Life history traits of pumpkinseed (Lepomis gibbosus) populations introduced into warm thermal environments

Life history theory predicts that ectotherms living in warm thermal environments should mature early because of fast juvenile growth, but it is unclear whether such early maturity will occur in the absence of conditions that promote fast juvenile growth. To assess this possibility and to determine the effect of warm thermal regimes on body size at maturity, we compared the growth and life history patterns of three populations of pumpkinseed (Lepomis gibbosus) introduced into warm, Mediterranean waterbodies in southern France with native populations living in cool thermal regimes in Ontario, Canada. Growth and life history traits of the French populations were determined from monthly samples collected from May to September. Mean age at maturity in the French populations ranged from 1.3-2.3 years, and was significantly earlier than that of populations inhabiting Ontario lakes. Length at age 2, an indicator of the juvenile growth rate, was not significantly different between the French and Ontario populations, and the French populations matured significantly earlier than Ontario lake populations even when juvenile growth was taken into account. Length at maturity in the French populations was also significantly smaller. and although there was no significant difference between the French and Ontario populations in mean GSI, the results of a previous reproductive allocation experiment suggest that French populations have a longer breeding season, and greater reproductive effort than Ontario pumpkinseeds. The earlier maturity of French pumpkinseeds could be a direct physiological effect of the warm thermal environment, but factors other than thermal regime may be contributing to the difference in life history traits between the French and Ontario populations.