Two Thresholds, Three Male Forms Result in Facultative Male Trimorphism in Beetles
J. Mark Rowland1* and
Douglas J. Emlen2
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
strategies.
2 Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA.
* To whom correspondence should be addressed. E-mail: rowland{at}unm.edu
