Urbanization affects the physiology, behavior, and life-history traits of a tolerant stream fish




Kolonin, Arseniy

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Anthropogenic land-use conversion is one of the main drivers of wildlife population extinctions and biodiversity loss. Freshwater fishes are among the taxa most affected by land-use conversion, with an estimated 25% of species at risk of extinction. Urbanization is a rapidly growing form of land-use conversion that has been negatively impacting stream ecosystems. The change in stream quality associated with urbanization often pushes native and intolerant fish species past their physiological limits. As a result, urbanization alters fish distributions and assemblages by reducing the amount and diversity of intolerant species, and increasing the abundance and dominance of tolerant species. I explored the effects of urbanization on the physiology, life-history, and behavior of Gambusia affinis, a species of live-bearing fish that frequently inhabits urban streams. I also examined how context-specific variation in glucocorticoid physiology affected their reproductive allotment across urban environments. I collected G. affinis from four streams in 2018 and four streams in 2019, which differed in their degree of urbanization. There was twice as much rainfall in 2019 than 2018, which is known to exacerbate the effects of urbanization. I found that urban populations of G. affinis had more offspring and heavier broods than rural populations. Additionally, urban populations had higher baseline cortisol release rates, which explained differences in reproductive allotment in 2018 but not 2019. However, the interaction between physiological responsiveness and recovery explained differences in reproductive allotment in 2019. There were behavioral differences across populations and years. Fish from the most urban site in 2018 spent less time moving compared to the three less urban populations and fish in 2019 differed in their shoaling behavior. My results suggest that baseline and stress-induced cortisol release rates play different roles in coping with environmental perturbations, depending on the severity and stochasticity associated with the environment. Lastly, I suggest that various components of glucocorticoid regulation help increase fitness across environments, thereby helping G. affinis to adapt and persist in urban streams.



Urbanization, Stress, Reproduction, Physiology, Fish


Kolonin, A. (2020). <i>Urbanization affects the physiology, behavior, and life-history traits of a tolerant stream fish</i> (Unpublished thesis). Texas State University, San Marcos, Texas.


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