The Evolution of Weeds

Gel electrophoresis of proteins has become a standard and powerful research tool for application in a multitude of biological disciplines One form of protein electrophoresis, isozyme analysis, has become particularly prominent in systematic and evolutionary biology as well as agronomy (Tanksley and Orton, 1983) Isozymes, or multiple molecular forms of enzymes, are enzymes that share a common substrate but differ in electrophoretic mobility (Markert and Moller, 1959) They are revealed when tissue extracts are subjected to electrophoresis in various types of gels and subsequently submersed in solutions containing enzyme-specific stains Genetic analysis may indicate that some of the variant electromorphs are encoded by alternate alleles at a single locus, in which case the allelic products are termed allozymes (Prakash et al, 1969) Data retrieved from electrophoretic gels consist of the number and relative mobilities of various enzyme products, which with appropriate genetic analyses become transformed into single or multilocus genotypes for each individual analyzed Reasons are many for the popularity of electrophoretic data (Avise, 1975; Gottlieb, 1977; Crawford, 1983), but foremost among these is that isozymes provide a series of readily scored, single-gene markers

Visualization and Interpretation of Plant Isozymes

http://science.sciencemag.org/content/sci/171/3973/757.full.pdf

Allelochemics: Chemical Interactions between Species

We compile and analyze data on the population genetic structure of broad-sense clonal plant populations where sexual recruitment is rare or absent. The data from 27 studies show a common theme: multiclonal populations of intermediate diversity and evenness tend to be the rule, most clones are restricted to one or a few populations, and widespread clones are exceptional. While a few studies have demonstrated that ecological differences among sympatric clones do occur, more experimental and theoretical studies are necessary to determine the role of selection and other evolutionary forces in maintaining clonal polymorphism.

https://www.jstor.org/stable/info/2444338

Patterns of Genotypic Diversity in Clonal Plant Species

The study of succession has been hampered by the lack of a general theory. This is illustrated by confusion over basic concepts and inadequacy of certain models. This review clarifies the basic ideas of pathway, mechanism, and model in succession. Second, in order to prevent inappropriate narrowness in successional studies, we analyze the mechanistic adequacy of the most widely cited models of succession, those of Connell and Slatyer. This analysis shows that models involving a single pathway or a dominant mechanism cannot be treated as alternative, testable hypotheses. Our review shows much more mechanistic richness than allowed by these widely cited models of succession. Classification of the mechanisms of specific replacement, called for by existing models, is problematic and less valuable than the search for the actual mechanisms of particular seres. For example, the “tolerance” mechanism of succession has at least two contrasting meanings and is unlikely to be disentangled from the “inhibition” mechanism in field experiments. However, the understanding of particular species replacements through experiment and knowledge of the conditions of a particular sere and species life histories is a reasonable and desirable goal. Finally, we suggest the need for a broad mechanistic concept of succession. Thus, based on classical causes of succession that have survived recent scrutiny, we erect a framework of successional mechanisms. This framework aims at comprehensiveness, and specific mechanisms are nested within more general causes. As a result of its breadth and hierarchical structure, the framework performs two important functions: First, it provides a context for studies at specific sites and, second, is a scheme for formulating general and testable hypotheses. The review of specific successional mechanisms and the general mechanistic framework can together guide future work on succession, and may foment the development of a broad theory.

Roger E. Wilson

Papers

Allelopathy as Expressed by Helianthus annuus and Its Role in Old-Field Succession

Biotype Selection in Erigeron annuus During Old Field Succession

Comparison of Four Techniques Used in the Extraction of Plant Enzymes for Electrophoresis