Résumé
Insular biodiversity hotspots of Southeast Asia are remarkable for their biodiverse faunas. With a marine larval phase lasting up to several months, the freshwater fish subfamily Sicydiinae has colonized most islands of these hotspots. However, Sicydiinae diversity is still poorly understood in Southeast Asia. With the objective of estimating intraspecific genetic diversity and inferring past demography, we conducted the molecular inventory of Sicydiinae species in Sundaland and Wallacea using 652 bp of the mitochondrial cytochrome oxidase I gene, species delimitation methods, and Bayesian Skyline plot reconstructions. In total, 24 Molecular Operational Taxonomic Units are delimited among the 603 sequences belonging to 27 species and 5 genera. Two cases of discordance between morphology and mitochondrial sequence are observed, suggesting ongoing speciation and/or introgression in 2 genera. Multiple new occurrences are reported, either for a single biodiversity hotspot or both, some of which correspond to observations of a few individuals far from the range distribution of their conspecifics. Among the 10 species or species groups whose intraspecific diversity was examined, high levels of genetic diversity and past population expansion are revealed by Tajima's D tests and Bayesian Skyline Plot reconstructions. Together, these results indicate that long-distance dispersal is common and suggest that most endemic species originated through founder events followed by population expansion. Patterns of sexual dimorphism and males' coloration among diverging species pairs seem to point to sexual selection as an important mechanism contributing to speciation in the Sicydiinae of Sundaland and Wallacea.