Taxonomic revision of a radiation of South-east Asian freshwater mussels (Unionidae : Gonideinae : Contradentini+Rectidentini)

Abstract

The tribes Contradentini and Rectidentini (Unionidae) comprise a diverse clade of freshwater mussels endemic to South-east Asia. Our understanding of the diversity and phylogeny of this radiation has improved dramatically in recent years, but this systematic transformation has not yet benefited from comprehensive museum sampling or phylogenomic methods. A synthetic taxonomic revision of the Contradentini+Rectidentini that leverages these useful and accessible methods is needed. We set out to (1) generate a phylogenomic reconstruction of the supraspecific relationships of the Contradentini+Rectidentini using anchored hybrid enrichment, (2) revise the taxonomy and geographic boundaries of the generic and species-level diversity of the radiation, and (3) identify patterns of freshwater mussel diversity and distribution in this clade and discuss the processes that may have precipitated them. Our phylogenomic reconstruction using over 1600 loci, with a total alignment length of over a half a million nucleotides, recovers a well supported phylogeny of the clade that resolves four independent multispecies radiations endemic to the Mekong drainage. We examined, digitised, and imaged 1837 records from 15 natural history museums that provided the necessary data to document the morphological variation and geographic distributions of the focal taxa. We also analysed 860 COI sequences, 519 of which were generated in this study, to better understand the species boundaries and geographic distributions of the recovered clades. We recognise 54 valid species in the tribes Contradentini and Rectidentini, including 9 described herein as new to science. Out of this revision emerged several interesting biogeographic patterns that appear to have resulted from recent stream capture, historical confluence, and intradrainage barriers to dispersal. We hypothesise that these phenomena shaped the diversity and distribution of the Contradentini+Rectidentini, contributing to the formation of several characteristic freshwater mussel provinces in South-east Asia.