From Atwell JW, Cardoso GC, Whittaker DJ, Campbell-Nelson S, Robertson KW, Ketterson ED, 2012. Boldness behavior and stress physiology in a novel urban environment suggest rapid correlated evolutionary adaptation. Behav Ecol 19: 10.1093/beheco/ars059:
Successful adaptation to new environmental conditions often requires coordinated changes in multiple characteristics. Urban environments, for example, present animals with diverse stressors and varied resources that demand shifts in behavior and stress physiology. Such changes could be achieved via rapid evolution or developmental plasticity. In this study, we examined how behaviors associated with boldness, tameness, and exploration of novel situations have diverged following a songbird’s entry into an urban environment. We also examined levels of a ‘stress hormone,’ corticosterone (CORT), which is thought to mediate behavioral and physiological responses to stressful stimuli. In southern California, USA, dark-eyed juncos (Junco hyemalis) typically only breed in higher elevation mountain forests.  However, in the early 1980s, juncos colonized an urban and coastal habitat in the greater city of San Diego. We compared exploratory behavior, flight initiation distances, and CORT levels between the urban colonist juncos in San Diego with a nearby ancestral-range population in both field studies and a captive ‘common garden’ study. Our goal was to characterize how behavioral and hormonal traits have rapidly diverged (field studies), and test whether observed differences likely have a genetic versus developmentally plastic basis (common garden studies). In both the field and the common garden, we found reduced CORT responses and bolder exploratory and tameness behavior in the urban juncos. Further, bolder exploratory behaviors were correlated with lower CORT levels. Together these results provide evidence indicating rapid adaptive evolution of correlated hormonal and behavioral traits following colonization of an urban habitat.