Date of Award

2002

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Zoology

Advisor

William E. Glanz

Second Committee Member

Mary S. Tyler

Third Committee Member

Malcolm L. Hunter

Abstract

Even while in ovo many amphibians can react to the world around them, as dissolved molecules are able to pass through their protective jelly matrix and interact with developing sensory systems. Although there are many potential signals dissolved in the water, two, natal-pond recognition cues and predator recognition signals (or kairomones), have been previously shown to be relevant to several species of developing anurans. My study used natural odorants in a test of natal pond learning, and in testing both short- and long-term effects of predator chemical cues on the development and behavior of wood frog, Rana sylvatica, embryos. In 1992 Hepper and Waldman published a series of experiments on wood frog embryos. They exposed individuals to orange, lemon-like, and strawberry essence water during the embryonic period. After hatching, the tadpoles were tested for their stimulus preference, and whether or not embryonic exposure had changed their native response to the stimulus. In both the orange and strawberry essence trials, tadpoles that had been exposed to the stimuli as embryos significantly preferred those stimuli, as compared to embryos that had been raised in unadulterated water. These experiments demonstrate that embryonic wood frogs possess the ability to 1) perceive and 2) learn chemosensory information present. However, the stimuli used were highly artificial and not analogous to any dissolved molecules present in natural bodies of freshwater. To test whether the tadpoles prefer orange extract water because it mimicked an "imprinting" experience on natal pond water, I exposed embryos to natural pond water in the laboratory. Tadpoles showed consistent preferences for water types high in turbidity in choice tests. However, the embryonic exposure to various natural water types did not play a part in larval forming preferences. To test whether the reaction to orange-flavored water was analogous to a potential anti-predator behavior, I raised embryos in the laboratory in various predator-labeled waters. In the first year I used fish, earthworm (as a non-predator animal control), and well water rearing treatments. These stimuli produced differences in timing and size at hatching, but for the earthworm control treatment only. However, at the time of metamorphosis the earthworm treatment showed no differences in size or anti-predator behavior, as compared to the fish and spring water treatments. In the second year, I expanded the treatments to include more realistic predators on wood frogs. I reared embryos in water containing fish, newts, larval caddisflies, larval dragonflies, and leeches; the control treatments contained earthworms or consisted of well water. The experiment ended at hatching, and no significant differences between any of the treatments were found. These experiments imply that the embryonic experiences in wood frogs do not seem to play a major role in future habitat choices. Importantly though, this study shows that embryonic phenotypic plasticity may exist in wood frogs. Finally, differences seen at hatching do not transfer to differences at metamorphosis.

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