Download Speciation

Review
 All populations of species have within them genetic
variation that results in qualitative and quantitative
differences in phenotype
 Environments cycle through periods of stasis and
flux
 Organisms best suited to compete for available
resources produce the most viable offspring
What are the sources of variation?
 Mutations in genes
 Recombination of alleles during
meiosis (crossing over)
 Orientation of homologous
chromosomes during metaphase I
 Fertilization (one sperm and egg
out of many variations)
What causes the change of variation (allele frequency) within
a population?
 Mutations
 Gene flow (immigration)
 Nonrandom mating
 Genetic drift (founder and
bottleneck effects)
 Selection (artificial and natural)
The Origin of Species
Mom, Dad…
There’s something
you need to know…
I’m a MAMMAL!
“That mystery of mysteries…”
Darwin never actually tackled how
new species arose…
Both in space and time,
we seem to be brought
somewhat near to that great fact
—that mystery of mysteries—
the first appearance of
new beings on this Earth.
So…what is a species?
 Biological species concept
 population whose members can interbreed & produce
viable, fertile offspring
 reproductively compatible
Distinct species:
songs & behaviors are different
enough to prevent interbreeding
Eastern Meadowlark Western Meadowlark
How and why do new species originate?
 Species are created by a series of evolutionary
processes

populations become isolated
geographically isolated
 reproductively isolated


isolated populations
evolve independently
 Isolation
 allopatric


geographic separation
sympatric

still live in same area
Speciation
 The process by which a new species is formed from a
related preexisting species
 The development of a new branch on the tree of life
 The formation of a new and isolated gene pool
Begin class by working on
speciation vocabulary
assignment for 10 minutes
Please do so QUIETLY
Hardy-Weinberg Equilibrium
 Assume a population of monkeys living on an island is in
Hardy-Weinberg equilibrium

No mutations, large population size, no gene flow, no genetic
drift, no natural selection.
 This means that the allele frequencies of the gene pool does
not change from one generation to the next.
1=p2 +2pq + q2
If 25% of the monkeys exhibit the dominant trait of black fur,
and there are 200 monkeys in the population, how many of
have a heterozygous genotype?
Factors the affect variation within a population
(Changes allele frequency in a gene pool)
Reduces
Variation
Increases
Variation
 Mutations
 Immigration
 Independent Assortment
 Bottleneck Effect
 Natural Selection
 Random Fertilization
 Emmigration
 Non-random Mating
In your notes, fill in the t-chart
above with the terms listed to the
right
 Crossing Over (meiosis)
Isolation Leads to Speciation
Types of Isolating Mechanisms
Pre-zygotic Isolating
Mechanisms
 Ecological
 Geographical
 Mechanical
 Temporal
 Behavioral
 Gametic
Post-zygotic Isolating
Mechanisms
 Reduced Hybrid
Viability
 Reduced Hybrid
Fertility
 Hybrid Breakdown
PRE-reproduction barriers
Obstacle to mating or to fertilization if mating occurs
geographic isolation
behavioral isolation
ecological isolation
temporal isolation
mechanical isolation
gametic isolation
Geographic isolation
 Species occur in different areas
 physical barrier


Ammospermophilus spp
Ex. canyon, river, forest, desert, ocean,
mountain, etc.
allopatric speciation

“other country”
Harris’s antelope
squirrel inhabits
the canyon’s
south rim (L). Just
a few miles away
on the north rim
(R) lives the
closely related
white-tailed
antelope squirrel
Geographical Isolation
Ecological isolation
 Species occur in same region,
but utilize habitats differently
so they rarely encounter each
other

Sympatric speciation (same
country)
2 species of garter snake, Thamnophis,
occur in same area, but one lives in
water & other is terrestrial
Ecological Isolation
 The Anopheles genus consists of
six mosquito species
 The species are virtually
indistinguishable
morphologically, but are isolated
reproductively
 They breed in different habitats.
 Some breed in brackish water,
others in running fresh water,
and still others in stagnant fresh
water.
Temporal isolation
 Species that breed during different times of day,
different seasons, or different years cannot mix
gametes
reproductive isolation
 sympatric speciation

Eastern spotted skunk
(L) & western spotted
skunk (R) overlap in
range but eastern mates
in late winter & western
mates in late summer
Temporal Isolation
Behavioral isolation
 Unique behavioral patterns & rituals isolate species
identifies members of species
 attract mates of same species •


courtship rituals, mating calls, etc.
Blue footed boobies mate
only after a courtship display
unique to their species
Recognizing your
own species
courtship songs of sympatric
species of lacewings
courtship display of
Gray-Crowned Cranes, Kenya
firefly courtship displays
Mechanical isolation
 Morphological differences can prevent successful
mating
Plants
Even in closely related
species of plants, the
flowers often have distinct
appearances that attract
different pollinators.
These 2 species of monkey
flower differ greatly in
shape & color, therefore
cross-pollination does not
happen.
Mechanical isolation
Animals
 For many insects, male &
female sex organs of
closely related species do
not fit together, preventing
sperm transfer

