@article {1966,
	title = {Horn possession reduces maneuverability in the horn-polyphenic beetle, Onthophagus nigriventris},
	journal = {Journal of Insect Science},
	volume = {6},
	number = {21},
	year = {2006},
	pages = {1-10},
	abstract = {Alternative male morphologies are common in a wide range of organisms and particularly extreme in horned beetles. Here, large males (majors) commonly develop extravagant weaponry such as horns or enlarged mandibles, whereas small males (minors) develop only rudimentary traits. In some taxa, including the genusOnthophagus, the transition from minors to majors occurs over a very small range of body sizes causing intermediate morphologies to be rare or absent from natural populations. Several studies have shown that majors use horns as weapons during male combat over females and that the possession of horns increases male fighting success, and presumably fitness. However, the advantages of a hornless morphology, if any, have remained elusive. Here the alternative male morphs are examined in the horn-polyphenic beetleOnthophagus nigriventris. In particular, the hypothesis was tested that lack of horns in minors increases their maneuverability inside tunnel systems in which these males sneak matings from major males. Using a simple behavioral assay the effects of horn possession on maneuverability were quantified inside an artificial tunnel. Minors were found to be significantly more mobile compared to majors. No such differences were found in mobility between similarly small and large females, which always lack horns. This suggests that mobility differences observed among male morphs are due to the presence or absence of horns rather than differences in body size. This notion was further supported in a second experiment in which surgical removal of horns significantly improved maneuverability, while subsequent re-attachment of horns reversed this effect. These results suggest that lack of horns increases male maneuverability inside tunnels and may thus be advantageous in the context of the particular social niche inhabited by minor males. The results are discussed in the context of the evolutionary ecology of horn-polyphenic beetles. },
	keywords = {ALTERNATIVE REPRODUCTIVE TACTICS, Horned beetle, phenotypic plasticity, Polyphenism, sexual selection},
	author = {Madewell, Richard and Moczek, Armin P.}
}
@article {2026,
	title = {Horn polyphenism in the beetle Onthophagus taurus: larval diet quality and plasticity in parental investment determine adult body size and male horn morphology},
	journal = {Behavioral Ecology},
	volume = {9},
	number = {6},
	year = {1998},
	pages = {636-641},
	keywords = {alternative phenotypes, facultative parental investment, Onthophagus, phenotypic plasticity, Polyphenism},
	author = {Moczek, Armin P.}
}
@article {2027,
	title = {Facultative paternal investment in the polyphenic beetle Onthophagus taurus; the role of male morphology and social context},
	journal = {Behavioral Ecology},
	volume = {10},
	number = {6},
	year = {1999},
	pages = {641-647},
	keywords = {beetles, facultative parental investment, honest indicators, Onthophagus, phenotypic plasticity, Polyphenism, sexual selection},
	author = {Moczek, Armin P.}
}
@article {2029,
	title = {The behavioral ecology of threshold evolution in a polyphenic beetle},
	journal = {Behavioral Ecology},
	volume = {14},
	number = {6},
	year = {2003},
	pages = {841-854},
	abstract = {Facultative expression of alternative male morphologies is thought to allow individual males to select the phenotype with the highest fitness gain given their competitive status relative to other males with which they compete for females. Choice of, or switching between, morphs commonly relies on developmental threshold responses. Evolutionary changes in developmental threshold responses are thought to provide an important avenue for phenotypic diversification and the evolution of morphological and behavioral novelties. However, the extent to which alternative male phenotypes and their underlying threshold responses actually evolve in natural populations is unclear. Likewise, the ecological factors that shape the evolution of threshold responses in natural populations are unexplored for most organisms, as are the consequences of such modifications for patterns of morphological diversity. I examined the ecological basis of rapid threshold evolution in exotic populations of the horn-polyphenic dung beetle Onthophagus taurus. Male O. taurus vary continuously in body size as a function of larval feeding conditions. Only males that exceed a critical threshold body size develop a pair of long horns on their heads, whereas males below this threshold remain hornless. Populations in two exotic ranges of this species, the eastern United States and western Australia, have diverged in the mean threshold body size, which has resulted in the evolution of highly divergent and novel horn length{\textendash}body size allometries in these populations. Populations in a third and previously unstudied exotic range of O. taurus in eastern Australia exhibit threshold body sizes roughly intermediate between the eastern U.S. and western Australian populations. I tested three hypothesis to explain how differences in ecological and demographic factors can drive allometric divergences between populations, using data derived from comparative, standardized sampling of a large number of populations in each exotic range. Results suggest that differences in the intensity of both intra- and interspecific competition have contributed to the evolution of divergent thresholds in these populations. My results do not support the hypothesis that shifts in threshold body sizes to larger body sizes are a consequence of increases in the mean body size of competing males. I discuss my results in the context of Onthophagus mating systems and the evolutionary implications of threshold evolution.},
	keywords = {adaptive phenotypic plasticity, developmental threshold, exotic species, horned beetles, male, Onthophagus, Polyphenism, resource competition, sex ratio evolution, status-dependent selection, threshold evolution, {\textendash}male competition},
	author = {Moczek, Armin P.}
}
