From a review to the field: Alternative coping styles under urbanisation

Jules Petit , Melanie Dammhahn, Sophia Kroker, Rupert Palme, Rebecca Rimbach

Under human-induced rapid environmental changes, behavioural and physiological responses of organisms are key to maintain homeostasis and minimise fitness loss. Both responses can be integrated, into among-individual correlations forming stress-coping styles or syndromes (SCS). Such SCS emerge from genetic correlations or adaptive trade-offs. In the context of environmental challenges, more proactive individuals are expected to show lower hypothalamic-pituitary-adrenal (HPA) axis (re)activity responses, whereas more reactive individuals show higher HPA axis responses. Urban environments are associated with new artificial stressors, which might alter or manifest trait integration into SCS. However, studies investigating urban-induced changes in SCS are scarce. Here, we aim to test the emergence of SCS in wood mice (Apodemus sylvaticus) under urbanisation. We tested for phenotypic variation in boldness (N = 140), spatial exploration (N = 137), defiantness (N = 131), and faecal corticosterone metabolite (FCM) levels (N = 93) along an urbanisation gradient in a middle-sized city (Münster) in Germany. Although all traits were repeatable over time, none changed along the imperviousness gradient (a proxy for urbanisation). We assessed behavioural and stress-coping syndromes between two non-urban and four urban sites. Analysing among-individual correlations in urban and non-urban sites separately, we found that bolder individuals were more defiant only in urban populations. However, against predictions of the SCS hypothesis bolder or more defiant individuals had higher FCM levels in urban populations. By performing a systematic review of the available literature on SCS under urbanisation, we found only two studies and those reported mixed SCS patterns. Our results highlight the complexity of organismal responses to human-induced environmental changes shaping new sets of correlated traits. Future research may focus on how differential individualised environmental feedback upon the phenotype might be key for new trait integration creating new fitness landscapes.