Abstracts (first author)
Do rising temperatures accelerate the evolutionary arms race of hosts and parasites?
Climate change is expected to impact host-parasite coevolution, but information on effects of climate variables on such systems is sparse. Here, three-spined sticklebacks (Gasterosteus aculeatus) infected with the tapeworm Schistocephalus solidus were experimentally exposed to different temperatures. Hosts and parasites were laboratory offspring of populations from Norway, Spain and Germany. Infections were done at 18°C and temperatures were changed to 13°, 24° or kept at 18°C. Whole transcriptome sequencing (RNAseq, Illumina) was performed with liver RNA from a subset (n=96) of control and infected sticklebacks maintained at 13° and 24°C. Temperature alone had significant effects on the gene expression. Exposure to the parasite boosted the temperature effects on genes expression. At 13°C S. solidus grew slower compared to 18° and 24°C, which might partially be explained by lower metabolic rates, but also by the higher activity of the stickleback’s immune system at 13° compared to 18°and 24°C. This was supported by the gene ontology (GO) analysis of the RNAseq data, which revealed that immune genes of infected sticklebacks were more strongly differentially expressed in infected sticklebacks at 13° compared to 24°C. Parasite growth rates did not simply increase with temperature and were lower at 24° compared to 18°C. This suggests that immune activity of sticklebacks is optimal and represses parasite growth around 13°C, while S. solidus grows best at 18°C. Similar observations were made with different origins of sticklebacks and S. solidus, but Norwegian parasites were more virulent and Norwegian sticklebacks were more resistant than the other origins. In ectothermic systems, at first parasites benefit from rising temperatures, but over-exploitation of hosts at very high temperatures might become maladaptive also for the parasites. The present data suggest that rising temperatures indeed have the potential to accelerate the arms race of hosts and parasites.