@article {2030,
	title = {Pupal remodeling and the development  and evolution of sexual dimorphism in horned beetles},
	journal = {The American Naturalist},
	volume = {168},
	number = {6},
	year = {2006},
	month = {dec},
	pages = {711-729},
	keywords = {allometry, evolvability, lability, Onthophagus, programmed cell death, pupal remodeling},
	author = {Moczek, Armin P.}
}
@article {2031,
	title = {Emerging model systems in evo-devo: horned beetles and the origins of diversity},
	journal = {Evolution and Development},
	volume = {9},
	number = {4},
	year = {2007},
	month = {jul/aug},
	pages = {323-328},
	abstract = {Horned beetles and beetle horns are emerging as a model system suited to address fundamental questions in evolutionary developmental biology. Here we briefly review the biology of horned beetles and highlight the unusual opportunities they provide for evo-devo research. We then summarize recent advances in the development of new approaches and techniques that are now available to scientists interested in working with these organisms. We end by discussing ways to implement and combine these new approaches to explore new frontiers in evo-devo research previously unavailable to reseachers working outside traditional model organisms. },
	author = {Moczek, Armin P. and Andrews, Justin and Kijimoto, Teiya and Yerushalmi, Yoram and Rose, Debra J.}
}
@article {2032,
	title = {Linear and threshold-dependent expression of secondary sexual traits in the same individual: insights from a horned beetle (Coleoptera: Scarabaeidae)},
	journal = {Biological Journal of the Linnean Society},
	volume = {83},
	year = {2004},
	pages = {473-480},
	abstract = {Elaborate horns or horn-like structures in male scarab beetles commonly scale with body size either (a) in a linear fashion with horn size increasing relatively faster than body size or (b) in a threshold-dependent, sigmoid fashion; that is, males smaller than a certain critical body size develop no or only rudimentary horns, whereas males larger than the threshold size express fully developed horns. The development of linear vs. sigmoid scaling relationships is thought to require fundamentally different regulatory mechanisms. Here we show that such disparate regulatory mechanisms may co-occur in the same individual. Large males of the south-east Asian Onthophagus  ( Proagoderus ) watanabei  (Ochi \& Kon) (Scarabaeidae, Onthophagini) develop a pair of long, curved head horns as well as a single thoracic horn. We show that unlike paired head horns in a large number of Onthophagus  species, in O. watanabei  the relationship between head horns and body size is best explained by a linear model. Large males develop dispropor- tionately longer horns than small males, but the difference in relative horn sizes across the range of body sizes is small compared to other Onthophagus  species. However, the scaling relationship between the thoracic horn and body size is best explained by a strongly sigmoid model. Only males above a certain body size threshold express a thoracic horn and males smaller than this threshold express no horn at all. We found a significant positive correlation between head and thoracic horn length residuals, contrary to what would be expected if a resource allocation tradeoff during larval development would influence the length of both horn types. Our results suggest that the scaling rela- tionship between body size and horn length, and the developmental regulation underlying these scaling relation- ships, may be quite different for different horns, even though these horns may develop in the same individual. We discuss our results in the context of the developmental biology of secondary sexual traits in beetles.},
	keywords = {allometry, developmental constraint, developmental tradeoff, Onthophagus, scaling},
	author = {Moczek, Armin P. and Bruhl, Carsten and Krell, Frank-Thorsten}
}
@article {2034,
	title = {Male horn dimorphism in the scarab beetle, Onthophagus taurus: do alternative reproductive tactics favour alternative phenotypes},
	journal = {Animal Behavior},
	volume = {59},
	year = {2000},
	pages = {459-466},
	abstract = {In a variety of organisms morphological variation is discrete rather than continuous. Discrete variation within a sex has attracted particular interest as it is thought to reflect the existence of alternative adaptations to a heterogeneous selection environment. The beetle Onthophagus taurus shows a dimor- phism for male horns: males that exceed a critical body size develop a pair of long, curved horns on their heads, while smaller males remain hornless. In this study we report on the alternative reproductive tactics used by males with these two morphologies, and present experimental and behavioural data suggesting that these alternative tactics selectively favour discretely different male phenotypes. Horned males aggressively defended tunnel entrances containing breeding females. Fights involved the use of horns, and males with longer horns were more likely to win fights. In contrast, hornless males employed nonaggressive sneaking behaviours when faced with competitively superior males. Sneaking behaviours appeared to require high degrees of manoeuvrability inside tunnels to access and mate with females despite the presence of a guarding male. Comparisons of running performances of males with identical body sizes but different horn lengths suggest that the possession of horns reduces male agility inside tunnels. Thus, horn possession confers a clear advantage to males using fighting behaviours to access females, whereas hornlessness may be favoured in males that rely primarily on sneaking behaviours. Combined, the two alternative reproductive tactics used by male O. taurus appear to favour opposite horn phenotypes, which may explain the paucity of intermediate morphologies in natural populations of O. taurus. },
	author = {Moczek, Armin P. and Emlen, Douglas J.}
}
@article {2035,
	title = {Threshold evolution in exotic populations of a polyphenic beetle},
	journal = {Evolutionary Ecology Research},
	volume = {4},
	year = {2002},
	pages = {587-601},
