@article {2036,
	title = {Rapid evolution of a polyphenic threshold},
	journal = {Evolution and Development},
	volume = {5},
	number = {3},
	year = {2003},
	pages = {259-268},
	abstract = {Polyphenisms are thought to play an important role in the evolution of phenotypic diversity and the origin of morphological and behavioral novelties. However, the extent to which polyphenic developmental mechanisms evolve in natural populations is unknown. Here we contrast patterns of male phenotype expression in native and exotic and ances- tral and descendant populations of the horn polyphenic bee- tle, Onthophagus taurus .  Males in this species express two alternative morphologies in response to larval feeding condi- tions. Favorable conditions cause males to grow larger than a threshold body size and to develop a pair of horns on their heads. Males that encounter relatively poor conditions do not reach this threshold size and remain hornless. We show that exotic and native populations of O. taurus  differ significantly in the body size threshold that separates alternative male phenotypes. Comparison with archival museum collections and additional samples obtained from the native range of O. taurus  suggests that allometric differences between exotic and native populations do not reflect preexisting variation in the native range of this species. Instead, our data sug- gest that threshold divergences between exotic and native populations have evolved in less than 40 years since the introduction to a new habitat and have proceeded in oppo- site directions in two exotic ranges of this species. Finally, we show that the kind and magnitude of threshold diver- gence between native and exotic populations are similar to differences normally observed between species. Our re- sults support the view that certain components of the de- velopmental control mechanism that underlie polyphenic development can evolve rapidly in natural populations and may provide important avenues for phenotypic differentia- tion and diversification in nature. We discuss the role of developmental control mechanisms in the origin of allo- metric diversification and explore potential evolutionary mechanisms that could drive scaling relationship evolution in nature.},
	author = {Moczek, Armin P. and Nijhout, H. Frederik}
}
@article {2037,
	title = {Trade-offs during the development of primary and secondary sexual traits in a horned beetle},
	journal = {The American Naturalist},
	volume = {163},
	number = {2},
	year = {2004},
	pages = {184-191},
	abstract = { Resource allocation trade-offs during development affect the final sizes of adult structures and have the potential to constrain the types and magnitude of evolutionary change that developmental processes can accommodate. Such trade-offs can arise when two or more body parts compete for a limited pool of resources to sustain their growth and differentiation. Recent studies on several holo- metabolous insects suggest that resource allocation trade-offs may be most pronounced in tissues that grow physically close to each other. Here we examine the nature and magnitude of developmental trade-offs between two very distant body parts: head horns and geni- talia of males of the horned scarab beetle Onthophagus taurus. Both structures develop from imaginal disklike tissues that undergo ex- plosive growth during late larval development but differ in exactly when they initiate their growth. We experimentally ablated the pre- cursor cells that normally give rise to male genitalia at several time points during late larval development and examined the degree of horn development in these males compared to that of untreated and sham-operated control males. We found that experimental males developed disproportionately larger horns. Horn overexpression was weakest in response to early ablation and most pronounced in males whose genital disks were ablated just before larvae entered the pre- pupal stage. Our results suggest that even distant body parts may rely on a common resource pool to sustain their growth and that the relative timing of growth may play an important role in deter- mining whether, and how severely, growing organs will affect each other during development. We use our findings to discuss the phys- iological causes and evolutionary consequences of resource allocation trade-offs. },
	keywords = {beetle horns, developmental timing, genitalia, imaginal disk, Juvenile hormone, Onthophagus, resource allocation trade-off},
	author = {Moczek, Armin P. and Nijhout, H. Frederik}
}
@article {2200,
	title = {Food availability controls the onset of metamorphosis in the dung beetle Onthophagus taurus (Coleoptera: Scarabaeidae)},
	journal = {Physiological Entomology},
	volume = {26},
	year = {2001},
	pages = {173-180},
	keywords = {developmental cues, dung beetle, larval development, Onthophagus, regulation of pupation, timing of metamorphosis},
	author = {Shafiei, Majid and Moczek, Armin P. and Nijhout, H. Frederik}
}
