Meeting Abstract
Human-induced habitat alteration from land use conversion is one of the main drivers of decreased biodiversity and health in freshwater ecosystems. Urbanized environments produce run-off that introduces pollutants and alters water temperature, chemistry, and hydrology which can affect the physiological stress response of resident fishes by elevating or dysregulating their primary stress hormone, cortisol. The stress response is an important and energetically costly hormone-mediated mechanism that allows organisms to adjust their behavioral, physiological, and life-history phenotypes in response to environmental disturbances. However, prolonged stress can become maladaptive and lead to long term suppression of growth, reproduction, and immune function, thereby directly influencing population declines. Some species of fish are able to persist despite environmental challenges and stressors while other are not. We explored the consequences of land use conversion on baseline cortisol release rates, stress response (to agitation), and life history plasticity of the common mosquitofish, Gambusia affinis, which persist in urbanized habitats while other fish perish. We sampled two urban and two rural streams (defined by % impervious cover) within geographical proximity. We found that G. affinis, in urban populations, has significantly elevated baseline and agitation cortisol levels compared to rural populations. Further, urban populations of G. affinis had higher reproductive allotment (RA: dry brood mass). There was also a significant positive relationship between RA and cortisol. Our findings suggest that G. affinis behave as opportunistic adaptors and are able to modulate their reproductive output in lower quality streams.
