In spite of the diversity of possible biological forms observed in nature, a limited range of morphospace is frequently occupied for a given trait. Several mechanisms have been proposed to explain this bias in the distribution of phenotypes including selection, drift, and developmental constraints. Despite extensive work on phenotypic bias, the underlying developmental mechanisms explaining why particular regions of morphological space remain unoccupied are poorly understood. To address this issue, we studied the sex comb, a group of modified bristles used in courtship that shows marked morphological diversity among Drosophila species. In many Drosophila species including Drosophila melanogaster, the sex comb rotates 90°to a vertical position during development. Here we analyze the effect of changing D. melanogaster sex comb length on the process of rotation. We find that artificial selection changes the number of bristles per comb without a proportional change in the space available for rotation. As a result, when increasing sex comb length, rather than displaying a similar straight vertical shape observed in other Drosophila species, long sex combs bend because rotation is blocked by a neighboring row of bristles. Our results show ways in which morphologies that would be favored by natural selection are apparently impossible to achieve developmentally. These findings highlight the potential role of development in modifying selectable variation in the evolution of Drosophila sex comb length.

Implication Statement If you want to offer your students an enjoyable and worthwhile interprofessional activity to learn about issues in community nutrition, your university can cook up these interprofessional culinary education workshops. Start with a few enthusiastic students from various health professional programs who can organize, promote, and lead. Include faculty and/or staff to support the students and apply for internal funding. Find workshop facilitators (e.g., chefs), and arrange for program evaluation. It is best to choose workshop topics and themes relevant to your local situation. Ensure workshops are structured to facilitate cooperative and experiential learning. Students will find these sessions informative, practical, and enjoyable.

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