Download Speciation

L5: 5-5
Speciation
Background:
 Microevolution: changes confined to a single gene pool
 Macroevolution: change above a species level
(Ex. dinosaurs
birds)
 Species: interbreeding population producing viable,
fertile offspring.
• Subspecies: a division within a species; members of
the subspecies are individual enough that they cannot
be lumped together, but they are not so distinct that
they are entirely different species. Different subspecies of the same species are capable of
interbreeding and producing fertile offspring.
 Example: the domestic dog, Canis lupus
familiaris, the wolf Canis lupus lupus, or the
dingo, Canis lupus dingo.
• All of these animals can interbreed, but they are
morphologically distinct, and they lead very
different lives.
 Some argue that subspecies arise during the process
of speciation = formation of a new species.
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L5: 5-5
 Before discussing mechanisms of speciation, what keeps
different species from interbreeding and/or producing
fertile offspring in the first place (Isolating
mechanisms)?
 Reproductive Isolation: biological factors that inhibit
the production of viable (fertile) offspring between 2
different species.
a. Pre-zygotic barriers = “before zygote”
formation; before fertilization
• geographical: separation in space
• ecological (habitat): separation in habitat or niche
• temporal: e.g. : habitats overlap but there are
different mating or fertility times
• behavioral: e.g. : divergent mating signals, mating
colors, dances, pheromones
• mechanical: e.g. : incompatible copulatory organs
or gametes, ploidy
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b. Post-zygotic barriers = “after zygote” formation;
after fertilization
• infertility of offspring
• failure of hybrid zygote formation or
development
- chromosomes can't function together in
development
 Mechanisms for SPECIATION
 Microevolutionary level
1. Mutation
2. Allopatric speciation (geographic isolation)
• Geographic isolation depends on organisms’ ability
to move.
a. With geographical remodeling – habitat is altered in
such a way that individuals cannot interbreed based
on new geographical regions.
- Ex. river re-formation, mountain reformation due to glaciation, body of water
shrinking into two smaller bodies of water.
b. Without geographical remodeling
- Ex. re-colonization to a remote area;
decedents are geographically isolated from
parent population. (Galapagos = genetic
drift = founder effect can lead to
speciation)
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L5: 5-5
3. Sympatric speciation (reproductive barriers within
overlapping geographical areas)
a. Chromosomal changes (NS, genetic drift, mutation)
b. Non-random mating (selection)
c. Reproductive isolation (pre or postzygotic)
d. Switch of habitat (competition)
e. Food source (competition)
 Macroevolutionary level:
4. Adaptive Radiation (allopatrically or sympatrically)
• Environmental changes cause lots of extinction
with few survivors
• Opens up new niches for remaining survivors
• Natural Selection and genetic drift effects
• Many different species (from original populations)
form during same time frame.
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L5: 5-5
 Time frame of speciation:
 Gradualism (Hutton): slow, gradual evolutionary change
- biochemical
- geography
 Punctuated equilibrium: spurts of relatively rapid
change interspersed with periods of little change.
- Periods with apparent little changes in
physiology (biochemical) and behavior cannot be
detected by fossil record.
- These times of stasis in the fossil record will
be broken up by visible, abrupt (punctuated)
changes in the fossil record)
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L5: 5-5
Teacher: Examples of reproductive isolation barriers
PRE-ZYGOTIC
 Geographical:
 Ecological (habitat):
- Northern Flycatcher (bird)
• Open woods and farmland
• Beech trees
• Alder trees
• Conifers
• Willowy trees
- Garter snakes
• Water
• terrestial



Temporal
- Wood and leopard frogs = specific time of season for mating
- North America = western spotted skunk & eastern spotted skunk
Behavioral
- Wood and Leopard frogs = different mating calls specific to each species
- Most birds and their mating calls
Mechanical
- Black Sage and White Sage
• Reproductive components are structurally different
• Different insect pollinate each
- Gametes incompatible in aquatic species that release gametes into water
- Male and female copulatory organs don’t match up
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