U. researchers publish model that predicts parasite survival

A new study published in Ecology Letters by postdoctoral researcher Peter Molnar and ecology and evolutionary biology professor Andrew Dobson outlines a model predicting the survival of parasites in certain regions of the globe as climate change progresses.

While scientists 20 years ago predicted climate change would cause parasitic disease to increase overall, Molnar said his model quantifies the idea that this picture is too simplistic.

“To sum these complications up, it basically depends on what parasite you’re looking at, its life history parameters and where in the world you’re looking,” Molnar explained.

Instead of a universal expansion of parasite populations, Molnar’s model predicts that under the influence of climate change, the future survival of parasites will depend on their thermal niche, or the range of temperatures in which a parasite can survive. Parasites at the low end of their temperature niche will be able to establish novel populations, while mortality will increase in parasites that are living at the high end of their possible temperature range.

Unlike previous models that were limited to analyzing data for a single parasite species, this theory can be applied to any species, Molnar explained.

“If you basically consider that there are 300,000 or more parasites of vertebrates, it will basically be impossible to ever gather enough data to understand climate change in each taxa separately,” Molnar said, referring to the data-gathering limitations on previous models.

Molnar’s theory generalizes parameters for the life cycle of any parasite species based on the metabolic theory of ecology, which establishes the relationship between an organism’s body mass, temperature and metabolic rate. This can be used to determine how the life cycle of a parasite changes with temperature. Scientists can then calculate parasite fitness and determine where species will live as the climate changes.

The team’s model has potential implications for health policy because it can be used to study host-parasite interactions, including parasites with human hosts, associate professor of veterinary medicine Susan Kutz explained.

“It allows us to step back, take a broader prospective and make some broader predictions where health policy can then target their research and mitigation measures,” she said.

The research was conducted in collaboration with Kutz and Ph.D. candidate Bryanne Hoar of the University of Calgary. Kutz and Molnar focused their fieldwork on Arctic nematodes with warm-blooded hosts, such as musk oxen. They also analyzed data from 13 other species to show that the postulated activation energy from their model matches the relationship between mortality and development patterns in these species.

The Arctic is a relatively simple system to which the theory can be applied because of the limited biodiversity of the region, Molnar said. Additionally, Kutz explained that this ecosystem will be markedly disrupted by climate change because it is warming faster than any other region, and Arctic hosts have historically had limited exposure to parasites.

Dobson was traveling and unavailable for comment.