Endemism and diversification in freshwater insects of Madagascar revealed by coalescent and phylogenetic analysis of museum and field collections

The biodiversity and endemism of Madagascar are among the most extraordinary and endangered in the world. This includes the island’s freshwater biodiversity, although detailed knowledge of the diversity, endemism, and biogeographic origin of freshwater invertebrates is lacking. The aquatic immature stages of mayflies (Ephemeroptera) are widely used as bio-indicators and form an important component of Malagasy freshwater biodiversity. Many species are thought to be microendemics, restricted to single river basins in forested areas, making them particularly sensitive to habitat reduction and degradation. The Heptageniidae are a globally diverse family of mayflies (>500 species) but remain practically unknown in Madagascar except for two species described in 1996. The standard approach to understanding their diversity, endemism, and origin would require extensive field sampling on several continents and years of taxonomic work followed by phylogenetic analysis. Here we circumvent this using museum collections and freshly collected individuals in a combined approach of DNA taxonomy and phylogeny. The coalescent-based GMYC analysis of DNA barcode data (mitochondrial COI) revealed 14 putative species on Madagascar, 70% of which were microendemics. A phylogenetic analysis that included African and Asian species and data from two mitochondrial and four nuclear loci indicated the Malagasy Heptageniidae are monophyletic and sister to African species. The genus Compsoneuria is shown to be paraphyletic and the genus Notonurus is reinstalled for African and Malagasy species previously placed in Compsoneuria. A molecular clock excluded a Gondwanan vicariance origin and instead favoured a more recent overseas colonization of Madagascar. The observed monophyly and high microendemism highlight their conservation importance and suggest the DNA-based approach can rapidly provide information on the diversity, endemism, and origin of freshwater biodiversity. Our results underline the important role that museum collections can play in molecular studies, especially in critically endangered biodiversity hotspots like Madagascar where entire species or populations may go extinct very quickly.