It turns out that army ants may have the capacity to evolve to regain their sight. Scientists have found that a change to a more challenging environment could help re-ignite and grow parts of the brain that have gone inactive over time.
In this latest study, the researchers examined several groups of tropical army ants. About 80 million years ago, the ancestors of these ants shifted to an underground lifestyle. The army ants that continued to live underground actually lost most, if not all of their vision. However, one genus, called Eciton, gained back its site when it returned to the surface about 18 million years ago.
"Most of the known examples of changes in brain investment involve shifts to simpler or 'reduced' environments," said Sean O'Donnell, a Drexel biology professor involved in the study. "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."
Interestingly, the researchers found that some of the ants that the researchers looked at grew back parts of the brain that were used for seeing. This, in particular, is a rare example of a species' brain tissue increasing over time following a move to a complex environment.
"Our data on visual investment suggest there is at least some room to regain or increase lost sensory and cognitive function," said O'Donnell. "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?"
More specifically, the researchers found that Eciton have large optic lobes and the largest brain regions in comparison to the other ants when it came to small. It also had the largest brain size overall.
"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," said O'Donnell. "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 increased brain investment."
The findings, published in the journal The Science of Nature reveal a bit more about the process of evolution. Not only that, but it shows how animals can effectively "re-evolve" portions of their brain.
