Managing the Emerging Risk of Trichinellosis in Organic and Free Range Pork
Location: Animal Parasitic Diseases
Title: Evidence for a population bottleneck in an Apicomplexan parasite of caribou and reindeer, Besnoitia tarandi
Submitted to: Infection, Genetics and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 2012
Publication Date: June 26, 2012
Citation: Madubata, C., Dunams, D.B., Elkin, B., Oksanen, A., Rosenthal, B.M. 2012. Evidence for a population bottleneck in an Apicomplexan parasite of caribou and reindeer, Besnoitia tarandi. Infection, Genetics and Evolution. DOI: 10.1016/j.meegid.2012.06.007.
Interpretive Summary: The amount of genetic variation present in a species reflects its evolutionary history, and in the case of infectious organisms genetic variations, also provides information about transmission patterns. Interesting patterns have emerged when sampling genetic variation in various coccidian parasites of livestock, most notably in the agent of toxoplasmosis. However, it has been difficult to interpret such data without comparable measures from other, related parasites. Here, we assessed the extent of variability in a parasite related to toxoplasmosis that infects caribou and reindeer, a parasite which can harm the value of leather and meat derived from these animals. Remarkably, this parasite (Besnoitia tarandi) was found to be genetically identical across its entire sampling range, which included several herds in the Canadian Arctic as well as in Finland. As a check on the adequacy of the markers employed in this study, we verified that other species of Besnoitia appeared distinct when assayed by the same methods. Using plausible estimates of mutation rate, we considered the natural and anthropogenic forces which may have given rise to such widespread genetic uniformity. This information will be of interest to wildlife biologists, veterinarians, epidemiologists, and population geneticists, and may aid future efforts to protect wild and domesticated herds of these animals. Likewise, these data will be of interest to the cattle industry, which (in Mediterranean countries for many years, and in Western Europe only recently) are confronting outbreaks of closely related species, Besnoitia besnoiti.
The evolutionary history and epidemiology of parasites may be reflected in the extent and geographic distribution of their genetic variation. Among coccidian parasites, the population structure of only Toxoplasma gondii has been extensively examined. Intraspecific variation in other coccidia, for example those assigned to the genus Besnoitia, remains poorly defined. Here, we characterize the extent of genetic variation among populations of Besnoitia tarandi, a parasite whose intermediate hosts include caribou and reindeer (Rangifer tarandus tarandus). Isolates from the Canadian and Finnish Arctic were genotyped at six microsatellite loci, the first internal transcribed spacer region of nuclear rDNA, and the RNA polymerase ß subunit (rpoB) encoded in the plastid genome. Remarkably, all isolates exhibited the same multilocus genotype, regardless of the isolate's geographic origin. This utter monomorphism occurred despite the capacity of these loci to vary, as established by evident differentiation between B. tarandi and two other species of Besnoitia. The surprising lack of genetic variation across the sampled range suggests that B. tarandi may have experienced a recent population bottleneck.