Day 13 October 21st Chapter 8

Dr Amy B HollingsworthThe University of Akron

Fall 2014

Most agricultural pests evolve resistance to pesticides.

How does this happen?

Winners versus Losers – the losers get removed from the population

Removing the Losers

“Survival of the Fittest” Reproductive success

Fitness• a measure of the relative amount of

reproduction of an individual with a particular phenotype, as compared with the reproductive output of individuals with alternative phenotypes

Fruit Fly Example One fly carries the genes for a version of a

trait that allows it to survive a long time without food.

The other fly has the genes for a different version of the trait that allows it to survive only a short while without food.

Which fly has the greater fitness?

The alleles carried by an individual with high fitness will increase their market share in a

population over time and the population will evolve.

There are three important elements to an organism’s fitness:

1. An individual’s fitness is measured relative to other genotypes or phenotypes in the population.

There are three important elements to an organism’s fitness:

2. Fitness depends on the specific environment in which the organism lives.

There are three important elements to an organism’s fitness:

3. Fitness depends on an organism’s reproductive success compared to other organisms in the population.

•If you are sterile, and can never have babies, your fitness is ZERO•On the other hand, if you inherit an allele that gives you a trait that causes you to die at half the age of everyone else, but also causes you to have twice as many offspring as the average while you are alive, your fitness is increased.

"Survival of the fittest" is a misnomer.

Why?

8.12 Organisms in a population can become better matched to their environment through natural selection.

Adaptation—the process by which organisms become better matched to their environment and the specific features that make an organism more fit—occurs as a result of natural selection.

8.13 Natural selection does not lead to perfect organisms.

Why doesn’t natural selection lead to the production

of perfect organisms?

Factors that Prevent Populations from Progressing Inevitably toward Perfection

1. Environments change quickly.

2. Variation is needed as the raw material of selection.

3. There may be multiple different alleles for a trait, each causing an individual to have the same fitness.

8.14 Artificial selection is just a special case of natural selection.

Apple growers - green, yellow, red, tart, sweet, large, and small.

8.15 Natural selection can change the traits seen in a population in several ways.

Directional SelectionIndividuals with one extreme from the range of variation in the population have higher fitness.The result of such selection is not surprising: between 1920

and 1945, average milk production increased by about 50% in the United

States. Farmers only let the cows with lots of milk breed

So, could this happen in nature?

How is medical technology undoing the work of natural selection in optimizing the number of

babies with normal birth weights?

Stabilizing SelectionIndividuals with intermediate phenotypes are most

fit.

22 lbs – mom was diabetic

Born preemie at 22 weeksWeighed less than 10 oz.

Should we save every baby born?

1. Yes, we should try to save every baby – human or animal.

2. Yes, we should save every human, but not try to save animal babies

3. No, We should only let the strongest animals and humans – the healthy ones – survive.

Disruptive SelectionIndividuals with extreme phenotypes experience the highest fitness, and those with intermediate phenotypes have the lowest.

8.16 Natural selection can cause the evolution of complex traits and behaviors.

Look at the betta fish!

1954, William Thompson trained a group of rats to run through a maze for a food reward

How can a wing evolve if 1% of a wing doesn’t help an organism fly or glide at all?

Often, structures appear because they serve some other purpose.

Functional Shifts

Biggest wings – hottest regions?

It is indeed remarkable that this theory [evolution] has been progressively accepted by researchers, following a series of discoveries in various fields of knowledge.

The convergence, neither sought nor fabricated, of the results of work that was conducted independently is in itself a significant argument in favor of this theory.

—Pope John Paul II, 1996

Five primary lines of evidence:

1. The fossil record

2. Biogeography

3. Comparative anatomy and embryology

4. Molecular biology

5. Laboratory and field experiments

8.17 The fossil record documents the process of natural selection.

Although it has been central to much documentation of the occurrence of evolution, it is a very incomplete record

In Darwin’s time, it was assumed that the deeper down in the earth a fossil was found, the older it was.“Relative Dating”

Happened in North America 55 million years ago

Many branches, not just a straight line

First found in northern Canada and estimated at 375 million years old, Tiktaalik fossils appear to represent a transitional phase between fish and land animals.

8-18. Geographic patterns of species’ distributions reflect their evolutionary histories.

History Matters Who arrived first?

Are numerous different habitats available?

In Hawaii, it appears that a finch-like descendant of the honeycreepers arrived 4-5 million years ago and rapidly evolved into a large number of diverse species. The same process has occurred and continues to occur in all locales, not just on islands.