Effective Population Size: Biological Duality, Field & Molecular Approaches

Biology is a field with numerous subdisciplines, each with apparently different questions and goals. Courses often emphasize the complexity and diversity of the subdisciplines rather than the common intellectual links. As a result, students can fail to make the connections between questions asked by molecular biologists and those asked by organismal and population biologists. One emphasizes the organisms as packages of DNA and other biochemical constituents, while the other stresses population structure, functional morphology, and behavior. The following laboratory exercise was developed to promote students’ understanding of the commonality of certain basic questions to all of biology and to demonstrate the power of using different approaches with very different assumptions. The exercise was specifically designed to force the students to experience simultaneously the same species both as packages of DNA and as distinct individuals with behavior. The core of the exercise can be done as a class over a five-week period in a setting where students can work for short periods outside of class as well as during class time. The specific goal of the laboratory exercises described here is to estimate effective population size (Ne) using two approaches. Effective population size is defined as the number of breeding individuals in a population. Effective population size is a major determinant of the relative heterogeneity of the population through its effect on inbreeding. As such, Ne affects the frequencies of phenotypes displayed at both the organismal (e.g. coat color,