Blow flies may be the answer to monitoring environment in a non-invasive manner

INDIANAPOLIS -- They say you are what you eat; that’s the case for every living thing, whether it’s humans, animals, insects, or plants, thanks to stable isotopes found within.

Now a new study explores these stable isotopes in blow flies as a non-invasive way to monitor the environment through changes in animals in the ecosystem. The work by IUPUI researchers Christine Picard, William Gilhooly III, and Charity Owings, was published April 14 in PLOS ONE.

A postdoctoral researcher at the University of Tennessee-Knoxville, Owings was a Ph.D. student at IUPUI at the time of the study.

“Blow flies are found on all continents, with the exception of Antarctica. Therefore, blow flies are effectively sentinels of animal response to climate change in almost any location in the world,” said Gilhooly, who said the disruptions of climate change has increased the need to find new ways to monitor animals’ environments without disturbing them.

The multidisciplinary research between the biology and earth science departments began more than four years ago to answer a fundamental ecological question: “What are they (blow flies) eating in the wild,” Owings asked. “We know these types of flies feed on dead animals, but until now, we really had no way of actually determining the types of carcasses they were utilizing without actually finding the carcasses themselves.”

“Stable isotopes are literally the only way we could do that in a meaningful way,” Picard added.

Stable isotopes include carbon, nitrogen, hydrogen, oxygen, among others. Stable isotopes are found in the food we eat, and become a part of us.

“When we eat a hamburger, we are getting the carbon isotopes that came from the corn that the cow was fed. Flies do the exact same thing,” said Gilhooly.

Picard and Owings set out to collect blow flies in Indianapolis, Yellowstone National Park and the Great Smoky Mountains.

“Collecting flies is easy: have rotten meat, can travel,” said Picard. “That is it, we would go someplace, open up our container of rotten meat, and the flies cannot resist and come flying in. Collections never took longer than 30 minutes, and it was like we were never there.”

Once the flies were collected, they were placed in a high-temperature furnace to convert the nitrogen and carbon in the blow fly into nitrogen gas and carbon dioxide gas. Those gases were then analyzed in a stable isotope ratio mass spectrometer, which shows slight differences in mass to reveal the original isotope composition of the sample.

“Nitrogen and carbon isotopes hold valuable information about diet. Animals that eat meat have high nitrogen isotope values, whereas animals that eat mainly plants have low nitrogen isotope values,” said Gilhooly. “Carbon isotopes will tell us the main form of sugar that is in a diet. Food from an American diet has a distinct isotope signature because it has a lot of corn in it, either from the corn fed to domesticated animals or high fructose corn syrup used to make most processed foods and drinks. This signal is different from the carbon isotopes of trees and other plants. These isotope patterns are recorded in the fly as they randomly sample animals in the environment.”

Identifying the stable isotopes allowed the researchers to determine if the blow flies were feeding on carnivores or herbivores when they were larvae.

“With repeated sampling, one can keep an eye on animal health and wellness,” said Picard. “If the flies indicate a sudden, massive increase in dead herbivores --and knowing what we know right now that typically the herbivores are readily scavenged and not available for flies, that could tell us one of two things: herbivores are dying yet the scavengers don’t want anything to do with them as they may be diseased, or there are more herbivores than the carnivores/scavengers, and perhaps the populations of these animals has decreased.”

In Indianapolis, the majority of the blow fly larvae feed on carnivores. The researchers speculate this is because of the large number of animals being hit and killed by cars, making carcass scavenging less likely and more available to the blow flies to lay their eggs.

However, they were surprised by their findings in the national park sampling sites, where the larvae fed on carnivores instead of the herbivores, despite the herbivores' greater numbers. They speculate the competition is higher to scavenge for the larger herbivore carcasses and not readily accessible for the blow flies.

In addition, Picard, Gilhooly and Owings observed the impact of humans on animals. The carbon isotopes from the flies found the presence of corn-based foods in Indianapolis, which was expected, but also in the Great Smoky Mountains. With the Smokies being the most visited park in the country, opportunistic scavengers have greater access to human food.

This wealth of information provided by the blow flies will be fundamental to detecting changes within the ecosystem,” said Picard.

“This research has the potential to revolutionize the way biologists investigate important global issues, especially in the era of climate change,” said Owings. “Researchers will no longer be restricted to finding animals themselves, which is a daunting task; the flies can easily find the animals and then can be ‘called in’ by scientists.”

In addition to providing a real-time early warning system for tracking ecosystem change in response to climate change, the distribution of blow flies makes this approach useful in almost any location.

“Compared to other approaches, the relative ease of collecting the flies and measuring their isotopes means that ecosystem monitoring efforts can be rapidly deployed in any environmentally sensitive region,” said Gilhooly.

This multidisciplinary research, which is making a meaningful contribution to science, wouldn’t have happened without having the genuine interest to learn more about the other’s science.

“This work would never have happened without that ability to share passions, and learn from each other. I am very thankful for Bill’s expertise, and I have learned tons from him, but also, we have learned more about our fly, and now have the ability to take this knowledge and apply it to current, immediate problems,” said Picard.

Gilhooly is in agreement.

“We've got great teamwork that combines the different scientific skills needed for this study. The crazy thing about this work is that it's so interdisciplinary that it was difficult to convince others that the idea would work. I'm glad we stuck with it and were able to demonstrate the utility of this new method,” said Gilhooly.

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