Global change is real. And, as I’ve written earlier, it affects many organisms (including us human beings). Mostly in a negative way. The rapid and often severe changes in environment represent a potential extinction risk for a wide variety of life-forms on earth. But wait, maybe evolution can help here? Evolutionary rescue is the idea that populations can adapt to conditions that were lethal to their ancestors. Of course this depends on a wide array of factors, such as population size, genetic variation, the rate of the environmental change, and so on.
A new study investigates the effects of sex and genetic diversity on the possibility of being ‘rescued’ by evolution. The study organism was a single-celled green alga, aka Chlamydomonas reinhardtii. The researchers established lines of this alga that differed in sexuality and the amount of genetic variation. Then, these lines were exposed to a relatively serious environmental change, the salt concentration. Starting with freshwater conditions, a steady increase of salt was implemented to eventually end up with near-marine conditions.
The results supported the hypothesis that a combination of sexual reproduction and high genetic diversity made evolutionary rescue more likely, allowing the lines of little algae that showed this combination to survive in conditions that would have killed their ancestors. In the experiment, two periods of ‘mass-extinction’ were noticed, each of which, so the authors hypothesize, representing a ‘genetic hurdle’ requiring adaptation for survival.
The reason that the combination of sex and high genetic variation was the most effective lifesaver is that sexual reproduction comes with recombination (mixing things up genetically), and this obviously works best if there’s more variation to throw into the mix.
Overall, the authors conclude:
We found that the combination of high initial diversity and obligate sexuality increased the likelihood of evolutionary rescue in populations exposed to a deteriorating environment by increasing their ability to respond to selection.
And so, our hero Evolution, and his friends Sex and Variation, once again bundle their forces to try to resist the (misunderstood?) villain Extinction, who is spurred on by evil mastermind Global Change… To be continued…?
! However, and this is important, this is not a license to pollute and destroy! If the environmental change is too big and/or happens too fast:
“Abandon all hope, ye who live here…”
Lachapelle, J, & Bell, G. (2012). Evolutionary Rescue of Sexual and Asexual Populations in a Deteriorating Environment. Evolution DOI: 10.1111/j.1558-5646.2012.01697.x