Limited population differentiation in the bearded limpet Patella barbara (Gastropoda : Patellidae) along the coast of South Africa

Patterns of genetic and morphological variation among eight populations of Patella barbara along the coast of South Africa were examined to see whethe r reported differences in shell morphology and behaviour between the west a nd east coasts were mirrored by other morphological and/or genetic differen ces. Morphological analyses of radular structure, gut-loop coiling and sper m microstructure revealed no differences between the populations. Discrimin ant functions analysis based on shell morphometrics showed major overlap be tween populations and failed to separate them. Electrophoretic analysis of 17 enzyme loci have an overall genetic identity (Nei) value of 0.995, a val ue which lies within the generally accepted range for conspecific populatio ns. In two of the populations, at Dwesa and Arniston, individuals were foun d to be 'gardening' algal resources. At Clovelly, a 'normal' form of P. bar bara was found on the rocks, whereas a reduced and tall-shelled form occurr ed on the ascidian Pyura stolonifera, demonstrating phenotypic morphologica l plasticity. It was concluded that different populations of Patella barbar a are both morphologically indistinguishable and genetically homogenous alo ng the coast of South Africa, thus providing good evidence for widespread g ene flow.