In the engagement phase of the investigation, students are introduced to the biology and evolutionary history of the drosophilid flies of Hawaii through a reading and set of review questions.

Student Objectives

• Learn about some aspects of the basic biology of drosophilid flies.

• Recognize that the banding patterns of polytene chromosomes from individual flies, combined with information about the morphology, habitats, and behaviors of those flies, can be used in some cases to trace the evolutionary relationships of separate fly species.

• Recognize that the unique history and geology of the Hawaiian islands contribute to the striking species diversity found there.

Materials

The materials provided are the Student Reading and Student Worksheet, a map of the major Hawaiian islands showing their ages, a diagram showing the evolutionary relationships among mammalian groups, and a photograph of a polytene chromosome.

Teaching Strategies

After students have completed the reading, teachers can ask them to answer the following questions, which also appear at the end of the reading. (These questions also can serve as a spring-board to a classroom discussion.)

1. What characteristics of the Hawaiian islands might have led to the enormous diversity of drosophilid species in the Hawaiian islands? (Among the possible responses are the variety of habitats found in relatively close proximity on the islands, the separation of habitats within and among islands, and the lack of competing organisms. Each of these characteristics can be compared to conditions on a larger landmass.)

2. How might the diversity of mating behaviors be related to the diversity of drosophilid species in the Hawaiian islands? (Students could explore the idea that the evolution of new mating behaviors may contribute to speciation.)

3. What evidence suggests that all of the drosophilid species in the Hawaiian islands have descended from a single fertilized female fly that colonized the islands millions of years ago? (Students could discuss such evidence as similarities in shape, details of body form, behavior, chromosomal structure, and protein or DNA sequences.)

4. How could individual flies spread from island to island? (Students could suggest several possible mechanisms and ways of gauging their plausibility.)