Joined: Dec. 2002
In the never-ending quest for "icons", I submit the following for everyone's consideration. Comments, additional references, and more examples that combine molecular and morphological perspectives would be most appreciated. (This is a slightly-modified version of a recent ARN post - suggestions to make it more suited for this board are invited as well.)
First, another accursed pubmed abstract (that need not be read in detail - instead, just note that some of the genes mentioned are known to be developmentally important ones Arabidopsis and other plants):
| Proc Natl Acad Sci U S A 2001 Aug 28;98(18):10208-13 |
Accelerated regulatory gene evolution in an adaptive radiation.
Barrier M, Robichaux RH, Purugganan MD.
Department of Genetics, Box 7614, North Carolina State University, Raleigh, NC 27695, USA.
The disparity between rates of morphological and molecular evolution remains a key paradox in evolutionary genetics. A proposed resolution to this paradox has been the conjecture that morphological evolution proceeds via diversification in regulatory loci, and that phenotypic evolution may correlate better with regulatory gene divergence. This conjecture can be tested by examining rates of regulatory gene evolution in species that display rapid morphological diversification within adaptive radiations. We have isolated homologues to the Arabidopsis APETALA3 (ASAP3/TM6) and APETALA1 (ASAP1) floral regulatory genes and the CHLOROPHYLL A/B BINDING PROTEIN9 (ASCAB9) photosynthetic structural gene from species in the Hawaiian silversword alliance, a premier example of plant adaptive radiation. We have compared rates of regulatory and structural gene evolution in the Hawaiian species to those in related species of North American tarweeds. Molecular evolutionary analyses indicate significant increases in nonsynonymous relative to synonymous nucleotide substitution rates in the ASAP3/TM6 and ASAP1 regulatory genes in the rapidly evolving Hawaiian species. By contrast, no general increase is evident in neutral mutation rates for these loci in the Hawaiian species. An increase in nonsynonymous relative to synonymous nucleotide substitution rate is also evident in the ASCAB9 structural gene in the Hawaiian species, but not to the extent displayed in the regulatory loci. The significantly accelerated rates of regulatory gene evolution in the Hawaiian species may reflect the influence of allopolyploidy or of selection and adaptive divergence. The analyses suggest that accelerated rates of regulatory gene evolution may accompany rapid morphological diversification in adaptive radiations.
Now, consider three plants from the group (pardon my taxonomical crudeness here) mentioned in this abstract: ,
It doesn’t take much of an eye to see stupendous morphological differences, easily dramatic enough to qualify as possibly macroevolutionary in nature. Of course, this could only be if it could be shown that these plants share a common ancestry.
And indeed it can be so shown. By a standard that even the staunchest YECer accepts, it can be strongly concluded that each of these (as well as other members of the Silversword alliance) share a common ancestry. This is because, the vast morphological differences aside, they are interfertile. As interestingly, for a number of other reasons (biological, geographic, historical, and molecular), it can be safely concluded that these vastly-different plants diverged from a common ancestor that looked something like
Reflect, now, on the abstract. In this study, evidence for positive selection of alleles (that must have arisen via mutation - this follows from the natural history of the different genera) of developmentally-important genes - genes involved in flower structure and evolution - was described. While it’s not a videotape, it stands as evidence of the sort that Wells claims does not exist - namely, that changes in developmentally-important genes are important in macroevolutionary progressions.
(Keep in mind that among the dramatic morphological differences that are seen in these examples are ones that involve floral structures. Also, while others might argue with me, I would claim here that the range of morphologies shown in this post exceeds the range seen in placental mammals - just to give readers an idea of the scope of the differences.)