Abstract
Epidemiological rate parameters of host generalist parasites are difficult to estimate, especially in cases where variation in parasite performance can be attributed to host species. Such cases are likely common for generalist parasites of sympatric grazing mammals. In this study, we combined data from experimental exposures in cattle and sheep and natural infections in elk to compare the recruitment, morphology and reproduction of adult Dicrocoelium dendriticum, a generalist trematode that has emerged in sympatric grazing hosts in Cypress Hills Provincial Park, Alberta. Overall, there were no significant differences in the recruitment of metacercariae and in the pre-patency period of adults in experimentally exposed cattle and sheep. All flukes reached reproductive maturity and the degree of reproductive inequality between individual flukes within each infrapopulation was moderate and approximately equal among the three host species. Neither fluke size nor per capita fecundity was constrained by density dependence. Thus, fitness parameters associated with growth and reproduction were approximately equivalent among at least three species of definitive host, two of which are sympatric on pastures in this Park. The generalist life-history strategy of this trematode, which is known to extend to other stages of its life cycle, has likely contributed to its invasion history outside its native range in Europe.
Highlights
Parasitologists have long recognized that a parasite’s position along the host specialist – host generalist continuum influences fundamental aspects of host/ parasite biology
The extent to which a parasite is a host specialist or host generalist impacts the nature of host immunological responses, the magnitude of transmission asymmetries among host species, and influences key components of parasite fitness, such as growth, reproduction and development (Combes, 2001; Hudson et al 2002; Poulin, 2007)
For parasites that are host specialists, key rate parameters such as transmission, growth, reproduction, senescence and parasite-induced host mortality can be estimated from experiments involving a single species of host
Summary
Parasitologists have long recognized that a parasite’s position along the host specialist – host generalist continuum influences fundamental aspects of host/ parasite biology. The extent to which a parasite is a host specialist or host generalist impacts the nature of host immunological responses, the magnitude of transmission asymmetries among host species, and influences key components of parasite fitness, such as growth, reproduction and development (Combes, 2001; Hudson et al 2002; Poulin, 2007). For parasites that are host specialists, key rate parameters such as transmission, growth, reproduction, senescence and parasite-induced host mortality can be estimated from experiments involving a single (or few) species of host. It follows that control strategies will be much simpler in cases involving single species of parasite in a single species of host.
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