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Speciation

Speciation. The actual “origin of species” Reduction in gene flow, genetic and phenotypic change in populations The study of speciation requires that species be real. Speciation. Speciation is the antidote to sex Keeps together adaptive groups of traits New species most often uniparental

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Speciation

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  1. Speciation • The actual “origin of species” • Reduction in gene flow, genetic and phenotypic change in populations • The study of speciation requires that species be real

  2. Speciation • Speciation is the antidote to sex • Keeps together adaptive groups of traits • New species most often uniparental • Phylogeny is genealogy of species • Branching tree

  3. Hybridization • Mules • Fertile interspecific hybrids are common in perennial plants

  4. Hybrid speciation • New species form from interspecific hybrids • Two parents • Phylogenetic pattern is reticulate • Enough examples to make it interesting • Not enough to disrupt the generally divergent pattern of phylogeny

  5. Alloploidy • Chromosome doubling (unreduced gametes or somatic doubling) • Alloploid effectively has one diploid set from each parent species • Instant Speciation™

  6. Homoploid hybrid speciation • No chromosome doubling • Two theoretical modes, both documented • Recombinational speciation • Speciation with external barriers

  7. Recombinational speciation • F1s of reduced fertility, chromosome differences • F2s more fertile than backcrosses • Fertility restored in new species by recombination of chromosome segments

  8. Speciation with external barriers • F1s not of reduced fertility • Few or no chromosomal differences between parents • Formation of backcrosses reduced by external barriers

  9. A long time ago, in a desert close at hand…

  10. So what’s an Encelia? • Asteraceae (sunflower family) • Mostly shrubs • Dry habitats, mostly deserts • Brittlebush (E. farinosa)

  11. A hybrid under every bush • “The bushes are hybrids” • All species are interfertile • No apparent reduction of fertility in F1, F2, backcross • Is it a syngameon?

  12. Spontaneous natural hybrids • E. farinosa× E. frutescens • E. farinosa× E. californica • E. farinosa× E. palmeri • E. farinosa× E. halimifolia • E. californica× E. asperifolia • E. ventorum× E. palmeri • E. ventorum× E. asperifolia • E. virginensis× E. frutescens • E. actoni× E. frutescens

  13. Encelia×laciniata • Named as a species • Hybrids between E. ventorum and E. palmeri • Selection against recombinants

  14. Phylogeny: always a good place to start • The days of cladistics before DNA • Two well-defined clades (californica clade and frutescens clade) • Relationships within clades less clear

  15. Not just morphology—phenotype • Standard morphology of heads, capitulescences, leaves • Micromorphology, especially trichomes • Secondary chemistry • Ultraviolet floral patterns • Anatomy of stems and leaves (petioles turned out to be useful) • More that I’ve probably forgotten

  16. Cladograms based on phenotype

  17. DNA sequence analysis • ITS (internal transcribed spacer of ribosomal DNA) • DNA doesn’t work so well for closely related species • Hybridization is more likely to be confusing in DNA sequence analysis than in morphological analysis

  18. Identifying species of hybrid origin • Species of hybrid origin not always intermediate between parents • Species of intermediate morphology not always of hybrid origin

  19. Preponderance of evidence • Intermediate morphology • Agreement with F1s • Apomorphies shared with parents

  20. Species of hybrid origin E. virginensis(parents: E. actoni and E. frutescenssubsp.frutescens) E. asperifolia(parents: E. californica and E. frutescenssubsp. glandulosa)

  21. Enceliavirginensis

  22. E. virginensis E. actoni E. frutescens

  23. Shared phenotypic apomorphies – E. virginensis • With E. frutescens • broad multicellular-based hairs • With E. actoni • none(E. actoni has no clear autapomorphies, but E. virginensis resembles it morphologically)

  24. Agreement with F1

  25. length of petiole • width of leaf • height of head • width of head • pedicel width • number of rays • length of ray • length of leaf

  26. Research by GeryAllan

  27. Chimeric ITS: E. virginensis (13 base difference)

  28. Enceliaasperifolia

  29. E. californica E. frutescens subsp. glandulosa E. asperifolia

  30. Shared phenotypic apomorphies– E. asperifolia • With E. frutescens • broad multicellular-based hairs • no benzopyrans or benzofurans • yellow stigmas • With E. californica • UV-reflective ray corollas • brown disk corollas • moniliform hairs

  31. RAPD data: E. asperifolia • Shared with E. californica • UBC 218 (0.8 kbase,1.6 kbase) • UBC 382 (1.4 kbase) • UBC 409 (0.5 kbase) • UBC 478 (1.4 kbase) • Operon B8 (0.75 kbase) • Shared with E. frutescens • UBC 149 (0.7 kbase) • UBC 375 (1.0 kbase)

  32. Chimeric ITS: E. asperifolia (21 base difference)

  33. Hybrid speciation by external barriers • E. ×laciniataprovides a model

  34. Conclusion • I’m done • What are the traits that adapt the new species to their new habitats? • Are there transgressive traits? • Plenty of other plant genera

  35. Acknowledgments Allan, Gery J. Axelrod, Daniel Braden, Gerald Bryant, Stephen Budzikiewicz, Herbert Carpenter, Kevin J. Charest, Nancy A. Clark, Emily Ehleringer, James R. Harrington, Daniel F. Isman, Murray B. Kinney, Michael Koukol, Scott R. Kyhos, Donald W. Lahmeyer, Sean C. Laufenberg, Gabriela Lee, Gregory J. Maepo, Linda Miller, David Nishida, Joy H. Panero, José Parra, Mima Patterson, Mark Politt, Ursula Proksch, Peter Rieseberg, Loren Rodriguez, Eloy Saccoman, Stephanie Sanders, Donald L. Schilling, Edward Thompson, William C. Weiler, Jeff Weisman, Kathy Wisdom, Charles Wollenweber, Eckhard Wray, Victor

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