Undergraduate Thesis Or Project
 

Pisaster poster with borders.ppt

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Abstract
  • Pisaster ochraceus occurs in a variety of colors; the major hues being orange, brown, and purple. Harley et al. (2006) found that in areas on the open Pacific coast, where Mytilus californianus was present, less than 10% of the population of P. ochraceus were purple whereas in areas of the San Juan Archipelago and the southern Strait of Georgia, where M. californianus was absent, approximately 95% of the P. ochraceus found were purple. This pattern suggests that the expression of the orange and brown pigmentations may be dependent on the consumption of M. californianus (Fox and Hopkins 1966). The purpose of my research was to investigate whether color is controlled by diet. I hypothesized that by feeding purple individuals M. californianus they would undergo a slight change in color as they began to express orange/brown pigmentation. There were two parts to this study: a laboratory experiment and field surveys. In the laboratory experiment, orange and purple sea stars were fed Pollicipes polymerus or Mytilus californianus. Pictures were taken of each individual twice a week to track any observable color changes over a period of four weeks. No significant color changes were observed in the laboratory. During the field surveys, I examined P. ochraceus diet—as well as other factors—at three sites over a period of four months. Despite previous studies providing suggestive evidence that color may be controlled by diet, I found no significant differences in diet between color morphs. There may be an underlying genetic component that affects color expression, as proposed by Harley et al. (2006). More research is needed to understand the biology of this keystone species.
  • Keywords: Color polymorphism, Sea star, Pisaster ochraceus
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