Meeting Abstract
Population range edges may result from trade-offs that limit adaptation to extreme environments. We assessed whether the northern boundary of the ant Aphaenogaster picea reflects a trade-off between intrinsic and plastic responses to low temperature. We measured occupancy with field surveys of A. picea across its northern range limit in Maine and used decision-tree models to predict occupancy from climatic variables. To evaluate cold tolerance, we lab-acclimated colonies and measured recovery time from cold shock with and without pre-exposure to a cold-hardening treatment, and estimated broad-sense genetic correlations between basal tolerance and hardening. High summer temperatures (Tmax > 24 °C) and low seasonality (SD < 101) predicted occupancy with 86% accuracy. The first eigenvector of the G-matrix revealed a trade-off between cold tolerance and hardening ability; colonies from cooler sites had higher basal tolerance but lower hardening ability than colonies from warmer sites. This suggests that populations adapt to colder temperatures by shifting from plastic to constitutive mechanisms, at the expense of coping with extreme events. Constraints imposed by physiological trade-offs may be an important determinant of poleward range limits in A. picea.
