Abstract
Organisms are exposed to strong selective pressures from several sources, including predators and pathogens. Response to such interacting selective pressures may vary among species that differ in life history and ecology in predictable ways. We consider the impact of multiple enemies (fish predators and trematode parasites) on the behavior of larvae of three anuran species (Lithobates ( = Rana) sylvaticus, L. clamitans and L. catesbeianus). We show that the three ranid species differ in response to the trade-off imposed by the simultaneous presence of fish predators and trematode parasites in the environment. Two more permanent pond breeders (L. clamitans and L. catesbeianus), which commonly encounter parasites and fish, increased activity when in the combined presence of parasites and a fish predator, resulting in a relatively lower parasite encystment rate. In contrast, the temporary pond breeder (L. sylvaticus), which does not commonly encounter fish in the wild, decreased activity in the combined presence of a fish predator and parasites similar to when only the predator was present. For L. sylvaticus, this suggests that the presence of an unknown predator poses a greater threat than parasites. Further, the presence of fish along with parasites increased the susceptibility of both L. sylvaticus and L. clamitans to trematode infection, whereas parasite infection in L. catesbeianus was unaffected by the presence of fish. Unpalatability to fish may allow some species to respond more freely to attacking parasites in the presence of fish. The results from this study highlight the importance of considering multiple selective pressures faced by organisms and how this shapes their behavior.
Highlights
IntroductionNone is as fundamental as the trade-off between the need to eat while simultaneously evading predators [1]
Animals are confronted with trade-offs on a daily basis
L. clamitans were collected as pre-foraging hatchlings (Gosner stage 20 [23]) from a pond near Rock Lake (45u319N, 78u249W) and a single L. catesbeianus egg mass was collected from Lake Sasajewun at the Wildlife Research Station
Summary
None is as fundamental as the trade-off between the need to eat while simultaneously evading predators [1]. Almost all free-living animals must be active in order to acquire resources and obtain mates, but this activity makes prey vulnerable to predators [2]. This is clear within the larval anuran system. A trade-off occurs because a more active tadpole is more conspicuous to predators and more vulnerable relative to an inactive counterpart [4]. Reduced activity in the presence of predators has been empirically demonstrated in larvae of several anuran species, e.g. Reduced activity in the presence of predators has been empirically demonstrated in larvae of several anuran species, e.g. [5,6]
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