One of the tenets of evolutionary theory that many students are aware of is the idea of a “race for survival”; in Lewis Carroll’s book Through the Looking Glass, the Red Queen explains how a race works to Alice: “Now, here, you see, it takes all the running you can do, to keep in the same place.” When considering this theory in relation to symbiotic relationships, the close and often long-term interaction of species, it is easy to understand it in light of parasitic relations; one species is constantly trying to ‘outpace’ the other.
However the so-called Red Queen Hypothesis did not seem to work when two species started working together as the one that evolved its ‘mutualist’ traits faster would end up providing more help than it received in return and getting a raw deal. But new research, published in the journal Nature Communications, appears to have turned this theory on its head after scientists discovered mutualists can actually evolve faster than those not tied to a partner.
The researchers had originally set out to uncover the genetic basis of mutualistic behaviour in ants, and in doing so decided to sequence the genomes of three mutualistic species of plant-ants (ants evolved to protect plants like the Acacia, which provide them with food and special chambers for nesting) and four of their closely related, non-mutualistic relatives. What they were surprised to find was that the mutualists actually had a higher rate of evolution across their genomes than the generalists.
They found that the mutualist ants were very aggressive, actively patrolling and attacking herbivores and invaders and when researchers then compared their speed of evolution with ordinary ants that lived in the same place in Costa Rica, they noted that these non-mutualist ants had starkly different behaviour, fleeing from aggressors even when their own nests are at risk.
While the reasons behind this more rapid rate of change are still unclear, the researchers speculated that larger populations and longer lifespans of the mutualistic ants could result in more genetic changes. Another driver could be that both the ants and plants might be trying to keep up with each other – as things can change in the future should the mutualistic relationship were to become more parasitic for one of the participating species.