Hormonal adjustments to urban conditions: stress hormone levels in urban and rural populations of Apodemus agrarius

Abstract

Animals' adaptation to life in cities is a widely studied issue in ecology. One such adaptation is the adjustment of stress response to new conditions and anthropogenic disturbances. There are various examples of such adjustments in urban birds, but the stress response of non-avian species has rarely been investigated. We studied an urban and a rural population of a small mammal, the striped field mouse Apodemus agrarius. We compared baseline corticosterone (CORT) concentration in faecal samples from mice, using ELISA tests with antibodies for this hormone. We found that although urban specimens have more anthropogenic stressors than their rural equivalents, they do not have an elevated level of CORT. This confirms the hypothesis that urban animals undergo hormonal adjustment to urban conditions. Moreover, the CORT concentrations of urban mice were lower compared to their rural conspecifics, while for body weight we observed an inverse relationship. A CORT level allows urban mammals to redirect more energy to weight gain (body fat); this is probably an effect of the lower pressure of competitors in urban areas, as well as better food availability (access to anthropogenic food). The results of this work show that species that have managed to overcome fear of humans and adapt to anthropogenic stressors can therefore achieve measurable ecological benefits.

Changes in the social behavior of urban animals: more aggression or tolerance?

“…Such a compromise is easier to accept for urban animals, because anthropogenic food, which is an important part of their diet, is often available ad libitum (Babińska-Werka 1981;Chavez-Zichinelli et al 2013). Higher body weight in urban animals (Andrzejewski et al 1978;Łopucki et al 2013) or lower stress levels (French et al 2008;Lodjak and Maegi 2014;Łopucki et al 2019) may, therefore, also be a result of more tolerant social behavior.…”

“…For urban birds, the impact of light and noise pollution on the behavior has also been shown (Moiron et al 2015;Swaddle et al 2015;Weaver et al 2019). Various indicators were used to study these phenomena: from measurements of home ranges, risk-taking behavior, success in solving problems, escape response, diurnal activity, or aggression levels to more sophisticated indicators such as noise-dependent changes in vocalization, stress hormone levels, or genetic markers (e.g., Bonier 2012;Francis et al 2015;Meillere et al 2015;Moiron et al 2015;Vincze et al 2016;Santangelo et al 2018;Schell et al 2018;Łopucki et al 2019;Solaro and Sarasola 2019).…”

Non-invasive monitoring of adrenocortical activity in free-ranging Namaqua rock mice Micaelamys namaquensis from South Africa in response to anthropogenic land use and season

“…This finding also underlines the impact of presumed small‐scale human‐mediated disturbances such as animal handling on small mammals, as is also the case with the African lesser bush baby Galago moholi (Scheun et al 2015). Łopucki et al (2019) also found that small mammals such as the striped field mouse Apodemus agrarius often experience elevated hormone concentrations in response to human‐mediated disturbances, followed by hormonal adjustments and a loss of the initial fear of humans. Although the chosen EIA determined changes in fGCM concentrations following a stressful event, further validation in the form of an ACTH challenge could underline the suitability of the EIA to monitor adrenocortical activity in M. namaquensis (Laver et al 2012).…”

Cross-Context Responses to Novelty in Rural and Urban Small Mammals

“…As study species, we selected common voles (Microtus arvalis, Arvicolidae) and striped field mice (Apodemus agrarius, Muridae). These are non-commensal rodents commonly found both in rural and urban areas of northern and central Europe (e.g., Riegert et al, 2009;Łopucki et al, 2019). Common voles are fossorial, mostly herbivorous, and inhabit open grasslands (e.g., Jacob et al, 2014).…”