lack of “fit” between sexual
organs:
hard to imagine for us… but a
big issue for insects with
different shaped genitals!
Damsel fly penises
Mechanical isolation
 Bush babies, a group of small
arboreal primates, are divided into
several species based on
mechanical isolation.
 Each species has distinctly shaped
genitalia that, like locks and keys,
only fit with the genitalia of its own
species.
Gametic isolation
 Sperm of one species may not be able to fertilize eggs
of another species

mechanisms

biochemical barrier so sperm cannot penetrate egg


receptor recognition: lock & key between egg & sperm
chemical incompatibility

sperm cannot survive in female reproductive tract
POST-reproduction barriers
 Prevent hybrid offspring from developing into a
viable, fertile adult
reduced hybrid viability
 reduced hybrid fertility
 hybrid breakdown

zebroid
Reduced hybrid viability
 Genes of different parent species may interact &
impair the hybrid’s development
Species of salamander
genus, Ensatina, may
interbreed, but most
hybrids do not complete
development & those
that do are frail.
Reduced hybrid fertility
 Even if hybrids are vigorous
they may be sterile

chromosomes of parents may differ in number or
structure & meiosis in hybrids may fail to produce
normal gametes
Mules are vigorous,
but sterile
Horses have 64
chromosomes
(32 pairs)
Donkeys have 62
chromosomes
Mules have 63 chromosomes! (31 pairs)
Reduced Hybrid
Fertility
The Liger
-massive, but sterile
Hybrid breakdown
 Hybrids may be fertile & viable in first generation,
but when they mate offspring are feeble or sterile
In some strains of cultivated
rice, hybrids are vigorous
but plants in next generation
are small & sterile.
On path to separate species.
Isolation Can Lead to Speciation
One Gene Pool
Isolation
Independent Adaptation
Many Generations
Removal of Barrier
Design an Experiment!
 Work with a partner, record your ideas on a separate sheet
of paper that will be turned in.
 Choose a laboratory organism…
 Fruit fly, convict cichlid, pea plant
 Develop an experiment that you think could result in the
formation of two distinct species from the original.

Describe your procedure in as much detail as you can, as if you were
going to perform this experiment.
 Hint: How will you know when two species have formed?
Trends in Evolution
 Adaptive Radiation
 Divergent Evolution
 Convergent Evolution
 Gradualism
 Punctuated Equilibrium
 Polyploidy
 Transient Polymorphism
 Balanced Polymorphism
Divergent Evolution
 Speciation often happens repeatedly, to form a group
of species from one ancestral lineage.
 Often these species evolve in different ways due to
random genetic variation and varying selective
pressures
 This is known as divergence
Adaptive Radiation
 Rapid and repeated divergence
 Often occurs when a multiple varying niches are
available
Convergent Evolution
 Organisms sometimes adapt similar solutions to
physiological problems presented by similar selective
pressures
 Unrelated species show striking similarities
Convergent Evolution of Marsupial and Placental
Mammals
Rate of Speciation
 Current debate:
Does speciation happen gradually or rapidly

Gradualism
Charles Darwin
 Charles Lyell


Punctuated equilibrium
Stephen Jay Gould
 Niles Eldredge

Niles Eldredge
Curator
American Museum of Natural History
Gradualism
 Gradual divergence over
long spans of time

assume that big changes
occur as the accumulation of
many small ones
Punctuated Equilibrium
 Rate of speciation is not
constant



rapid bursts of change
long periods of little or no
change
species undergo rapid change
when they 1st bud from parent
population
Visualizing Evolution
The Cambrian Explosion:
Evidence of Punctuated
Equilibrium
The Tale of Two Snails
Environment Changes
Snails in new environment adapt
Two different population
Environment keeps changing
Survival of the Fittest
Everything’s back to normal (kind of)
The Fossil Record
Polyploidy
 Errors during meiotic cell division result in extra sets of chromosomes, a
condition called polyploidy
 30-70% of flowering plants thought to be polyploid
 Polyploid







types are labeled according to the number of chromosome sets
in the nucleus:
triploid
(three sets; 3x), for example the phylum Tardigrada
tetraploid
(four sets; 4x), for example Salmonidae fish
Pentaploid (five sets; 5x)
hexaploid
(six sets; 6x), for example wheat, kiwifruit
octaploid
(eight sets; 8x), for example Acipenser (genus of sturgeon fish)
decaploid
(ten sets; 10x), for example certain strawberries
dodecaploid (twelve sets; 12x), for example the plant Celosia argentea and
the amphibian Xenopus ruwenzoriensis
Speciation via polyploidy
 A diploid cell undergoes failed meiosis, producing
diploid gametes, which self-fertilize to produce a
tetraploid zygote.
Polymorphisms: Traits with multiple, distinct
phenotypes (morphs)
Transient Polymorphisms
 One morph or allele with
gradually replace the
other as generations pass
because it confers a
reproductive advantage
 Pepper Moth is the
classic example of this.
Pepper Moths
Balanced Polymorphism
 The various morphs are
maintained with a
population throughout
multiple generations
 Sickle Cell Anemia is the
most thoroughly
researched example of
this.
Evolution is not goal-oriented
An evolutionary trend does not mean that
evolution is goal-oriented.
Surviving species do not represent the peak of
perfection.
There is compromise & random chance involved
as well
Is this also true for humans as well?