Under gradual environmental change, selection for a moving optimum may cause permanent maladaptation of traits (or trait combinations) that are under pure stabilizing selection (i.e., orthogonal to the direction of the optimum).
As shown by Charlesworth [ 18], selection pressure on a rec-modifier when a trait is subject to selection with a steadily moving optimum should be sufficient to account for observed increases in rf in artificial selection experiments, especially for organisms with small chromosome number, like D. melanogaster.
Theoretical analysis shows that the fitness epistasis caused by truncation selection with a steadily moving optimum can have a powerful effect on selection for increased recombination in large populations [ 18].
Therefore, weak selection in combination with a constantly moving optimum represents a 'slippery slope' that can be very dangerous for population survival (see discussion in Bürger and Lynch 1995 and Huey and Kingsolver 1993).
There are many potential factors that might affect a population's adaptation to a moving optimum.
The only situation under which the species closest to the optimum experiences a major negative effect of competition occurs when selection on the trait responding to the moving optimum is very strong and the optimum is moving slowly.
The final mechanistic detail of interest, illustrated by Figure 4c, is that the tendency for the predators to eat the least well-adapted individuals is an intrinsic evolutionary outcome of a predator-prey system responding to a moving optimum.
The time to extinction for the predator is also usually higher when it is interacting with the prey than when it is simply evolving in response to the moving optimum.
On the other hand, sufficiently weak selection in combination with a moving optimum increases lag load, because the population will follow the optimum at a greater distance.
Our focus is on quantitative-genetic models with selection for a moving phenotypic optimum.
