A few centuries ago the German philosopher Ludwig Feuerbach said "we are what we eat". A brilliant intuition, which would make sense with time. He was right. A truth for every living being, whether humans, animals, insects or plants, thanks to the stable isotopes found within foods.
Now a new study explores these stable isotopes in flies as a non-invasive way to monitor the environment through changes in animals in the ecosystem. The work, led by IUPUI researchers Christine Picard, William Gilhooly e Charity Owings, was published yesterday on PLOS ONE.
Swarms of “sensors” everywhere in the world
“Flies are found on every continent except Antarctica,” Gilhooly says. True.
Put this together with the fact that disruptions to climate change have necessitated new ways to monitor animal habitats without disturbing them, and you will have the reasons for this study.
Flies are true sentinels of the response of animals to climate change in almost all places in the world.
William Gilhooly, author of the research
Research on flies
A path born more than four years ago to answer a fundamental ecological question: “What do flies eat (and therefore, to put it in Feuerbach's words, “what are they”)?”
We know that, in essence, these types of insects feed on dead animals, but until now we had no way of actually determining which ones.
“Stable isotopes are literally the only way we can do this in a meaningful way,” says Christine Picard.
Stable isotopes, which include carbon, nitrogen, hydrogen and oxygen, are found in the food we eat and literally become part of us.
When we eat a hamburger, we absorb the carbon isotopes that come from the corn the cow ate. The same goes for flies.
Fly collectors
“Collecting flies is easy: all you need is some rotten flesh,” Picard says. “That's all: we would go somewhere, open our container of rotten meat, and the flies would come.”
Once collected, the flies were placed in a high-temperature furnace to convert the nitrogen and carbon within them into nitrogen and carbon dioxide. These gases were then analyzed in a mass spectrometer to reveal the original isotopic composition of the sample.
“Nitrogen and carbon isotopes contain valuable information about diet,” says Gilhooly. “Animals that eat meat have high nitrogen isotope values, those that eat mainly plants have lower nitrogen isotope values.”
How can we monitor the ecosystem starting from the isotopes of flies?
Carbon isotopes tell us the main form of sugar found in a diet.
For example, food on an American diet has a distinct isotope signature because it contains a lot of corn. From that fed to pets, or from the high fructose corn syrup used to make most processed foods and beverages.
Identification of stable isotopes allows researchers to determine whether flies feed on carnivores or herbivores, starting as larvae.
“With repeated sampling, you can keep an eye on the health and well-being of the animals,” Picard says.
An example: if the isotopes of flies indicate a sudden, massive number of dead herbivores, this shows us two possibilities. Fine, herbivores are dying, and scavengers want nothing to do with them because they may be sick. Second, there are more herbivores than carnivores / scavengers, and perhaps the populations of these animals have decreased.
This wealth of information provided by flies will be critical for detecting changes within the ecosystem
Christine Picard
A revolutionary potential
This research has the potential to disrupt the way biologists investigate important global issues, especially in times of climate change.
Researchers will no longer be limited to finding animals on their own to analyze them. The flies, which are easier to catch, will do all the data-gathering work.
The distribution of these insects will provide a real-time early warning system to monitor ecosystem changes in response to climate change.
