Gene-flow in the rock hyrax (Procavia capensis) at different spatial scales

[摘要] ENGLISH ABSTRACT: Limited dispersal, territoriality and the occupation of patchy habitats; characters that typify most African rock-dwelling (saxicolous or rupicolous) species, often result in structured genetic patterns with little or no gene-flow among populations (e.g., velvet worms, net-winged midges, elephant shrews, red rock rabbits and a variety of lizards and agamas). In an attempt to deepen our understanding of taxa that inhabit these 'terrestrial islands the distribution of genetic variation was studied at several spatial scales in the rock hyrax, Procavia capensis. This species has a polygynous social system that is unusual among taxa with similar ecological requirements, and a morphology that would intuitively be associated with poor dispersal capabilities (short limbs and a squat, heavy body). Possibly as a consequence of these considerations, few studies have attempted to determine the distance of migration by rock hyraxes and the influence that their social system and the surrounding landscape has on dispersal success. This investigation therefore tests hypotheses of how the ecology, distribution, social structure and the connectivity of the surrounding landscape have contributed to shaping the structure of rock hyrax genetic variation across the Namaqualand and western Fynbos regions. To do so, mitochondrial and microsatellite markers were used to document gene-flow at a fine spatial scale (an isolated population comprising 5 koppies), an intermediate spatial scale (across known geographic barriers to saxicolous taxa - the Cape Flats and Knersvlakte), and a regional spatial scale (across the Namaqualand/western Fynbos regions of South Africa - regions exhibiting contrasting landscape connectivity). In addition the genetic diversity, spatial clustering, sex-biased dispersal and relatedness (fine-scale) of colonies is described and the major genetic breaks detected in the investigation dated using a relaxed molecular clock approach. Finally, these results were compared to other studies that identified the Cape Flats and Knersvlakte as phylogeographic disruptors.The genetic patterns at a fine spatial scale were complex: Gene-flow was restricted by the social structure of the rock hyrax rather than geographic distance, dispersal was female-biased and there was significant genetic structure. Genetic structure was also evident at the intermediate and regional spatial scales. In the Hottentots Holland Mountains and Cape Peninsula gene-flow was restricted (in both data sets) in comparison to localities that traversed the Cape Flats. In contrast, gene-flow across the Knersvlakte was restricted in the mitochondrial DNA data set but not so with microsatellites. A similar pattern was observed at a regional scale pointing to male-biased dispersal within this species - a result of its polygynous social structure. In addition to sex-biased dispersal, landscape connectivity also influenced gene-flow on a regional spatial scale as the Namaqualand region, which has greater intermediate suitable habitat compared to the western Fynbos region, displayed significantly higher levels of gene-flow between sampling localities. Consequently, colonies in Namaqualand were genetically more diverse compared to those of the western Fynbos region. Two major matrilineal clades were evident on both side of the Knersvlakte - one to the north of this biogeographic break (Namaqualand), and the other to the south (western Fynbos). This was not, however, evident from the microsatellite data (reflecting the influence of male dispersal) where seven nuclear clusters were found. In keeping with other studies on saxicolous vertebrate taxa straddling the same region, this area of low connectivity has acted (and probably still does) as a barrier to gene-flow. Importantly, unlike in many other (admittedly invertebrate) species, no evidence of a genetic break was detected among hyrax populations across the Cape Flats. Colonies across the Hottentots Holland Mountains and Cape Peninsula regions may have been subject to founder-events and breeding isolation.This investigation demonstrated the importance of using a well-structured sampling regime that included both mitochondrial and nuclear markers and it underscores the need to apply appropriate statistical programmes for inferring genetic patterns. It shows that landscape genetics may be useful in a conservation context and should be taken into account when planning conservation initiatives that include the implementation of corridors. In brief, the information contained in this study advances our knowledge of the dispersal capability and genetic diversity of contemporary rock hyrax populations.

[发布机构] Stellenbosch University