Urban environments are on the rise, bringing with them pollutants from run-off which alters water temperature, chemistry, and hydrology, ultimately driving a decrease in biodiversity. These disturbances can affect the physiological stress response of fishes by increasing or dysregulating their primary stress hormone, cortisol, and potentially altering their reproductive allocation.
Arseniy Kolonin, a master’s student at Texas State University, investigated how populations of the western mosquitofish (Gambusia affinis) differ in cortisol release rates and reproductive allocation between urban and rural habitats. To do this, he collected mosquitofish from two rural streams and two urban streams and measured their cortisol release rate, embryo number, total dry brood mass, and individual embryo mass. He found that the urban populations had significantly elevated cortisol release rates compared to rural populations. Further, mosquitofish were able to mount a stress response across all population indicating that they were not chronically stressed. Additionally, there was a higher reproductive allocation in urban populations as well as a positive relationship between reproductive allotment and cortisol.
These results suggest that western mosquitofish are acting as opportunistic adapters to urban environments and are successfully able to modulate their reproductive output in streams of low quality.
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