such questions.) For this case study, we presented the students with
work by Douglas Emlen and colleagues, who used the large, charis-
matic horned beetle Trypoxylus dichotomus to assess the importance
of insulin receptors in the evolution of allometric relationships
(Emlen et al., 2012). The researchers conducted an RNAi experiment
that targeted insulin receptors in last-instar larvae and measured the
resulting adult length of three traits that differed in their allometric
relationships (aedeagus, wing, and head horn). We introduced our
students to this study by presenting them with length measurements
of the three traits of control animals, which were plotted against
body size (available in Emlen et al., 2012). Using these data, the stu-
dents were asked the following questions:
(a) Which of the three types of allometric relationships apply to
each trait in untreated individuals (isometric, hypoallomet-
(b) Which of the three traits is most/least sensitive to nutrient
(c) Which of the three traits has the highest/lowest number of
insulin receptors under normal conditions?
(d) How would you expect RNAi of the insulin receptor to affect
each of the traits?
(e) Do the results of the RNAi experiment match your predictions?
After team discussions, most students correctly predicted that
horns, which are a hyperallometric trait, are expected to be most
sensitive to nutrient availability (as they grow faster than body size).
Based on this answer, pupal horn tissues are expected to bear a
large number of insulin receptors on the membrane of each cell.
Consequently, horns are also expected to be particularly sensitive
to a reduction of insulin receptors via RNAi and, thus, are expected
to experience the most significant growth reduction for a given
body size. On the other hand, aedeagi exhibit a hypoallometric
relationship and, thus, are expected to be less sensitive to nutrient
availability, which might be mediated by a reduced number of
available insulin receptors on the cell membrane. Given their limited response to nutrient availability, a further reduction in insulin
receptors is expected to lead to little change in the overall growth
rates of aedeagi, which is supported by the researchers’ results.
Insects, with their relatively simple yet extraordinarily varied body
plans, were particularly integral as research subjects in the advent
and subsequent flourishing of evo-devo as a discipline. In turn,
our understanding of insect developmental genetics and morphological evolution has grown disproportionately in relation to other
taxonomic groups. Here, we have argued that a more comprehensive assimilation of evo-devo research into entomology instruction
might enhance and solidify students’ understanding of insect biology beyond that achieved through traditional approaches.
We thank Dr. Teiya Kijimoto (University of West Virginia) for help
on the insulin signaling pathway (text and figure), Dr. Yoshinori
Tomoyasu (University of Miami) for providing us with pictures of
RNAi treated beetles, and four anonymous reviewers for their suggestions on the manuscript.
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