MULTIDIMENSIONAL ADAPTIVE EVOLUTION OF A FEED-FORWARD NETWORK AND THE ILLUSION OF COMPENSATION
Version of Record online: 6 AUG 2012
© 2012 The Author. Evolution© 2012 The Society for the Study of Evolution.
Volume 67, Issue 1, pages 49–65, January 2013
How to Cite
Bullaughey, K. (2013), MULTIDIMENSIONAL ADAPTIVE EVOLUTION OF A FEED-FORWARD NETWORK AND THE ILLUSION OF COMPENSATION. Evolution, 67: 49–65. doi: 10.1111/j.1558-5646.2012.01735.x
- Issue online: 4 JAN 2013
- Version of Record online: 6 AUG 2012
- Accepted manuscript online: 16 JUL 2012 01:42PM EST
- Received March 6, 2012, Accepted June 13, 2012
- gene regulation;
- natural selection
When multiple substitutions affect a trait in opposing ways, they are often assumed to be compensatory, not only with respect to the trait, but also with respect to fitness. This type of compensatory evolution has been suggested to underlie the evolution of protein structures and interactions, RNA secondary structures, and gene regulatory modules and networks. The possibility for compensatory evolution results from epistasis. Yet if epistasis is widespread, then it is also possible that the opposing substitutions are individually adaptive. I term this possibility an adaptive reversal. Although possible for arbitrary phenotype-fitness mappings, it has not yet been investigated whether such epistasis is prevalent in a biologically realistic setting. I investigate a particular regulatory circuit, the type I coherent feed-forward loop, which is ubiquitous in natural systems and is accurately described by a simple mathematical model. I show that such reversals are common during adaptive evolution, can result solely from the topology of the fitness landscape, and can occur even when adaptation follows a modest environmental change and the network was well adapted to the original environment. The possibility of adaptive reversals warrants a systems perspective when interpreting substitution patterns in gene regulatory networks.