Population variation in physiological and behavioural responses to artificial light at night

Artificial light at night (ALAN) is a ubiquitous urban stressor that disrupts circadian and seasonal behaviour and is associated with a reduction in health and fitness in a range of species. However, little is known about population-level variation in such responses, which inhibits our understanding of the magnitude and scale of ALAN's phenotypic and evolutionary effects. We explored the life-history and behavioural responses of three populations (urban, semirural and rural) of Australian field crickets, Teleogryllus commodus, reared in common garden conditions but exposed to either chronic ALAN or dark-at-night conditions over their lifetime. We measured male and female developmental duration, body mass and condition and gonadic investment. To separate the impacts of developmental versus immediate ALAN exposure on adult behavioural responses, we tested female responses to male advertisement calls in the presence or absence of an artificial light source. ALAN negatively affected survival in both sexes and reduced body condition in males. Female mate-searching depended on the interaction of developmental ALAN exposure, immediate ALAN exposure and population origin, consistent with the context-specificity of female behavioural responses. There was considerable population variation in the majority of life-history and behavioural traits measured. These differences may be driven by variation in density, resource availability, predator-prey dynamics and, potentially, the level of historical exposure to ALAN at each site. Understanding the impact of ALAN, both within and across populations, is critical in informing conservation management strategies in response to an increasingly urbanized world.