1. Natural Selection The Evolution of Clamys sweetus

2. Question: Is there any survival advantage to having a brown shell?
Indicate that this is one of the questions that was asked at the science conference. Ask students to discuss what they might need to know in order to answer this question.

3. Natural Selection in Action
Tell students that a research team studying pocket mouse populations shared their research during the conference. This other research team provided two video clips.
Have students watch the first clip and then discuss the questions on the next slide.
The video clip is “Pocket Mouse and Predation” located on Disc One of Evolution:Constant Change and Common Threads by HHMI.
Pocket Mouse and Predation
Disc One of Evolution: Constant Change and Common Threads by HHMI

4. What do you think?
Does fur color influence which pocket mouse survives and which does not?
Could the pocket mouse information apply to C. sweetus?
What do you need to know to make this decision?
• Fur color does influence which mouse survives and which does not. However, it depends on the environment….the color of the ground.
• Allow students to speculate.
• Students might indicate that they need to know the color of the soil where the clams are found. Is the soil the same color everywhere they live? Are there any changes occurring in the clams environment such as a volcanic eruption or increased pollution that darkens the water/soil.

5. Question: Could the presence of a few brown clams eventually lead to a population that is mostly brown clams?
Tell students that the pocket mouse researchers asked the very same question about the animals they were studying. They provided a video that shows their findings.The video is the next slide.

6. Change in the Pocket Mouse Population
The video clip is “Pocket Mouse Evolution” located on Disc One of Evolution:Constant Change and Common Threads by HHMI.
Pocket Mouse Evolution
Disc One of Evolution: Constant Change and Common Threads by HHMI

7. What do you think?
Could the pocket mouse information apply to C. sweetus?
If it does, what caused the brown color to appear in the clam population?
Allow students to discuss these questions.
Students should realize that a mutation occurred. Ask students if there are any other sources of variation. They should be able to indicate that the recombination of genes during sexual reproduction is a source.
The overall discussion should lead to even more questions about the clam population.

8. Question: Does a brown shell provide some survival advantage?
The spread of the brown color seems feasible under certain conditions. Does the variation provide a survival advantage? For example, does it provide protection from the arthropod..camouflage or shell strength?