Changes In Bluegill Life History In Response To Thermal Extremes
Robert U. Fischer, Biology Department, Eastern Illinois University, Charleston, IL 61920; (217) 581-2817; FAX (217) 581-7141; cfruf@eiu.edu
Extreme environments provide the opportunity to evaluate population divergence in life history evolution in response to acute and chronic environmental perturbation. Bluegill were sampled from both a thermally impacted pond (Pond C) and an ambient habitat (Par Pond) located on the Savannah River Site near Aiken, South Carolina to determine the influence of 35 years of thermal extremes on life history patterns. Fish were collected using an electroshocking boat and then frozen and returned to the lab for later analysis. Sagittal otoliths were also removed from each bluegill and stored dry for determination of growth rate and age at first reproduction. In addition, gonads from spawning females were removed and stored in Gilson fluid for later analyses of the reproductive parameters of egg size and egg number. Bluegills from Par Pond (normothermic site) exhibited increased growth rates and delayed maturity compared to bluegill from the heated site (Pond C). The increase in growth rates and delayed sexual maturity may be a response to the increased juvenile bluegill mortality caused by the relatively large bass population occupying Par Pond. Fish from the heated site (Pond C) had a higher reproductive investment (increased egg number), and shorter life span than did bluegill from the ambient environment (Par Pond). The differences observed in Pond C bluegill might be a response to the unpredictable food resources and the relatively high mortality rate from thermal death. Thus, bluegill from both the heated (Pond C) and normothermic (Par Pond) sites have altered their life histories either genetically or phenotypically in response to site specific environmental factors.