Seeing the light: Army ants evolve to regain sight and more in return to surface

March 9, 2016 by Frank Otto, Drexel University
Eciton burchellii ants, among the above-ground species that appeared to regrow the parts of the brain used for sight. Credit: Photo by Sean O'Donnell/Drexel University.

A change to a more challenging environment could, over time, re-ignite and grow old parts of the brain that have gone inactive, according to a study of army ants led by a Drexel biology professor.

Sean O'Donnell, PhD, professor in the College of Arts and Sciences, studied several genera (groups of related species) of tropical whose ancestors moved to living mostly underground almost 80 million years ago. The army ant species that continued to live underground appeared to have lost most, if not all, of their vision, but the genus Eciton appeared to gain back sight after returning to live on the surface about 18 million years ago.

"Most of the known examples of changes in investment involve shifts to simpler or 'reduced' environments," O'Donnell said. "Classic examples are cases of light-living surface species giving rise to dark-living cave-dwellers. These are frequently—almost always—associated with reduced vision-processing brain regions."

But some of the ants that O'Donnell and his research partners studied appeared to grow back parts of the brain used in seeing. It appeared to be a rare example of a species' increasing over time following a move to a more complex environment.

A diagram depicting the different sections of an ant's brain. Credit: Photo courtesy of Sean O'Donnell/Drexel University.

"Our data on visual investment suggest there is at least some room to regain or increase lost sensory and cognitive function," O'Donnell said. "We don't yet know how well Eciton can see and how their eyes work. We found anatomical suggestions that their eye structure is distinct from most other above-ground insects. Have Eciton reinvented the eye to some extent?"

O'Donnell, along with four co-authors, recently published their findings in "Into the black, and back: The ecology of brain investment in Neotropical army ants" in The Science of Nature.

In their study, the Drexel researchers found that the ants that lived mostly on the surface—Eciton hamatum, Eciton mexicanum and Eciton burchellii parvispinum—had significantly larger optical lobes, which are parts of the brain used in sight. Species in other genera that live mainly underground, like Nomamyrmex and Cheliomyrmex, had much smaller optical lobes.

But other brain regions suggested that evolution of vision does not tell the whole story.

A diagram comparing the optical lobes in the brains of above and below-ground genera of army ants. Credit: Sean O'Donnell/Drexel University.

In addition to larger optic lobes, Eciton had the largest used in smell, and the largest brain size overall. In contrast, the mushroom body calyces—parts of the brain that are involved in memory and sensory integration—were found to be the smallest in Nomamyrmex and Cheliomyrmex, the most subterranean of the species the researchers studied.

Together these patterns pointed to light not being the only factor dictating larger brains in surface-dwellers.

"For me, the most exciting and novel patterns are those suggesting the below-ground world is not just different, such as emphasizing olfaction over vision," O'Donnell said. "The data suggest the underground is a simpler world, one that is less cognitively challenging, overall, than the above-ground world. The challenge now is to figure out what about the above-ground environment selects for increased brain investment."

In their paper, O'Donnell and the co-authors suggested a few aspects of the above-ground world that are more complex and require the evolution extra brain space: a diversity in prey, the presence of predators and the variation between day and night-time activities.

"In the case of army ants, we know almost nothing about what behavioral and cognitive abilities are affected by increased brain region size, but our data suggest the army ants are an interesting group to explore these questions," O'Donnell said.

Having more brain tissue (also described as brain investment) is—genetically speaking —an "expensive" evolutionary trait. Brain tissue requires a lot of energy to build and maintain through the consumption of food. So a species won't last long unless there is a good reason to carry that extra brain capacity.

"This study shows that brains closely track animal ' ecology, and that brain evolution can respond to new ecological challenges even after tens of millions of years," O'Donnell said.

Explore further: Underground ants can't take the heat: Climage change models may not look closely enough at microhabitats

More information: S. Bulova et al. Into the black and back: the ecology of brain investment in Neotropical army ants (Formicidae: Dorylinae), The Science of Nature (2016). DOI: 10.1007/s00114-016-1353-4

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betterexists
1 / 5 (2) Mar 09, 2016
Just Use CRISPR.
BartV
1 / 5 (6) Mar 09, 2016
Find a useful trait in an organism is completely unrelated to the fantasy world of evolution. We are made in such a wonderful way that an honest person cannot possibly think that we "evolved" by chance. Each function/part that we have is so dependent on other parts so that it could not have evolved separately. For example (very simply), a mouth that eats needs a tube, which needs a stomach that has the ability to use the food, and which would require a tube to dispense the remains. If you don't have all of these together, each part is useless and would never benefit an organism.

