Abstract
The ‘abundant-centre hypothesis’ is a well-established ecological hypothesis which states that
the abundance of a species is highest at the centre of its range and decreases towards the edges,
where conditions are less favourable. This implies that genetic diversity also increases from
centre to edge. In this study, the genetic implications of the abundant-centre hypothesis on
South African marine mussels were tested, including the assumption that genetic diversity is
highest at the centre of the range, and that the edge populations either have low genetic diversity
or are represented by genetically distinct evolutionary lineages. The study organisms for this
research were the native mussel Perna perna (of which a temperate western lineage and a
subtropical eastern lineage occur in South Africa), and the European species Mytilus
galloprovincialis, which has recently invaded South Africa’s temperate coasts. Previous
studies revealed a strong divergence of Perna perna into two distinct lineages. Biparentallyinherited
nuclear DNA microsatellite data were generated for both species, and in addition,
maternally-inherited mitochondrial DNA COI sequences were generated for Perna perna.
Microsatellite data revealed a clear genetic differentiation between the western and eastern
populations of P. perna, confirming divergence previously detected with COI data. For both
markers, the genetic diversity indices between the centre and edge populations did not differ
much, and the hypothesis that centre populations have greater genetic diversity than edge
populations is rejected. Interestingly, the alternative hypothesis that edge populations are
represented by distinct lineages is also rejected. Instead, it was found that the lineages of Perna
perna hybridise in the temperate/subtropical contact zone, a novel finding that could not
previously be detected with maternally-inherited mtDNA data. I show that this is likely a result
of adaptation to intermediate environmental conditions in the hybrid zone. Environmental
results revealed that temperature plays a major role in influencing genetic structures. Mytilus...
M.Sc. (Zoology)