V. SPECIATION A. Allopatric Speciation B. Parapatric Speciation

1. V. SPECIATION A. Allopatric Speciation B. Parapatric Speciation (aka Local or Progenitor - Derivative) C. Adaptive Radiation D. Sympatric Speciation [Polyploidy]

2. A. Allopatric Speciation “different homes” 1. subdivision a. geographic isolation -- non-biological b. extinction of intermediate pops. c. result: NO GENE FLOW

3. 2. gradual accumulation of mutations 3. genetic divergence over time 4. reproductive isolation [follows divergence] BUT…  5. intercontinental disjunct congeners in plants are fertile! e.g. Datisca, Platanus, Magnolia, Liriodendron, etc.

4. Platanus P. orientalis SW Asia P. occidentalis SE USA P. × acerifolia

5. Datisca glomerata California Datisca cannabina SW Asia

6. Nei’s genetic identity = 0.142

7. Molecular Clocks I.Molecular divergence is positively correlated with time (Zuckerkandl & Pauling, 1965) A. difficult with protein data – not neutral B. today there is abundant DNA data, but the “accuracy” of molecular clocks is questionable e.g. Hillis et al. 1996, Molecular Systematics p. 531-541 r = K / 2T r = rate for neutral mutations T = divergence time K = number of substitutions per site

8. II. Clock Calibrations “the Achilles heal” • Estimates of T are never precise, • subject to under and overestimates • 1.volcanic islands • e.g. Hawaii, Canary Islands • 2.biogeographic reconstruction • a. Gondwanan and Laurasian distributions • b. 2-25 mya estimates for 12 E. Asian- E. N. Am. disjuncts see Wen ARES 30:421-55, 1999 • c. long distance dispersal is always a possibility

9. 3. Fossils a. relationship to extant taxa uncertain b. no unequivocal fossil DNA c. DNA degradation confounds mutation rate estimates III. Model-based approaches 1. see Sanderson, 1998 (Mol. Syst. Plants 2) for an introduction 2. take into account the stochasticity of divergence estimates, and imprecision of time estimates

10. B. Local Speciation (Progenitor - Derivative) Parapatric Speciation 1. isolation a. migration b. long distance dispersal c. peripheral population

11. 2. genetic bottlenecks a. population reduction b. increased inbreeding & genetic drift c. adaptation ?? maybe, maybe not i.e. selection pressure could cause the fixation of genetic differences, but so might random events 3. examples of adaptation: a. edaphic endemics [serpentine, limestone, heavy metals] b. pollinators

12. 4. fixation of mutations between populations a. with or without reproductive isolation b. faster than allopatry c. reduced genetic diversity in derivative d. relatively high genetic identity betw. progenitor & derivative

13. 5. Chromosomal Rearrangements a. rearrangement established [e.g. translocation] b. hybrid sterility ex. Clarkia species (H. Lewis; L. Gottlieb)

15. 6. Mating System Change a. self-compatibility arising from self-incompatibility e.g. Stephanomeria malheurensis Oregon endemic, described in 1975

17. C. Adaptive Radiation 1. open habitats 2. little competition 3. radiation into new ecological niches - 4. often w/o genetic reproductive isolation 5. generally w/o much genetic divergence 6. can result in a “star phylogeny”

18. Hawaiian tarweed adaptive radiation

19. Rapid diversification, inferred from short branches & unresolved polytomy