And yet there are still deluded scientists that claim evolution is science. Pity them!

kochevnik
4.6 / 5 (9) Mar 10, 2016
Cells specialize. Why didn't you ever specialize and learn anything more than fairy tales, BartV? Only a gawd can make you learn something?
Tektrix
5 / 5 (6) Mar 10, 2016
We are made in such a wonderful way that an honest person cannot possibly think that we "evolved" by chance.


Those who substitute gods for comprehension are bound to ignorance.
TehDog
5 / 5 (4) Mar 10, 2016
"The data suggest the underground is a simpler world, one that is less cognitively challenging, overall, than the above-ground world."
What a surprise /s

"The challenge now is to figure out what about the above-ground environment selects for increased brain investment."

Quite possibly due to the increased situational awareness needed. In a tunnel attention is primarily focused forward. In an open environment "Look up, look down, look all around" is a good survival strategy.

"In addition to larger optic lobes, Eciton had the largest brain regions used in smell,"

Ants have olfactory receptors in their antenna (I think, I'm posting without checking :)
Stereo processing? Even detecting changes via difference from the tip to the root?
Damn, fascinating little buggers they are, annoying as they can be :)
Whydening Gyre
5 / 5 (5) Mar 10, 2016
"The challenge now is to figure out what about the above-ground environment selects for increased brain investment."

Quite possibly due to the increased situational awareness needed. In a tunnel attention is primarily focused forward. In an open environment "Look up, look down, look all around" is a good survival strategy.


Not to make it sound like it was easy, but;
As environment gains complexity, so does the response. Equal and opposite reaction, remember?
Life at the cellular level, way back when, was pretty much was just a stomach, anyway, right?
Everything else was a response to environmental changes...
TehDog
5 / 5 (4) Mar 11, 2016
"As environment gains complexity, so does the response."
Yeah, That was pretty much my point, though not so much "Equal and opposite reaction" as "Needs must" . More inputs means more processing if you're to retain the same granularity of analysis. Hmm, there's probably a better way to express that, but it's late so I'll sleep on it :)
Whydening Gyre
5 / 5 (2) Mar 11, 2016
"As environment gains complexity, so does the response."
Yeah, That was pretty much my point,

Was just lettin ya know I got it...;-)
though not so much "Equal and opposite reaction" as "Needs must" .

Was a generalization from an artist POV.
More inputs means more processing if you're to retain the same granularity of analysis.

Yep.
Hmm, there's probably a better way to express that, but it's late so I'll sleep on it :)

Will look forward to it...;-)
TehDog
5 / 5 (3) Mar 11, 2016
@WG
"More inputs means more processing if you're to retain the same granularity of analysis"
Honestly, I can't think of a better way to put it, which is annoying, I can usually express myself better.
Basically you need a bigger brain to handle a bigger environment?
That works I think :)
The paper is paywalled at http://link.sprin...6-1353-4
also
http://www.livesc...rts.html

and thanks for spiraling me off into some interesting stuff :)
http://www.ncbi.n...4441025/
HocusLocus
1 / 5 (2) Mar 13, 2016
Press release missing painfully obvious climate change guilt tie-phrase. Please resubmit.
Whydening Gyre
5 / 5 (1) Mar 13, 2016
@WG
"More inputs means more processing if you're to retain the same granularity of analysis"

Honestly, I can't think of a better way to put it, which is annoying, I can usually express myself better.
Basically you need a bigger brain to handle a bigger environment?
That works I think :)

No worries, I get it...:-)
Now. Think about this - was the re-introduction of the sensors driven by increased neuronal evolution? Or was it already there?
TehDog
5 / 5 (3) Mar 13, 2016
Well, they moved underground, didn't evolve there, so presumably they had the dna available to restore their optic lobes.

Dammit, how the hell did I miss this on about 3 re-readings...

"We found anatomical suggestions that their eye structure is distinct from most other above-ground insects. Have Eciton reinvented the eye to some extent?"

Ok, so maybe the blueprint (dna) is not a template but a suggested framework...

Torbjorn_L, where are you? We need your expertise here :)
Whydening Gyre
5 / 5 (2) Mar 13, 2016
Well, they moved underground, didn't evolve there, so presumably they had the dna available to restore their optic lobes.

Ya, that's what I was thinkin'...
Dammit, how the hell did I miss this on about 3 re-readings...
"We found anatomical suggestions that their eye structure is distinct from most other above-ground insects. Have Eciton reinvented the eye to some extent?"
Ok, so maybe the blueprint (dna) is not a template but a suggested framework...

Originally, their eyes (and also noses), as well as the associated processing circuitry, evolved to compete in a different world, environmentally. So, it might be different template They then moved to a more closed environment (and then back out again). Little bastards should make up their minds...
Torbjorn_L, where are you? We need your expertise here :)

Here, here. TL's input would be helpful...:-)

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