02835nas a2200277   4500008004100000245004900041210004900090260000800139300001000147490000700157520204700164653003502211653002602246653002902272653002402301653002802325653002102353653000902374653001602383653003802399653003102437653001202468653002402480100001902504856003402523       2002                        eng d00aAllometric plasticity in a polyphenic beetle0 aAllometric plasticity in a polyphenic beetle  cFeb  a58-670 v273 a1. Environmental conditions. such as variation in nutrition. commonly contribute to morphological variation among individuals by affecting body size and the expression of certain morphological traits however the scaling relationship between a morphological trait and body size over a range of body sizes is generally assumed not to change in response to environmental fluctuation (allometric plasticity), but instead to be constant and diagnostic for a particular trait and species or Population. The work reported here examined diet- induced allometric plasticity in the polyphenic beetle Onthophagus taurus Schreber (1759) (Coleoptera: Scarabaeidae). 2. Male O. taurus vary in body size depending on larval nutrition, Only males above a critical body size threshold express fully developed horns: males smaller than this threshold develop only rudirrientary horns or no horns at all. 3. Field populations that naturally utilise two different resources for feeding larvae (horse dung vs. cow manure) exhibited significant differences in the average scaling relationship between body size and male horn length over the same range of body sizes. Males collected from cow manure populations expressed consistently longer horns for a given body size than males collected from horse dung Populations. 4. Males reared in the laboratory on horse dung or cow manure also exhibited significant differences in the average scaling relationship between body size and horn length. Differences between laboratory populations reared on horse dung or cow manure were of the same kind and magnitude as differences between field populations that utilise these different resources naturally. 5. These findings suggest that between- population differences in scaling relationships between horn length and body size can be the product of differences in the quality of resources available to developing larvae. Results are discussed in the context of onthophagine mating systems and recent insights in the developmental and endocrine control of horn polyphenisms.10aadaptive phenotypic plasticity10aallometric plasticity10aalternative reproductive10aalternative tactics10adevelopmental threshold10ahorn polyphenism10amale10aOnthophagus10aonthophagus-acuminatus coleoptera10astatus-dependent selection10atactics10athreshold evolution1 aMoczek, A., P.  u<Go to ISI>://00017436120000803111nas a2200313   4500008004100000245011200041210006900153300001000222490000700232520208700239653001502326653001402341653001302355653001602368653001602384653001402400653002602414653002902440653002002469653001302489653001802502653001902520653000802539653005802547653002302605100001902628700001802647856013202665       1999                        eng d00aProximate determination of male horn dimorphism in the beetle Onthophagus taurus (Coleoptera: Scarabaeidae)0 aProximate determination of male horn dimorphism in the beetle On  a27-370 v123 aThe existence of discrete phenotypic variation within one sex poses interesting questions regarding how such intrasexual polymorphisms are produced and modified during the course of evolution. Approaching these kinds of questions requires insights into the genetic architecture underlying a polymorphism and an understanding of the proximate mechanisms determining phenotype expression. Here we explore the genetic underpinnings and proximate factors influencing the expression of beetle horns - a dramatic sexually selected trait exhibiting intramale dimorphism in many species. Two relatively discrete male morphs are present in natural populations of the dung beetle Onthophagus taurus (Scarabaeidae, Onthophagini). Males exceeding a critical body size develop a pair of long, curved horns on their heads, while those smaller than this critical body size remain essentially hornless. We present results from laboratory breeding experiments designed to assess the relative importance of inherited and environmental factors as determinants of male morphology. Using father-son regressions, our findings demonstrate that horn length and body size of male progeny are not predicted from paternal morphology. instead, natural variation in an environmental factor, the amount of food available to larvae, determined both the body sizes exhibited by males as adults and the presence or absence of horns. The nonlinear scaling relationship between the body size and horn length of males bred in the laboratory did not differ from the pattern of variation present in natural populations, suggesting that nutritional conditions account for variation in male morphology in natural populations as well. We discuss our results by extending ideas proposed to explain the evolution of conditional expression of alternative phenotypes in physically heterogeneous environments toward incorporating facultative expression of secondary sexual traits. We use this synthesis to begin characterizing the potential origin and subsequent evolution of facultative horn expression in onthophagine beetles.10aallometry-10aAnimalia-10aAnimals-10aArthropoda-10aArthropods-10abody-size10aColeoptera-: Insecta-10aEvolution-and-Adaptation10ahorn-dimorphism10aInsects-10aInvertebrata-10aInvertebrates-10amor10aOnthophagus-taurus [dung-beetle] (Coleoptera-): male-10aPopulation-Studies1 aMoczek, A., P.1 aEmlen, D., J.  uhttps://scarabnet.myspecies.info/proximate-determination-male-horn-dimorphism-beetle-onthophagus-taurus-coleoptera-scarabaeidae