Host-parasite interactions of two sympatric small mammals from South Africa

Patterns of ectoparasite burden among hosts can be linked to differences in abiotic (i.e. climatic conditions) and biotic (i.e. host characteristics) factors. Although this is well documented for small mammals in the northern hemisphere, similar data for southern Africa, particularly South Africa, is scant. In addition, interspecific interactions in parasite communities may contribute to the distribution of parasites across a host population, however, they are not fully understood due to a lack of studies investigating more than one parasite species. Also, by definition parasites are detrimental to their hosts, reducing host fitness either directly by feeding off the host or indirectly by causing the host to initiate energetically expensive behavioural or immune defences. The Namaqua rock mouse (Micaelamys namaquensis) and the eastern rock sengi (Elephantulus myurus) are two sympatric small mammals widely distributed throughout southern Africa, however they have divergent life-history traits. Despite their large geographical distribution there are no systematic studies of the parasite community of M. namaquensis and those on E. myurus are largely limited to their ticks. The present study aimed to close this gap in our knowledge by firstly assessing the ectoparasite community of M. namaquensis and E. myurus and furthermore identifying the main parasite species exploiting each host. In addition, I evaluated the effects of abiotic and biotic factors on parasite burden for these two species. In order to assess the contributions of interspecific interactions within the ectoparasite community on parasite distribution I furthermore manipulated the ectoparasite community of sengis using Frontline® to reduce the abundance of fleas and ticks over a period of two years and documented the effect of this treatment on the ectoparasite population dynamic as well as the body condition index (BCI) of sengis. During the initial assessment a total of 43,900 ectoparasites were collected from both hosts, however, the two hosts sustained very different ectoparasitic burdens. While Namaqua rock mice harboured 23 ectoparasite species, sengis only sustained ten. The ectoparasite community of rock mice was dominated by three species of flea (Xenopsylla brasiliensis, Epirimia aganippes and Chiastopsylla godfreyi) and two species of tick (Rhipicephalus distinctus and Haemaphysalis spp.) whereas in sengis it was four species of tick (R. warburtoni/arnoldi, R. distinctus, Rhipicentor nuttalli and Ixodes spp.). In addition, both hosts sustained large numbers of unidentified ectoparasites. All ectoparasite species exhibited seasonal peaks in abundance coinciding with the warm/wet season probably as a result of favourable climatic conditions during spring and summer. Direct host effects on parasite abundance were observed for the rodent, while there was only weak evidence of a sex bias in parasite burden probably as a result of the contrasting mating systems (promiscuous vs. monogamous). I observed few direct effects of Frontline® on the parasite burden or BCI in sengis. However, over the study period the abundance of the Rhipicephalus warburtoni/arnoldi decreased significantly, while the opposite was true for chiggers suggesting that the treatment was indeed effective and that there might be a competitive interaction between these two species. The lack of similar effects in the other three common ectoparasites might be a result of their low abundances. Although I found no direct effects of any of the main parasite species on sengi BCI, the decrease in tick abundance coincided with an increase in the BCI in sengis suggesting that ticks may have substantial fitness costs for these afrotheres. The present study highlighted the complexity of interspecific interactions within a parasite community on small mammal populations as well as the role such interactions may play in generating the patterns of parasite distribution across their host population.