Abstract

Temperature is the most important abiotic factor affecting physiology, ecology and evolution in ectotherms. Do organisms broadly distributed along a latitudinal gradient adapt to local differences in temperature? In ectotherms this question has played a central role in evolutionary physiology. By means of an extensive field study and laboratory experiments, we tested the existence of local adaptations in thermal traits along 10° of latitude in northern-central Chile. We studied behavioural and thermal traits that have been directly connected with the thermal physiology of ectotherms, along the latitudinal gradient. Using three populations of the common woodlouse (terrestrial isopod), Porcellio laevis, we examined changes in thermal physiology traits (i.e. thermal tolerance, thermal performance) and behavioural traits (i.e. thermoregulation in the field and the laboratory). Performance (i.e. righting response speed) reached a maximum value at intermediate temperatures, and was highest for the northern population. Chill-coma temperature showed an increase towards high latitude, while heat-coma temperature did not vary between populations. On the other hand, optimum temperature was negatively correlated with latitude. Thus, southern woodlice appear to have evolved towards becoming low-temperature specialists, whereas woodlice from warm regions demonstrate low cold tolerance as well as a higher optimum temperature. Our results demonstrate that P. laevis woodlice from different parts of the distribution range show patterns in thermal physiology that covary with the thermal environment (i.e. latitude); thus, P. laevis adapts to local environments to increase its performance.