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Start by doing whats necessary, then whats possible and suddenly you are doing the impossible' St' F

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A species is a group of potentially interbreeding animals (a gene pool) ... Hypothetical-- No definite examples in wild animal populations. Gametic isolation ... – PowerPoint PPT presentation

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Title: Start by doing whats necessary, then whats possible and suddenly you are doing the impossible' St' F


1
Start by doing whats necessary, then whats
possible and suddenly you are doing the
impossible.-St. Francis of Assisi
Linnaeus
2
Speciation Concepts
3
What is a species?
  • Latin for type
  • Biologists agree that a species is a fundamental,
    natural unit
  • Biologists do NOT agree on what the exact
    definition of the word species is
  • 2 main definitions morphological and biological

4
Phenetic species concept
  • Based on physical traits alone
  • Example the red-tailed hawk, Buteo jamaicensis,
    is a large brown hawk with a brick red tail

5
red-tailed hawk (Buteo jamaicensis)
6
But what if 2 red-tailed hawks were to mate, and
the offspring looked like this bird?
Is this individual also a Buteo jamaicensis? Or
is it a new species?
7
Problems with morphological species concept
  • Doesnt account for individual or geographic
    variation
  • There should be more to being a species than
    appearance alone
  • Do these species exist in reality, or just in our
    minds?

8
Biological Species Concept
  • Ernst Mayr 1942
  • Most widely accepted definition
  • A species is a group of potentially interbreeding
    animals (a gene pool)
  • Must produce fertile offspring
  • Individuals do not interbreed with other species

9
Phenetic and biological species are not the same
Drosophila pseudoobscura
Drosophila persimilis
Look identical but will not interbreed if kept
together
10
Why dont similar-looking species living in the
same area breed?
  • The integrity of a species is maintained by
    reproductive isolating mechanisms
  • Categorized according to when they affect
    reproduction (before or after mating)
  • Premating mechanisms prevent mating in the first
    place
  • Postmating mechanisms reduce the chance of
    survival of any offspring

11
Premating mechanisms
  • Behavioral isolation
  • Seasonal isolation
  • Habitat isolation
  • Mechanical isolation
  • Gametic isolation
  • Isolation by different pollinators (in plants
    only)

12
Behavioral Isolation
  • Prevents mating in the first place
  • Many animals have important behavioral components
    of courtship and mating, such as songs, displays
    and rituals

black skimmers Rynchops niger
13
least flycatcher Empidonax minimus
acadian flycatcher Empidonax virescens
Look very similar but have different songs
14
Seasonal isolation
  • Species breed at slightly different times of the
    year
  • Fowlers emerges from hibernation after American
    toads have finished breeding

Fowlers toad Bufo woodhouseii fowleri
American toad Bufo americanus
15
Habitat isolation
  • 2 species live in the same area, but occupy
    slightly different habitats
  • Warblers forage in different parts of tree canopy

16
Mechanical isolation
  • 2 species cant physically accomplish mating for
    some anatomical reason
  • Hypothetical-- No definite examples in wild
    animal populations

17
Gametic isolation
  • Egg and sperm will not form a zygote

18
Postmating reproductive isolating mechanisms
  • Hybrid inviability
  • Hybrid sterility
  • Hybrid breakdown

The offspring that results from the mating of 2
different species is a hybrid
19
Hybrid sterility
  • Hybrid is healthy, but cant produce young of its
    own
  • Mules are the sterile offspring of horses and
    donkeys

20
Hybrid inviability
  • Hybrid cant live or has a low chance of survival
  • Female deer mice x male beach mice produce very
    small offspring
  • In the reciprocal cross, the offspring are
    oversized and typically die before birth.

deer mouse Peromyscus maniculatus
beach mouse Peromyscus polionotus
21
Haldanes Rule
  • When the hybrids of one sex are affected
    negatively, while hybrids of the opposite sex are
    healthy
  • The negatively affected sex will almost always be
    the male
  • No one is 100 sure why this rule is true

