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

Visser, Jacobus Hendrik (2013-12)

Thesis (MSc)--Stellenbosch University, 2013.

Thesis

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.

AFRIKAANSE OPSOMMING: ‘n Beperkte spreidingsvermoë, territorialiteit en die bewoning van yl-verspreide habitat is kenmerkend van die meeste klip-bewonende spesies in Afrika en dit veroorsaak gereeld gestruktureerde genetiese patrone met min of geen genevloei tussen populasies (bv., die velvetwurms, net-vlerk muggies, klipklaasneuse, klipkonyne en ‘n verskeidenheid akkedisse en koggelmanders). In ‘n poging om kennis oor taksa wat hierdie “terrestriële eilande” bewoon te verdiep, het ons die die verspreiding van genetiese variasie bestudeer oor verskeie ruimtelike skale in die klipdassie, Procavia capensis. Hierdie spesie het ‘n veelwywige sosiale sisteem, wat vreemd is onder taksa met soortgelyke ekologiese vereistes, en ‘n morfologie wat intuïtief verbind kan word met swak spreidingsvermoëns (kort bene en ‘n kort, dik liggaam). As ‘n moontlike resultaat van hierdie oorwegings het min studies tot dusver daarop gefokus om die migrasie-afstand van klipdassies en die invloede van hulle sosiale sisteem en die omliggende landskap op spreidings-sukses te bepaal. Hierdie studie toets daarom hipoteses oor hoe die ekologie, verspreiding, sosiale struktuur en die konnektiwiteit (verbindheid) van die omliggende landskap bydra om die struktuur van genetiese variasie in klipdassies oor die Namakwaland en westelike Fynbos streke te beïnvloed. Derhalwe is mitochondriale en mikrosatelliet merkers gebruik om genevloei te bepaal op ‘n fyn ruimtelike skaal (‘n geïsoleerde populasie bestaande uit 5 koppies), ‘n gemiddelde ruimtelike skaal (oor bekende geografiese grense vir klipbewonende taksa - die Kaapse Vlakte en die Knersvlakte), en op ‘n streeks (groot) ruimtelike skaal (oor die Namakwaland/westelike Fynbos streke van Suid-Afrika - streke met kontrasterende konnektiwiteit van die landskap). Bykomend is die genetiese diversiteit, ruimtelike groepering, seksuele eensydigheid in spreiding en genetiese verwantskappe (fyn skaal) van kolonies beskryf en die hoof genetiese skeiding gedateer deur gebruik te maak van ‘n ontspanne molekulêre klok. Laastens het is die resultate van hierdie studie vergelyk met dié van ander studies wat die Kaapse Vlakte en Knersvlakte as filogeografiese skeidings gevind het. Die genetiese patrone op ‘n fyn ruimtelike skaal was kompleks: Genevloei is beperk deur die sosiale struktuur van die klipdassie eerder as geografiese afstand, migrasie was wyfie-spesifiek en daar was beduidende genetiese struktuur tussen kolonies. Genevloei was beperk in die Hottentots Holland berge en die Kaapse Skiereiland (in beide datastelle) in vergelyking met lokaliteite oor die Kaapse Vlakte. In kontras was genevloei oor die Knersvlakte beperk in die mitochondriale DNA, maar nie in die mikrosatelliete nie. ‘n Soortgelyke patroon is waargeneem op ‘n streeks skaal wat dui op mannetjie-spesifieke spreiding in hiérdie spesie - ‘n resultaat van die veelwywige sosiale struktuur. Bykomend, saam met geslag-spesifieke spreiding, het landskaps konnektiwiteit ook genevloei beïnvloed op ‘n streeks skaal omdat die Namakwaland streek, wat meer tussenleggende geskikte habitat bevat in vergelyking met die westelike Fynbos streek, beduidende hoër vlakke van genevloei tussen lokaliteite getoon het. Gevolglik was kolonies in Namakwaland geneties meer divers in vergelyking met dié van die westelike Fynbos streek. Twee hoof moederlike genetiese groepe is waargeneem op elke kant van die Knersvlakte - een aan die noorde van hierdie biogeografiese skeiding (Namakwaland) en een in die suide (westelike Fynbos). Dieselfde patroon was egter nie waarneembaar in die mikrosatelliet data nie (wat die invloed van mannetjie-spesifieke spreiding toon) waar sewe nukluêre groepe gevind is. In ag genome ander studies op klipbewonende gewerwelde taksa oor dieselfde verspreiding, het hierdie area van lae konnektiwiteit histories (en heelmoontlik ook huidiglik) as ‘n grens vir genevloei gedien. Belangrik, anders as in ander (hoewel ongewerwelde) spesies, kon ons geen bewyse verskaf van ‘n genetiese skeiding tussen klipdassie populasies oor die Kaapse Vlakte nie. Kolonies in die Hottentots Holland berge en Kaapse Skiereiland is dus onderhewig aan moontlike vestigings-effekte en telings-isolasie. Hiérdie studie demonstreer die belang van die gebruik van ‘n goed-gestruktureerde monsternemingskema, die insluiting van beide mitochondriale en nukluêre merkers en dit beklemtoon ook die noodsaaklikheid van die gebruik van toepaslike statistiese programme vir gevolgtrekkings oor genetiese patrone. Dit toon ook dat landskapsgenetika nuttig mag wees in ‘n bewaringskonteks en in ag geneem moet word in die beplanning van bewarings inisiatiewe wat die implementering van korridors insluit. Kortliks, die informasie in hierdie studie bevorder ons kennis oor die spreidingsvermoë en genetiese diversiteit van kontemporêre klipdassie populasies.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/85673
This item appears in the following collections: