Noise and light pollution elicit endocrine responses in urban but not forest frogs

Urban areas are characterised by the presence of sensory pollutants, such as anthropogenic noise and artificial light at night (ALAN). Animals can quickly adapt to novel environmental conditions by adjusting their behaviour, which is proximately regulated by endocrine systems. While endocrine responses to sensory pollution have been widely reported, this has not often been linked to changes in behaviour, hampering the understanding of adaptiveness of endocrine responses. Our aim was, therefore, to investigate the effects of urbanisation, specif-ically urban noise and light pollution, on hormone levels in male urban and forest tungara frogs (Engystomops pustulosus), a species with reported population divergence in behaviour in response to urbanisation. We quan-tified testosterone and corticosterone release rates in the field and in the lab before and after exposure to urban noise and/or light. We show that urban and forest frogs differ in their endocrine phenotypes under field as well as lab conditions. Moreover, in urban frogs exposure to urban noise and light led, respectively, to an increase in testosterone and decrease in corticosterone, whereas in forest frogs sensory pollutants did not elicit any endo-crine response. Our results show that urbanisation, specifically noise and light pollution, can modulate hormone levels in urban and forest populations differentially. The observed endocrine responses are consistent with the observed behavioural changes in urban frogs, providing a proximate explanation for the presumably adaptive behavioural changes in response to urbanisation.

Automated summary

This study investigates the effects of urbanization on hormone levels in tungara frogs and found that urban frogs and forest frogs have different endocrine phenotypes. Exposure to urban noise and light pollution led to an increase in testosterone and a decrease in corticosterone in urban frogs, while forest frogs showed no endocrine response to sensory pollutants. These results suggest that urbanization can modulate hormone levels and influence behavior in frogs.