Checkmating the "Red King Theory"
In Lewis Carroll's book "Through the Looking-Glass," the Red Queen tells Alice how a race is run in Wonderland, stating: "Here, you see, it takes all the running you can do, to keep in the same place." This statement holds true in nature. Competitive species are under constant pressure to evolve rapidly to outgun their competition — the Red Queen Theory.
The Red Queen Theory
The rabbit needs to outrun the fox to avoid
being eaten; whereas the fox needs to catch
the rabbit in order to avoid starvation.
Statistical modeling also suggests the inverse (since 2003) or the Red King Theory. If two species are mutualists — or, each benefits from the activity of the other — they should evolve at a slower rate, in order to avoid interrupting their partnership. Makes sense, right? Think again! In a new study published in Nature Communications, comparative genomic analysis shows that the complete opposite may actually be true.
"We originally set out to uncover the genetic basis of mutualistic behavior in ants. So, we sequenced the genomes of three mutualistic species of plant-ants and four of their closely-related, non-mutualistic relatives.
"We were surprised to learn that mutualists actually had a higher rate of evolution across their genomes than generalists."
Benjamin Rubin PhD, University of Chicago, The Field Museum, and Postdoctoral Fellow, Princeton University, Illinois, USA.
Specifically, genes that are under significant pressure are those attributed to neurogenesis and muscle activity — exactly what you might expect to see. Neurogenic genes are tied to behavior, while muscle activation genes likely help ants protect their host plants through increased activity and speed.
This study is in surprising contrast to the Red King Theory, which has been supported by the scientific community over the past decade.
However, since 2003, numerous advances have been made in the field of scientific technology. Whole-genome sequencing used to take teams of scientists years to perform. Now sequencing can be completed in a few, short days by just a couple of researchers. These advances have enabled scientists to re-examine theories like the Red King Theory and provide evidence that supports or contradicts their original conclusions.
So, why do mutualists have a higher rate of evolution than generalists? The question warrants more study, but Dr. Corrie Moreau, Field Museum Curator and Professor, has an explanation:
"Just like all organisms, mutualists need to constantly adapt to their environments to ensure survival. However, they also have the additional task of evolving in relation to one another.
"Many species flip between mutualism and parasitism over time.
"Even mutualism is a costly relationship that evolution will select against, if it is no longer advantageous.
"All of this likely factors into the accelerated rate of evolution among these species."
There are still many questions about the evolution of DNA and genomes: what are all the factors that contribute to an increased rate of evolution among mutualists; what does genetic adaptation look like in other symbiotic relationships? This study provides a new framework to begin a new line of questions. What is clear, though, is this research has moved its piece on the chessboard of science, stared down the Red King Theory, and confidently declared, "Checkmate."
Symbiosis—the close and often long-term interaction of species—is predicted to drive genome evolution in a variety of ways. For example, parasitic interactions have been shown to increase rates of molecular evolution, a trend generally attributed to the Red Queen Hypothesis. However, it is much less clear how mutualisms impact the genome, as both increased and reduced rates of change have been predicted. Here we sequence the genomes of seven species of ants, three that have convergently evolved obligate plant–ant mutualism and four closely related species of non-mutualists. Comparing these sequences, we investigate how genome evolution is shaped by mutualistic behaviour. We find that rates of molecular evolution are higher in the mutualists genome wide, a characteristic apparently not the result of demography. Our results suggest that the intimate relationships of obligate mutualists may lead to selective pressures similar to those seen in parasites, thereby increasing rates of evolution.
Citation to original article: Rubin, B. E. R. & Moreau, C. S. (2016). Comparative genomics reveals convergent rates of evolution in ant-plant mutualisms. Nature Communications.
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Sep 2, 2016 Fetal Timeline Maternal Timeline News News Archive
Mutualistic Pseudomyrmex plant-ants and acacia plants.
Image Credit:The Field Museum