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-scarabaeidae01957nas a2200193   4500008004100000245007300041210006900114300001200183490000700195520133700202653001401539653001101553653001601564653002101580653002101601100002301622700002201645856009601667       2000                        eng d00aThe development and evolution of exaggerated morphologies in insects0 adevelopment and evolution of exaggerated morphologies in insects  a661-7080 v453 aWe discuss a framework for studying the evolution of morphology in insects, based on the concepts of ‘‘phenotypic plasticity’’ and ‘‘reaction norms.’’ We illustrate this approach with the evolution of some of the most extreme morphologies in insects: exaggerated, sexually selected male ornaments and weapons, and elaborate social insect soldier castes. Most of these traits scale with body size, and these scaling relationships are often nonlinear. We argue that scaling relationships are best viewed as reaction norms, and that the evolution of exaggerated morphological traits results from genetic changes in the slope and/or shape of these scaling relationships. After reviewing literature on sexually selected and caste-specific structures, we suggest two possible routes to the evolution of exaggerated trait dimensions: (a) the evolution of steeper scaling relationship slopes and (b) the evolution of sigmoid or discontinuous scaling relationship shapes. We discuss evolutionary implications of these two routes to exaggeration and suggest why so many of the most exaggerated insect structures scale nonlinearly with body size. Finally, we review literature on insect development to provide a comprehensive picture of how scaling relationships arise and to suggest how they may be modified through evolution.10aallometry10acastes10aPolyphenism10asexual selection10athreshold traits1 aEmlen, Douglas, J.1 aNijhout, Frederik  uhttps://scarabnet.myspecies.info/development-and-evolution-exaggerated-morphologies-insects02476nas a2200133   4500008004100000245004600041210004600087300001200133490000600145520207300151100002202224700002202246856007402268       2003                        eng d00aRapid evolution of a polyphenic threshold0 aRapid evolution of a polyphenic threshold  a259-2680 v53 aPolyphenisms 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.1 aMoczek, Armin, P.1 aNijhout, Frederik  uhttps://scarabnet.myspecies.info/rapid-evolution-polyphenic-threshold02565nas a2200217   4500008004100000245009600041210006900137300001200206490000800218520181500226653001702041653002502058653001402083653001802097653002102115653001602136653003402152100002202186700002202208856011702230       2004                        eng d00aTrade-offs during the development of primary and secondary sexual traits in a horned beetle0 aTradeoffs during the development of primary and secondary sexual  a184-1910 v1633 a 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. 10abeetle horns10adevelopmental timing10agenitalia10aimaginal disk10aJuvenile hormone10aOnthophagus10aresource allocation trade-off1 aMoczek, Armin, P.1 aNijhout, Frederik  uhttps://scarabnet.myspecies.info/trade-offs-during-development-primary-and-secondary-sexual-traits-horned-beetle00792nas a2200205   4500008004100000245012300041210006900164300001200233490000700245653002300252653001600275653002300291653001600314653002700330653002800357100001900385700002200404700002200426856013800448       2001                        eng d00aFood availability controls the onset of metamorphosis in the dung beetle Onthophagus taurus (Coleoptera: Scarabaeidae)0 aFood availability controls the onset of metamorphosis in the dun  a173-1800 v2610adevelopmental cues10adung beetle10alarval development10aOnthophagus10aregulation of pupation10atiming of metamorphosis1 aShafiei, Majid1 aMoczek, Armin, P.1 aNijhout, Frederik  uhttps://scarabnet.myspecies.info/food-availability-controls-onset-metamorphosis-dung-beetle-onthophagus-taurus-coleoptera-scarabaeida