Division of Biological Sciences
University of Montana
Missoula, MT USA
"Evolution of a developmental threshold in Onthophagus dung beetles (Coleoptera: Scarabaeidae)"(abstract number 800)
Males in many species of Onthophagus beetle (Coleoptera: Scarabaeidae) wield elaborate horns. Male horn expression is facultative, and regulated by a developmental threshold: males growing larger than a threshold size produce horns, whereas males remaining smaller than this size do not. One major avenue of morphological evolution in this genus involves changes in this developmental threshold. Artificial selection, comparison of allopatric populations, and comparisons of related species all reveal shifts in the critical size for horn expression. I use preliminary knowledge of horn development to suggest how threshold evolution may have occurred. I combine results from several experiments (diet-manipulation, Radioimmune Assay, topical application of methoprene) into a functional model for the endocrine regulation of male horn expression, and identify specific components of this mechanism most relevant to the developmental threshold. I use this information to predict how individuals may vary in horn expression, and to suggest likely avenues by which threshold evolution could have occurred.
Onthophagus taurus; male-dimorphism; polyphenism;
sexual selection; horns
PUBLICATIONS
Emlen, D. J. 2000. Integrating development with evolution: A case study with beetle horns. BioScience. 50: 403-418. (with Cover)
Emlen, D. J. 2000. Dig it, and they will come: A female dung beetle in her tunnel is sure to attract suitors big and small. Natural History May Issue: 64-69.
Emlen, D. J. and Nijhout, H. F. 2000. The development and evolution of exaggerated morphologies in insects. Annual Review of Entomology. 45: 661-708.
Moczek, A. P. and Emlen, D. J. 2000. Male horn dimorphism in the scarab beetle Onthophagus taurus: do alternative tactics favor alternative phenotypes? Animal Behaviour. 59: 459-466.
Stern, D.L.S. and Emlen, D.J. 1999. The developmental basis for allometry in insects. Development 126: 1091-1101.
Emlen, D.J, and Nijhout, H.F. 1999. Hormonal control of male horn length dimorphism in the horned beetle Onthophagus taurus. Journal of Insect Physiology 45: 45-53.
Moczek, A, and Emlen, D.J. 1999. Proximate determination of male horn dimorphism in the beetle Onthophagus taurus (Coleoptera: Scarabaeidae). Journal of Evolutionary Biology 12: 27-37.
Nijhout, H.F and Emlen, D.J. 1998. Competition among body parts in the development and evolution of insect morphology. Proceedings of the National Academy of Sciences 95: 3685-3689.
Emlen, D.J. 1997. Alternative reproductive tactics and male dimorphism in the horned beetle Onthophagus acuminatus. Behavioral Ecology and Sociobiology 41: 335-341.
Emlen, D.J. 1997. Diet alters male horn allometry in the beetle Onthophagus acuminatus (Coleoptera: Scarabaeidae). Proceedings of the Royal Society of London, Series B 264: 567-574.
Emlen, D.J. 1996. Artificial selection on horn length-body size allometry in the horned beetle Onthophagus acuminatus. Evolution 50: 1219-1230.
Emlen, D.J. 1996. Dung beetles unaffected by army and swarm. Journal of the Kansas Entomological Society 69 (suppl.) 405-406; George Eickwort memorial edition.
Emlen, D.J. 1994. Environmental control of horn length dimorphism in the beetle Onthophagus acuminatus (Coleoptera: Scarabaeidae). Proceedings of the Royal Society of London, Series B, 256: 131-136.
Emlen, D.J. 1996. Evolution of male horn length dimorphism in the dung beetle Onthophagus acuminatus (Coleoptera: Scarabaeidae). Doctoral Dissertation, Princeton University, June 1994; UMI Dissertation Services, Ann Arbor, MI.
Emlen, D.J. 1993. New method for observing underground and soil surface behaviors. Coleopterists Bulletin, 47: 243-244.
Emlen, D.J. 1992. Observations of a high altitude
population of the Sage stem-galling fly Eutreta diana (Diptera: Tephritidae)
and its associated parasitoids. J. Kans. Ent. Soc., 65: 203-207.
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