Christopher Macquaid

Christopher Macquaid

Rhodes University, South Africa

Title: Hidden benefits of genetic diversity: interactions between invasive and indigenous species


Christopher McQuaid holds the Chair of Zoology at Rhodes University in South Africa and the South African SARChI chair in Marine Ecosystem Research. His broad interests involve deciphering how the physical environment provides a framework within which species interactions shape marine communities. This covers a wide range of research topics that presently include the interaction of grazing effects with upwelling, coupling larval dispersal with recruitment rates in mussels and the foraging ecology of penguins and other seabirds. He has over 200 publications in the peer reviewed literature on subjects ranging from bacteria to whales, but his main fields have been rocky shore ecology and the biological oceanography of the Southern Ocean, including Antarctica. He has collaborated with colleagues in Asia, North and South America, Africa, Australia and Europe in the search for ecological generality.


Definitions of biodiversity can be extended beyond species to include genetic diversity, yet the direct benefits of conserving genetic diversity have been suggested, rather than demonstrated. Here we examined the interaction between an invasive marine mussel and an indigenous species, including the effect of genetic resolution. The intertidal Mediterranean mussel, Mytilus galloprovincialis, has become invasive on every continent on the planet except Antarctica, encountering a variety of native mussel species. In South Africa, it has effectively displaced the indigenous musselspecies on the cool-temperate west coast, but on the warm-temperate south coast it interacts with a different indigenous species, Perna perna. Perna and Mytilus show partial habitat segregation by height on the shore, while overlapping and co-existing in the middle of the zone occupied mussels.On the south coast, Mytilus reaches a distributional limit towards the east that coincides with a phylogeographic break in Perna. This limit lies precisely in the region where two genetic lineagesof Perna, an eastern and a western lineage, overlap. In situ competition and translocation experiments indicate that Mytilus is capable of living farther east than it presently occurs. However, on that part of the shore where the two species can co-exist in mixed mussel beds, it is outcompeted by the eastern lineage of Perna and not the west lineage with which it presently co-exists. These results provide a clear example of a hidden benefit of genetic diversity with the spread of Mytilus towards the east held in check not by abiotic conditions, but by interaction with a different genetic lineage of Perna.