that led to the current biogeographic zonation - for example, the drastically different herpetofaunas of north-eastern and central-eastern Madagascar, which inhabit an apparently continuous rainforest belt (e.g., Boumans et al. 2007).
• develop reliable models of the extinction processes and conservation priorities in Madagascar under different scenarios and at different scales, to be able to predict the future of the species diversity and evolutionary history in this (probably "hottest") hotspot for biodiversity conservation worldwide (e,g, Andreone et al. 2005).
Vences, M., M. Thomas, R. M. Bonett & D. R. Vieites (2005): Deciphering amphibian diversity through DNA barcoding: chances and challenges. Philosophical Transactions of the Royal Society London, Ser. B, 360: 1859-1868.
Andreone, F., J. E. Cadle, N. Cox, F. Glaw, R. A. Nussbaum, C. J. Raxworthy, S. N. Stuart, D. Vallan & M. Vences (2005): Species review of amphibian extinction risks in Madagascar: conclusions from the Global Amphibian Assessment. Conservation Biology 19: 1790-1802.