Two thresholds, three male forms result in facultative male trimorphism in beetles

DOI
10.1126/science.1167345
Publication Year
2009
Publication Site
Science
Journal Volume
323
Page Numbers
773–776
Family
Scarabaeidae
General topic
Evolution
Morphology
Specific topic
genetics
Author

Rowland, J. Mark; Emlen, Douglas J.

Abstract Note

Male animals of many species deploy conditional reproductive strategies that contain distinct alternative phenotypes. Such facultatively expressed male tactics are assumed to be due to a single developmental threshold mechanism switching between the expression of two alternative phenotypes. However, we discovered a clade of dung beetles that commonly expresses two threshold mechanisms, resulting in three alternative phenotypes (male trimorphism). Once recognized, we found trimorphism in other beetle families that involves different types of male weapons. Evidence that insects assumed to be dimorphic can express three facultative male forms suggests that we need to adjust how we think about animal mating systems and the evolution of conditional