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Speciation. The How and Why of Species. What is a Species?. A species is one or more populations of organisms with the potential to interbreed with one another but NOT with members of other such groups naturally. . “But… What about the liger?” We’ll get there. I promise!.

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speciation

Speciation

The How and Why of Species

what is a species
What is a Species?

A species is one or more populations of organisms with the potential to interbreed with one another but NOT with members of other such groups naturally.

“But… What about the liger?”

We’ll get there. I promise!

biological species concept
Biological Species Concept
  • Proposed by Ernst Mayr who said:
    • “Species are groups of interbreeding natural populations that are reproductively isolated from other such groups."
  • Explains why the members of a species resemble one another and differ from other species.
    • Breeding organisms pass genes to offspring
    • By contrast, genes are not transferred to other species, and different species therefore look different
  • Has some fallacies: asexual organisms, hybrids, ring species, chronospecies
slide5

What Leads

to New Species?

what leads to new species
What leads to New Species?
  • Diversifying or Directional Selection can lead to new species.
    • More on this later!
  • When differences between subpopulations become large enough that gene flow between them may stop.
reproductive isolating mechanisms8
Reproductive Isolating Mechanisms
  • Prezygotic Barriers
    • Geographic Isolation
    • Ecological Isolation.
    • Temporal(Time) Isolation
    • Behavioral Isolation
    • Mechanical Isolation
    • Gametic Isolation
reproductive isolating mechanisms9
Reproductive Isolating Mechanisms
  • Postzygotic Barriers
    • Reduced Hybrid Viability
    • Reduced Hybrid Fertility
    • Hybrid Breakdown
allopatric speciation
Allopatric Speciation
  • New species arise as a result of geographic isolation
  • Allopatric means “different homelands”
sympatric speciation15
Sympatric Speciation
  • Two subpopulations become reproductively isolated within the same geographic area.
  • First proposed by Darwin in the 1850s.
rate of speciation17
Rate of Speciation
  • Often can take millions of years, but can occasionally occur faster.
    • Banana trees  moth species
  • Gradualism
  • Punctuated equilibrium
and now those hybrids19
And Now, Those Hybrids…
  • Ligers – hybrid between lions and tigers
  • Zebroids – hybrid between horses and zebras
  • Cama – hybrid between a camel and a llama (artificial insemination)
  • Wolphin - bottlenose dolphin and a false killer whale
  • Remember, most of these hybrids are sterile and cannot reproduce with each other.