Coping With Urban Habitats Via Glucocorticoid Regulation: Physiology, Behavior, and Life History in Stream Fishes

Abstract

As environments become urbanized, tolerant species become more prevalent. The physiological, behavioral and life-history mechanisms associated with the success of such species in urbanized habitats are not well understood, especially in freshwater ecosystems. Here we examined the glucocorticoid (GC) profiles, life-history traits, and behavior of two species of fish across a gradient of urbanization to understand coping capacity and associated trade-offs. We studied the tolerant live-bearing Western Mosquitofish (Gambusia affinis) for two years and the slightly less tolerant, egg-laying, Blacktail Shiner (Cyprinella venusta) for one year. We used a water-borne hormone method to examine baseline, stress-induced, and recovery cortisol release rates across six streams with differing degrees of urbanization. We also measured life-history traits related to reproduction, and for G. affinis, we measured shoaling behavior and individual activity in a novel arena. Both species showed a trend for reduced stress responsiveness in more urbanized streams, accompanied by higher reproductive output. Although not all populations fit this trend, these results suggest that GC suppression may be adaptive for coping with urban habitats. In G. affinis, GC recovery increased with urbanization, and individuals with the lowest stress response and highest recovery had the greatest reproductive allotment, suggesting that rapid return to baseline GC levels is also an important coping mechanism. In G. affinis, urban populations showed altered life-history trade-offs whereas behavioral traits did not vary systematically with urbanization. Thus, these tolerant species of fish may cope with anthropogenically modified streams by altering their GC profiles and life-history trade-offs. These results contribute to understanding the mechanisms driving species-specific adaptations and thereby community structure in freshwater systems associated with land-use converted areas.

Gut Bacterial Communities Vary across Habitats and Their Diversity Increases with Increasing Glucocorticoids in Toad Tadpoles

“…Tadpoles from both urban and agricultural habitats had stronger stress response as well as more efficient negative feedback than those in natural habitats. These facets of glucocorticoid regulation are related to fitness in birds and fish [42,52,53], and so is the microbiome in some mammals [83,89]. Yet, here we found no correlation between the corticosterone stress response and negative feedback on the one hand, and bacterial diversity and F/B ratio on the other hand.…”

“…Similar results have been found for other species (red squirrel [32], fish [37]) whereas other studies have found no relationship in unmanipulated populations [38][39][40]. Anthropogenic environments can alter glucocorticoid physiology in wildlife including aquatic vertebrates [41,42], but little is known about the relationship between land use change, associated shifts in host and environmental microbial communities, and stress physiology in the host. Understanding these interactions would provide additional insight into the mechanism associated with tolerance to environmental change.…”

“…We also examined if there was a relationship between gut bacterial communities and major components of the host glucocorticoid profile, specifically the baseline levels of corticosterone (the main glucocorticoid hormone of amphibians), the stress-induced change in corticosterone, and the rate of post-stress recovery in corticosterone. These aspects of glucocorticoid regulation are related to fitness in vertebrates [42,52,53] and differ between natural and anthropogenic habitats in our study species, the common toad Bufo bufo [41]. This species is widespread in Europe, where it breeds in standing water bodies.…”

Using behavioural ecology to explore adaptive responses to anthropogenic change — introduction

“…It is also possible to link or explore both physiology and behaviour if organisms can be sampled non-invasively and repeatedly, so both can be measured from the same individual. Kolonin et al (2022) found that mosquitofish (Gambusia affinis) showed flexible glucocorticoid profiles that aid in coping with urban streams, but behavioural traits did not vary systematically with urbanisation. Indeed, Lapiedra (2018) indicated that by understanding the mechanistic basis of behavioural variation associated with urbanisation, we could gain a better understanding of how to manage population declines.…”

An integrated physiological perspective on anthropogenic stressors in the Gulf coast toad (Incilius nebulifer)

“…The corticosterone profile illustrates how corticosterone varies in response to stressors. Comprehensive studies of the complete corticosterone profile can aid in understanding how species cope with anthropogenic environmental change (Wingfield, 2013;Sinsch et al, 2020;Bókony et al, 2021;Kolonin et al, 2022).…”