Abstract
Biodiversity is disappearing at an exceptional rate, engendering a considerable
effort of the scientific community to conserve the rarest and most threatened species.
Biodiversity Hotspots were designed for this purpose and Madagascar, showing the
highest levels of endemism and imbalance across taxa, rapidly became their flagship.
The processes that lead to such exceptional biodiversity patterns on the island remain
poorly understood and the lack of efficacy of traditional taxonomy to catalogue
tropical endemic biodiversity hinders the scientific advances in this domain. This
study tackles insect endemism in Madagascar, aiming at identifying the evolutionary
and ecological factors responsible for their present diversity patterns. Aquatic beetles,
living in standing or running water, submit to differences in habitat stability,
potentially affecting dispersal patterns and hence endemism patterns. We chose them
as a target group for these reasons, and first achieved a DNA level inventory of the
fauna. We identified 169 species, showing high congruence with the morphological
taxonomy and corresponding to 74% of the total estimated species richness. The
mitochondrial dataset revealed high spatial turnover at the species and haplotype
levels. A phylogenetic tree from three gene markers was used for ancestral state
character reconstruction and suggested the dependent evolution of endemism and
habitat use. Secondly, our results highlight a combination of low dispersal activity
and important climatic constraints for the lotic fauna, explaining the local scale
endemism in this group, whereas the lentic species turnover correlated the least to
both climate and geographic distance. Last, a distribution modelling approach
revealed the uniqueness of Malagasy climate niches and the absence of conservation
of environmental envelopes at higher phylogenetic levels. We conclude that
endemism in Madagascar is best explained locally by the dependence to
environmental variability of the lotic species, and that dispersal capacities are the
primary hindrance to colonising external suitable habitats.