27 November 2007
Roberta has suggested an article for the week after Thanksgiving that explores several of the issues related the plasticity, which we've touched on previously. In an article from Evolution earlier this year, Winterhalter and Mousseau have examined the heridibility of plasticity in diapuase in ground crickets. This work also explores the adaptive significance of phenotypic plasticity.
Patterns of phenotypic and genetic variation for the plasticity of diapause incidence. (2007.) Wade E. Winterhalter, and Timothy A. Mousseau. Evolution 61(7): 1520-1531. [Link to HTML & PDF]
13 November 2007
Early cell fate decisions in the purple sea urchin embryo provide one of the most well-understood systems of gene network interactions. In last week's issue of Science the Davidson Lab presents a study examining the timing of network events in this systems. Hopefully this short article will lead us to consider the importance of temporal aspects of developmental models, as well as potential molecular mechanisms of heterochronic evolution, and other topics.
Smith, J., Theodoris, C. and Davidson, E. H. (2007). A Gene Regulatory Network Subcircuit Drives a Dynamic Pattern of Gene Expression. Science 318: 794-797. [Link to HTML & PDF]
6 November 2007
For this week Carl has suggested a paper that examines the issue of convergence from a morphological and biomechanical perspective. Through a study of the jaws of shrews, Young and colleagues look at how developmental and functional integration among traits correlates with evolutionary diversification of morphological structures and convergence of function.
Young, R. L., Haselkorn, T. S. and Badyaev, A. V. (2007). Functional equivalence of morphologies enables morphological and ecological diversity. Evolution 61: 2480-2492. [Link to HTML & PDF]
So far this semester we've examined several specific developmental genetic mechanisms which might influence evolution. This week Roberta has suggested a paper from 2002 that uses a population genetic model to explore how changes in developmental mechanisms should effect speciation and post-zygotic isolation in general. This work re-examines the classic Dobzhansky-Muller model in the light of developmental change.
Porter, A.H. and Johnson, N.A. (2002). Speciation despite gene flow when developmental pathways evolve. Evolution 56(11): 2103-2111. [Link to HTML & PDF]
Carl has suggested a paper for this week that examines the development of a fascinating, tasty, and under-studied group of animals. Jackson and coworkers have examined the expression of genes involved in development of the shell in the abalone Haliotis asinina. They discuss their findings in the context of the molecular evolution of genes involved in biomineralization and the evolutionary success of the mollusks.
Jackson, D. J., Worheide, G. and Degnan, B. M. (2007). Dynamic expression of ancient and novel molluscan shell genes during ecological transitions. BMC Evolutionary Biology 7: 160. [Link to HTML & PDF]
Ghalambor, C. K., McKay, J. K., Carroll, S. P. and Reznick, D. N. (2007). Adaptive versus non-adaptive phenotypic plasticity and the potential for contemporary adaptation in new environments. Functional Ecology 21: 394-407. [Link to HTML & PDF]
This week let's get into a bit more experimental detail. Past discussions have touched on the ideas of phenotypic plasticity and genetic assimilation and their potential importance as a mechanism of phenotypic evolution. Elizabeth has suggested a paper exploring the connection between chromatin regulation and phenotypic plasticity in Drosophila. How well do we understand what causes phenotypic plasticity? How might different mechanisms of plasticity play into ideas of evolution by genetic assimilation?
Gibert, J.-M., Peronnet, F., Schlotterer, C. (2007). Phenotypic Plasticity in Drosophila Pigmentation Caused by Temperature Sensitivity of a Chromatin Regulator Network. PLoS Genetics 3(2): e30.
Last week saw an interesting discussion on the meaning and nature of constraints, and whether genetic regulatory networks could present internal evolutionary constraints. The article by Erwin made prominent mention of a previous article written with Eric Davidson, in which they make the case that highly conserved, ancient genetic regulatory networks are highly resistant to change. The persistence of these "kernels", they argue, has been a constraint preventing phylum-level disparity to appear in ages since the Cambrian, when these mechanisms presumably became established. Let's examine this article and their idea.
Davidson, E. H., and Erwin, D. H. (2006). Gene Regulatory Networks and the Evolution of Animal Body Plans. Science 311(5762): 796-800. [Link to HTML & PDF]
Let's also consider a slightly contrasting idea from Gerhart & Kirschner, who propose that the structure of genetic networks is in fact important in facilitating the appearance of disparity.
Gerhart, J., and Kirschner, M. (2007). The theory of facilitated variation. PNAS 104 suppl 1 8582-8589. [Link to HTML & PDF]
Our first articles this semester will examine ideas about the connection between developmental mechanisms and the macroevolution of organisms, particularly the Cambrian radiation of animal forms.
Erwin, D. H. (2007). Disparity: Morphological pattern and developmental context. Palaeontology 50(1): 57-73. [Link to HTML & PDF]
The article by Erwin makes prominent citation of an earlier article by Harmon et al. describing evolutionary radiations in lizards.
Harmon, L. J., Schulte, J. A., II, Larson, A., and Losos, J. B. (2003). Tempo and Mode of Evolutionary Radiation in Iguanian Lizards. Science 301(5635): 961-964. [Link to HTML & PDF]