Predation Effects in Long and Short Term Exposure in Rana Sylvatica
Dakota A. Starkey, Vassar College '13, Prof. Erica J. Crespi and Research Associate Robin Warne
In order to investigate whether exposure to predation threat causes changes in behavior, physiology and metamorphic timing, two experiments were conducted. In the first experiment, Rana sylvatica (wood frogs) were exposed to a predator cue for the first week of the experiment, from Gosner stage 36 (limb development) till the end of the experiment, during the entire experiment or not at all. Additionally the wood frogs were also given either food once a week or twice a week. All the other tadpoles were kept until metamorphosis at which point they had body measurements taken. After approximately 7 weeks the juveniles went through an "open field test" in which they were placed in large container with 10 flies and behavior was observed to assess long-term effects of the predator. There was no significant difference in body measurements in the tadpoles collected from early exposure and the juveniles that had body measurements taken. While the type of predator exposure did not affect behavior, body weight was positively correlated with the number of strikes at prey and number of flies eaten and negatively correlated to the time before the first strike at prey. This suggests that an environmental stressor that effects growth and metamorphic weight have an effect on efficiency in foraging and potential to survive. In the second experiment, wood frogs were exposed to a predator cue or an empty container for 2, 4, 24 and 48 hour time intervals to assess behavior and physiological changes that occur early after the introduction to a predator. Before and during the introduction of the predator photographs were taken of the tadpole containers to assess overall stratification and how it was effected by the predator or the control container. After each time interval, tadpoles were collected to assess body measurement and corticosterone levels. Behavioral modulation was seen as a response to the introduction of a predator; however, there was no significant difference in body measurements between the control group and the predator group for each time interval. Taken together, the results of these experiments suggest that wood frog tadpoles have a quick reaction to the predation cue, but do not manifest long-term effects of the predation cue on developmental timing or growth.