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Integrative taxonomy

Integrative taxonomy. Gustav Paulay Florida Museum of Natural History University of Florida. BSC and ESU. Biological species concept No gene flow Independent evolutionary tracks Reproductive isolation Tested experimentally or sympatric Evolutionary Significant Unit No gene flow

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Integrative taxonomy

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  1. Integrative taxonomy Gustav Paulay Florida Museum of Natural History University of Florida

  2. BSC and ESU • Biological species concept • No gene flow • Independent evolutionary tracks • Reproductive isolation • Tested experimentally or sympatric • Evolutionary Significant Unit • No gene flow • Independent evolutionary tracks • Untested for reproductive isolation, allopatric

  3. Speciation • Formation of species • Requires isolation of two populations leading to no/little mating between them • Leads to divergence of populations • Divergence of genotype • Mutations – changes in DNA • Fixation of mutations: • Genetic drift or selection • Mutations accumulate • interbreeding becomes impossible • or leads to poor hybrids • speciation

  4. ESU:demonstrate lack of gene flow • Defined as reciprocally monophyletic populations • i.e. fixed for different traits

  5. ESU:demonstrate lack of gene flow • Reciprocally monophyletic in at least independent 2 traits

  6. ESU: 2 independent traits • Any two independent traits w/ genetic basis • Morphological characters • Genetic characters • Independent loci (mtDNA – all one) • Geography • Any combination of these

  7. Integrative taxonomy • Use of multiple lines of evidence • Field - museum - lab • Ecology - behavior - morphology - genetics - geography • Distinguishing between morphs and species • Two or more independent characters showing distinction between species

  8. Integrative taxonomy:Actinopyga mauritiana - guamensis

  9. Two major types of challenges • Not seeing species where there are • Seeing species where there aren’t • Cause: rate of evolution varies among traits • phenotype: morphology, behavior, color pattern... • genotype: sequence divergence • reproductive isolation

  10. Not seeing species where there are • unequal rates of evolution • phenotype divergence - SLOW • sequence divergence • reproductive isolation • cryptic species

  11. Cukes vs. primates • Different foci for sensory perception • Humans – visual cues • Cukes - chemical cues • Do cukes care about each other’s colors or ossicles when meeting?

  12. Supposed distribution of Scutellastra flexuosa and exusta Powell, 1968

  13. but what is really going on... NJ K2P COI

  14. Synapta maculata

  15. Not seeing species where there are • unequal rates of evolution • phenotype divergence • sequence divergence • reproductive isolation - FAST

  16. Actinopyga obesa complex

  17. Echinometra mathaei complex Rapid secondary sympatryFacilitated by rapid evolution of fertilization proteins? ~1 Ma COI Bindin Bindin COI Landry et al. 2003 Proc Roy Soc

  18. Seeing species where there aren’t • ecophenotypic variation • ontogenetic variation • geographic variation • ecological variation - depth, habitat, etc • polymorphism • paralogous loci • former divergence now united

  19. Polymorphism / phenotypic variation

  20. Paralogous loci:mitochondrial genes gone nuclear in Alpheus Williams & Knowlton 2001 Mol Biol Evol

  21. ESU vs. BS • Need demonstration of no possibility for reuniting into one species • No problem when sympatric as gene flow is tested • Can’t assume reproductively isolated in allopatry • need test experimentally – mating essays

  22. Cypraea tigris a species differentiated, then united • 15% divergence in COI • Type A – Indian only • Type B – mostly Pacific • some Indian • A and B in Indian identical in all other characters

  23. BS test – marginal overlap

  24. ESU - reciprocal monophyly • DNA - gene flow - BSC • reciprocal monophyly implies lack of recent genetic connections • need several samples of each form to test • reliability of conclusion depends on depth of intra- vs. inter-specific variation • in sympatry - separate biological species • in allopatry - separate ESUs, species status subjective

  25. Where are the species limits?

  26. Lack of reciprocal monophyly • morphs rather than species • distinct species, but: • introgression • insufficient time for sorting • deep coalescent • rapid speciation

  27. Introgression in Astralium

  28. Introgression in Bohadschia argus? • Unusual form only in W Pacific; never seen in Polynesia, etc. • Need compare independent markers to test

  29. Insufficient time for sortingGene trees vs. species trees:coalescence theory Avise 1999 Phylogeography

  30. Evolution of reproductive isolation • Slow • most gastropod • deep divergence among allopatric ESUs • clear reciprocal monophyly • slow to secondary sympatry / biological species • Rapid • echinoids, holothuroids • shallow divergence among sympatric species • potential paraphyletic species • rapid to secondary sympatry / biological species

  31. Astralium rhodostomum complex • Two deeply divergent clades: A & B sympatric on 8 island groups • 30 ESUs so far • Pigmentation separates major and minor clades.

  32. Persistence of allopatry - Cypraeidae 94% divergences < 10 Ma retain allopatry (115 of 122) 94% divergences < 10 Ma retain signal (115 of 122) Geographic signal no signal

  33. Echinometra mathaei complex Rapid secondary sympatryFacilitated by rapid evolution of fertilization proteins? ~1 Ma COI Bindin Bindin COI Landry et al. 2003 Proc Roy Soc

  34. Stichopus variegatus complex

  35. Advantages of sequence data • Directly test genetic connections • Very large number of characters • Independent markers - independent sources • “Independent” of morphology - so can trace evolution of form, etc on gene tree without circularity

  36. Potential problems with sequence data • depth of coalescent vs. interspecific divergence • paralogous sequences • introgression • selective sweeps • homogenization through drift

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