Plant Speciation – Part 1

1. Plant Speciation – Part 1 Spring 2012

2. Major topics • Variation in plant populations and species (1) • Gene flow and reproductive isolating barriers (1) • Speciation mechanisms (2) • Species concepts (2)

3. Anagenesis versus Cladogenesis

4. A B C D E F Cladogenesis Cladogenesis Cladogenesis Anagenesis Cladogenesis

5. Biological Variation • All populations of organisms have inherent variation within them – a range of genetic variation of which part is expressed as phenotypic variation • Influences of the environment can change how this variation is expressed = phenotypic plasticity • Observations by biologists can be interpreted in a number of ways to determine the similarities or differences in groups of organisms, depending on which characteristics are measured or emphasized • Need to understand speciation (the process) in order to understand patterns of diversity (and vice versa) and to provide a means to define species

6. Variation in Plant Populations and Species

7. One P. jeffreyi ecotype is adapted to serpentine soils. This ecotype has less overall genetic diversity than ecotypes of this species adapted to more fertile soils.

8. Clinal variation within a species

9. Genetic variation within and among species of native American canes

10. Mutation is the ultimate source of all genetic diversity.

11. Types of mutations • Point mutations (change in one base) • Insertions, deletions, inversions, duplications of parts of a chromosome • Gains or losses of whole chromosomes (aneuploidy) • Multiples of whole genomes (the full set of chromosomes in the nucleus) (polyploidy)

12. Genetic Recombination

13. Review of Mitosis and Meiosis http://www.pbs.org/wgbh/nova/miracle/divide.html

14. Genetic Drift: chance fixation of genes (alleles) in small populations (5/10 plants leave offspring) (2/10 plants leave offspring) Generation 3 Generation 2 Generation 1

15. Gene flow and reproductive isolating barriers Figure 13.3A, B

16. Gene flow • Gene flow = exchange of genes (alleles) between populations • In plants, occurs through the dispersal of pollen or fruits/seeds • Expected to occur between populations of the same species, but in plants also occurs between populations of different species (hybridization)

17. Usually measured in meters, but can occur over longer distances.

18. Gene flow • Gene flow within and between populations of a species tends to maintain the cohesiveness of a species • Lack of gene flow (due to reproductive isolating barriers) between populations is normally required for speciation to occur

19. Reproductive Isolating Barriers Pre-mating Ecological or habitat isolation Temporal isolation Behavioral isolation Post-mating Mechanical or physiological isolation Gametic isolation Post-zygotic Hybrid inviability Hybrid sterility Hybrid breakdown See Table 19.1

20. Habitat isolation Prairie Woodland White lady’s slipper Yellow lady’s slipper

21. Temporal Isolation Red = staminate plants Blue = carpellate plants

22. Behavioral Isolation: Adaptation to different pollinators Two species of orchids each with a different bee pollinator. The labellum may be a “key” innovation driving diversification.

23. Variation in the orchid labellum

24. Two species of Aquilegia (Ranunculaceae)

25. Habitat isolation & floral isolation Columbines (Aquilegia) in California Aquilegia formosa mesic sites < 3,050 m Aquilegia pubescens exposed, xeric sites > 2,750 m

26. Post-mating: Mechanical or physiological isolation

27. See Ch. 13: 574-576.

28. Beetle pollination is relatively unspecialized and probably ancestral for angiosperms.

29. Bee Pollination -showy, colorful (blue, purple, yellow) flowers -fragrant -day-flowering -bilateral landing platform -nectar and/or pollen rewards

30. Moth pollination -white or pale, usually large flowers -sweet, strong scent -nectar reward -no nectar guides but may have nectar spurs -night- or dusk-flowering

31. Yucca and the Yucca moth http://vimeo.com/7048122 Pistil-packing mama

32. Fly pollination -brown or maroon flowers -fetid odor (rotting meat) -day- or night-flowering -usually no reward -some operate as trap flowers

33. Bird pollination -brightly colored, often red flowers -no scent -day-flowering -usually copious nectar reward -often tubular corolla, often with an inferior ovary

34. Bat pollination -usually large, whitish or colorful flowers -musky, strong scent -night-flowering -usually copious nectar and/or pollen reward

35. Moraceae – The Fig and The Fig Wasp

36. Wind pollination -small, numerous often unisexual flowers with reduced or absent perianth -large quantities of pollen, individual grains smooth -feathery styles -no scent

37. Breeding Systems • Outcrossing = fertilization between different individuals; depends on ability to screen pollen by the stigma and style (incompatibility) • Uniparental reproduction • Self-fertilization (pollen from a flower fertilizes ovules of the same individual) • Agamospermy (production of seed without fertilization)

38. Breeding systems are not necessarily mutually exclusive! Later season, closed, self- pollinated flowers in Viola Early season, open, cross- pollinated flowers in Viola

39. http://www.youtube.com/watch?v=4YQ5q1cjEU4