Parasite Genotypes Identify Source Populations of Migratory Fish More Accurately Than Fish Genotypes

Abstract

DNA-based assignment of individuals to their population of origin has many applications such as mixed-stock analysis, identifying individuals from protected populations, and elucidating migration patterns. However, low genetic differentiation among populations will cause misassignments. Thus, an alternative means of determining an individual's population of origin is needed in cases where there is little or no neutral differentiation among source populations. Here, we test the hypothesis that parasite genotypes can be used to identify the origins of hosts more accurately than host genotypes. Using microsatellite markers from steelhead trout and their trematode parasites, we show that the odds of correct assignment are four times greater with the parasite's genotypes than with the host's genotypes. Our analyses show that this result is simply explained by the greater genetic structure among populations of the trematode parasite. Recent studies on the comparative genetic structure of other host and parasite species suggest that our results are not unusual or unique to the host-parasite system we studied. Thus, our work indicates that parasites will be useful for a wide range of applied and basic research that requires the assignment of individuals to source populations.

Low genetic variation in the salmon and trout parasite Loma salmonae (Microsporidia) supports marine transmission and clarifies species boundaries

“…Sequence variation was greater in Loma salmonae from freshwater (rainbow and brook trout) than from anadromous hosts, supporting the general principle that where isolation is higher, such as in freshwater systems, variation is higher (McCusker et al 2000, Waples et al 2001, Criscione & Blouin 2004, Criscione et al 2006. This tends to be amplified in farms and hatcheries where fish and parasites may come from numerous sources with historical biogeographic genetic substructuring (Nielsen et al 1994, Narum et al 2004, Verspoor et al 2005.…”

Pneumocystis diversity as a phylogeographic tool

“…Indeed, when parasite populations are more diversified than their host populations, gene trees of parasites can be used to infer recent migration events of infected hosts (Nieberding & Olivieri 2007). For instance, parasite genotypes identify source populations of migratory salmon more accurately than do fish genotypes (Criscione et al 2006). Another example is the detailed study of the comparative phylogeography of the rodent Apodemus sylvaticus and one of its specific endoparasites, the nematode Heligmosomoides polygyrus (Nieberding et al 2004, Nieberding & Olivieri 2007.…”

“…In some cases, parasites provide an additional source of information, since parasite data can better reconstruct the common history of host and their parasite (Nieberding & Olivieri 2007). For this reason, some parasites have been recently used as phylogeographic markers (Nieberding et al 2004, Taylor et al 2005, Criscione et al 2006, Nieberding & Olivieri 2007. The Pneumocystis species have been shown to be a powerful tool in phylogenetic studies , Hugot et al 2003, Aliouat-Denis et al 2008.…”

Meet the Parasites: genetic approaches uncover new insights in parasitology

“…Mackenzie (2002) reviews how parasites can be used as biological tags in a variety of marine organisms, since populations of a given species that experience different environmental conditions may acquire specific parasites that can then be used for identification and tracking. Indeed, research by Criscione et al (2006) determined that genotyping the trematode parasites of steelhead trout (Oncorhynchus mykiss) was four times more effective in correctly assigning the fish to its population of origin than genotyping the fish itself. In terrestrial systems, pathogens such as the gastric bacterium Helicobacter pylori have been used to track human migration through sequencing strain variation that replicate colonization events.…”