No strong associations between temperature and the host-parasite interaction in wild stickleback

Environmental parasitology: stressor effects on aquatic parasites

Anthropogenic stressors are causing fundamental changes in aquatic habitats and to the organisms inhabiting these ecosystems. Yet, we are still far from understanding the diverse responses of parasites and their hosts to these environmental stressors and predicting how these stressors will affect host-parasite communities. Here, we provide an overview of the impacts of major stressors affecting aquatic ecosystems in the Anthropocene (habitat alteration, global warming, and pollution) and highlight their consequences for aquatic parasites at multiple levels of organisation, from the individual to the community level. We provide directions and ideas for future research to better understand responses to stressors in aquatic host-parasite systems.

The importance of considering the duration of extreme temperatures when investigating responses to climate change

The frequency and duration of heatwaves are increasing because of human activities. To cope with the changes, species with longer generation times may have to rely on plastic responses. The probability that their responses are adaptive is higher if the species have experienced temperature fluctuations also in their evolutionary past. However, experimental studies investigating responses to heatwaves often use exposure times that are significantly shorter than recent heatwaves. We show that this can lead to faulty conclusions and that the duration of higher temperature has to be considered in experimental designs. We recorded the response of threespine stickleback to prolonged duration of higher temperature during the breeding season, using a population that has experienced large fluctuations in temperature in its past and, hence, is expected to endure temperature changes well. We found males to adaptively adjust their reproductive behaviours to short periods of higher temperature, but not to longer periods that extended across two breeding cycles. Males initially increased their reproductive activities-nest building, courtship and parental care-which ensured high reproductive success during the first breeding cycle, but decreased their reproductive activities during the second breeding cycle when exposed to sustained high temperature. This reduced their courtship success and resulted in fewer offspring. Thus, a species expected to cope well with higher temperature suffers fitness reductions when the duration of high temperature is prolonged. The results stress the importance of considering the duration of extreme environmental conditions when investigating the impact that human activities have on species. Responses to short-term exposures cannot be extrapolated to assess responses to longer periods of extreme conditions.