AWRI Newsletter #61: February 2007

Aaron Parker, an Annis Water Resources Institute (AWRI) graduate student working under Dr. Don Uzarski, is in the final stages of his research, which was funded by an AWRI assistantship and a grant from the Michigan Department of Environmental Quality. The research focused on yellow perch, a native fish to the Great Lakes region and a popular sport fish, and which serves important ecological functions.

Parker's research focused on questions about the genetics and morphological characteristics of yellow perch within the Great Lakes. This is important because very little was previously known about yellow perch body morphology and information about yellow perch genetics is still evolving. Yellow perch were collected from Lake Michigan, drowned river mouth systems adjacent to Lake Michigan, Saginaw Bay nearshore (this area is defined as being deeper than the wetlands and less than 30 m depth), and the wetlands along Saginaw Bay. After the yellow perch were collected, stomach contents were examined, fish were aged, and 21 body part measurements and six counts of enumerable features (e.g. number of dorsal spines) were made on a total of 422 fish. This project was in collaboration with the University of Toledo's Great Lakes Genetics Laboratory where they assessed the genetic variability of a subset of these fish.

Parker found that Great Lakes yellow perch exhibit very low genetic diversity, and actually are quite inbred. Even yellow perch from Lake Michigan and Saginaw Bay were genetically similar. However, the study did show that as yellow perch switch from eating insects and zooplankton to eating fish, their body morphologies changed. Yellow perch that consumed insects and zooplankton were found to have proportionally larger paired fins and longer, but fewer gill rakers than the yellow perch that ate fish. The yellow perch that fed on other fish had proportionally deeper bodies and larger mouths than the smaller yellow perch. The differences between the two feeding types appear to be related to increasing their feeding efficiency. For example, the yellow perch that feed on insects can use their large paired fins for increased three-dimensional movement efficiency, a trait that is especially useful in structurally complex environments such as wetlands. In contrast, the deep body cavity of the fish-eating yellow perch may allow for a faster start when chasing prey.

Because there were no genetic differences among any of the yellow perch, differences in body morphologies are not a result of any type of evolutionary process. Rather, the differences are most likely the result of a biological phenomenon known as phenotypic plasticity. Phenotypic plasticity is the ability of an organism's phenotype (or body morphology) to change based on environmental pressures on the organism's genotype (genetic make-up). This evidence that yellow perch may exhibit phenotypic plasticity may help explain why yellow perch are able to inhabit and exploit habitats as diverse as wetlands and large cold lakes.

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