1. Changing phenotypes in Spadefoot toads

2. What is a Gene?
Go over definitions of genotype/phenotype.

3. What is a Gene?
A gene is a piece of DNA that codes for a specific trait. It is passed from parent to offspring
Go over definitions of genotype/phenotype.

4. What is a genotype? What is a Gene?
A gene is a piece of DNA that codes for a specific trait. It is passed from parents to offspring (they are heritable)
What is a genotype?
Go over definitions of genotype/phenotype.

5. What is a genotype? What is a Gene?
A gene is a piece of DNA that codes for a specific trait. It is passed from parents to offspring (they are heritable)
What is a genotype?
The genetic makeup of an organism, including all the genes that an individual has
Go over definitions of genotype/phenotype.

6. What is a phenotype?

7. What is a phenotype?
The observable characteristics of an organism. Your genotype codes for your phenotype
Phenotype can be both physical traits, such as hair color, but they can also be behaviors or physical abilities. For example, being able to roll your tongue is a genetically coded phenotype.
(if needed) Environment is important in shaping phenotype. Example could be that you have the genes to be very tall, but if you don’t eat enough food while you’re young, you won’t reach that height.

8. Tadpole phenotypes
Compare the variation in phenotypic traits between these two tadpoles. How are they similar and different?
How does this relate to their genotype?
Ask students to describe the phenotypes of the two tadpoles and describe how that relates to their genotypes.

9. Tadpole phenotypes What are the phenotypes of these tadpoles?
How does this relate to their genotype?
I have big nasty teeth!
Students will probably just say one looks bigger than the other, but point out that the bottom one has a much larger tail for fast movement, and much more developed jaw muscles. It also has sharp teeth while the upper one does not. While the two tadpoles share many of the same genes (resulting in the same color, same species, etc.) there are also some key genetic differences that cause them to look different.
Why might these two tadpoles have such different phenotypes? Because one eats primarily meat and the other eats primarily plant matter.
What this would mean for their genotypes is that the bottom tadpole has the genes for bigger body size, big jaw muscles, and big teeth, while the top tadpole has the genes for small body size and grinding teeth.

10. Tadpole phenotypes I like to eat rotting plants!
I like to eat my friends!
In fact, these two different types of tadpoles are called omnivores and carnivores. Omnivores eat primarily dead plant matter, while carnivores eat shrimp and sometimes even other tadpoles (both other species and their own...these guys can be cannibals!). Their different genotypes result in these very different phenotypes, even though they are the same species.

11. Tadpoles grow up in desert ponds
Spadefoot toads
Omnivore
tadpole
Carnivore
tadpole
Tadpoles grow up in desert ponds
Adults lay eggs, which hatch into tadpoles
Metamorphosis
Grow up to be adults
Go through life cycle of these tadpoles. They belong to a species known as “spadefoot toads.” The toads live in the deserts of the US (Arizona/New Mexico), and tadpoles grow up in temporary ponds. When they get big enough, they metamorphose into toads (but still look kind of tadpole-like, with a tail), which allows them to leave the ponds and go find food on land. They eat enough to become full-grown toads, at which point, they’ll go back to ponds to lay eggs, creating more tadpoles

12. Desert Toads
What might be some challenges of being a toad in the desert?
Ask students what they think would be difficult about being a toad in the desert. Students should quickly point out that it doesn’t rain much there, which means that they need to metamorphose FAST before the pond dries up.

13. Let’s see how these differences in tadpole traits lead to changes in phenotype across generations!

14. Activity: Natural Selection in Spadefoot Toads
This class is now a population of spadefoot toad tadpoles!
You will each receive an envelope giving you a phenotype: omnivore or carnivore.
We will see how this population evolves under different environmental conditions. - Evolution is a change in the frequency (proportion) of different genotypes or phenotypes from one generation to the next.

15. SCENARIO ONE
Very heavy rainfall over a couple nights resulted in a large, deep pond forming. Your population of tadpoles that hatched in this pond has access to plenty of vegetation as well as fairy shrimp and small tadpoles of other frog species. The pond takes 35 days to dry up, a long time for a pond in the desert!

16. SCENARIO ONE Carnivores Omnivores # Offspring # Students
Total Offspring 1 2 3 4 5
Total
# Offspring
# Students
Total Offspring 1 2 3 4 5
Total

17. SCENARIO TWO
The summer has been very dry, but the desert finally experienced a little rain, resulting in a small, shallow pond. Toads desperately came to the pond and bred, but now that the tadpoles have hatched, there is fierce competition for resources. Because the pond is smaller, there is not much plant matter for the omnivores to eat, but there are plenty of starving tadpoles around for carnivores to eat. Also, because the pond is so shallow and small, it dries up in only 18 days.

18. SCENARIO TWO Carnivores Omnivores # Offspring # Students
Total Offspring 1 2 3 4 5
Total
# Offspring
# Students
Total Offspring 1 2 3 4 5
Total

19. Natural Selection
Natural selection: varying survival and/or reproduction of individuals that differ in one or more traits
(survival and reproduction = fitness)
Natural selection can lead to Evolution: change in frequency of genotypes in a population between generations
Now that students have seen how different environmental conditions change the population of tadpoles from year to year, ask them if they know the name of this process-> guide them to ‘natural selection’
Tell students that natural selection is the main mechanism by which animals evolve! It explains the biodiversity we see today.
Ask what is necessary for natural selection. Guide them towards: tadpoles are different (variation in the population), some tadpoles survive better and some reproduce more than other tadpoles as the environment changed (differential selection), and the population could only change because tadpoles passed their traits on to their offspring

20. What do we need for natural selection to occur?
Tadpoles need to be different → trait variation
Some tadpoles survive better or reproduce more than others → Variation in fitness
Tadpoles pass their traits on →Heritability of traits

21. What other traits can natural selection act on?
Ability to find food
Avoiding predators
Attracting mates
In the case of the tadpoles, natural selection took place because the environment was changing and the tadpoles developed at different rates. Natural selection can also occur via other mechanisms.
Darwin’s finches have evolved very different-looking beaks because birds that had beaks that were best suited to the available foods survived better. This allowed them to reproduce, and their offspring were all birds with beaks that were suited to a particular food.
The peppered moth is an example of animals evolving to avoid being eaten. Before the industrial revolution, pale-colored moths were less likely to be eaten by birds (harder to find on trees), so they were very common in the population, while dark-colored moths were very uncommon. During the industrial revolution in England, soot covered trees, and the dark-colored moths were less likely to get eaten, and therefore became very common in the population.
Ask students to think about why attracting mates is something that natural selection can act on. It’s because the definition of natural selection involves organisms with unequal fitnesses. Therefore being able to convince someone to mate with you is integral to having any fitness at all. This will lead to their homework sheet