High-latitude connectivity of the scleractinian coral Acropora tenuis in the south-western Indian Ocean, identified using nuclear intron and mitochondrial sequence data

Abstract

All scleractinian corals in southern Africa occupy the high-latitude margins of their biogeographical range, with some straddling multiple biogeographical regions. Connectivity among these populations is essential to maintain genetic diversity, and thus their conservation value. Therefore, the aim of this study was to elucidate the genetic diversity, connectivity and structure of Acropora sp. populations. Acropora sp. were sampled at four intertidal and subtidal sites over a distance of ~320 km, and assessed using primers that amplify the 3/550 nuclear intron found within the carbonic anhydrase gene and the mitochondrially encoded cytochrome oxidase I region of DNA. Results resolved the presence of four putative Acropora clades, genetically disparate according to 3/550 nuclear intron data. In contrast to this, cytochrome oxidase I data confirmed the presence of a single species: A. tenuis. Cytochrome oxidase I data were highly conserved at species level, supporting previous notions that this gene may not be suitable for species level delineation in acroporids. Genetic structuring and diversity of A. tenuis among the four sites revealed similar characteristics to Acropora austera of northern KwaZulu-Natal and Mozambique. Little genetic differentiation was found between all possible regions, suggesting no significant genetic differentiation across the biogeographical regions tested. A higher degree of isolation and lower differentiation and moderate to high connectivity indices suggested periods of lower-latitude colonisation and periods of population attrition may be a feature in the ecology of this species.