Abstract
BackgroundThe specialist-generalist variation hypothesis (SGVH) in parasites suggests that, due to patchiness in habitat (host availability), specialist species will show more subdivided population structure when compared to generalist species. In addition, since specialist species are more prone to local stochastic extinction events with their hosts, they will show lower levels of intraspecific genetic diversity when compared to more generalist.ResultsTo test the wider applicability of the SGVH we compared 337 cytochrome oxidase I mitochondrial DNA and 268 nuclear tropomyosin DNA sequenced fragments derived from two co-distributed Laelaps mite species and compared the data to 294 COI mtDNA sequences derived from the respective hosts Rhabdomys dilectus, R. bechuanae, Mastomys coucha and M. natalensis. In support of the SGVH, the generalist L. muricola was characterized by a high mtDNA haplotypic diversity of 0.97 (±0.00) and a low level of population differentiation (mtDNA Fst = 0.56, p < 0.05; nuDNA Fst = 0.33, P < 0.05) while the specialist L. giganteus was overall characterized by a lower haplotypic diversity of 0.77 (±0.03) and comparatively higher levels of population differentiation (mtDNA Fst = 0.87, P < 0.05; nuDNA Fst = 0.48, P < 0.05). When the two specialist L. giganteus lineages, which occur on two different Rhabdomys species, are respectively compared to the generalist parasite, L. muricola, the SGVH is not fully supported. One of the specialist L. giganteus species occurring on R. dilectus shows similar low levels of population differentiation (mtDNA Fst = 0.53, P < 0.05; nuDNA Fst = 0.12, P < 0.05) than that found for the generalist L. muricola. This finding can be correlated to differences in host dispersal: R. bechuanae populations are characterized by a differentiated mtDNA Fst of 0.79 (P < 0.05) while R. dilectus populations are less structured with a mtDNA Fst = 0.18 (P < 0.05).ConclusionsThese findings suggest that in ectoparasites, host specificity and the vagility of the host are both important drivers for parasite dispersal. It is proposed that the SGHV hypothesis should also incorporate reference to host dispersal since in our case only the specialist species who occur on less mobile hosts showed more subdivided population structure when compared to generalist species.
Highlights
The specialist-generalist variation hypothesis (SGVH) in parasites suggests that, due to patchiness in habitat, specialist species will show more subdivided population structure when compared to generalist species
Specialist species are more prone to local stochastic extinction events than their more generalist counterparts, and this will result in lower levels of genetic diversity in specialist when compared to more generalist parasites [16]
When the mites occurring on the two Rhabdomys host species are considered separately, the mtDNA haplotypic diversity of the mites occurring on R. bechuanae are higher (mtDNA = 0.91 (±0.02); Table 2) when compared with L. giganteus occurring on R. dilectus (mtDNA = 0.62 (±0.00); Table 2)
Summary
The specialist-generalist variation hypothesis (SGVH) in parasites suggests that, due to patchiness in habitat (host availability), specialist species will show more subdivided population structure when compared to generalist species. Comparative phylogeographic studies on parasites and their hosts are important to address ecological, evolutionary, and applied questions in parasitology [1] Amongst others, it can facilitate the detection of cryptic lineages [2,3,4,5,6,7], aid in predicting the spread of diseases [8, 9] and can provide insights into the mechanisms that play a role in parasite dispersal and gene flow [10,11,12,13]. Some generalizations emerge such as the specialist-generalist variation hypothesis (SGVH) as proposed by Li et al [16] This hypothesis proposed that since the habitat of specialist parasite species are patchier due to host availability, especially when compared to generalist species, specialist will show a more subdivided population structure [16]. Specialist species are more prone to local stochastic extinction events (together with their hosts) than their more generalist counterparts, and this will result in lower levels of genetic diversity in specialist when compared to more generalist parasites [16]
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