Cold acclimation response of non-native Italian wall lizard (Podarcis siculus) populations from New York and California

Abstract

Understanding how organisms respond to climatic variability and novel conditions is becoming an increasingly important task for ecologists. For ectotherms in the northern hemisphere, the response to cold is of special interest, considering that poleward range expansion events and increasing variability of temperatures during winter are already being observed as consequences of a warming planet. Though direction of change in physiological variables in response to cold is well studied in ectotherms, the extent to which traits can change and the rate at which they can change is not. We compared the extent and rate of change in cold tolerance (CT min ) between two long-term captive populations of the Italian wall lizard ( Podarcis siculus ) during a lab cold-acclimation treatment. Heat tolerance (CT max ), thermal preference (T pref ), temperature dependent rates of oxygen consumption (SMR O2 ), and temperature dependent rates of water loss (EWL) were also compared between Italian wall lizards previously introduced to Long Island, NY and San Pedro, CA before and after the lab cold acclimation treatment. Because our study coincided with a cold snap during the spring 2018 season for the San Pedro, CA population, we also studied the effects of cold acclimatization on wild lizards from the CA population. After initial lab acclimation of the lizards to laboratory conditions, SMR O2 at 15°C and EWL at 10°C were higher in NY lizards compared to CA lizards. Lizards from the two populations did not differ in any other variables measured before the cold acclimation treatment. We found that lizards from the NY population experienced an 80% decrease in CT min following a switch from 20°C:18°C to 17.5°C:16°C (12h light:12h dark) acclimation treatment. Lizards from the CA population did not decrease CT min in response to the same cold acclimation treatment. Overall, NY lizards decreased CT min , CT max , and T pref following cold acclimation, whereas CA lizards decreased CT max only. Wild CA lizards decreased CT max following the cold spring 2018 season in a manner similar to that of lab acclimated NY and CA lizards, suggesting that these lizards do not maintain a high CT max when the environment is unlikely to expose them to high temperatures. Thermal sensitivity (Q 10 ) of SMR O2 and EWL was lower in NY lizards, suggesting physiological adaptation to fluctuation in diurnal temperatures. The ratio of CO 2 produced to O 2 consumed (respiratory exchange ratio, RER) measured at 15°C increased in NY lizards following cold acclimation suggesting an increased use of carbohydrates and/or an increased production of lipids in the colder conditions. These responses in combination with the higher observed plasticity in NY lizards are in accordance with the climatic variability hypothesis, which predicts that organisms from more variable climates will be…