Science & Environment

Cannibal fruit flies: Lab maggots hunt one another

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Media captionResearcher Roshan Vijendravarma explains how this video showing fruit fly larvae eating a larger one could reveal some of the biology of cannibalism

Researchers studying the innocuous-seeming fruit fly have found that the insects have cannibalistic tendencies.

In "crowded laboratory conditions", the larvae, or maggots, will often pursue, attack and eat one another, footage reveals.

Scientists investigating the effects of malnourishment on the flies found that they were able to rear keener, more capable cannibals.

The findings are reported in the journal Nature Communications.

The team, from the University of Lausanne, Switzerland, says that because the fruit fly Drosophila melanogaster is so well-studied, the observations pave the way to discovering the biological secrets of cannibalism.

This might sound like a macabre endeavour, but cannibalism is an important part of nature.

It can be a crucial source of nutrition - some crickets and locusts that migrate in vast swarms rely on eating each other to survive the journey.

And it occurs in many larger carnivores; many big cats for example will kill and eat the offspring of their rivals - eliminating the competition by eating it.

"For a long time, cannibalism has been known as a factor that contributes to evolutionary processes," says lead researcher Dr Roshan Vijendravarma.

"But it's risky: Pathogens [disease-causing organisms] are more likely to be transmitted from eating one of your own species or a closely related species."

What made this observation even more interesting for the scientists is that fruit flies are vegetarian.

"Presumably they're poorly equipped to hunt other animals, including their own species, so it's an evolutionary question as to why cannibalism still exists among non-carnivorous animals," he said.

Dr Vijendravarma's primary research was focused on the effects of malnourishment on the flies.

And although all fruit flies he studied would cannibalise one another to some degree, the flies he and his team reared - even generations after their relatives were food deprived - had a "greater propensity to cannibalise".

'Cow eating rabbit'

The gruesome larval attacks also appeared to be chemically co-ordinated; once a larva had injured its victim, others were attracted by the injury and joined the feeding frenzy.

The larvae used their mouth hooks - hooks with serrations, or teeth, on their surface.

"The cannibal uses the mouth hooks to rasp across the victims' flesh and then rips it open," explained Dr Vijendravarma.

And a diet of fellow fruit fly actually made the larvae develop more effective flesh-eating mouthparts; larvae raised on a cannibalistic diet developed more of these tiny teeth of their mouth hooks.

Prof Matthew Cobb, a biologist from the University of Manchester, also studies fruit flies.

He explained that the flies had been a valuable tool, used for over a century - first to understand the basic laws of genetics, and more recently to reveal how animals develop from a single cell into a complex, functioning organism.

Image caption The mouth hooks of larvae raised on a cannibalistic diet (r) developed more teeth

"They are simple vegetarian insects that eat yeast and can be reared on porridge," he said.

"This study shows that we still have to learn about them.

"Although the authors don't think this occurs very often in the wild, you only have to search on the internet for 'cow eating rabbit' to come up with a well-known image of a malnourished cow eating a dead rabbit in order to get vital nutrients.

"Even the hardiest of vegetarians may have to turn to meat-eating in harsh conditions, giving us an insight into how different feeding habits may have evolved in the past."

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