Does the parasitic load affect cortisol responses in the context of acute stress in the pumpkinseed sunfish Lepomis gibbosus ?

Background/Question/Methods

Cortisol is an endocrine hormone that acts as an initiator of several physiological responses associated with stress and leads to changes in the behaviour and performance of individuals in the short and long term. A meta-analysis has shown that parasites may be considered a source of stress in their vertebrate hosts but due to a considerable shortcoming in scientific papers regarding the effects and roles of parasites on their hosts, the relationships between cortisol responses and parasite load are still to be explored. By focusing on the black-spot disease-infected pumpkinseed sunfish (Lepomis gibbosus) model in a freshwater lake, about 100 fish with an observable gradient of parasitic intensity were captured during summer 2021. These were divided into different study groups that received, or did not receive, single or repeated acute stress, and plasma samples were collected and analyzed using radioimmunoasssays (RIA).

Results/Conclusions

Preliminary results show that, when we performed a single acute stress stimulus, cortisol levels in heavily parasitized L.gibbosus tend to decrease towards the baseline levels seen in parasitized control fish. Such results could indicate a potential parasite manipulation favoring a diminished avoidance to predators, which in this case would mean the final host in the parasite life cycle. This study will allow a better understanding of parasite-host relationships in a context where the prevalence of certain parasites increases with climate change.