Search

Rates of sequence evolution in plastid genomes are generally low, but numerous angiosperm lineages exhibit accelerated evolutionary rates in similar subsets of plastid genes. These genes include clpP1 and accD, which encode components of the caseinolytic protease (CLP) and acetyl-coA carboxylase (ACCase) complexes, respectively. Whether these extreme and repeated accelerations in rates of plastid genome evolution result from adaptive change in proteins (i.e., positive selection) or simply a loss of functional constraint (i.e., relaxed purifying selection) is a source of ongoing controversy. To address this, we have taken advantage of the multiple independent accelerations that have occurred within the genus Silene (Caryophyllaceae) by examining phylogenetic and population genetic variation in the nuclear genes that encode subunits of the CLP and ACCase complexes. We found that, in species with accelerated plastid genome evolution, the nuclear-encoded subunits in the CLP and ACCase complexes are also evolving rapidly, especially those involved in direct physical interactions with plastid-encoded proteins. A massive excess of nonsynonymous substitutions between species relative to levels of intraspecific polymorphism indicated a history of strong positive selection (particularly in CLP genes). Interestingly, however, some species are likely undergoing loss of the native (heteromeric) plastid ACCase and putative functional replacement by a duplicated cytosolic (homomeric) ACCase. Overall, the patterns of molecular evolution in these plastid-nuclear complexes are unusual for anciently conserved enzymes. They instead resemble cases of antagonistic coevolution between pathogens and host immune genes. We discuss a possible role of plastid-nuclear conflict as a novel cause of accelerated evolution.

We have developed a laboratory course that demonstrates how evolution can be taught as a participatory, investigative science at the undergraduate college or advanced secondary high school level. The course emphasizes the applied importance of evolution to areas such as medicine and agriculture. Because many instructors face budgetary or other constraints, we have developed labs that can be run with minimal resources and a wide range of possible materials. To provide access to these materials, we have created a website aimed at instructors of evolutionary biology (http://www.evolutionkills.org OR http://www.faculty.virginia.edu/evolutionlabs). Included on the website are detailed descriptions of the course materials, a database of other articles describing laboratory and field exercises in evolution, and links to other sources of information pertinent to the teaching of evolution. We believe that this website provides a much needed resource for instructors of evolution and encourages inquiry-based learning approaches to the study of evolutionary biology at the undergraduate level. (Contains 2 figures.)

Speed profile models can be used as a diagnostic tool by highway engineers. Previous work has investigated relationships between operating speed and geometric roadway elements for permanent roadway conditions on predominantly two-lane rural roads. However, little research of this type has been directed specifically toward construction work zones. In this study, a speed profile model for construction work zones on high speed highways was developed using artificial neural networks and made available for use by practitioners through a MS EXCEL interface. The model inputs include horizontal and vertical alignment variables, cross section dimensions and traffic control features. A linear reference system is used for model input and output. Three categories of vehicles--cars, trucks, and all vehicles--were used in this study. Models for the 15th percentile speed, mean speed, and 85th percentile speed were developed. DOI: 10.1061(ASCE)0733-947X(2007)133:3(198) CE Database subject headings: Traffic speed; Highway construction; Neural network; Workspace; Models.

The American chestnut (Castanea dentata; Fagaceae) was a dominant canopy tree in the Appalachian Mountains of North America. Since the introduction of the chestnut blight fungus (Cryphonectria parasitica; Valsaceae) in America, the American chestnut has been reduced to a predominantly clonal, understory species. Our objective was to determine whether the ecological changes and absence of new recruits have influenced the population genetics of American chestnut. Leaf samples were collected from four populations in southwestern Virginia. Electrophoretic data from five polymorphic loci were used to determine the genetic diversity and population structure of the populations and subpopulations. Growth data and infection status were recorded for one of the populations to determine their relationship with heterozygosity. F statistics revealed a significant amount of differentiation among subpopulations and an excess of heterozygotes within subpopulations. Heterozygous individuals also had higher rates of vegetative growth. The superior performance and excess of heterozygotes suggests that selection favors heterozygous individuals. The prolonged absence of sexual reproduction in C. dentata has allowed subtle fitness differences to accumulate to the extent that they have had significant effects on the genetics of chestnut populations. Key words: allozyme variation; Castanea dentata; Cryphonectria parasitica; Fagaceae; genetic diversity; heterozygosity; population structure.