22
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23
Hybrid breakdown
  • Hybrid is healthy, but its offspring dont live
    or are sterile

24
Speciationthe forming of new species
25
How were new species formed in the first place?
  • Darwin called this the mystery of mysteries
  • Humans have never created a new species of animal
    in the laboratory (plants, yes)
  • Theories based on attempts to reconstruct the
    evolutionary history of species based on
    available evidence

26
2 species could become reproductively isolated
  • A species usually consists of a number of
    discrete, separate populations
  • Genetic information is usually exchanged, at
    least occasionally, between populations. This is
    called gene flow
  • If gene flow is interrupted, reproductive
    isolating mechanisms can arise

27
3 ways gene flow could be interrupted and lead to
the splitting of the species into 2
  • Allopatric speciation
  • Parapatric speciation
  • Sympatric speciation

28
Allopatric Speciation
  • allo other, patric homeland
  • Populations become geographically isolated
  • A barrier forms, separating 2 or more groups
  • Isolating mechanisms arise over time
  • The one species has become 2
  • If the barrier is removed before the isolating
    mechanism works, gene flow may be reestablished

29
Evidence for allopatric speciation
  • Geographic variation within individual species
    exists today
  • Species for which this scenario could have taken
    place exist today
  • In the laboratory at least 11 cases of fruitfly
    species developed isolating mechanisms
  • Wild fruitfly species have stronger isolating
    mechanisms in regions where they co-occur than
    where each lives in isolation

30
Variation within a species
  • Bergmans Rule
  • the further north you go the larger the animals
    in a given species
  • Allen's Rule
  • the further north you go the darker the color of
    animals in a given species

31
Individual variation in corn snake (Elaphe
guttata)
32
Desert pupfishgeographical isolation
33
Florida and Western Scrub Jaysperipheral
populations
34
Parapatric speciation
  • para next to, patric homeland
  • Could occur when populations are distributed
    along an environmental gradient (dry to moist,
    hot to cold, etc.)
  • Different characteristics may be favored at
    differing points along the gradient, gradually
    producing larger differences among populations
    until a new species is formed

35
Sympatric speciation
  • sym same, patric homeland
  • A species could split without any separation of
    its geographic range
  • Controversial theorymany biologists dont
    believe it is possible
  • Might have occurred in green lacewings and
    3-spined sticklebacks

36
Sympatric speciation?
  • 2 sympatric species, one dark green all year, the
    other light green in spring, brown in fall
  • Dark green species lives in conifer trees
  • Light green lives in fields
  • In the lab can produce a hybrid that is
    intermediate in color
  • No evidence the 2 were ever allopatric

green lacewing (Chrysopaerla sp.)
37
Sympatric speciation?
  • 2 species in each of 5 different lakes in British
    Columbia
  • 1 species lives in littoral zone, the other
    benthic
  • From different lakes, benthic will breed with
    benthic, littoral with littoral
  • Thought to have split from one
  • sympatric species in all 5 lakes

3-spined stickleback (Gasterosteus sp.)
38
Changes in chromosomes
  • A mutation could affect the chromosomes,
    preventing successful mating and resulting in new
    species
  • Humans have 46 chromosomes, gorillas, chimpanzees
    and orangutans have 48

39
Endemic speciesthe founder effect
  • Certain species are found only on an islands
  • A few individuals (founders) may have come to
    the island from the mainland
  • A new species arises due to smaller gene pool

40
Vocabulary
  • Species
  • Speciation
  • Ring species
  • Biological species concept
  • Reproductive isolating mechanism
  • Gamete
  • Zygote
  • Chromosome
  • gradient
  • Hybrid
  • Inviable
  • sterile
  • Haldanes rule
  • Bergmans rule
  • Allens rule
  • Peripheral
  • Allopatric
  • Sympatric
  • Parapatric
  • Endemic
  • Founder effect
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