New taxa of freshwater mussels (Unionidae) from a species-rich but overlooked evolutionary hotspot in Southeast Asia

Ivan N Bolotov,Alexander V Kondakov,Olga V Aksenova,Ilya V Vikhrev,Ekaterina S Konopleva,Sakboworn Tumpeesuwan,Mikhail Yu Gofarov

doi:10.1038/s41598-017-11957-9

Abstract

Southeast Asia harbors a unique and diverse freshwater fauna of Mesozoic origin, which is under severe threat of extinction because of rapid economic development and urbanization. The largest freshwater basins of the region are certainly the primary evolutionary hotspots and they attract the most attention as key biodiversity areas for conservation. In contrast, medium-sized rivers are considered low-importance areas with secondary biodiversity, whose faunas originated via founder events from larger basins during the Pleistocene, although such a scenario has never been tested by using a phylogenetic approach. In this investigation, we used freshwater mussels (Unionidae) as a model to estimate the levels of endemism within the Sittaung, a little-known remote basin in Myanmar, compared with the surrounding larger rivers (Irrawaddy, Salween and Mekong). We discovered that the Sittaung represents an exceptional evolutionary hotspot with numerous endemic taxa of freshwater mussels. On the basis of our extensive dataset, we describe two new tribes, two genera, seven species and a subspecies of Unionidae. Our results highlight that medium-sized basins may represent separate evolutionary hotspots that harbor a number of endemic lineages. These basins should therefore be a focus of special conservation efforts alongside the largest Southeast Asian rivers.

Highlights

We use mussels in the family Unionidae, or naiads, as a model group for the assessment of spatial patterns of freshwater biodiversity across western Indo-China
Our findings highlight that the medium-sized basins may represent separate evolutionary hotspots that should be considered in future conservation planning for freshwater biodiversity in Southeast Asia
The molecular operational taxonomic units (MOTUs) of the multi-rate PTP model were comparable to those of the two other models, but in some cases, the mPTP revealed larger clusters, which occasionally joined all of the species within a certain genus (e.g., Indonaia and Radiatula) into a single MOTU (Fig. 1)

Summary

Introduction

We use mussels in the family Unionidae, or naiads, as a model group for the assessment of spatial patterns of freshwater biodiversity across western Indo-China. This is the most species-rich bivalve family, with ~620–680 extant species[14,15,16,17]. From the comprehensive phylogenetic study of the Unionidae across the primary basins of the Oriental Region, Bolotov et al.[9] showed that each large river system of this region is a separate evolutionary hotspot harboring a unique endemic naiad fauna.

Methods

Results

Conclusion