Contents:

1) Researchers evolve a complex genetic trait in the laboratory (Press Release)

Duke University biologists have evolved a complex trait in the laboratory -- using the pressure of selection to induce tobacco hornworms to evolve the dual trait of turning black or green depending on the temperature during their development. The biologists have also demonstrated the basic hormonal mechanism underlying the evolution of such dual traits.

Their experiments, they said, offer important insight into how complex traits involving many genes can abruptly "blossom" in an organism's evolution...

..."It's long been known that polyphenisms are controlled by hormones, with the brain sensing environmental signals and altering the pattern of hormonal secretions," said Nijhout. "In turn, these hormonal patterns turn sets of genes on or off to produce different traits. However, we understood only the developmental mechanism, and how it is possible with a single genome in an animal to produce two very different phenotypes," he said...

..."Homeostatic mechanisms tend to stabilize a phenotype such as color and, therefore, allow the accumulation of underlying, covert mutations just as an electrical capacitor acts to accumulate charge. And eventually, these mutations could 'break out' of that constraint to produce a sudden phenotypic change; and one way for them to break out is for a mutation to happen -- for example, one that alters a hormonal level -- releasing all this variation.

Full text at:

http://www.eurekalert.org/pub_releases/2006-02/du-rea012706.php 


2) Evolution of a Polyphenism by Genetic Accommodation (Science)

[Suzuki & Nijhout, Science, Feb '06]

Abstract:

Polyphenisms are adaptations in which a genome is associated with discrete alternative phenotypes in different environments. Little is known about the mechanism by which polyphenisms originate. We show that a mutation in the juvenile hormone-regulatory pathway in Manduca sexta enables heat stress to reveal a hidden reaction norm of larval coloration. Selection for increased color change in response to heat stress resulted in the evolution of a larval color polyphenism and a corresponding change in hormonal titers through genetic accommodation. Evidently, mechanisms that regulate developmental hormones can mask genetic variation and act as evolutionary capacitors, facilitating the origin of novel adaptive phenotypes.

http://www.sciencemag.org/cgi/content/abstract/311/5761/650

This is very interesting stuff from my point of view but as usual I don't have a subsciption to Science ('sigh') - I'll let you know if I can get hold of a copy!

John

Model of an Internal Evolutionary Mechanism
http://members.aol.com/jorolat/index.html