Flies sympathize, show solidarity with their dead peers - study

It is well known that elephants mourn when a member of their family dies; they stay with the body for a day or two before moving on. But do flies sympathize when insects like themselves die?

Researchers led at the University of Michigan have found a link between death perception and aging in flies. Their new study, just published in the journal PLOS Biology under the title “Ring neurons in the Drosophila central complex act as a rheostat for sensory modulation of aging,” shows that a specific group of brain cells in the fly called R2 and R4 neurons are activated when flies encounter dead flies and that this increased activity leads to more rapid aging. Seeing the dead triggers R2/R4 neuronal activation, leading to reduced lifespans.

Aging is a complex process that can be affected both by environment and genetics. While we know that perceptual experiences can affect aging, how this happens is still mostly a mystery. One example is the effect of “death perception” in fruit flies. 

Previously, the group at the University of Michigan headed by molecular and integrative physiology Prof. Christi Gendron reported that when fruit flies see other dead fruit flies (Drosophila melanogaster), they experience advanced aging, and that this depends on a type of serotonin receptor. In their new follow-up study, the researchers report the details of how and why this occurs. 

The experiment conducted for the study

A series of experiments in fruit flies showed that a specific group of neurons is responsible. Fluorescent tagging showed that exposure to dead flies led to increased activity in a region of the fly brain called the ellipsoid body. Silencing different ring neurons in this region revealed that two types of ring neurons, R2 and R4, are necessary for the effect, and other tests showed that the key is the serotonin receptor 5-HT2A located in these neurons. 

Finally, the researchers showed that when these neurons were artificially activated, fruit fly lifespans decreased, even when flies did not actually experience any death perception. Understanding how neural circuits like this regulate aging could eventually lead to targeted drug therapies in humans that slow the aging process.