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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

Speciation

Process by which species originate

Origin of diversity we observe in nature

outline
Outline
  • Species concepts
  • Species numbers through time
  • What drives speciation? Two examples
  • Discussion
species concepts
Species Concepts
  • Typological
  • Biological
  • Evolutionary
  • Genealogical
  • Ecological
  • Cohesive
typological species concept
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?

biological species concept

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?
evolutionary species concept
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?

genealogical species concept
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?

ecological species concept

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?

cohesion species concept

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.

mimulus cardinalis and mimulus lewisii a case study of prezygotic isolation leading to speciation

Mimulus cardinalis and Mimulus lewisii: A case study of prezygotic isolation leading to speciation.

Top: M. cardinalis Bottom: M. lewisii

mimulus cardinalis and mimulus lewisii a case study of prezygotic isolation leading to speciation12

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

slide14

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

results from mimulus studies
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
effects of yup allele substitution
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.
feeding behavior driving morphological differences
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

quagga the missing link
Quagga: the missing link

Quagga (Equus quagga quagga) in Londoner Zoo, 1870

questions
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)?