Evolution for
Ecology
The Importance of Evolution in
Ecology
 Ecologists
questions:

study proximate or “how”
How nutrients flow through ecosystems
 Evolutionary
biologists study ultimate or
“why” questions:

Why does a stickleback fish have armor in
one lake but not another?
The Importance of Evolution in
Ecology
 Evolutionary
processes can work
surprisingly fast.

This is increasingly important in agriculture
and medicine.
Pink Bollworms
 Farmers
consistently had to
spray their crops
with insecticides to
control the pests.
Pink Bollworms
 Transgenic
cotton
incorporates a gene
from a bacterium that
causes the caterpillars to
die when they eat the
plant.

Few applications of
insecticide needed.
Resistance
 The
problem with
pesticides is that
pests evolve
resistance to them
and they become
less effective over
time.

Would this happen
with transgenic
cotton?
Pink Bollworm Experiment
 Did
the Pink Bollworms evolve resistance
to the Bt toxin in the transgenic cotton?
Pink Bollworm
Experiment
 Yes,
in just one
generation!

Evolution can be fast!
 So,
is transgenic cotton
useful? How can we
prevent resistance from
becoming established?
Rapid Evolution in Sticklebacks
 Armor
plates
protect the fish
from predators.
 But there is a cost
to plates – slower
growth, breed
later, and have
lower winter
survival rates.
Rapid Evolution in Sticklebacks
 Cutthroat
trout are predators of
sticklebacks.

Use vision to find prey – easiest to find
sticklebacks in clear water.
Rapid Evolution in Sticklebacks
 So,
if a murky lake is cleaned up and is
now clear, what would you expect to
happen to the plate count on the fish?



Plate count will increase?
Plate count will decrease?
Plate count will stay the same?
Rapid Evolution in
Sticklebacks
 As
the lake
cleared, predation
became more of a
problem and plate
number increased.
Rapid Evolution of Invasive
Species

The snowy campion
is native to Europe,
introduced to North
America 200 years
ago.

No enemies
Smut (fungus)
 Hadena bicruris
caterpillars


Now a common
agricultural weed.
Rapid Evolution of Invasive
Species
 Two
possible ways
to allocate
resources.
 Which is best will
depend on levels
of predation,
infection etc.
Rapid Evolution of Invasive
Species
 Europe
– more
enemies so bigger
investment in
defense.
 North America –
fewer enemies so
more invested in
reproduction &
growth.
The Logic of
Evolution by
Natural
Selection
Sticklebacks
 Plating
in
sticklebacks is
determined
genetically.

Set at birth & can’t
change.
Natural Selection
 Variation
occur.

is essential for natural selection to
Populations of sticklebacks contain a variety of
plate counts.
Natural Selection
 Heredity
is also
essential for natural
selection to occur.

Traits are passed
genetically from
parents to
offspring.
Natural Selection
 Survival
and
reproduction are
selective
 In a lake with high
predation,
sticklebacks with
more plates survive
better & reproduce
more.
Natural Selection
in the Medium
Ground Finch
 Daphne
Major –
Galapagos
 No fresh water
source – rely on
short spring rains.
 Medium ground
finches eat seeds.
Natural Selection
in the Medium
Ground Finch
 The
finch
population
contains:


Variation
Heritibility
Natural Selection
in the Medium
Ground Finch
 1977
drought –
birds had to rely on
seeds from
previous year.
 Small soft seeds
eaten first, larger
tougher seeds left.
 Many birds starved.
 After drought,
average beak size
was larger.
Natural Selection
in the Medium
Ground Finch
 When
the survivors
reproduced, their
offspring also had
larger beaks.
Genetics and
Evolution
Some terms
 Assertions:
 1.

Populations vary in their phenotype
What they look like
 2.
Differences in the phenotype are due at
least in part to difference in genotype.

Which alleles are present
 Alleles
 3.
are different versions of a gene
Some phenotypes and thus some
genotypes survive better & reproduce more.
Some terms
 Consequence:
The beneficial trait will
spread through the population.


The alleles for the beneficial trait will
increase in the population.
Alleles associated with failure will disappear.
 Total
reproductive contribution is an
individual’s fitness.
 Evolution involves changes in the
frequencies of alleles in the population.
Genetics of Plating in
Sticklebacks
 Plating
is controlled
by a gene called
Eda.

There are two
versions, or alleles
c
for complete
plating
 l for light or low
plating

Codiminant
Genetics of Plating in
Sticklebacks
 Tradeoff
between fast growth &
overwinter survival vs protection from
predators.
 Different phenotypes (& therefore
genotypes) will be selected for in different
situations.

Different environmental pressures.
Genetics of Plating in
Sticklebacks
 You
can see
here how the
population
varied over
time as the
lake cleared.
Adaptation
 Over
time, natural selection leads to
adaptation to the environment.

Traits beneficial in a particular environment
have accumulated in the population.
 Move
the organisms to a different habitat
and the tight fit may be gone.
Genetic Drift
 Genetic
drift is another mechanism of
evolution.



Does NOT result in adaptation.
Due to random chance.
Does result in a change in the frequency of
alleles in the population.
 Migration
can also change the frequency
of alleles in the population.
Managing the
Evolution of
Resistance
Pink Bollworms
 Recall
that pink bollworms can evolve
resistance to the Bt toxin in the transgenic
cotton.

Resistance is recessive.
 rr
are resistant
 sr and ss are susceptible
 There
are several different resistance alleles
Pink Bollworms
 Tradeoff:

Susceptible
worms grow
faster and
mature sooner,
but are killed
by Bt toxin.
Pink Bollworms
 Resistant
worms have a much higher
fitness on transgenic (Bollgard) cotton,
while susceptible worms have a
somewhat higher fitness on normal
cotton.


The latter means that resistance alleles will
be rare where Bollgard has never been
used.
Goal: delay evolution of resistance
Integrated Pest Management
 IPM
involves the use of a variety of
techniques to battle pests.


Use two different types of Bt toxin.
Parasitic nematodes – more lethal to
resistant bollworms.
Managing a Bollworm
Infestation
 High


dose / refuge strategy
Part of a field planted with Bollgard cotton,
part with normal cotton.
The refuge (normal cotton) allows some of
the susceptible worms to survive which
decreases the fitness advantages
associated with resistance.