Pumpkinseed sunfish (Lepomis gibbosus) from littoral and limnetic habitats differ in stress responsiveness independent of environmental complexity and presence of conspecifics

Abstract

In the face of a changing world, there has been increasing interest in the behavioural and physiological responses of wild animals to stressors. Many factors can influence stress responsiveness, but two that have not been extensively studied during the stress-induced phase are environmental complexity and the presence of conspecifics. Using wild pumpkinseed sunfish (Lepomis gibbosus (L., 1758)) collected from limnetic and littoral sites, we tested whether glucose and cortisol were affected by environmental complexity and the density of conspecifics during the period of maximum response following a standardized air stressor. Overall, environmental complexity and conspecific density did not have a significant effect on maximum stress. However, in the environmental complexity experiment, fish collected from the littoral site had significantly higher concentrations of maximum glucose and cortisol, and tended to have higher glucose and cortisol responsiveness, than limnetic fish. This indicates that although the collection site did not affect a fish’s baseline values, intraspecific variation in site use is associated with divergent sensitivity of the hypothalamic–pituitary–interrenal axis to stressors. The importance of capture location on maximal response from stressors represents a potential sampling bias and source of variation, and may be even more pronounced in species that are habitat specialists.