01783nas a2200193   4500008004100000245011700041210006900158300001000227490000700237520107400244653001801318653002101336653002001357653001601377653001401393100002301407700002201430856013701452       1999                        eng d00aHormonal control of male horn lenght dimorphism in the dung beetle Onthophagus taurus (Coleoptera: Scarabaeidae)0 aHormonal control of male horn lenght dimorphism in the dung beet  a45-530 v453 aMale dung beetles (Onthophagus taurus) facultatively produce a pair of horns that extend from the base of the head: males growing larger than a threshold body size develop long horns, whereas males that do not achieve this size grow only rudimentary horns or no horns at all. Here we characterize the postembryonic development of these beetles, and begin to explore the hormonal regulation of horn growth. Using radioimmune assays to compare the ecdysteroid titers of horned males, hornless males, and females, we identify a small pulse of ecdysteroid which is present in both hornless males and females, but not in horned males. In addition, we identify a brief period near the end of the final (third) larval instar when topical applications of the juvenile hormone analog methoprene can switch the morphology of developing males. Small, normally hornless, males receiving methoprene during this sensitive period were induced to produce horns in 80% of the cases. We summarize this information in two models for the hormonal control of male dimorphism in horn length.10aHorned beetle10aJuvenile hormone10amale dimorphism10aPolyphenism10aThreshold1 aEmlen, Douglas, J.1 aNijhout, Frederik  uhttps://scarabnet.myspecies.info/hormonal-control-male-horn-lenght-dimorphism-dung-beetle-onthophagus-taurus-coleoptera-scarabaeidae