Genetic Variation in Phenotypic Plasticity in a Freshwater Snail

Frehswater snails (e.g., pond snails, Physa gyrina) are known for altering the architecture of their shells during growth and development as a means of reducing the probabiltiy of successful predation. In this thesis project performed by Sarah Calloway, we sought to determine if snail families differed with respect to how much they could alter their shell shape in response to chemical cues from crayfish predators. Detecting such differences would demonstrate genetic variation in the plasticity of shell shape, as well as genetic variation in shell shape itself.

	Photo: One of the crayfish used to generate the necessary predator chemical sues in the study.
	Pond snails were collected on campus, paired into separate cups in an aquarium, and allowed to reproduce in lab. Each pair produced several offspring; families were kept separate from each other so that family identity of individual snails could be tracked.
	Each family consisted of many offspring. At an early stage of development, individual offspring were collected from family cups, and assigned, by family, to grow in iether the presence or absence of predator cues.
	All snails were photographed with a digital camera before being assigned to treatments and at the end of the experiment. Differences among families in the difference in mean shell size and shape (aspect ratio) between predator and non-predator treatments indicated the degree of genetic variation among families in phenotypic plasticity.

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