Latitudinal trends in seasonal life-history strategies: comparisons of bluegill and crappie.
Joe Beuchel, M.S. student, D. Derek Aday (North Carolina State University), and Elizabeth Marschall.

Energy-allocation strategies are the product of environmental factors, such as latitude and seasonality, as well as species-specific characteristics such as timing and length of the spawning season. The magnitude of influence each of these factors has on energy allocation strategies and reproduction is unknown and affects our expectations regarding the evolution of life history strategies. White crappie (Pomoxis annularis) and black crappie (P. nigromaculatis) spawning seasons closely follow the end of winter when prey are not abundant. Conversely, the bluegill (Lepomis macrochirus) spawning season begins later and lasts longer, potentially allowing individuals to develop their gonads immediately prior to reproduction. Predictions and field data have shown that crappie begin building gonads in the fall, well in advance of their spawning period (Bunnell and Marschall 2003. Evolutionary Ecology Research 5: 439-457.), whereas bluegill may not have to allocate energy to reproduction until just prior to spawning. Consequently, we expect their energy allocation patterns to differ throughout the year.

This study aims to quantify patterns of energy allocation in individuals of bluegill and crappie. In this investigation, we will examine seasonal patterns of energy allocation in bluegill and crappie and quantify differences based on size, sex, latitude, and species. By quantifying energetic patterns throughout the year for bluegill and crappie, we hope to uncover patterns that arise as a result of their different reproductive strategies. These field collections will aid in the development of theoretical models designed to predict the optimal energy-allocation strategies for bluegill and crappie across latitudes.

Using dynamic programming, we seek to predict size-, sex-, and latitude-specific growth and reproductive strategies throughout the year for bluegill and crappie. Dynamic programming is ideal for situations in which optimal decisions reflect state dependence in order to maximize expected lifetime fitness. In these models, optimal decisions that maximize future fitness will be determined using backwards iteration (Mangel and Clark. 1988. Dynamic modeling in behavioral ecology. Princeton University Press, Princeton, NJ.).

Our goal in developing these models is to examine how latitudinal and seasonal differences in conditions (temperature, food availability, etc) affect energy allocation in fish with different reproductive strategies. This model will make predictions for fish at northern, central, and southern latitudes of the United States.

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Joe Beuchel can be emailed at beuchel.1 "at" osu.edu