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Speciation

Speciation. Process by which species originate Origin of diversity we observe in nature. Outline. Species concepts Species numbers through time What drives speciation? Two examples Discussion. Species Concepts. Typological Biological Evolutionary Genealogical Ecological Cohesive.

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Speciation

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  1. Speciation Process by which species originate Origin of diversity we observe in nature

  2. Outline • Species concepts • Species numbers through time • What drives speciation? Two examples • Discussion

  3. Species Concepts • Typological • Biological • Evolutionary • Genealogical • Ecological • Cohesive

  4. Typological Species Concept A species is a set of organisms that resemble one another and is distinct from other sets (Linnaeus) -Type • Do large differences in phenotypes always reflect large differences in relatedness among organisms? • How well are we able to discern small but significant differences?

  5. Biological Species Concept Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from each other (Mayr 1942; Dobzhansky 1935). • How do we evaluate “potentially interbreeding” for populations that are geographically separated? • How much reproductive isolation is needed? • How does this apply to asexual organisms?

  6. Evolutionary Species Concept A species is a single lineage of organisms that maintains its identity from other such lineages and has its own evolutionary tendencies and historical fate (Wiley 1978) • How much identity is needed? • How can the historical fate of a population be determined? • What criteria is used determine the “evolutionary tendency of a population?

  7. Genealogical Species Concept A species is the smallest monophyletic group of common ancestry (de Queiroz & Donoghue 1990). • Will a currently monophyletic “group” remain monophyletic? • Genetic polymorphisms can be shared for a long period of time, does this alone prevent speciation?

  8. Ecological Species Concept A species is a lineage that occupies a niche minimally different from that of any other lineage in its range and which evolves separately from all lineages outside its range (Van Valen 1976). • Might many different genotypes converge upon the phenotype allowing survival in this range? • How can it be known if a lineage will evolve separately in the future?

  9. Cohesion Species Concept “The most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic mechanisms (genetic and/or demographic exchangeability)” Templeton 1989.

  10. Increase in number of marine genera over time (Sepkoski 1997)

  11. Mimulus cardinalis and Mimulus lewisii: A case study of prezygotic isolation leading to speciation. Top: M. cardinalis Bottom: M. lewisii

  12. Mimulus cardinalis and Mimulus lewisii: A case study of prezygotic isolation leading to speciation. M. cardinalis-hummingbird pollinated, high in anthocyanins M. lewisii-bee polinated, low in anthocyanin and carotenoid pigments Top: M. cardinalis Bottom: M. lewisii

  13. Mimulus relationships

  14. M. lewisii (A), an F1 hybrid (B), M. cardinalis (C), and examples of variation in floral traits found in F2 hybrids (D–L). Schemske and Bradshaw PNAS October 12, 1999 vol. 96 no. 21 p11911

  15. Results from Mimulus Studies • Pollinators of the two species have strict fidelity • 99.915% occurrence of parental M. lewisii and • M. cardinalis in seeds collected from a • sympatric population in the Sierra Nevada • Floral traits associated with pollination are under relatively simple control • Adaptive shift in pollinator preference may be initiated by a single major mutation in the YUP allele

  16. Effects of YUP allele substitution M. lewisii NIL’s with the M. cardinalis yup allele had yellow-orange flowers and received 68 times more hummingbird visits than wild type M. cardinalis NIL’s with the M. lewisii yup allele had dark pink flowers and received 74 times more bee visits than wild type • a, b, M. lewisii; c, d, M. cardinalis.The wild-type allele at the YUP locus (a, c) has been substituted by introgression with the allele from the other species (b, d). Flowers in each NIL pair (a and b, c and d) are full siblings.

  17. Bradshaw and Schemske Nature 2003

  18. Feeding behavior driving morphological differences • Differential expression of the gene Bmp4 accounts for big morphological differences • Micro- vs Macroevolution different mechanisms or different scales? Top: Metriaclima zebra Bottom: Labeotropheus fuelleborni

  19. Quagga: the missing link Quagga (Equus quagga quagga) in Londoner Zoo, 1870

  20. Progression?

  21. Questions • What defines a species? • Are there clear examples of Macroevolution? • Is the species concept equivocal across all taxa? (are evolutionary processes similar across taxa?) • Why is it that the issue of formation of new species is so contentious (and so important to demonstrate and elucidate)?

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