Re-assessing the origins of the invasive mussel Mytilus galloprovincialis in southern Africa

Retracing the origins of invasive species is a first critical step in identifying potential mechanisms of introduction, implementation of management strategies and forecasting the spread of the invader. Mytilus galloprovincialis is an intertidal mussel that is widely distributed in many temperate and subtropical regions. It is invasive worldwide and the most successful invasive marine species in southern Africa. Previous studies have examined genetic relationships between a few South African populations from the south-western coast and other worldwide populations, presenting evidence of a north-eastern Atlantic origin of the invasion. Here, a combination of nuclear (Me15/16 PCR-based) and mitochondrial (16S restriction fragment-length polymorphism; 16S RFLP) DNA assays was applied to infer the origin of this strong invader across its entire southern African distribution (South Africa and Namibia). The 16S RFLP confirmed the northern hemisphere as being the likely sole source of invasion. Additionally, the frequencies of haplotypes at the 16S marker and alleles at the Me15/16 locus point to north-eastern Atlantic shores as the most likely origin throughout the Namibian and South African distribution of the species.