Evolution for Ecology

The Importance of Evolution in Ecology Ecologists study proximate or “how”

questions: 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 is essential for natural selection

to occur. 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 are different versions of a gene 3. 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.