Fine scale biogeography: tidal elevation strongly affects popula tion genetic structure and demographic history in intertidal fishes

Numerous studies have demonstrated population genetic structuring in marine species, yet few have investigated the effect of vertical zonation on gene flow and population structure. Here we use three sympatric, closely related clinid species, Clinus cottoides, C. superciliosus and Muraenoclinus dor salis, to test whether zonation on South African intertidal rocky shores affects phylogeographic patterns. We show that the high shore restricted species has reduced gene flow and considerably higher FST val ues (FST = 0.9) than the mid and low shore species (FST < 0.14). Additionally, we provide evidence for remarkably different demographic and evolutionary histories, ranging from extreme population bottle necks to population persistence, which are probably linked to effective population size and habitat spe cialisation. This study further highlights the need for a multispecies approach to unravel the biological and evolutionary processes that drive extant population genetic patterns in marine species, as even closely related species with similar life histories show highly variable results.