Intraspecific variation in traits in relation to environment and sex in an insect

Individuals within species frequently show differences in traits. Yet, until relatively recently, researchers treated all conspecifics as ecologically equivalent. I investigated how environmental variation, temperature and sex may influence intraspecific variation in behavioural, morphological and physiological traits, and their covariance, in the ground beetle Carabus hortensis - a species that is currently undergoing range expansion. By examining intraspecific variation in morphological traits across the C. hortensis expansion front, I showed that male, but not female, body size increased with proximity to the range edge. This may suggest that males evolved larger bodies and longer legs to increase mate searching efficiency where female density is low. Secondly, I found intraspecific variation in C. hortensis thermal biology, with males being active over a wider range of temperatures than females, and large females being more thermally sensitive than smaller females. Additionally, I showed that male and female movement in the wild is differentially influenced by temperature, and that laboratory measures of animal personality differences can be predictive of intraspecific variation in movement patterns in the wild. I then tested the relationships between metabolic rate, exploratory behaviour and morphology, finding that the strength, direction, and temperature dependency of relationships differed between the sexes. Finally, I demonstrated that that relationships between metabolic rate and body mass are uninfluenced by temperature, and that individuals with high average metabolic rates and exploratory behaviour are more thermally sensitive. My findings provide new insights into the roles of sex and thermal sensitivity in shaping intraspecific variation in traits, and their implications for individual fitness and population dynamics under continued climate change. Overall, my results suggest that increasing temperatures may select for smaller individuals and those with lower average metabolic rates and exploratory behaviour.