Allopatric speciation in reef fish

A while ago, Kerry presented a paper presenting a study aiming to evaluate the mode of speciation in an Indo-Pacific reef fish species complex: Dascyllus trimaculatus. From both mt DNA sequences and a set of 16 microsatellites, they defined the population/species boundaries between the different groups morphologically distinct. From their results, they found that the mode of speciation in this taxon fit well with allopatry, but found some support for additional factors such as ecological factors. Thanks Kerry.

From Leray M, Beldade R, Holbrook SJ, Schmitt RJ, Planes S and Bernardi G. Evolution, 2009, 64-5: 1218–1230

Title: Allopatric divergence and speciation in coral reef fish: the three-spot dascilllus, Dascillus trimaculatus, species complex

Abstract

Long pelagic larval phases and the absence of physical barriers impede rapid speciation and contrast the high diversity observed in marine ecosystems such as coral reefs. In this study, we used the three-spot dascyllus (Dascyllus trimaculatus) species complex to evaluate speciation modes at the spatial scale of the Indo-Pacific. The complex includes four recognized species and four main color morphs that differ in distribution. Previous studies of the group using mitochondrial DNA revealed a non congruence between color morphs and genetic groupings; with two of the color morphs grouped together and one color morph separated into three clades. Using extensive geographic sampling of 563 individuals and a combination of mitochondrial DNA sequences and 13 nuclear microsatellites, we defined population/species boundaries and inferred different speciation modes. The complex is composed of seven genetically distinct entities, some of which are distinct morphologically. Despite extensive dispersal abilities and an apparent lack of barriers, observed genetic partitions are consistent with allopatric speciation. However, ecological pressure, assortative mating, and sexual selection, were likely important during periods of geographical isolation. This study therefore suggests that primarily historical factors later followed by ecological factors caused divergence and speciation in this group of coral reef fish.