RE: Evolution of phenotypic plasticity

Patrick: Your question is quite complex, and I think some of the answers are not known. The first part of the question pertains to the genetic vs. environmental source of phenotypic plasticity. I'm not quite sure what you're getting at here. Because phenotypic plasticity is a name for a response to environmental conditions, its expression is under environmental control. However, the ability of an organism to employ phenotypic plasticity is controlled by genetics. The genome provides a potential for plasticity and the environment determines what phenotype is expressed. If I have misunderstood your question, please enlighten me.

OB The next part of your question concerns microevolution versus macroevolution. Well, most experts now believe that macroevolution is a real phenomenon, but no one knows how it works, or when! Certainly phenotypic plasticity is heritable and can affect fitness, so it will function at the microevolutionary level. If clades differ in their degree of phenotypic plasticity (and this appears to be true as well) then phenotypic plasticity can affect macroevolutionary selection, assuming that macroevolution is real. However, it is possible that the selective effect of differences among clades in phenotypic plasticity is too small to, in practice, influence macroevolution.

Your suggestion at the end of your question, that phenotypic plasticity might serve as a buffer, preventing the action of selection on genes by providing the "desired" morphology without genetic change, is obviously true. Indeed, here is the benefit of phenotypic plasticity: it gives the organism the opportunity to adapt to environmental conditions during its ontogeny (and without dying), rather than through the much longer process of differention survival and reproduction over numerous generations.

So the evolutionary role of phenotypic plasticity is to confer on those who possess it a reduced death rate and rapid response to environmental change. In fact, it may have permitted organisms with long generations to colonise highly variable niches that they could not otherwise have occupied.

I hope that helps,
David