Effects of predator exposure on baseline and stress‐induced glucocorticoid hormone concentrations in pumpkinseedLepomis gibbosus

Abstract

We compared baseline and maximal cortisol concentrations between predator exposure and prey blood samples in pumpkinseed Lepomis gibbosus, captured using a standardised fishing event underneath osprey Pandion haliaetus nests and away from osprey nests. We did not detect differences in cortisol or glucose between sites.These findings suggest that predictable sources of predation risk may not confer stress-related costs in teleosts. FISHdirectly overhead, etc.), may signal fish to mount an anti-predator behavioural (Gallagher et al., 2016) and physiological responses (Cooke et al., 2003;Sunardi et al., 2007;Sundström et al., 2005). Thus, if the osprey is simply nest-tending while in the vicinity, then antipredator activities by L. gibbosus may not necessarily manifest with the osprey not serving as a chronic stressor in this particular context.Contextual effects such as sex and or season are also factors to consider in interpreting L. gibbosus responsiveness. Our fish were collected just prior to their spawning period, which could conceivably affect the operation of the HPI axis (Carruth et al., 2000;Leatherland et al., 2010) and affect our results in a way outside of our control (e.g., higher baseline cortisol titres in pre-spawning fish). As well, other factors such as sex (Cook et al., 2012), inherent individual-level variation in HPI-axis responsiveness (i.e., high v. low responders; verli et al., 2002) and other physiological traits (e.g., body condition, parasite burden, feeding status, etc.) may have influenced the baseline glucose and cortisol levels observed in this study. As this study did not take lethal samples, the sex of individual fish could not be determined and we recognise this as a shortcoming. We did, however, detect a subtle difference in baseline glucose levels across sampling sites, independent of treatment type and size effects on maximal plasma cortisol concentrations and the cortisol responsiveness, suggesting that there may be some level of intraspecific variation here.Physiological stress is viewed as a fundamental link between predation and the function of entire ecosystems (Hawlena & Schmitz, 2010). Our preliminary work suggests that, in the particular context, living close to predators may not actually confer physiological changes associated with perceived chronic stressors in L. gibbosus. However, given the lack of responsiveness, further work is needed to address the role of predators in constituting a chronic stressor in a wild setting, while accounting for how intraspecific variation in the population drives these effects. Presumably, these processes act on a continuum through which the strength of interaction may be a driving influence by which prey species respond to predation threats.

Effects of predation risk on egg steroid profiles across multiple populations of threespine stickleback

“…Acknowledging that many maternal steroids play a role in offspring development and can vary in a coordinated fashion within eggs, will help us move beyond the focus on maternally derived glucocorticoid steroids 2,38,77 . That we did not see a consistent pattern of predation regime on steroid profiles was unexpected (but see 78 ), particularly given the role of glucocorticoids in dealing with predator encounters 2,14,79 , as well as the findings that stress-induced cortisol levels can be sensitive to rearing conditions 80 , heritable 80,81 , and respond to selection 82 . Not only is there no obvious difference between lakes with and without predatory trout, but exposure to piscine predators for 25 or fewer generations (stocked lakes) and ~6,000 generations (native lakes) have similar consequences for the steroid profiles.…”

Early predation risk shapes adult learning and cognitive flexibility

“…Similarly, hormonal implants causing a long-term moderate elevation of corticosterone levels in mountain chickadees (Poecile gambeli) enhance food caching behaviour and spatial memory, important fitness traits for these birds as successful cache retrieval can be crucial for survival (Pravosudov 2003). Additionally, although predation risk is often associated with increased glucocorticoid levels in prey, some studies have also reported no association between predator regimes and cortisol levels (Gallagher, et al 2019, McGhee, et al 2020, highlighting the complexity of the link between predation risk, stress hormones, and cognitive performance. In our study, predation risk reduced performance in the simple associative learning task, which could be consistent with a "nonadaptive" scenario predicting detrimental effects of stress on cognition (Lupien, et al 2009, Piato, et al 2011, Sapolsky 2015.…”

Pinnipeds and salmon farming: Threats, conflicts and challenges to co‐existence after 50 years of industrial growth and expansion

“…The presence of predators stresses captive and wild fish [63][64][65] and may negatively affect immunocompetence, metabolism and growth in salmonids and other fish, 66,67 especially during critical life stages such as smoltification. 27 Because these potential effects are being likely, we found no quantitative evidence relating pinniped attacks or presence around salmon farms with increased fish susceptibility to diseases, reduced growth rates or any other related productive loss.…”