a1 Port Erin Marine Laboratory, University of Liverpool, Port Erin, Isle of Man, IM9 6JA.
Allozyme electrophoresis was used to estimate the genetic divergence between three species of South African Helcion and the north-east Atlantic H. pellucidum (Patellidae). At a finer level the genetic relationships among South African Helcion were explored. Twenty-one loci were resolved for all the species. High values of expected heterozygosities (0·202–0·341) were found for the genus. Phenetic analysis (UPGMA (unweighted pair-group method with artihmetic averaging) and Distance Wagner Procedure) and cladistic parsimony methods (alleles as binary characters and loci as multistate unordered characters) agreed in showing the same topology for the tree which represents the genetic relationships among Helcion species. The north-east Atlantic H. pellucidum was the most divergent species showing high values of Nei's genetic distances (1·423–1·654) with its South African congeners. In the literature such values of genetic divergence have been associated with non-congeneric species. The degree of genetic divergence (0·351–0·615) found within the South African branch was characteristic for congeneric species. The results of this study supported the monophyletic condition of this branch, and showed H. pectunculus and H. pruinosus to be more closely related to each other than to H. dunkeri. Nevertheless, the monophyly of the genus Helcion is uncertain and therefore its taxonomic status was questioned. A possible independent origin for northern and southern hemisphere species of Helcion is considered.
p1 Present address: Departamento de Química, Laboratório de Bioquímica Marinha, Fundaçāo Universidade do Rio Grande, Eng. Alfredo Huch 475, Caixa Postal 474, Rio Grande-RS 96201–900, Brazil.
p2 Department of Zoology and Entomology, Rhodes University, Grahamstown, 6140, South Africa.
p3 Present Address: Biodiversty and Ecology Division, University of Southampton, School of Biological Sciences, Southampton, SO16 7PX