Glossogobius callidus exhibits broad salinity tolerance and is distributed in both estuarine and freshwater environments in southern Africa. Previous studies revealed substantial morphological and molecular variation among populations, suggesting they constitute a species complex. The present study utilised phylogenetic and population structure analyses of molecular sequence data from mitochondrial (cytochrome b) and nuclear (S7 intron 1) DNA markers to evaluate the genetic structure of the species. Two reproductively isolated lineages, 8.7% and 1.1% divergent, respectively, were identified. Lineage 1 represented the true G. callidus distributed mainly among estuarine systems including the type locality (Bushmans River, Eastern Cape, South Africa). Lineage 2 probably represents a cryptic species that is likely to be widespread in tropical and subtropical regions. Pairwise comparisons of both genetic markers within lineages detected high genetic diversity and numbers of private haplotypes. Mozambican haplotypes were divergent (2.7%, cyt b) and restricted to Lineage 2. Both datasets identified a shallow but consistent phylogeographic break between warm-temperate/subtropical and tropical regions. Analysis of Lineage 1 recovered three geographic groups in the warm-temperate region that could be associated with isolation of upper reaches resulting from past river capture and sea level changes. These results are indicative of a complex history of isolation and reconnection in river drainages and/or multiple colonisation events.
Keywords: cryptic species, cytochrome b, genetic structure, phylogeography, S7 intron 1
African Journal of Aquatic Science 2013, 38(Suppl.): 15–29