The molecular phylogenetics of the New Zealand freshwater mussels

Abstract

The taxonomy of the New Zealand freshwater mussels has been confounded because it is based on the highly variable shell morphology of the various species. It has been predicted that the virtually unknown genetics of the New Zealand species could hold the key to resolving the taxonomic confusion within this group and their standing within the worldwide mussel fauna. The aims of this study were to collect mitochondrial and nuclear DNA from many samples of the New Zealand freshwater mussels to determine the number of species and their phylogenetic origins. There has been some speculation into the mode of dispersal for freshwater mussels including the possibility of mixing between watersheds facilitated on bird's feet. The common New Zealand mussel Echyridella menziesii has a wide distribution and was found in this study from Spirits Bay in the far north of the country to Lake Manapouri in the south. Haplotypes of this species are studied in an attempt to uncover patterns of dispersal within and between populations. For this study specimens were collected from a variety of sites throughout New Zealand in 2005-2006. Echyridella McMichael & Hiscock, 1958 is elevated to genus level on the basis of interpretation of published molecular data. A new species of freshwater mussel, Echyridella onekaka, is described from the north-western South Island of New Zealand. Diplodon menziesi lucasi Suter, 1905 is resurrected from synonymy under E. menziesii as a distinct species of Echyridella. E. aucklandica, formally known as Hyridella aucklandica and Cucumerunio websteri is clarified. Analysis of COI and 28S sequences show that the New Zealand species are more closely related to each other than to their next closest relatives, the freshwater mussels of Australia and South America and are therefore placed in a single genus Echyridella. The relationships of the New Zealand, Australian and South American species are explored and it is found that the distribution of the New Zealand species probably results from vicariant Gondwanan origins. The population genetics of E menziesii are explored and high levels of genetic structure are found within populations with many unique haplotypes, it could be argued that the haplotype distributions of this species reflects the geological histories of the North and South Islands of New Zealand. Evidence is presented that there is limited gene flow between catchment populations of New Zealand freshwater mussels. The findings of this study have implications for the taxonomy of freshwater mussels and resource management and species conservation in New Zealand.