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 apparen tly monogamous, biparental mouth-brooding cichlid. microsatellite allele fr equencies were determined at four polymorphic loci for nine populations of Eretmodus cyanostictus. We provide empirical support fbr the hypothesis tha t a species employing this breeding strategy should exhibit high levels of population substructuring. Stretches of sand represent considerable barrier s to dispersal and, in contrast to the rock-dwelling cichlids of Lake Malaw i, distance alone. alone a continuous rocky shoreline is sufficient to redu ce 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 an d that juveniles establish territories close to their natal site. Despite l imited dispersal. E. cyanostictus populations are not significantly more in bred 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. Hig h 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.