Characterizing the impact of multiple potential enemies (predators and parasites) on the behaviour of ranid tadpoles

In order to fully understand an organism's behaviours the interactions between multiple enemies or selective pressures need to be considered, as these interactions are usually far more complex than the simple addition of their effects in isolation. In this thesis, I consider the impact of multiple enemies (fish predators and parasites) on the behaviour of three larval anurans (Lithobates sylvaticus, L. clamitans and L. catesbeianus). I also determine whether species that differ in life-histories and habitat preferences possess different antipredator mechanisms and how this affects species responses to multiple enemies. I show that the three Ranid larvae respond differently to the trade-off imposed by the presence of both fish predators and trematode parasites within the environment. The two more permanent pond breeders (L. clamitans and L. catesbeianus) increased activity when in the combined presence of predators and parasites. In contrast, the temporary pond breeder (L. sylvaticus) decreased activity in the combined presence of predator and parasites, in the same manner as they responded to fish alone. 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. A second experiment to assess palatability of the three anuran species to fish, revealed a range of palatabilities, with L. catesbeianus being least palatable, L. clamitans being somewhat unpalatable, and L. sylvaticus being highly palatable. This result helps to explain the species differences in tthe observed behaviour to the combined presence of fish and parasites. In conclusion, the results from this study highlight the importance of considering multiple selective pressures faced by organisms and how this shapes their behaviour

Characterizing the Role of Dietary Antioxidants as Immune-enhancing Molecules in Larval Anurans

The effects of stress (disruption of homeostasis) and stressors (factors that cause changes in homeostasis) and their impacts on animal health, physiology, behaviour and fitness have received enormous attention within the scientific community. From an evolutionary stand point, understanding the way in which animals cope with stress or how stress tolerance has evolved is important, as chronic stress can lead to loss of fitness. From an ecological stand point, identifying stressors within the environment and understanding how additive stressor effects can impact the way in which animals cope is crucial for understanding population declines and or possible extinctions. One coping mechanism used by some animal taxa is diet. When consumed, dietary antioxidants (secondary metabolites produced by plants) can provide protection from oxidative damage that can result from exposure to stressors. My dissertation focuses on the effects of these compounds on tadpole immune function. I choose to focus on tadpoles, as populations of numerous amphibian species are declining worldwide and some have gone extinct. In addition, tadpoles, which are strictly aquatic, are exposed to a wide variety of both abiotic and biotic stressors. I focus on three areas of study: 1) the effect of dietary antioxidants and natural stressors on immune function; 2) whether or not tadpoles detect these compounds in their food and whether or not they have the ability to self-medicate; 3) a potential trade-off between immune function and antipredator defense mediated by dietary antioxidants and the environmental availability of these compounds in natural tadpole habitats. My work will contribute to the field of ecology and amphibian biology by investigating the effects of these potentially beneficial compounds and the effects on amphibian immune function, in an attempt to determine if there are any natural immune enhancers to help amphibian's combat mortality via immunosuppression.Ph.D.2016-11-30 00:00:0

Correction: The Behavioral Response of Larval Amphibians (Ranidae) to Threats from Predators and Parasites.

[This corrects the article DOI: 10.1371/journal.pone.0049592.]

The behavioral response of larval amphibians (Ranidae) to threats from predators and parasites.

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

Analysis of variance table for final model estimating post-treatment time active in tadpoles in response to effect of species, fish presence or absence, parasite presence or absence and the covariate of time active pre-treatment (actPRE).

<p>Analysis of variance table for final model estimating post-treatment time active in tadpoles in response to effect of species, fish presence or absence, parasite presence or absence and the covariate of time active pre-treatment (actPRE).</p

Additional behaviors performed by tadpoles of the three species to four different treatments.

<p>Number of tadpoles engaged in a) extreme swimming, b) body twisting, and c) tail flicking behavior post-treatment. See text for behavior descriptions. N = 20 for each treatment combination and data were treated as binomial (i.e. individual in replicate did (score = 1) or did not (score = 0) perform behavior). For both extreme swimming and body twisting, species differed significantly and there was a significant effect of parasite. In body twists, the effect of fish was also significant. For tail flicking, significant species by parasite and species by fish interactions occurred. All effects are based on generalized linear analysis (see text for details).</p

Response of tadpoles to the presence of parasites and predators and the hypothesized response to the presence of both, which will depend on the relative vulnerability of the tadpole to the predator.

<p>The dotted line in each plot represents baseline activity level, i.e. the activity level of the tadpole when no predator or parasite is present. We hypothesize that species such as <i>Lithobates sylvaticus</i>, which is highly vulnerable to fish predators, will show decreased activity in the presence of both fish and parasites, while species such as <i>L. catesbeianus</i>, which is relatively invulnerable to fish predators will increase activity in the presence of both fish and parasites.</p