Associate professor Lien Luong in the Department of Biological Sciences is studying the impact of parasites in the environment on hosts. Photo credit: John Ulan
The mere presence of parasites can have a negative effect on hosts, according to new research by University of Alberta parasitologists.
The study, led by Lien Luong, associate professor in the Department of Biological Sciences, examined the effects on fruit flies of living amongst parasitic mites. The results indicate that flies who are exposed to, but not infected by, parasitic mites expend more energy, have a shorter lifespan, and produce fewer offspring than those who do not.
"For fruit flies and other organisms, there are costs associated with just living in an infectious world-even if you're not actually infected," said Luong. "And these indirect costs can have long-term consequences."
An infectious environment
The research illustrates a concept called the ecology of fear, and is one of the first studies to show this phenomenon at play in the relationship between parasites and host organisms. Ecology of fear illustrates the role that environmental indicators of predators or parasites, such as smells, sounds, or visuals, can have on prey or host animals. This can result in a number of consequences for prey or host animals, including changing foraging behaviour or habitat use-and in the case of fruit flies, behavioural and physiological changes.
"We found that flies that lived near mites had reduced longevity, or didn't live as long, and produced fewer offspring than those who did not live near mites," explained Luong. "We also saw an increased metabolic rate, which makes sense. Using energy in response to nearby parasites means having less energy for other important activities, such as foraging for food or reproducing."
The results demonstrate that we may have underestimated the impact of parasites on host populations, added Luong.
"When we think about infectious disease, we generally think about the effects in terms of host morbidity and mortality-the direct effects of becoming infected. This study shows that indirect effects have a fitness cost, which suggests that the negative impact of parasites is even greater than we have previously predicted."
The paper, "Ecology of fear: environment-dependent parasite avoidance among ovipositing Drosophila," was published in Parasitology (doi: 10.1017/S0031182019000854).
Fruit flies have more to fear than just infection by parasitic mites, like the one pictured here. Image courtesy of Lien Luong