Experimental climate warming affects the emergence of free-living stages in wildlife parasites

Background/Question/Methods

Seasonal and inter-annual variations in climate are important in life history strategies of plants and animals, and environmental changes can be a major influence on population dynamics, community structure and species interactions.  Our previous work on the long-term dynamics of parasites in free-living populations of rabbits in Scotland has measured differences in the intensity of infection for two common gastrointestinal helminths (Trichostrongylus retortaeformis and Graphidium strigosum) in relation to climate variations that have been recorded in recent years.  Here, we used a laboratory and field approach to test the prediction that variations in temperature affect the free-living stages of these parasites, and that this could help explain changes in long-term patterns of infection.  In the laboratory we studied the timing and hatching success of T. retortaeformis and G. strigosum eggs placed under constant, cyclic or stochastic temperature regimes that mimic changes in temperature observed from our long-term climate data.  

Results/Conclusions

In both species, results of the constant temperature regimes showed a logistic pattern in the percentage of eggs that hatched as temperature increased, as well as a shorter hatching time, but warmer temperatures affected G. strigosum more than T. retortaeformis.  Similar differences in response between the two species were measured in cyclic and stochastic temperatures, but on average, warmer temperature regimes shortened the timing of hatching and increased hatching success.  Field experiments that manipulated temperature generally corroborated the patterns from the lab studies; specifically, infective larvae were recovered earlier and in larger quantities from elevated temperature treatments relative to ambient temperature controls during certain months of the year.  These data are discussed in relation to the long-term dynamics of infection for these parasites in wild rabbit populations.  Thus far, our findings support the idea that climate changes can alter the dynamics of parasitic infections, but differences in parasite life history strategies and the mechanisms through which parasites and hosts interact directly might help modulate the effect of projected long-term changes in the environment.