MEPS 337:135-144 (2007)  -  doi:10.3354/meps337135

Unexpected genetic structure of mussel populations in South Africa: indigenous Perna perna and invasive Mytilus galloprovincialis

G. I. Zardi1,*, C. D. McQuaid1, P. R. Teske1,2, N. P. Barker2

1Department of Zoology and Entomology, and 2Molecular Ecology and Systematics Group, Botany Department, Rhodes University, Grahamstown 6140, South Africa

ABSTRACT: Genetic structure of sedentary marine organisms with planktonic larvae can be influenced by oceanographic transport, larval behaviour and local selection. We analysed the population genetic structure (based on mtDNA) of the invasive mussel Mytilus galloprovincialis and the indigenous mussel Perna perna along the southern African coastline. Low genetic divergence of M. galloprovincialis confirms its recent arrival in South Africa. In contrast, the genetic structure of P. perna revealed strong divergence on the south-east coast, forming a western and an eastern lineage. The distribution of the 2 lineages is extraordinary. They overlap for ca. 200 km on the south-east coast, and the western lineage includes animals occurring on either side of a 1000 km break in distribution across the Benguela upwelling system. In cluster analyses, animals on the south coast grouped with others 1000s of km to the west, rather than with those only 200 km to the east. This genetic disjunction may be caused by the south-flowing Agulhas Current preventing larval dispersal, or by different selective forces acting on local populations. M. galloprovincialis spread eastward along the south coast for 15 yr, but its range extension has virtually ceased in the region of genetic disjunction in P. perna, again indicating an oceanographic barrier to larval dispersal or selection driven by sharp gradients in environmental conditions. The results suggest that local selection can produce genetic structure opposite to that predicted by oceanographic data and that determining the population structure of indigenous species with similar larval dispersal can help us understand domain expansion of invading species.

KEY WORDS: Mytilus galloprovincialis · Perna perna · Invasion · Biogeographic region · Currents · mtDNA

Full text in pdf format