In the elaboration phase of the investigation, students can deepen and enrich their understanding of the evolution of the drosophilid flies of Hawaii by analyzing additional data and by modifying their narratives to take those data into account. This phase of the investigation is open-ended, in that students can do as much as they wish with the additional data. Typically, completing this phase will require devoting a third or fourth class period to the exercise.

Student Objectives

  • Recognize that hypotheses often must be modified in the light of new data.

  • Recognize that a particular data set does not necessarily support an explanation.

  • Identify what additional data are needed to extend the explanation.

Materials Needed

Students will continue to work with the data in Table 1 and with the map of the Hawaiian islands. They also can refer to the data in Table 2.

Teaching Strategies

One way to demonstrate to students how their narratives need to be modified in light of new data is to lead a guided class discussion, using these questions:

  1. Based on the data included in Table 1, how could the species D. setosimentum be added to the evolutionary tree? (As shown in Table 1, D. setosimentum has the same inversions as does D. primaeva, but because D. setosimentum lives on Hawaii and D. primaeva lives on the older island of Kauai, a logical hypothesis is that D. setosimentum originated through a founder event.)

  2. What additional data could be used to test this hypothesis, and what data would support it? (For example, would additional inversions found in D. setosimentum that are not found in D. primaeva support this hypothesis?)

  3. Does each species always have a new and different set of inversions?

Another possible elaboration would be to add to the earlier phylogenetic tree the species D. silvestris, which is also represented in Table 1. The following questions could lead students to examine these data:

  1. Where does D. silvestris fit into the evolutionary tree relative to the other four species? (Since it has same inversions and is found on the youngest island, the inversion data indicate that it may have evolved relatively recently.)

  2. Is it possible to determine whether D. heteroneura or D. silvestris is the more recently evolved species? (On the basis of the data in Table 1, it is not possible.)

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