Behavioural, morphological and life-history adjustments in the early steps of colonising restricted semi-natural environments in wild house mice

Abstract Background Invasive species often exhibit rapid adjustment and establishment in novel environments. However, the mechanisms underlying this process remain poorly understood, particularly during the early stages of invasion. Understanding how behavioural, morphological, and life-history traits vary across generations under different environmental conditions is important for identifying the factors that contribute to invasion success. We investigated how different diet compositions influence these traits across multiple generations (F0-F3) of wild house mice in semi-natural enclosures, with one enclosure assigned to each dietary regime. By experimentally altering the composition of the diet, we aimed to determine the role of diet as one of the specific components of the Island syndrome, which is associated with rapid adjustment to a novel habitat. Results Our results showed that stress-coping behaviour did not differ significantly across diets or generations. However, the F0 generation exhibited lower body weight than subsequent generations, sperm count was higher in this generation as well, suggesting an immediate physiological response to altered dietary conditions to help with population establishment. Survival rates remained stable across generations for mice on Hard and Soft but decreased for animals on Veggie diet. Conclusions Overall, the findings suggest that early responses to invasion are driven more by phenotypic plasticity and life-history shifts, albeit not necessarily in an adaptive way.