	abstract = {Polyphenic development is thought to play an important role in the evolution of phenotypic diversity and morphological novelties, yet the evolution of polyphenisms has rarely been docu- mented in natural populations. Here we compare the morphologies of male dung beetles (Onthophagus ttaurus; Coleoptera: Scarabaeidae) from populations introduced to Australia and the eastern United States. Males in this species express two alternative morphologies in response to larval feeding conditions. Males encountering favourable conditions grow larger than a threshold body size and develop a pair of horns on their heads, whereas males that encounter poor conditions do not reach this threshold size and remain hornless. Australian and US populations did not differ in overall body size ranges, but exhibited significant differences in the location of the critical body size threshold that separates alternative male morphs. Australian males remained hornless at much larger body sizes than males in US populations, resulting in substantial and significant differences in the average body size{\textendash}horn length allometry between exotic populations, as well as significant differences in morph ratios. The phenotypic divergence observed between field populations was maintained in laboratory populations after two generations under identical environmental conditions, suggesting a genetic basis to allometric divergence in these populations. Divergence between exotic O. taurus populations was of a magnitude and kind typically observed between species. We use our results to examine potential causes of allometric divergence in onthophagine beetles, and discuss the evolutionary potential of threshold traits and polyphenic development in the origin of morphological and behavioural diversity.},
	keywords = {adaptive phenotypic plasticity, alternative tactics, developmental threshold, exotic species, horn polyphenism, Onthophagus, status-dependent selection, threshold evolution.},
	author = {Moczek, Armin P. and Hunt, John and Emlen, Douglas J. and Simmons, Leigh W.}
}
@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 {2098,
	title = {Rapid antagonistic coevolution between primary and secondary sexual characters in horned beetles},
	journal = {Evolution},
	volume = {62},
	number = {9},
	year = {2008},
	month = {sep},
	pages = {2423-2428},
	abstract = {Different structures may compete during development for a shared and limited pool of resources to sustain growth and differ- entiation. The resulting resource allocation trade-offs have the potential to alter both ontogenetic outcomes and evolutionary trajectories. However, little is known about the evolutionary causes and consequences of resource allocation trade-offs in natural populations. Here, we explore the significance of resource allocation trade-offs between primary and secondary sexual traits in shaping early morphological divergences between four recently separated populations of the horned beetle Onthophagus taurus as well as macroevolutionary divergence patterns across 10 Onthophagus species. We show that resource allocation trade-offs leave a strong signature in morphological divergence patterns both within and between species. Furthermore, our results suggest that genital divergence may, under certain circumstances, occur as a byproduct of evolutionary changes in secondary sexual traits. Given the importance of copulatory organ morphology for reproductive isolation our findings begin to raise the possibility that secondary sexual trait evolution may promote speciation as a byproduct. We discuss the implications of our results on the causes and consequences of resource allocation trade-offs in insects. },
	keywords = {Aedeagus, Horned beetle, Onthophagus, resource allocation trade-off, speciation},
	author = {Parzer, Harald F. and Moczek, Armin P.}
}
@article {2109,
	title = {Rapid shape divergences between natural and introduced populations of a horned beetle partly mirror divergences between species},
	journal = {Evolution and Development},
	volume = {10},
	number = {2},
	year = {2008},
	pages = {166-175},
	abstract = {Onthophagus taurus is a polyphenic beetle in which males express alternative major (horned) and minor (hornless) morphologies largely dependent on larval nutrition. O. taurus was originally limited to a Turanic--European-- Mediterranean distribution, but became introduced to several exotic regions in the late 1960s. Using geometric morphometrics, we investigate the present-day morphological shape differentiation patterns among native (Italian) and introduced (Western Australian and Eastern US) popu- lations. We then contrast these divergences to those observed between native O. taurus and its sympatric sister species O. illyricus. Our analysis failed to find significant divergences between O. taurus populations in external morphological traits (head, pronotum) when analyses were conducted separately for each sex. However, when sexes and male morphs were analyzed together, three important differences among populations emerged. First, relative warp analyses showed that native and introduced populations diverged in certain shape components that normally distin- guish major and minor male morphs. Second, comparison of covariation of body regions (head vs. pronotum) in the three populations showed that populations diverged in the nature of this covariation, suggesting that different body regions are not totally constrained to evolve in concert. Lastly, and most importantly, the analysis of genitalic shape revealed little to no divergence of female genitalia, but unexpected substantial differentiation of male genitalia among the three O. taurus populations. This suggests that genitalic shape divergence can occur extremely rapidly even in the absence of sympatry and possible reinforcement, and that the genitalia of males and females may diverge independent of one another, at least during the early stage of interpopulational divergence. Interpopulation divergences in O. taurus mirrored aspects of interspecific divergences between O. taurus and O. illyricus in some cases but not others. },
	author = {Pizzo, A. and Roggero, A. and Palestrini, Claudia and Moczek, Armin P. and Rolando, Antonio}
}
@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}
}
