MUSE | Natural Selection | Unit Overview and Materials | Section 4: Extending the Natural Selection Model... | 4A: Monarch/Viceroy Case | Student Handout #1
Student Handout #1: Monarch/Viceroy
Each group will receive a folder with information on species that exhibit a particularly interesting biological phenomenon. The materials in the folders will include narrative descriptions of the organisms and their natural history, pictures, and data tables or graphs that should help you understand the biology of the characteristics under study.
For each of these cases, your group will develop a scientific argument that will attempt to explain the evolution of the trait or phenomenon in question from a Darwinian perspective. This means using the Darwinian model along with all the prior knowledge and beliefs on which it is based. All the material in the folder should be considered data that can be used to develop and then justify your Darwinian explanations.
Your group's task is to:
1. Develop a Darwinian explanation that fully accounts for the particular phenomenon in question. In your explanation be sure to include all the elements of Darwin's model.
2. Next, describe what data or material from the case you could use to support the explanation you developed. Be as specific as possible in identifying both data you used and what specific statements in your explanation that data supports.
Each of the above components are to be written after group discussion on a separate sheet of paper. As we have seen from our previous work in class, the use of precise language is extremely important in developing proper evolutionary explanations. Please be as clear and explicit as possible. Use complete sentences and proper grammar throughout the activity.
Your work will be evaluated based on:
As you can see, the viceroy and monarch butterflies closely resemble each other. Both have orange wings with black stripes and white spots that are easily seen against the colors of the meadows in which they live.
Given the information provided in this folder, construct a Darwinian explanation for the development of the similarity in coloration between the viceroy and monarch.
Materials available in the folder:
Throughout the summer, female monarchs seek out milkweed plants in meadows and abandoned fields in the northern U.S. and Canada. Females lay their eggs exclusively on milkweed plants, and each female lays about 400 clear green oval eggs. The monarch egg (no bigger than the head of a pin) is attached to the underside of a milkweed leaf. Within a few days the egg hatches and a yellow, black and white striped caterpillar emerges, beginning its life cycle.
As caterpillars, monarchs are totally dependent on milkweed plants. Milkweed contains toxic substances called cardenolides that are poisonous or distasteful to other animals, but harmless to the monarch. After eating the egg from which they hatch, the tiny caterpillar begins eating milkweed leaves. The larva are voracious eaters, growing rapidly. In the two weeks following hatching, the caterpillar sheds its skin four times to accommodate its growth.
After two weeks, at five centimeters in length and 3,000 times its birth weight, the caterpillar is ready for its transformation. It spins a cocoon and develops into a butterfly using the reserves built up by the caterpillar. The monarch butterfly emerges after approximately five days. The adult butterfly has no jaws and feeds instead with its long tongue on nectar and sap.
Viceroy Life History
Throughout the summer, female viceroys seek out poplar and willow trees in the northern United States and Canada and lay their eggs on the leaves. The viceroy egg is attached to the underside of poplar and willow leaves. Within a few days, the egg hatches and the caterpillar emerges.
As caterpillars, viceroys remain in the trees on which they were hatched and the leaves provide their sole source of nutrition. The mature caterpillar looks mildly fearsome with its hunched and horned foreparts. The chrysalis (cocoon) bears a striking resemblance to bird droppings, giving it protection from predators.
After a few days, the adult viceroy emerges from the chrysalis and spreads its colorful monarch-like wings. The adult butterfly has no jaws and feeds instead with its long tongue on nectar and sap.
Adult viceroys have few natural predators. Blue jays are known to be one of the birds that prey upon them. Predation of viceroys by blue jays, however, is rather low. On average these birds consume roughly 0.2 individuals per day.
Population Density Table
Blue jays are widespread in eastern North America and can be easily identified by their distinctive crest and blue striped wings. They are usually seen alone or in pairs in woodlands with clearings. Males are responsible for feeding females who are incubating eggs, and they also help the female feed nestlings. Young blue jays stay with their parents for two or three months and the family can be seen hunting together during this time.
Blue jays are very agile and lively and spend a large part of their day searching for food. Although blue jays are chiefly vegetarian, they are opportunistic feeders and will freely take a variety of food if it is readily available. To supplement their diet of nuts and seeds they often eat human food waste and insects. When hunting insects they are visual predators, relying on movement and coloration to help them identify their prey. They have the ability to vomit up food that is unpalatable (tastes bad) or poisonous and appear to learn from the experience as they avoid those food items in the future.
They are the primary flying insect predator in this type of meadow. The insects on which they normally feed are similar in coloration to one another. Most are dull green or gray and do not stand out from the vegetation in the environment.