Ch 23 Part II, Ch 24

1. Ch 23 Part II, Ch 24 Evolution : Mechanisms Natural Selection (only one that consistently leads to adaptive evolution) Genetic Drift Genetic Flow

2. Alleles drift but how does that look? • Survival of the fittest? • Adaptive advantage can lead to greater relative fitness • Relative fitness: contribution an individual makes to the gene pool of the next generation • PHENOTYPE DIRECTLY

3. Original population Frequency of individuals Fig. 23-13 Phenotypes (fur color) Original population Evolved population (b) Disruptive selection (c) Stabilizing selection (a) Directional selection

4. Sexual Selection • Likelihood of mating • Can result in sexual dimorphism • Intrasexual selection : mostly males competing physically with each other • Intersexual selection: usually females choose

5. EXPERIMENT Female gray tree frog SC male gray tree frog LC male gray tree frog Fig. 23-16 SC sperm  Eggs  LC sperm Offspring of SC father Offspring of LC father Fitness of these half-sibling offspring compared RESULTS Fitness Measure 1995 1996 NSD LC better Larval growth NSD LC better Larval survival Time to metamorphosis LC better (shorter) LC better (shorter) NSD = no significant difference; LC better = offspring of LC males superior to offspring of SC males.

6. What preserves genetic variation? • (Tendency of directional and stabilizing selection is to reduce variation) • Mechanisms to preserve variety: • Diploidy (“hide” recessive) • Balancing Selection • Heterozygote advantage • Frequency dependent selection: fitness of a phenotype decreases if it becomes too common • Neutral variation: no affect on protein fxn

7. Why Can’t We Be Perfect? • 1. Selection can only act on existing variations (may not be ideal) • 2. Evolution is limited by historical constraints (bats, birds from walking) • 3. Adaptations are often compromises • 4. Chance, natural (founders effect does not ensure fit alleles in new pop) selection,and the environment interact

8. Fig. 23-19

9. Ch 24 Origin of Species • Biological Species concept • Populations • Reproductively compatible • Gene flow even over long distances can hold gene pool together ( if NS or drift = divergence) • *emphasizes separateness of species

10. Types of Isolation • Reproductive isolation: barriers will isolate a gene pool • Prezygotic barriers • Postzygotic barriers

11. Prezygotic barriers Postzygotic barriers Habitat Isolation Behavioral Isolation Temporal Isolation Mechanical Isolation Gametic Isolation Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown Fig. 24-4 Individuals of different species Viable, fertile offspring Mating attempt Fertilization (c) (e) (f) (a) (g) (h) (l) (i) (d) (j) (b) (k)

12. 3 types of species concepts unity within a species • morphological species concept: body shape and other structural features (sexual and asexual, most used method) • Ecological species concept: niche, interaction with enviro. Disruptive selection • Phylogenetic species concept: smallest group that share a common ancestor

13. Allopatric: gene flow is interrupted by a geographic barrier cuts a population off from the main Colonists Evidence: frogs, squirrels, highly subdivided regions tend to have more species than areas with fewer barriers Reproductive isolation increases with distance Sympatric: speciation occurs in populations that live in same geography Less common Gene flow is reduced by polyploidy, (plants) habitat differentiation sexual selection Sympatric vs Allopatric speciation

14. Mantellinae (Madagascar only): 100 species Rhacophorinae (India/Southeast Asia): 310 species Fig. 24-7 Other Indian/ Southeast Asian frogs 100 60 20 80 40 0 1 2 3 Millions of years ago (mya) 1 3 2 India Madagascar 56 mya 88 mya 65 mya

15. Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation

16. Polyploidy • A species may originate from an accident during cell division that results in extra sets of chromosomes • Autopolyploid: extra sets of chromosomes derived from a single species • Ex, failure in cell division • Tetraploid offspring tend to be less fertile • Can produce fertile offspring with self fertilization or with other tetrapods • One generation can be reproductively isolated

17. Fig. 24-10-3 2n 2n = 6 4n = 12 4n Failure of cell division after chromosome duplication gives rise to tetraploid tissue. Gametes produced are diploid.. Offspring with tetraploid karyotypes may be viable and fertile.

18. Allopolyploid • Two different species interbreed and have infertile offspring • Propagate asexually • Plants more tolerant of meiotic and mitotic errors • After several generations a sterile hybrid can become fertile with each other not the parent species • Frog (occasionally in animals) • 80% plant species may have formed this way)

19. Species B 2n = 4 Unreduced gamete with 4 chromosomes Unreduced gamete with 7 chromosomes Fig. 24-11-4 Hybrid with 7 chromosomes Meiotic error Viable fertile hybrid (allopolyploid) 2n = 10 Normal gamete n = 3 Normal gamete n = 3 Species A 2n = 6

20. Apple maggot fly(slow hawthorn tree vs apple tree) Temporal isolation and post zygotic (helpful alleles in one tree, harmful in the other) Habitat or food source not used by parent population Female driven selection of male coloration patterns in cichlids Habitat Differentiation & Sexual Selection

21. EXPERIMENT Monochromatic orange light Normal light Fig. 24-12 P. pundamilia P. nyererei

22. Speciation can occur rapidly or slowly and can result from changes in many or a few genes • Punctuated Equilibria: periods of apparent stasis punctuated by sudden change • Relatively rapidly • Gradualism • Adaptive Radiation

23. (a) Punctuated pattern Fig. 24-17 Time (b) Gradual pattern

24. Adaptive Radiation • Over the last 250 my diversity of life has increased in the fossil record • Periods of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles or niches • Large scale after each of the 5 mass extinctions • Seed plants, mammals etc..

25. 50 40 Fig. 25-16 30 Predator genera (percentage of marine genera) 20 10 0 Cenozoic Paleozoic Mesozoic Era Period P D C P C N E O J S Tr 200 145 359 65.5 0 488 444 542 416 299 251 Time (millions of years ago)

26. Ancestral mammal Monotremes (5 species) Fig. 25-17 ANCESTRAL CYNODONT Marsupials (324 species) Eutherians (placental mammals; 5,010 species) 50 200 250 100 150 0 Millions of years ago

27. Close North American relative, the tarweed Carlquistia muirii Fig. 25-18 1.3 million years MOLOKAI KAUAI 5.1 million years Dubautia laxa MAUI OAHU 3.7 million years Argyroxiphiumsandwicense LANAI HAWAII 0.4 million years Dubautia waialealae Dubautia scabra Dubautia linearis

28. New roles in community lead to radiations • Rise of photosynthetic prokaryotes • Evolution of large predators in the Cambrian explosion • Colonization of land by • plants, (stems, waxy coat) • insects • Tetrapods The radiation of plants stimulated radiation of insects