A strange tiny species of crustacean has challenged the way we think about natural selection and evolution.
This microscopic animal, known as a water flea or Daphnia pulex, generates genetic variation in a bizarre way, according to a new paper in the journal Proceedings of the National Academy of Sciences.
Even in stable environments where there is no strong pressure from natural selection, researchers discovered that individual genes have varying degrees of natural selection acting upon them from year to year.
This may allow Daphnia pulex to more easily adapt to a change in their environment, as they have a greater degree of genetic variation
Natural selection is the process by which certain traits become more or less common in a population due to the differential survival and reproduction of individuals with those traits, driven by the pressures of the environment. This is a key mechanism of evolution that leads to the adaptation of populations to their environments, and requires genetic variation within a population.
In the paper, the researchers describe how they studied DNA from over 1,000 of these tiny crustaceans, and found that natural selection varies in strength on different individual genes from year to year. They discovered that in stable environments, there was a large degree of fluctuations in different forms of the same genes—known as alleles—despite there being a net zero selection across the entire genome.
These discoveries challenge the traditional thinking about natural selection, and imply that it can operate much more subtly than we first thought.
"This study has, for the first time, given us a glimpse into the kinds of temporal changes in gene frequencies that occur even in seemingly constant environments, a sort of ongoing churn of genetic variation distributed across the genome," Michael Lynch, a professor at the School of Life Sciences at Arizona State University, said in a statement.
Daphnia have an incredible ability to adapt to stresses in their environment, and this could be a way that they generate enough genetic variation to be able to roll with the punches.
The researchers also found that genes close to each other on chromosomes tended to evolve together, meaning that gene combinations that are beneficial can be inherited together. This could also help to speed up the process of adaptation, and may explain why species sometimes evolve faster than we expect.
These findings could therefore also help to predict how other species may adapt to changes in their environment with the encroaching effects of climate change.
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