Contrasting phylogeographic patterns of intertidal mites (Acari, Oribatida) along the South African shoreline

Abstract

The South African coast is known to harbor four different species of intertidal oribatid mites and their distribution strongly correlates with marine ecoregions. Relatively little is known about the dispersal of these organisms and how populations of different locations are connected. To test dispersal abilities and connectivity of these South African species, we performed a morphometric and molecular genetic study. COI gene sequences of two of the widely distributed South African intertidal oribatid mite species revealed clearly contrasting patterns. Halozetes capensis, which occurs in the Agulhas Ecoregion, shows distinct genetic structuring, whereas Fortuynia elamellata micromorpha, which is distributed in the Natal Ecoregion, exhibits gene flow between all populations. The paleoenvironmental history and specific ocean current pattern are suggested to be responsible for these patterns. During the last glacial maximum, the colder climate and the weakening of the Agulhas Current possibly resulted in a bottleneck in the warm-adapted F. e. micromorpha populations, but the subsequent global warming allowed the populations to expand again. The cold-adapted H. capensis populations, on the other hand, experienced no dramatic changes during this period and thus could persist in the Agulhas Ecoregion. Considering transport on ocean currents, the Agulhas Current could be further responsible for the connectivity between the Fortuynia populations. But the deflection of this current in the Agulhas Ecoregion could support the isolation of Halozetes populations. The concomitant morphometric study demonstrated morphological homogeneity among populations of Fortuynia and thus confirms strong connectivity. The Halozetes populations, on the other hand, form two different morphological groups not reflecting geography.