Lecture 11 Background

Ricklefs Ch. 6 p. 115-124 (version 6)

Evolution and Adaptation

Ch 6 examines the many ways in which populations and individuals respond to changes in their surroundings.

  • Adaptations result from natural selection on heritable variation in traits that affect evolutionary fitness
  • Through the process of evolution, traits of individuals within populations are continually adjusted to changes in the environment
  • Genotype - the unique genetic constitution of each individual within a population
  • Phenotype - the outward expression of the genotype in an individual's structure and function
  • Phenotypic Plasticity - the capacity of an individual to exhibit different responses to environmental variation
  • Alleles - different forms of a particular gene (i.e. eye color, blood type, etc)
  • Alleles can be dominant or recessive (dominant allele will mask the expression of the other)

Sources of Genetic Variation - mutation

Genetic variation among individuals in a population is pervasive and has many consequences

When genetic factors cause differences among individuals in survival and reproductive success, evolutionary change comes about through natural selection. 3 main ingredients of natural selection:
1. Variation among individuals
2. Inheritance of that variation
3. Differences in survival and reproductive success, or fitness, related to that variation (hence natural selection)

Natural selection occurs because of differences in reproductive success among individuals with their environment

3 types of selection

  • Stabilizing Selection - when individuals with intermediate (average) phenotypes (generally the most common in the population) have higher reproductive success than those with extreme phenotypes
  • Directional Selection - when the fittest individuals have a more extreme phenotype than the average of the population
  • Disruptive Selection - when individuals with extreme phenotypes have higher fitness than individuals with intermediate phenotypes (leads to an increase of genetic and phenotypic variation within a population)

Population Genetics

  • Populations are continually engaged in dynamic evolutionary relationships with their environments that shape ecological interactions
  • The potential for evolution exists in every population
  • Rapid environmental changes can exceed the capacity of a population to respond by evolution

Ricklefs Ch. 21 p. 276-279

In the absence of mutation and immigration, a population will eventually become genetically uniform (coalescence)

Genetic Drift - the process by which allele frequencies change and genetic variation is lost due to random variations in fecundity, mortality, and inheritance of gene copies through male and female gametes

Effective population size - the size of the ideal population that undergoes genetic drift at the same rate as an observed population

Additional interesting background

Prof. Allan mentioned that evolution typically occurs very slowly and gradually, but that there are some examples of very rapid evolution. One fascinating study is about rapid evolution in response to human changes on a lake ecosystem. Nelson Hairston Jr and colleagues studied the evolution of fish and were able to revive dormant eggs that lay beneath the lake sediment. They could study the evolutionary adaptation to the new lake conditions that had occurred in just a few decades. A press release about the research is here (see especially the second to last paragraph): http://www.news.cornell.edu/stories/July09/Hairston.html. If you want to read the full article, you can get it through the UM library and this is the citation: Hairston, N. G., Jr., W. Lampert, C. E. Cáceres, C. L. Holtmeier, L. J. Weider, M., U. Gaedke, J. Fischer J. A. Fox, and D. M. Post. 1999. Rapid evolution revealed by dormant eggs. Nature 401:446.

Prof. Allan also briefly mentioned the research of Peter and Rosemary Grant who study evolution in finches in the Galapagos. Here is an article about their work: http://www.newjerseynewsroom.com/science-updates/princetons-peter-and-rosemary-grant-honored-with-kyoto-prize-for-insights-into-evolutionary-theory

From 3m1ly: I suspect that some people might be interested in more views on sex and evolution. Of note, one belief of Darwin's I hope fewer people subscribe to is that the evolutionary path caused the typicality of males being sexually aggressive, while females fend off their advances… I hope you don't mind me putting up this controversial article, which shows instances of homosexuality in nature—take it, or leave it, as you will:
Here's where I first found the link to the article, on a blog which talks about how a teacher was suspended for assigning it:

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