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.

Molecular phylogeny reveals a new genus of freshwater mussels from the Mekong River Basin (Bivalvia: Unionidae)

“…The separation of closely related taxa between the Middle Mekong River and Lower Mekong River basins is well documented in other unionid mussels. Almost all the examined genera display this biogeographic pattern (Pfeiffer et al 2018(Pfeiffer et al , 2021Muanta et al 2019), suggesting a shared biogeographic history among these taxa.…”

“…2) and large genetic distances from other genera (11.02-12.42% uncorrected COI p-distance; Table 2) also support it as a distinct genus. The discovery of a new mussel genus from Southeast Asia, and especially from the Mekong River Basin, is not unexpected since several new genera and a dozen new species were discovered during the last decade (Kongim et al 2015;Jeratthitikul et al 2019a;Konopleva et al 2019Konopleva et al , 2021Bolotov et al 2020;Pfeiffer et al 2021).…”

“…Nevertheless, freshwater mussels from the Mun River Basin generally show a deep genetic divergence from other parts of the Mekong River Basin (i.e., Songkhram River Basin in the northern Korat Plateau and Tonle Sap Basin in the Lower Mekong River Basin). Usually, they are represented as distinct species (Pfeiffer et al 2018(Pfeiffer et al , 2021Jeratthitikul et al 2019b;Muanta et al 2019). Therefore, there is a possibility that the population from the Mun River Basin is a different species from the currently assigned N. inkhavilayi gen. et sp.…”

“…The currently known richness of freshwater mussels in the Mekong River Basin comprises 67 species across 21 genera (Graf & Cummings 2021a;Konopleva et al 2021). Several of these genera and a dozen of these species were discovered within the last decade (Kongim et al 2015;Jeratthitikul et al 2019a;Konopleva et al 2019Konopleva et al , 2021Bolotov et al 2020;Pfeiffer et al 2021). Moreover, 59 species are endemic to the basin, and five genera are considered monotypic, highlighting the extraordinary endemism within the tributaries (Brandt 1974;Pfeiffer et al 2018;Bolotov et al 2020;Graf & Cummings 2021a;Konopleva et al 2021).…”

Systematics, distribution, biology, and conservation of freshwater mussels (Bivalvia: Unionida) in China

“…Owing to a lack of detailed analyses of those specimens, we maintain the species under ‘ Lamellidens ’ within inverted commas to show our reservations about this assignment. The same principle has been used for Chinese species at present assigned to the genera Scabies and Pseudodon considering the recent work of Pfeiffer et al (2021).…”