Scharsack JP, Wieczorek B , Schmidt-Drewello AM, Büscher J , Franke F , Moore AD , Branca A , Witten A , Stoll M, Bornberg-Bauer E , Wicke S, Kurtz J
Temperature variation shifts immune and metabolic activity in three-spined sticklebacks (Gasterosteus aculeatus) infected with the cestode Schistocephalus solidus
Global Change Biology, 2020

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Temperature variation in natural habitats is currently altered by global climate change and temperature effects on organismic live are re-evaluated. An important question is how species by species, e.g., host-parasite, interactions are influenced by temperature change. It was predicted that parasites will become more frequent in global warming scenarios, thus accelerating the fitness costs to their hosts. With the present study, we tested experimentally how elevated temperature influences interactions of an aquatic ectothermic vertebrate host,
the three-spined stickleback, with the cestode S. solidus. We investigated temperature effects on immunity, body condition and liver transcriptomes of the host and fitness parameters of the parasite. Indeed, S. solidus grew faster and produced more viable offspring at elevated temperature, no matter if it originated from a German or a Spanish population. Interestingly, at the intermediate temperature tested (18°C), parasites grew more and produced more eggs compared to high temperature (24°C), whereas the slowest parasite development was
observed at a cooler experimental temperature (13°C). By contrast, the stickleback hosts grew faster and had higher activity of their immune system at the low experimental temperature. Sequencing of stickleback whole liver transcriptomes revealed that mainly metabolic processes were upregulated by temperature, this was most prominent in infected sticklebacks. Interestingly, sticklebacks that had defeated the parasite presumably weeks before the end of the experiment, showed elevated numbers of differentially regulated genes, in a similar
magnitude as infected sticklebacks. The present study clearly supports the prediction that elevated environmental temperatures speed up the development of parasites. However, temperatures exceeding the optimal range of the parasite ceased its development, which might be confounded by detrimental effects of high temperatures on the host (s fitness and immunity). Vice versa, low temperature was beneficial to the host (s fitness and immunity) which might have facilitated control of the parasite growth by the hosts’ immune system. We propose that both, host and parasites have specific temperature optima whereby that of the host lays well below that of the parasite, which would favor the parasites development in a global warming scenario.