CHAPTER 2: BIOLOGICAL EVOLUTION Evidence for Evolution

Transcription

1 CHAPTER 2: BIOLOGICAL EVOLUTION Evidence for Evolution

2 Evidence for evolution Evolution: a phenomenon resulting from the interplay of evolutionary processes and evolutionary patterns. Evolutionary processes: innovative forces (natural selection, genetic drift). Evolutionary patterns: constraints (inheritance). Evolution implies genealogical links. Paradoxically, stable characters combined with change provide the best evidence for evolution. Major sources of evidence: Molecular genetics. Embryology. Anatomy. Biogeography. Paleontology. Contemporary evidence.

3 Molecular genetics: DNA Bases (the sequence of bases carries information needed to make proteins in the cell s cytoplasm)

4 Molecular genetics: gene expression Protein Cell cytoplasm Cell nucleus mrna hnrna DNA Translation (Protein synthesis from RNA) Splicing (Removal of introns, joining of exons) Transcription (Copying DNA into RNA) Replication (Production of DNA replicas) DNA: deoxyribonucleic acid hnrna: heterogeneous nuclear ribonucleic acid mrna: messenger ribonucleic acid

5 Molecular genetics: genetic code Amino acids: Phe: phenylalanine Leu: leucine Ser: serine Etc. Amino acids are the building blocks of proteins. There are twentysomething amino acids in nature, coding for a very large number of proteins. The genetic code is common to all animals (and, in fact, with minor variations, to all life).

6 Molecular genetics: From DNA to protein Video Duration: 2:41 min

7 Molecular genetics: building phylogenetic trees based on molecular data Candida Saccharomyces Neurospora Moth Screw worm Tuna Snake Turtle Penguin Chicken Duck Pigeon Kangaroo Rabbit Pig Donkey Horse Dog Monkey Man Average Minimal Mutation Distance This tree is based on the sequence of amino acids in a protein known as cytochrome-c, involved in oxygen transport.

8 Embryology: phylotypic stages I II III Fish Salamander Tortoise Chick Hog Calf Rabbit Human Phylotypic stage: a developmental stage common across species of the same phylum.

9 Anatomy Human Lizard Cat Whale Bat Frog Bird Humerus 5 Ulna Radius Carpal Homology of arm structure in tetrapod vertebrates: size and shape of these bones vary, but their relative positions remain constant. Different functions are achieved with the same bone structure.

10 Biogeography Glyptodont (fossil) Armadillo (living) Local faunas: species are not randomly distributed in continental masses and islands. Rather, similar animal species tend to be confined to the same areas.

11 Paleontology Fossils: extinct species appear orderly across geological periods.

12 Paleontology Wings Teeth Feathers Bony tail Transitional forms: Archaeopteryx litographica is an extinct species with a mixture of avian and reptilian characters.

13 Contemporary evidence: Inclusive fitness Natural selection A female opossum with offspring Direct fitness offspring Indirect fitness relatives A group of female lions (sisters) Reciprocity friends A coalition of male baboons

14 A female opossum with offspring Direct fitness offspring

15 Contemporary evidence: Adaptation by natural selection Video Duration: 3:51 min

16 Contemporary evidence: Real-life examples European conquest of the Americas Evolution of antibiotic-resistant strains

17 Logic of natural selection Natural selection will occur when these conditions are met by a population of living organisms: Phenotypic variation Differential reproductive success Inheritance

18 Logic of natural selection Generation 1, infants Generation 1, reproductive age Generation 2, infants Variability in developmental programs Differential death before reproduction Spread of successful variants through inheritance

19 Insipient speciation in nature: California salamanders Video Duration: 3:44 min

20 David Wake: Insipient speciation in California salamanders Salamanders of northern California are genetically and phenotypically variable. Over the last 10M years these salamanders have been moving south. One line migrated along the Sierra Nevada mountains. These salamanders evolved cryptic coloration (camouflage). A second line migrated along the coastal mountains. These salamanders evolved bright coloration (Mullerian mimicry). Hybrids found in southern California are neither cryptic nor bright, thus lacking the benefits conferred by extreme phenotypes.

21 Natural selection and phenotypic change Frequency of Phenotypes (a) Stabilizing (b) Directional (c) Disruptive

22 Measuring natural selection in wild populations: Lions 4 Males 0.08 Females Reproductive Success Monthly Reproductive Rate Coallition Size Pride Size

23 Evolutionary processes Natural selection: differential reproductive success of alternative traits. Correlation of characters: a trait that evolves because it is genetically associated to a selected trait, rather than because of direct positive selection. Genetic drift: random (nonselective) change in allele frequency in a population. Mutation: random alterations in the sequence of bases in the DNA molecule produced by copying errors, radiation, chemicals, etc. Sexual reproduction: maintenance of genetic variability due to the independent assortment of alleles from both parents.

24 Contemporary evidence Video Paul Ewald: Can we domesticate germs? Duration: 17:42 min

25 Paul Ewald: Can we domesticate germs? Why are some disease organisms more harmful than others? How can we make harmful organisms evolve toward benignness? Germ s eye view: disease organisms have to get from one host to another. Harmful: do not require host mobility (e.g., dispersed by water). Benign: require host mobility (e.g., person-to-person contact). Blocking water transmission could force harmful organisms to evolve more benign forms. Coevolution of virulence and antibiotic resistance. Cholera bacteria

26 Measuring natural selection in wild populations: Galapagos finches

27 Variations in beak depth as a function of rainfall in G. fortis Abundant small seeds Smaller beak advantage Higher reproductive output Abundant large seeds Larger beak advantage Higher reproductive output

28 Contemporary evidence: Domestic animals and plants Dogs: East Asia, Middle East, 14,700 ya. Chili peppers: Central Mexico, 6,500 ya Cattle: Turkey, 10,500 ya Maize: Central Mexico, 9,000 ya