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.
This study consisted of two experiments. The first was a environmental complexity experiment. Pumpkinseed were angled from the limnetic and littoral locations. Upon landing, the fish underwent a 3 minute standardized air stressor and a blodd sampe was taken. The fish were then introduced into one of four treatment tanks. Treatments varied in environmental complextiy (eg, bottom substrate, percent vegetative cover). fish remained in treatment containers for 42 minutes and then blood was sampled again. The two samples were used as baseline and maximum cortisol and glucose concentrations. In the second experiment fish were caught in the same manner as the first experiment. The four treatment tanks differed from the first experiment and exposed fish to different numbers of conspecifics. baseline and maximum blood cortisol and glucose samples were taken the same as in the fiorst experiment.