Genetic lines of least resistance, continued

Good explanation of the genetic lines of least resistance, Simone.

I just wanted to add a few comments on the subject. Schluter mentions that when traits covary (in the ways Simone described earlier) the amount that one trait covaries with another will affect how far evolution will be pulled away from the direction in which selection is at its strongest. Take the finch beak example that Simone gave, and imagine that selection is strongest in the direction favoring an extremely long, narrow beak. If beak width and length depend on each other to a great extent, so that selection on one automatically changes the other dramatically (selection for a longer beak leads to a wider beak too), then this interaction would lead to evolution in a direction that is greatly skewed off of the path of strongest directional selection. If the traits did not affect each other as much, the direction of evolution would deviate from the direction of strongest selection to a smaller extent.

Schluter mentions that over time this effect of genetic constraint can be overcome and a population may make it to the top of an adaptive peak. But the stronger the covariance between the traits is, the stronger the skew will be away from the direction of strongest selection, and the longer it will take to make it up the peak.

One cool result of this whole covariance thing is that the degree of covariance between traits can help you more accurately predict the direction of evolution. If you realize that selection is strongest in a certain direction on an adaptive landscape, you can examine phenotypic traits that would be affected by selection, and based on how these traits covary you could make predictions about the direction of evolution along the landscape. Neat!

Now that’s really it for the Ecology of Adaptive Radiation…Speciation here we come!