Living a century in warm thermal conditions: introduced populations of Pumpkinseed (Lepomis gibbosus) inhabiting the Iberian Peninsula (Spain) show reduced adaptation to North American winter conditions

In this study, we demonstrate that non-native Pumpkinseed (Lepomis gibbosus) introduced into Spanish water-bodies almost 100 years ago have a reduced capacity to tolerate winter conditions typically experienced by northern native populations. Overwinter survival and changes in lean weight and lipid content of Pumpkinseed from artificial colonies established from two Canadian and two Iberian source populations were compared under winter conditions typically experienced in the northern native range. Adult survival in outdoor ponds was higher in Canadian populations (68 and 78 %) than Iberian populations (31 and 49 %). Under simulated winter conditions in the laboratory, juvenile Iberian Pumpkinseed experienced higher mortality earlier in the winter period than Canadian populations. Lipid content of Iberian juveniles decreased on average by 49 % during the first half of the winter, while that of Canadian populations decreased by only 12–20 %. These results indicate that Iberian Pumpkinseed have lower tolerance of winter conditions relative to native Canadian populations, and suggest that relatively short exposure to warm climates can result in adaptive change in the physiology and bioenergetics of wild fish populations.