Station Activity: Natural Selection/Adaptation

Station Activity: Natural Selection/Adaptation

Information Station

Analyzing an article

LOS ANGELES — Pity the poor male common Mormon swallowtail butterfly. His potential female mates bear four different color patterns, only one of which looks familiar. The rest look suspiciously like other species, and poisonous ones at that.

That deception is good news for 75 percent of the Papilio polytes ladies, who can avoid predators that have learned not to dine on the real toxic butterfly. They’re a classic example of “parasitic” mimicry. A strictly one-sided affair, their mimicry benefits only the imitator, and leaves the male and the masculine-colored female at risk.

Biologists have studied mimicry cases since the dawn of Charles Darwin’s theory of evolution. This is because they provide a field test for the process of natural selection. In a nutshell, natural selection is the process by which organisms that are better suited to their environment survive, while others do not.

Organism is a broad term that covers all living things, including animals, plants, and single-celled life forms. Organisms often develop their advantageous traits through mutations, or changes, in the structure of their genes. The slow changes to an entire species that come out of this process of natural selection is known as evolution.

Remains A Mystery

But while mimicry has long been studied, it remains something of a mystery just how it becomes restricted to females of a species.

Scientists suspected the handiwork of a “super gene.”

“They figured that this is a cluster of tightly linked genes, and each individual gene was doing some subset of that color pattern, but they were so close together that they would all be inherited as a single unit,” said University of Chicago evolutionary biologist Marcus R. Kronforst, who has studied butterflies for decades. “That’s where the name ‘super gene’ came from. They just couldn’t imagine that a single gene could do all this.”

Researchers had found evidence of a unified gene cluster in one butterfly species. So Kronforst sought out the super gene of the Mormon swallowtail by mating butterflies of different wing patterns and mapping genes and gene expression of some 500 offspring.

“We essentially expected to see the same thing, that there would be a cluster of very tightly linked genes,” Kronforst said. “But that’s not what we found. In this butterfly, in this one species at least, it is just one gene. And it’s doublesex. That’s the name of the gene.”

The Signaling Gene

Doublesex happens to be the signaling gene that selectively drives the gender divide in certain cells — though it is not the one that actually determines gender for the organism.

“It’s not on the sex chromosomes,” said Kronforst, who published his research team’s findings online Wednesday in the journal Nature. “It reads a message from the sex chromosomes and then it forms two different types of proteins. There’s a male type of protein and a female type of protein, and that’s what tells the other cells in the body: You are male and you are female.”

When he looked more closely at the mimetic, or mimicking, females, Kronforst found that doublesex was holding on to about 1,000 base pair mutations. Base pairs are sets of complimentary molecules. What he saw was similar to the way super genes lock up groups of mimicry genes.

“It basically locks all of the mutations into one unit so they can’t recombine,” Kronforst said.

Exactly what mutations may be responsible for which colors remains a mystery that Kronforst plans to explore.

Other broad questions remain too. “If mimicry is helping these females survive, why on Earth aren’t the males getting the same advantage?” Kronforst said. “We simply do not understand the answer to that question.”

Counterbalancing Selection?

And how does the non-mimicking female pattern survive? “If she really was that bad off, that copy of the gene would simply disappear from the population,” Kronforst said. “The individuals that were mimetic would do so much better that she would just disappear. But that pattern hangs on. There’s also something that’s keeping the males in the non-mimetic pattern that we still don’t understand.”

Kronforst believes that counterbalancing selection may be at play — some advantageous trait is paired with the seemingly disadvantageous one, and both are conserved. In humans, that counterbalancing arrangement pairs sickle cell with malaria resistance.

“Basically what the butterflies have done is they have grabbed this mechanism that they already use to tell males from females, and they’re using it again to tell females that you’ll like A, B, C or D,” Kronforst said.

In other words, doublesex is not only forming male and female proteins, it is also selecting one of four color patterns.

Kronforst wants to find out how the gene operates in other species that have similar male-female mimicry differences. What other characteristics might it drive? Does it change flight patterns as well?

“It’s possible that this gene is doing lots of other stuff,” Kronforst said.

Answer the following questions using evidence from the article. Use the word wall when writing your explanations

1) What is the difference between natural selection and evolution?

The difference between natural selection and evolution is ….

2) How does the trait for mimicking increase the Mormon Swallowtail Butterfly’s probability for survival?

The trait for mimicking increases the butterfly’s probability for survival because…

3) How does the genetic variation in these Mormon Swallowtail Butterflies relate to the variations of beaks seen in the Galapagos Finches?

The genetic variation in these butterflies relates to the variations of beaks seen in the finches because …

Observation Station

Why do finches have different beaks?

1) Why do finches have different beaks? Use evidence from the video to support what you think.

I predict finches have different beaks because

Investigation Station

ADAPTATION OF THE HUMAN HAND

Name:______Date:______Period:______

INTRODUCTION:

Living things have bodies that are adapted for the places they live and the things they do. Fish have gills so that they can remove oxygen that is dissolved in water. Most plants have green leaves which contain chlorophyll so that they can make food. Jellyfish have stinging cells to capture prey. Birds have hollow spongy bones so that they will be light enough to fly. Arctic animals have layers of fat and thick coats of fur to keep warm in the frigid Arctic climate. There are hundreds of examples of ways that organisms are adapted for a successful lifestyle.

Humans, too, are adapted for the things they do. One of our adaptations is our hand. Humans, as well as monkeys, gorillas, and other primates, have a hand that can grasp objects. In this lab exercise, you will perform several common actions. Then you will change your hand so that it resembles that of a non-primate animal. You will determine whether or not you can successfully perform the same actions. This will demonstrate how the human hand is adapted for the actions it performs. You will work with a partner to do this exercise.

PROCEDURE:

1. Do each of the following activities and have your partner time how long it takes you to do each one.

Record the times in the data sheet.

A. Tie a knot in a piece of string.

B. Remove one shoe and replace it on your foot.

C. Unscrew a bottle cap or jar cover.

D. Unbutton two buttons and button them again.

E. Open a door.

F. Write your name on a piece of paper.

2. Using masking tape, have your partner tightly tape each of your thumbs to the palm of the hand.

3. After your thumbs are securely taped, try each of the activities listed in Procedure 1 again. Time each activity as you did before and record the time in the data chart. If an activity is not done in two minutes, record the word "unsuccessful."

4. Repeat the same tasks you performed before (above in bold).

Table 1: Time Taken To Perform Various Actions

CONCLUSIONS:

1. Explain why dog and cat paws are not adapted for doing the six actions you tested.

2. What are cat and dog paws adapted for?

3. Describe how your hand is adapted for doing the actions you tested.

4. You have an opposable thumb. Explain what you think this means.

5. Why do you feel that human hand adaptations have helped to make humans such a successful species on earth? (List and explain at least 2 reasons.)

Communication Station

Directions: Arrange the following events, listed below, in the order they occur during speciation. Write a brief description of each event by using the example of Darwin’s finches.

Events: Ecological competition; Reproductive isolation; Changes in the gene pool; Separation of populations; Founding of new population; Continued evolution.