evolution by natural selection Todays lecture is about

… evolution by natural selection?

Today’s lecture is about 3. Selection Summary of Darwin’s evidence and main ideas on the Origin of Species by Means of Natural Selection Convergent evolution Three types of natural selection and experimental demonstration of two of them

Charles Darwin 1809 -1882 On the Origin of Species by Means of Natural Selection Darwin produced a synthesis based upon a number of different types of evidence http: //www. pbs. org/wgbh/evolution/index. html

Biogeography: Voyage of the Beagle Variation and similarity between organisms in different regions suggested organisms were related The Fossil Record

Comparative Anatomy Homologous Structures – evolved from a common original structure Analogous Structures - evolved from different original structures but function similarly Vestigial Structures - functioned in an ancestral organisms, but that are reduced (in structure and function) in the descendant Examples in humans: caudal vertebrae of coccyx appendix of intestines Homologous structures suggested common ancestors and variation in evolution since those ancestors

Comparative embryology Comparing the general appearance of embryos from different species at various stages in development shows them to be quite similar Certain embryonic structures are shared by all chordates, but show interesting structural and functional changes during development, e. g. gill slits

Artificial Selection

… mutation?

Mutation is the source on which natural selection is going to act

Darwin’s main ideas: Natural selection is differential success in reproduction Natural selection occurs through an interaction between the environment and the variability inherent among the individual organisms making up a population The product of natural selection is the adaptation of populations of organisms to their environment

Convergent evolution Species from different evolutionary branches may come to resemble one another if they live in similar environments Astrophytum asterias Cactaceae Mexico and Texas Euphorbia valida Euphorbiaceae South Africa

Three types of Natural Selection Fig 13. 20

Is stabilizing selection the process that has enabled organisms with long geological histories, or at least ancient ancestors, to survive? What does it require?

Escherichia coli A group of individuals Colonies on agar in a Petri dish Escherichia coli is a typical gram negative rod bacterium. It is cylindrical, about 1. 0 -2. 0 micrometers long, with radius about 0. 5 micrometers.

SEM picture Kingdom: Eubacterium Scientific Name: Escherichia coli Image Courtesy of: Shirley Owens, Center for Electron Optics, MSU Image Width: 9. 5 microns Image Technology: SEM (Scanning Electron Microscope)

Inducing evolutionary change in E. coli Start with a wild-type population that can be stored and grown for comparative purposes 1. Take some of the wild-type, grow it on a agar with glucose for a day (about 6. 6 generations). 2. Next day plate out onto a fresh petri dish with new glucose. 3. At intervals take the ‘glucose fed’ population and compare it’s growth rate on glucose with the original wild-type population

Trajectory of comparative fitness relative to ancestor during 10, 000 generations of experimental evolution in E. coli Each point is the mean of 12 replicates. The error bars are 95% confidence limits Stabilizing, directional or diversifying selection? Is this an example of stabilizing, directional or diversifying selection?

An experiment: place E. coli in a solution in a chemostat – a vessel that has a constant input of glucose Introduce the T 4 virus!

E coli Stabilizing, directional or diversifying selection? T 4 virus Emergence of an E. coli resistant mutant How did the virus survive after emergence of a resistant mutant? The mutant was less efficient at glucose metabolism – so non-mutants out competed it Is this an example of stabilizing, directional or diversifying selection?

Sections you need to have read 13. 1 13. 2 13. 3 13. 4 13. 5 13. 6 13. 7 13. 20 and the Introduction to Chapter 10 Courses that deal with this topic Biology 102 General Biology 454 Evolutionary Mechanisms