"This research shows that global warming could shift the balance between parasites and their hosts with potentially serious implications for fish populations."
The scientists found that parasitic worms infecting stickleback fish grew four times faster in experimentally infected sticklebacks raised at 20C than when raised at 15C.
In contrast, the fish grew more slowly at the higher temperature, suggesting that fish parasites cope with higher temperatures much better than the fish they infect.
Dr Barber said: "The results are important because the size these parasites attain in their fish hosts also determines their infectivity to fish-eating birds like kingfishers and herons the next hosts in the parasite's life cycle and also the number of parasite eggs that they will go on to produce. Bigger larval parasites in the fish go on to become larger adult worms in birds, which produce more eggs.
"After the 8 weeks of the study, all of the worms infecting the fish held at 20C were ready to infect fish-eating birds, whereas none of those held at the lower temperature had reached a size at which they were ready to be transmitted."
In a follow up study, the authors also showed that fish infected with the largest worms showed a preference for warmer water, suggesting that these parasites also manipulate the behaviour of host fish in ways that benefit the parasites and maximize their growth rates.
The results provide some of the first evidence that increasing environmental temperatures can lead to a shift in the delicate balance that exists between co-evolved hosts and parasites, increasing the speed with which parasites complete their life cycles that could lead to an increase in the overall level of parasitism in natural animal populations.
|Contact: Dr. Iain Barber|
University of Leicester