The influence of parasite ecology on the genetic structure of parasite populations.

摘要

Parasites are unique study organisms for evolutionary ecologists. Yet, molecular ecology studies on parasites have lagged far behind those on free-living organisms. The goal of the review in Chapter 2 was to illustrate areas of research that may be of particular interest in relation to the parasitic life style and to highlight areas that require additional study. While parasite molecular ecology is still in its infancy, it is obvious that molecular techniques have numerous applications for understanding the basic biology of parasites (e.g., elucidating life cycles). Reciprocally, parasite ecology is useful for predicting genetic patterns within and among parasite populations. Chapters 3 and 4 examine hypotheses about the influence of parasite ecological characteristics on the genetic structure of parasite populations. Chapter 3 is a broad scale analysis in which life cycle patterns were used to predict the potential for gene flow among geographic populations. Three freshwater trematode species that cycle exclusively in aquatic hosts are much more subdivided among streams than another trematode species from the same locations but whose life cycle includes highly mobile terrestrial hosts. These results show how variation in life cycles can shape parasite evolution by predisposing them to vastly different genetic structures. Chapter 4 focuses on a local scale dynamics in the salmonid trematode Plagioporus shawi. The transmission dynamics and mating system (selfing vs. outcrossing) of a parasite will determine the levels and patterns of genetic diversity within populations. The results of this study challenge the previous paradigm that segregation of parasites into infrapopulations (all the parasites in a single host) cause low genetic diversity. We found high levels of genetic diversity, and that a posteriori inference of population structure overwhelmingly supports the component population (all the parasites among a host population) as the deme. Furthermore, genetic data indicate P. shawi is largely outcrossing. Aquatic transmission and the use of multiple intermediate hosts likely promote high genetic diversity and well-mixed infrapopulations.