Phylogeography of southern hemisphere blue mussels of the genus Mytilus: Evolution, biosecurity, aquaculture and food labelling

Abstract

Smooth-shelled blue mussels of the genus Mytilus have long been a major focus of research because such mussels have an interesting global (antitropical or bipolar) distribution, have a complex phylogeographic history, are ecosystem engineers, are economically important as an aquaculture product, are very successful as bioinvaders, hybridise readily both naturally and after accidental introduction, and have a complex and still incompletely resolved taxonomy. Historically, most research has been focussed on Northern hemisphere mussels, and investigation has spanned a range of different methodological approaches that have set the foundation for our current understanding of the global situation. However, research into native blue mussels in the Southern hemisphere has tended to lag behind that in the Northern hemisphere. The result has been that native Southern hemisphere mussels have often been viewed only in the perspective of their Northern hemisphere congeners. Recently, however, the application of new molecular markers - single nucleotide polymorphisms, SNPs - has substantially improved our understanding of the taxonomy of Southern hemisphere blue mussels, their biogeography and indirectly their evolutionary histories. Based largely on new SNP surveys of native and non-native blue mussels from all major Southern hemisphere regions, we highlight the need for recognition of distinct species that are consistent with a large body of evidence, both SNP-based and other, and can be understood in the context of Southern hemisphere oceanography. We also highlight with the new SNPs-based data the ongoing difficulty of agreeing on what constitutes a distinct species by emphasising different interpretations of the data, and discussing how the use of species delimitation models may remove some of the qualitative assessment that is so often applied to the problem. The recognition of new species has implications for management, including the identification of bioinvasive mussels, the conservation of native genetic diversity, aquaculture production statistics, food labelling and traceability.