Microsatellites reveal high levels of population substructuring in the species-poor Eretmodine cichlid lineage from Lake Tanganyika

This study investigated fine-scale population substructuring ill an apparently monogamous, biparental mouth-brooding cichlid. microsatellite allele frequencies were determined at four polymorphic loci for nine populations of Eretmodus cyanostictus. We provide empirical support fbr the hypothesis that a species employing this breeding strategy should exhibit high levels of population substructuring. Stretches of sand represent considerable barriers to dispersal and, in contrast to the rock-dwelling cichlids of Lake Malawi, distance alone. alone a continuous rocky shoreline is sufficient to reduce gene flow significantly There was a significant pattern of isolation by distance both along the whole study area and over the stretch of continuous shoreline? suggesting that this species has poor dispersal capabilities and that juveniles establish territories close to their natal site. Despite limited dispersal. E. cyanostictus populations are not significantly more inbred than a more-widely dispersing rock-dwelling cichlid from Lake Malawi. This finding may cast doubt on the hypothesis that polyandry has evolved as a mechanism for maintaining genetic diversity in Lake Malawi cichlids. High levels of substructuring may not always promote high levels of speciation, and other factors such as the intensity of sexual selection. may be mole important in determining the speciation potential of a lineage.