“Population density, not host competence, drives patterns of disease in an invaded community”

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Catherine L. Searle, Michael H. Cortez, Katherine K. Hunsberger, Dylan C. Grippi, Isabella A. Oleksy, Clara L. Shaw, Solanus B. de la Serna, Chloe L. Lash, Kailash L. Dhir, and Meghan A. Duffy

Information on host competence alone cannot accurately predict how an invasive species will influence disease

Can scientists predict the effects of invasive species on disease?

An adult female Daphnia lumholtzi (top left) and an adult female Daphnia dentifera (bottom right).
(Credit: Isabella A. Oleksy)

Humans are remarkably good at moving species around. What happens to native host-parasite interactions when a new species is introduced? Are there key characteristics that we can use to predict the effects of an invasive species on disease? To figure out if such predications are possible – and what information is needed to make them – a team of researchers carried out a study with an invasive water flea that has spread in freshwaters in the United States. Their study asked how this invasive species is affecting a dominant native water flea and its common fungal parasite.

Because the invasive species became infected very easily, the researchers predicted that it would cause an increase in disease because it would spread the fungus. To see if these predictions were correct, they used buckets to create miniature indoor lakes, where they varied whether or not the invasive species was present. They found that the invasive species actually decreased disease, the opposite of what was predicted. To understand why this occurred, the researchers created a mathematical model to mimic the conditions in the buckets. They found that the invasive species reduces disease because it is a strong competitor, reducing the number of individuals present in the buckets. When there are fewer individuals in a population, the fungus has a harder time finding new individuals to infect, reducing disease. This study shows that, in order to predict how an invasive species will affect disease, scientists will need information on many characteristics of the invasive species, including how it affects the number of organisms in a community.

This work was carried out by a team of researchers led by Catherine Searle (Purdue University). The team included an expert in mathematical biology, Michael Cortez (Utah State University), as well as various members of Meghan Duffy’s lab at the University of Michigan, including technicians Katherine Hunsberger and Isabella Oleksy, graduate students Dylan Grippi and Clara Shaw, and undergraduates Solanus de la Serna, Chloe Lash, and Kailash Dhir. Read the Article