Résumé
It is commonly assumed that dispersal and, thus, gene flow and genetic connectivity of reef fishes are limited as adults, which are strongly reef-associated, and are rather maintained by the occurrence of planktonic eggs or pelagic larval stages. Where the reproductive biology includes benthic tended eggs and/or short pelagic larval phases, it would be reasonable to expect little dispersal, low connectivity and marked genetic differentiation across a species distribution. Here, we contrast the patterns of genetic differentiation and connectivity of two widely-distributed damselfish across the Western Indian Ocean (WIO): the domino (Dascyllustri maculatus) and the sergeant major (Abudefduj Vaigiensis). Both species are assumed - by virtue of their biology and ecology, and counter to their widespread nature - to be capable of only limited dispersal. Five and 30 individuals of each species were sampled from a minimum of ten localities across the WIO. DNA sequence data were generated from two mitochondrial gene fragments and one nuclear gene fragment. Data were analysed using phylogeographic and phylogenetic approaches. The domino showed low levels of genetic diversity and provided no indication of spatial genetic structure across its WIO distribution. This suggests a high degree of historical or contemporary connectivity. This is in accordance with patterns from the species' wider distribution (Indo-West Pacific). By contrast, the sergeant major showed high levels of genetic diversity and a number of unique genetic lineages. Some of these lineages are widespread across the WIO, whereas others appeared to be geographically restricted, suggesting limited dispersal - at least historically. The maintenance of these patterns and the differences in genetic structure between the species will be explored. These patterns are also placed in the context of results emerging from parallel studies on other WIO reef fish, and their implications for conservation and resource management considered.