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Divergent Evolution in the Ferns

Divergent Evolution in the Ferns. Botany 209 16 March, 2010. DIVERGENT SPECIATION in the FERNS. Incomplete divergence (versus secondary contact) in Athyrium filix-femina Allopatric speciation in Polypodium Peripatric speciation in Pleopeltis

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Divergent Evolution in the Ferns

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  1. Divergent Evolution in the Ferns Botany 209 16 March, 2010

  2. DIVERGENT SPECIATION in the FERNS Incomplete divergence (versus secondary contact) in Athyrium filix-femina Allopatric speciation in Polypodium Peripatric speciation in Pleopeltis Species limits and speciation in Asplenium nidus

  3. Phylogeny of Isoetes species based on ITS sequence data

  4. Kelloff et al. 2002. Differentiation of eastern North American Athyrium filix-femina taxa: evidence from allozymes and spores. Amer. • Fern Journal 92:185-213.

  5. Athyrium filix-femina subsp. angustum Athyrium filix-femina subsp. asplenioides

  6. Characterangustumasplenioides Rhizome habit erect or ascending ascending or creeping Leaf shape tapered at base barely tapered at base Spore color yellowish brownish-yellow to black Spore surface features sparsely papillate wrinkled or reticulated

  7. A. f.-f. subsp. angustum A. f.-f. subsp. asplenioides

  8. Isozyme Results At the four most polymorphic loci (Idh-1, Pgm-2, Pgi-2, and Tpi-2) population allele frequencies were quite similar within taxon, but quite different between taxa.

  9. DIVERGENT SPECIATION in the FERNS Incomplete divergence (versus secondary contact) in Athyrium filix-femina Allopatric speciation in Polypodium Peripatric speciation in Pleopeltis Species limits and speciation in Asplenium nidus

  10. Lisa Andrews Hooper Chris Haufler • Haufler, C. H., E. A. Hooper, and J. P. Therrien. 2000. • Modes and mechanisms of speciation in pteridophytes: • implications of contrasting patterns in ferns representing • temperate and tropical habitats. Plant Species Biology 15: 223- 236.

  11. Polypodium sibiricum (2x) Polypodium appalachianum (2x) Polypodium amorphum (2x) Polypodium virginianum (4x)

  12. Mean genetic identity between species = 0.460

  13. Haufler’s divergence scenario for Polypodium: • P. sibiricum occurs in glaciated regions. Perhaps, like other boreal taxa, P. sibiricum populations migrated south in advance of the ice sheet. • Following retreat of the ice, populations returned to their northern haunts, but perhaps some populations persisted in the mountains of eastern and western North America. Isolation and divergence perhaps led to speciation of P. amorphum in the west and P. appalachianum in the east.

  14. The low I values for the three species suggest that these events did not take place in the most recent ice age. In fact, secondary contact following southerly migration of P. sibiricum during more recent episodes of glaciation may have initiated both P. virginianum and P. saximontanum, a western tetraploid.

  15. The mode of speciation in the P. sibiricum complex is thus fits the classic allopatric model.

  16. DIVERGENT SPECIATION in the FERNS Incomplete divergence (versus secondary contact) in Athyrium filix-femina Allopatric speciation in Polypodium Peripatric speciation in Pleopeltis Species limits and speciation in Asplenium nidus

  17. So why the low identities among congeneric • species in the ferns? • One possibility is that they diverged long ago. • Another is that, in the absence of pre-zygotic isolating mechanisms (pollination biology, pollen-stigma interactions, different flowering times, etc.) to maintain barriers between species, there may be strong selection for the evolution of post-zygotic isolating mechanisms.

  18. Pleopeltis sp.

  19. Pleopeltis polypodioides

  20. Mean genetic identity between species = 0.849

  21. Why the difference? Perhaps the mode of speciation here is peripatric, including peripheral isolation and rapid adaptation to differing habitats.

  22. The greater complexity of tropical habitats may provide increased opportunities for ecological isolation and speciation.

  23. DIVERGENT SPECIATION in the FERNS Incomplete divergence (versus secondary contact) in Athyrium filix-femina Allopatric speciation in Polypodium Peripatric speciation in Pleopeltis Species limits and speciation in Asplenium nidus

  24. Yatabe on the Asplenium nidus complex Yoko Yatabe with Kato and Gong Wu su. China 2001

  25. Yatabe on the Asplenium nidus complex Yatabe et al. 2009

  26. Yatabe on the Asplenium nidus complex Yatabe et al. 2009

  27. Yatabe on the Asplenium nidus complex Yatabe et al. 2009

  28. Yatabe on the Asplenium nidus complex Yatabe et al. 2009

  29. Yatabe on the Asplenium nidus complex Yatabe et al. 2009

  30. Yatabe on the Asplenium nidus complex Yatabe et al. 2009

  31. Yatabe on the Asplenium nidus complex Yatabe et al. 2009

  32. DIVERGENT SPECIATION in the FERNS Incomplete divergence (versus secondary contact) in Athyrium filix-femina Allopatric speciation in Polypodium Peripatric speciation in Pleopeltis Species limits and speciation in Asplenium nidus

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