Abstract

1. Results of Survival Experiment Abstract • Prior exposure to chemical cues had no effect on the survival of tadpoles. For aquatic amphibians, the expression of antipredator behaviors may be essential for survival. In most cases, chemical cues from predators are important triggers for those behaviors. We conducted a study to determine if tadpoles of green tree frogs (Hyla cinerea) from ponds without fish predators would exhibit antipredator behavior, and if prior exposure to chemical cues from the predator (bluegill, Lepomis macrochirus) was necessary to elicit such behavior. We also conducted a survival experiment to determine if tadpoles with prior exposure to predator cues had a higher chance of survival when exposed to a predator for 24 hrs. During the behavioral trials, tadpoles with prior exposure to chemical cues were less active and spent less time near the predator than those without prior exposure. There was no significant difference between survival of tadpoles with and without prior exposure to chemical cues of predators. Our results suggest that prior exposure to predator cues may trigger antipredator behavior in tadpoles, even from populations that do not coexist with fish predators. Hypotheses Results of Behavioral Experiment t=0.394, df=18, p=0.699 • Tadpoles with prior exposure to chemical cues from predators will be less active and spend less time in close proximity to the predator • Tadpoles with prior exposure to chemical cues from predators will have a higher rate of survival when exposed to the predator for 24 hrs • Tadpoles with prior exposure to chemical cues showed less activity than naïve tadpoles. Altig et al. Figure 2. Hyla cinerea tadpole t=-2.326, df=48, p=0.024 Experienced Naïve Figure 7. Average number of surviving tadpoles Conclusions • Although tadpoles from this site do not coexist with fish predators, they have maintained their ability to respond to predator cues • Prior exposure was necessary to elicit antipredator behavior • Reduction in activity and avoidance of visual predators (e.g., fish) may reduce the likelihood of predation • However, the results of our survival experiment suggest that antipredator behavior of tadpoles may have lost some effectiveness over evolutionary time Experienced Naïve Figure 4. Average time that tadpoles spent moving Methods • Collection and Experiment Preparation • Tadpoles of Hyla cinerea collected at Red Lake at Ruffner Mountain in Birmingham, AL • The night before each test, bluegill isolated and fed 5 tadpoles • Behavioral experiment: tadpoles immersed for 15 min in either water with predator cues (experienced) or dechlorinated water (naïve) • Survival experiment: tadpoles immersed for 2 hr in either water with predator cues (experienced) or dechlorinated water (naïve) • Behavioral Experiment • Tadpole acclimated for 10 min in experimental chamber • Bluegill in a screen cage added to chamber and behaviors observed for 15 min • Activity level and time in proximity to the predator recorded • N=25 tadpoles for each group • Survival Experiment • After experiment preparation, 10 tadpoles (either experienced or naïve) added to survival chamber and allowed to acclimate • Bluegill added to chamber • 24 hrs later, number of survivors recorded • N=10 trials for each group Figure 1. Study organism (Hyla cinerea) Background Figure 5. Predator bluegill (Lepomis macrochirus) • Active prey may be more conspicuous to predators (Lawler, 1989) • When in the presence of fish predators, limiting movement may be advantageous (Wellborn et al, 1996) • Many larval amphibians have the ability to detect and respond to chemical cues from predators (Gallie et al., 2001; Laurila, 2000) • Some species of tadpoles significantly reduced activity when exposed to fish chemical cues (Laurila, 2000; Stauffer and Semlitsch, 1993) • Prior exposure may be necessary to elicit antipredator behavior (Murray et al., 2004) • Tadpoles previously exposed to chemical cues spent significantly less time within 10 cm of the predator. Purpose t=-2.141, df=48, p=0.037 Figure 8. Chris and Nikki collecting at Red Lake To determine if there is a difference between antipredator behavior of green tree frog (Hyla cinerea) tadpoles with and without prior exposure to chemical cues from bluegill (Lepomis macrochirus). Literature Cited Altig, R., R. W. McDiarmid, K. A. Nichols, and P. C. Ustach. Tadpoles of the United States and Canada: A Tutorial and Key. http://www.pwrc.usgs.gov/tadpole Gallie, J. A., R. L. Mumme, and S. A. Wissinger. 2001. Experience has no effect on the development of chemosensory recognition of predators by tadpoles of the American toad, Bufo americanus. Herpetologica 57: 376-383. Laurila, A. 2000. Behavioral responses to predator chemical cues and local variation in antipredator performance in Rana temporaria tadpoles. Oikos 88:159-168. Murray, D. L., J. D. Roth, and A. J. Wirsing. 2004. Predation risk avoidance by terrestrial amphibians: the role of prey experience and vulnerability to native and exotic predators. Ethology 110: 635-647. Lawler, S.P.1989. Behavioral responses to predators and predation risk in four species of larval anurans. Anim. Behav. 38:1039-1047. Stauffer, H. P., and R. D. Semlitsch. 1993. Effects of visual, chemical, and tactile cues of fish on the behavioural responses of tadpoles. Anim. Behav. 46:355-364. Wellborn, G. A., D. K. Skelly, and E. E. Warner. 1996. Mechanisms creating community structure across a freshwater habitat gradient. Ann. Rev. Ecol. Sys. 27: 337-363. Experienced Naïve Figure 6. Average time that tadpoles spent in close proximity to the predator Figure 3. Collection site: Red Lake THE EFFECT OF PRIOR EXPOSURE TO CHEMICAL CUES ON THE ANTIPREDATOR BEHAVIOR OF HYLA CINEREA TADPOLESNIKKI ROMBOUGH, CHRISTOPHER BRENNAN, and MEGAN E. GIBBONS