Flirtatious yeast cells confirm theory of evolution
Posted by Science Oxford on October 13, 2009 | comments
Yet another study that claims to be able to show evoltion occuring in the lab.
The research conducted in London looks at yeast and found that favourable genes spread quickly through the population. This spread matched the predictions of sexual selection theory.
Read on to find out more:
Visit this page »Some flirtatious yeast cells have confirmed a part of Charles Darwin’s theory of evolution that was never tested as successfully as the rest of the theory, biologists say.
This somewhat special part of the theory is the concept of evolution through “sexual selection.”
In general, evolutionary theory holds that species gradually change because of certain mutations that spread through their populations. These mutations spread if, and only if, they’re beneficial—so that individuals possessing them survive longer, reproduce more or both. Thus the mutated trait appears increasingly often in succeeding generations.
Evolution has been observed in action numerous times, because in short-lived species, many forms of evolution occur fast enough for humans to watch the changes occur.
But one form of evolution has not been directly seen: evolution through sexual selection, notes a paper in the Oct. 7 online issue of the research journal Proceedings of the Royal Society B.
This variety of evolution is what biologists believe accounts for the appearance of sexual-advertising traits such as a peacock’s bright tail, or perhaps musical ability.
Such traits are believed to evolve for much the same reason as others: those who have a certain characteristic mate more, and thus spread the genes for that feature. The chief difference between this form of evolution and others is that with sexual selection, the driving factor in the process is sexual competition, rather than other exigencies of survival more generally.
Sexual selection is an intriguing aspect of evolution because it drives the evolution of traits that on their face, seem less than clearly beneficial, said Duncan Greig of University College in London, one of the paper’s authors.
“For example a peacock’s tail might be conspicuous to predators,” he noted in an email. Or for a human equivalent: “Ferrari drivers might be more likely to end up splatted against a tree than Buick drivers.” For both examples, “the simple explanation is that the cost is more than balanced by the benefit of extra mating.”
In the new paper, Greig, along with David W. Rogers of Imperial College in London, claim to have observed evolution through sexual selection for the first time. “Our yeast system is a powerful tool for investigating the genetics of sexual selection,” they wrote.
Yeast cells occur in two different mating types, somewhat akin to male and female. Each type signals to potential partners of the other type by producing an attractive chemical, called a pheromone. But cells vary widely in how strongly they can signal; the differences are genetic.
Rogers and Greig engineered one of the “sexes” of yeast cells, called MAT-alpha, to have either very high or very low signaling strength. They then mixed both types of cells with those of the opposite “sex” group, called MATa. This mixing was done in two different ways: in one, the MAT-alpha cells were few, and so faced little competition among each other; in the other, they were many, so that they faced tough competition for mating opportunities.
Only under the high-competition situation, the strong-signalling gene variant spread quickly through the population at the expense of the weak-signalling variant, Rogers and Greig found. This matched the predictions of sexual selection theory, they added.
“We have tested the simplest possible sexual selection scenario,” they wrote. “Observing the real time evolution of novel sexually selected traits, and preferences for them, is the ultimate test for sexual selection theory.”
What do you think?