LB 31-300 - Aiming high: The effect of elevation on host-parasite interactions

Background/Question/Methods:

Environmental factors can affect species interactions, including host-parasite relationships. Environmental conditions can differ across the geographic range of the hosts, and the location at which the hosts and parasites interact can alter parasite effects or host defense strategies. For example, higher elevations have lower temperatures and oxygen levels, and both factors have been shown to affect hosts and their parasites. However, most studies focus on a single population, which may not extrapolate across multiple populations.


The goal of our study was to determine the influence of elevation on host reproductive success and ectoparasite abundance across their geographic range. Specifically, we used citizen science-collected data from the Nest Parasite Community Science Project to monitor nestling survival of Eastern bluebirds (Sialia sialis) and abundance of parasitic nestflies (Protocalliphora sialia).

Results/Conclusions:

Blowflies were only found at higher latitudes (above 39 degrees) of the bluebird range. At higher latitudes, we found that elevation significantly affected nestling survival and blowfly abundance. Nestling survival was lower and parasite abundance at higher elevations compared with lower elevations. These results suggest that blowflies are only found above a latitude at which temperatures drop below freezing temperatures during the winter. Since blowflies are not interacting with their hosts during the winter, the flies must evolve strategies to survive the winter to the next bird breeding season. Flies might require a hibernation life stage to survive the non-breeding period. Furthermore, we found that nestling survival was lower at higher elevations where more flies were found. This may be due to blood loss from parasitism reducing the amount of hemoglobin in the blood, and further limiting the lower amount of oxygen available to the nestling at a higher elevation. Our results suggest that elevation can be a key predictor of parasite abundance and host health across the range in which they interact. Since climate change is affecting temperature along elevational gradients, our study suggests that host-parasite interactions could be affected.