Evolution

1. Evolution The Process of Evolution (Variation, Heredity and Differential Reproduction)

2. Important things to recall • DNA • deoxyribonucleic acid, the macromolecule, composed of two polynucleotide chains in a double helix, that is the carrier of genetic information in all cells • Genes • Heredity unit containing specific genetic information. A gene can mutate to various forms called alleles. • Alleles • Any of the alternative forms of a given gene • Allele Frequency • The relative proportion of all alleles of a gene that are of a designated type. DNA (gene) → RNA → protein → trait

3. Definition of Evolution • Any process of change over time. • Classically • A change in the relative frequencies of heritable traits within a population across generations. • Modern • A change in the distribution of relative frequencies of genes (which code for heritable traits) within a population across generations.

4. Classical Evolution • A change in the relative frequencies of heritable traits within a population across generations • Relative frequency: 50% Tall plants 50% Short plants 55 generations later 25% Tall plants 75% Short plants

5. Modern Evolution • A change in the distribution of relative frequencies of genes (which code for heritable traits) within a population across generations

6. Differential Survival of Traits • Differential survival of traits in a population means that some characteristics will become more frequent while others occur less or are lost. • There are four known processes that affect the survival of a characteristic; or, more specifically, the frequency of an allele: • Mutation – error in duplication • Genetic drift - stochasticity • Gene Flow – movement of genes from pop. to pop. • Natural selection • The production and redistribution of variation is produced by three of the four agents of evolution: mutation, genetic drift, and gene flow. Natural selection, in turn, acts on the variation produced by these agents.

7. Mutation occurs in the trait An example of a spontaneous mutation during the development of plant leaves For evolution to occur via this mechanism, what has to be true of the mutation? The mutation has to be heritable • Mutation directly changes gene frequencies The mutation of fruit flies with four wings is an inherited mutation

8. The population size is small • Genetic drift – random fluctuations in the allele frequencies Only 5 of 10 plants leave offspring Only 2 of 10 plants leave offspring Generation 1 p (frequency of R) = 0.7 q (frequency of r) = 0.3 Generation 2 p = 0.5 q = 0.5 Generation 3 p = 1.0 q = 0.0

9. Gene flow • Immigration or emigration occurs based on the trait

10. Microevolution • Microevolution is the occurrence of small-scale changes in gene frequencies in a population over a few generations, also known as change at or below the species level.

11. Mechanisms of Evolution (cont.) • Natural Selection • Natural selection, the last of the four forces, is based on three principles: • (a) there is VARIATION within a species and this variation is HERITABLE • (b) parents have more offspring than can survive • (c) surviving offspring have favorable traits • The mechanism by which it operates is termed survival of the fitter meaning differential mortality and fertility. • Differential mortality is the SURVIVAL rate of individuals before their REPRODUCTIVE AGE. If they survive, they are then selected further by differential fertility – that is, their total genetic contribution to the next generation. VARIATION HERITABLE SURVIVAL TO REPRODUCE

12. Darwin’s Observations • Biogeography • It is the study of distributions of organisms, both past and present, and of related patterns of variation over the earth in the numbers and kinds of living things • Agriculture • Selective breeding • Fossils • Evidence of organisms no longer present • Evidence that many living organisms were not present in the past • Geology • New ideas about the age of the Earth via plate tectonics • Economics • Competition for resources and the effects of overpopulation

13. Evolution by Natural Selection (a mechanism of evolution) • Population level: • If variation exists and • If variation is heritable and • If differential reproduction (differential selection) exists • Then over time, those variations that enhance the ability of the organism to reproduce will increase in any population • Natural Selection leads to ADAPTATION

14. Adaptation • A biological adaptation is an anatomical structure, physiological process or behavioral trait that has evolved over a period of time by the process of natural selection that increases the likely hood of producing larger numbers of offspring or its reproductive success. • A heritable characteristic of an organism that helps it to survive and reproduce in a particular environment.

15. Adaptation vs. Acclimatization • Evolutionary biologists refer to an adaptation as a trait that evolved as the result of natural selection. • Physiologists use “adaptation” when they mean “acclimatization” – • A nerve “adapts” to a continual stimulus or • our eyes “adapt” to darkness does not involve genetic change!

16. Adaptation refers to traits that are heritable • Acclimation: Changes in the structure or physiology of an individual over its lifetime • Examples: • Increasing muscle mass via weightlifting • High altitude acclimation: But, neither of these involves genetic change!

17. Human example of an adaptation: Sickle Cell Anemia • In North America, sickle cell anemia is uncommon and a disadvantage. • However, in other parts of the world, specifically areas where malaria is common, the occurrence of sickle cell anemia is greater. • Why?

18. Sickle Cell Anemia • Because the heterozygous (SS, Ss, ss) Sickle Cell Anemia genotype gives a higher resistance to malaria, however a homozygous genotype is still a disadvantage.

19. Sickle Cell Anemia • Because the heterozygous (SS, Ss, ss) Sickle Cell Anemia genotype gives a higher resistance to malaria, however a homozygous genotype is still a disadvantage. DNA (gene) → RNA → protein → trait

20. Flattened tail – aids in swimming • Long, sharp claws – Aid in clinging to rocks • Salt gland – Allows drinking of salt water • Diving adaptations. While diving they: • Reduce blood flow to body surface- helps retain heat • Lower metabolic rate – conserves O2

21. fitness trait performance feeding defense fitness trait thermoregulation Imperfect Adaptations Multi-tasking may force an evolutionary compromise Can’t simultaneously optimize distinct functions.

22. Adaptation – organisms are not perfectly adapted ( have to make due with your genetics) • Examples: panda thumb

23. All traits evolve from something else, so carry historical baggage thus can be “contrivances” (make do!) • Homologous structures which have a common origin.

24. Divergent Evolution • Divergent evolution is the process of two or more related species becoming more and more dissimilar. • The red fox lives in mixed farmlands and forests, where its red color helps it blend in with surrounding trees. • The kit fox lives on the plains and in the deserts, where its sandy color helps conceal it from prey and predators.

25. Convergent Evolution • Convergent evolution is an evolutionary process in which organisms not closely related independently acquire some characteristic or characteristics in common, or the evolution of species from different taxonomic groups toward a similar form. • This usually reflects similar responses to similar environmental conditions. • Structures that are the result of convergent evolution are called analogous structures or homoplasies; they should be contrasted with homologous structures which have a common origin.

26. Wings