The environment in which an animal lives can profoundly influence its biology, including physiological responses to external stressors. To examine the effects of environmental conditions on physiological stress reactions in colonial tuco-tucos (Ctenomys sociabilis), we measured glucocorticoid (GC) levels in captive and free-living members of this species of social, subterranean rodent. Analyses of plasma and fecal samples revealed immunoreactive corticosterone (metabolites) to be the most prevalent GC in this species. An adrenocorticotropic hormone challenge confirmed that fecal corticosterone metabolites are responsive to exogenous stressors and provided validation of the commercial enzyme immunoassay kit used to detect these metabolites. Comparisons of adult female C. sociabilis from natural and captive environments revealed significantly higher baseline concentrations of corticosterone metabolites and significantly greater individual variation in metabolite concentrations among free-living animals. These findings suggest that the natural environment in which these animals occur is more challenging and more variable than the captive housing conditions employed. In addition to providing the first evaluation of GC levels in captive and wild colonial tuco-tucos, our findings indicate that the influence of environmental conditions on stress physiology may have important implications for understanding the social behavior of this species in the laboratory and the field.
The salmon-eating Southern Resident killer whales (Orcinus orca) of the north-eastern Pacific Ocean are listed as endangered both in the United States and Canada. Their critical habitat has been defined as the region of the inland waters of Washington State and British Columbia known as the Salish Sea, where they have traditionally spent much of their time from spring through fall. Using reports from experienced observers to sightings networks, we tracked the daily presence of the Southern Residents in these waters from 1 April to 30 June from 1994 through 2016. We found that the escapement estimates of spring Chinook salmon (Oncorhynchus tshawytscha) on the Fraser River in British Columbia were a significant predictor of the cumulative presence/absence of the whales throughout the spring season. There was also a difference in both whale presence and salmon abundance before and after 2005, suggesting that the crash in Chinook salmon numbers has fallen below threshold where it is worthwhile for the whales to spend as much time in the Salish Sea. The use of the Salish Sea by the Southern Residents has declined in the spring months as they are either foraging for Chinook salmon elsewhere or are shifting to another prey species. In order to continue providing necessary protections to this endangered species, critical habitat designations must be re-evaluated as this population of killer whales shifts its range in response to prey availability.
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