Abstract
BackgroundOceanography and life-history characteristics are known to influence the genetic structure of marine species, however the relative role that these factors play in shaping phylogeographic patterns remains unresolved. The population genetic structure of the endemic, rocky shore dwelling Caffrogobius caffer was investigated across a known major oceanographic barrier, Cape Agulhas, which has previously been shown to strongly influence genetic structuring of South African rocky shore and intertidal marine organisms. Given the variable and dynamic oceanographical features of the region, we further sought to test how the pattern of gene flow between C. caffer populations is affected by the dominant Agulhas and Benguela current systems of the southern oceans.ResultsThe variable 5' region of the mtDNA control region was amplified for 242 individuals from ten localities spanning the distributional range of C. caffer. Fifty-five haplotypes were recovered and in stark contrast to previous phylogeographic studies of South African marine species, C. caffer showed no significant population genetic structuring along 1300 km of coastline. The parsimony haplotype network, AMOVA and SAMOVA analyses revealed panmixia. Coalescent analyses reveal that gene flow in C. caffer is strongly asymmetrical and predominantly affected by the Agulhas Current. Notably, there was no gene flow between the east coast and all other populations, although all other analyses detect no significant population structure, suggesting a recent divergence. The mismatch distribution suggests that C. caffer underwent a population expansion at least 14 500 years ago.ConclusionWe propose several possible life-history adaptations that could have enabled C. caffer to maintain gene flow across its distributional range, including a long pelagic larval stage. We have shown that life-history characteristics can be an important contributing factor to the phylogeography of marine species and that the effects of oceanography do not necessarily suppress its influence on effective dispersal.
Highlights
Oceanography and life-history characteristics are known to influence the genetic structure of marine species, the relative role that these factors play in shaping phylogeographic patterns remains unresolved
The South African coastline offers a unique setting to study the relative importance of oceanography on the genetic structuring of marine organisms
Similar estimates for expansion time have been found in other South African marine organisms, for example the lobsters Palinurus delagoae [41]Palinurus gilchristi [42] and Jasus tristani [43], as well as a hake species, Merluccius capensis [40], and it is likely that changing sea levels and temperatures during this time contributed to demographic changes
Summary
Oceanography and life-history characteristics are known to influence the genetic structure of marine species, the relative role that these factors play in shaping phylogeographic patterns remains unresolved. Given the variable and dynamic oceanographical features of the region, we further sought to test how the pattern of gene flow between C. caffer populations is affected by the dominant Agulhas and Benguela current systems of the southern oceans. There are two contrasting current systems that meet as the continental shelf widens between Cape Agulhas and the Cape Peninsula (Figure 1). These are the warm Agulhas Current, which flows southwards from Mozambique along the eastern coast of the country, and the cold Benguela Current that runs northwards along the western coast [7].
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