ENZYMATIC THERMAL OPTIMUM OF MULTIPLE CRAYFISH SPECIES

Previous researchers have shown that extraregional invasive crayfish possess certain life-history and ecological traits that facilitate their ability to successfully invade large areas in distant regions, whereas extralimital invaders tend to remain localized and occupy smaller ranges.  Physiological traits may provide additional explanatory power for realized and potential range of crayfish species. In this study, we tested for thermal performance differences related to respiratory physiology among multiple crayfish species with narrow to broad native and invasive ranges. We hypothesized that species with broad ranges would be thermal generalists relative to species confined to limited ranges. To test this hypothesis, we generated thermal performance curves of respiratory enzymes in the electron transport system (ETS) for 12 individuals from each of five species. Optimal thermal range was defined as the temperature range within which ETS enzyme activity was within 10% of the maximum observed value.  Contrary to our original hypothesis, optimal thermal range of respiratory enzymes was not correlated with geographic range, but was lowest in the most widespread species (Procambarus clarkii) which was also the only species with a strong propensity to burrow.  We also found that the two extraregional invaders (Faxonius virilis and P. clarkii) had significantly lower enzymatic activity levels at optimal temperatures than did the extralimital invader (F. neglectus) or the two native species with restricted ranges (F. eupunctus and F. marchandi).  Results thus far suggest that enzymatic thermal breadth may be more closely tied to habitat plasticity whereas enzyme activity level may be a more useful predictor of geographic range. Additional species are currently being analyzed to better assess the robustness of these conclusions.