The Experts below are selected from a list of 1743 Experts worldwide ranked by ideXlab platform
Leigh W. Simmons - One of the best experts on this subject based on the ideXlab platform.
-
Ultrastructure of spermatozoa of Onthophagus taurus (Coleoptera, Scarabaeidae) exhibits heritable variation
Naturwissenschaften, 2011Co-Authors: Michael Werner, Leigh W. SimmonsAbstract:Sperm competition is thought to be an important selective pressure shaping sperm form and function. However, few studies have moved beyond gross examinations of sperm morphology. Sperm length is subject to sexual selection via sperm competition in the scarab beetle Onthophagus taurus. Here, the structure and ultrastructure of spermatozoa in this species were investigated using light and electron microscopy. Spermatozoa were found to be filiform, measuring about 1,200 mm in length. The sperm head consists of a three-layered acrosome and a nuclear region bearing the anterior extension of the centriole adjunct. Acrosome and nuclear regions are bilaterally symmetric, with their axes of symmetry being orthogonal to each other. Head and flagellar structures are connected by a well-developed centriole adjunct. The sperm heads are asymmetrically surrounded by accessory material and embedded into the cytoplasm of the spermatocyst cell. The accessory material is produced inside the spermatids and then transferred to the outside due to a new membrane formed around the sperm’s organelles. The old spermatid membrane separates the accessory material from the cyst cell. The flagellum contains a 9+9+2 axoneme, two accessory bodies, and two mitochondrial derivatives of unequal size. The major mitochondrial derivative is significantly larger than the minor one. The axoneme is arranged in a sinusoidal manner parallel along the major mitochondrial derivative. The spermatozoa show no progressive motility when released in buffer solution which is likely to be the result of the flagellar arrangement and the structure of the major mitochondrial derivative. The cross-sectional area of the minor and the major mitochondrial derivatives show different patterns of genetic variation. The data provide the first estimates of genetic variation in sperm ultrastructure for any species, and give evidence for the persistence of genetic variation in ultrastructure required for the rapid and divergent evolution that characterizes spermatozoa generally.
-
optimal maternal investment in the dung beetle Onthophagus taurus
Behavioral Ecology and Sociobiology, 2004Co-Authors: John Hunt, Leigh W. SimmonsAbstract:Optimal investment theory is based on the assumption that the proximate constraint acting on parental investment is resource based. A trade-off between per offspring investment and total investment seems intuitive. Consequently, a parent’s investment strategy is expected to represent a trade-off between the benefits of investment for current offspring and the costs to future reproduction for parents. In this study, we provide clear evidence that the costs and benefits of maternal provisioning in the dung beetle Onthophagus taurus influence the amount of provisions provided by the mother. Horse dung is typically of a higher nutritional value than cow dung and females were shown to provide 20% less dung to offspring when provisioning with horse dung. By reducing their investment per offspring and exhibiting a clear preference to provision offspring with horse dung, females were able to produce significantly more offspring. Females provisioning with horse dung received greater fitness returns per unit of investment and experienced lower provisioning costs, in terms of the minimum amount of dung required to produce a surviving offspring, than females provisioning with cow dung. Females provisioning in soil of low moisture content were found to have higher tunneling costs than those provisioning in soil of high moisture content, while the fitness returns per unit of investment did not differ. We adopted a marginal value theorem (MVT) approach to calculate the theoretical optimal level of investment for each dung type and for each soil moisture. Predicted levels of provisioning were lower for horse dung than for cow dung and for moist soil than for dry soil. Therefore, the results of this study are in qualitative agreement with MVT predictions and provide empirical support for the proposal that females can adaptively adjust their level of investment in response to resource and/or habitat quality. However, the theoretically predicted optimal investment yielded a poor quantitative fit with our observed levels of investment, with females providing over twice the investment predicted by the MVT approach. We suggest that this difference may reflect either our inability in directly quantifying all the necessary costs and benefits of investment in O. taurus and/or the applicability of the underlying assumptions of MVT.
-
Behavioural dynamics of biparental care in the dung beetle Onthophagus taurus
Animal Behaviour, 2002Co-Authors: John Hunt, Leigh W. SimmonsAbstract:Abstract In the dimorphic dung beetle Onthophagus taurus major males provide assistance during offspring provisioning. We examined the behavioural dynamics of biparental care to quantify directly how males and females allocate time to parental and nonparental behaviours and to determine whether parents adjust their level of investment relative to their partner's contribution. Females allocated more of their time budget to parental behaviours than males. The proportion of time females allocated to parental behaviours increased after oviposition while that of a male decreased. Male paternity assurance behaviours were negatively associated with male and female parental behaviours. Theoretical models predict that the investment provided by the members of a cooperative pair should be negatively correlated and that any shortfall of one parent should be partially compensated for by the other. In the absence of a male, unassisted females allocated more time to parental care, and performed more parental behaviours. However, compensation was incomplete as unassisted females performed fewer parental behaviours than pairs, resulting in significantly lighter brood masses (the egg and its associated dung supply). Males performed more parental behaviours when paired with small females, and small females more than large females. Contrary to prediction, the investments provided by males and females in a cooperative pair were positively correlated. Males coordinated their parental behaviours with the females rather than acting independently. Since parental behaviours were directly related to the weight of brood masses, the observed parental interactions will have important fitness consequences in this species. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.
-
a cost of maternal care in the dung beetle Onthophagus taurus
Journal of Evolutionary Biology, 2002Co-Authors: John Hunt, Leigh W. Simmons, Janne S KotiahoAbstract:Parental care theory assumes that investment in current offspring will trade against future investment. A number of field studies on birds have used clutch size manipulations to demonstrate a survival cost to chick rearing. However, such studies do not account for costs accrued during earlier stages of reproduction because not all aspects of reproductive effort are manipulated by varying the number of nestlings. In this study, we investigate the effect of reproductive effort on female survival in the dung beetle, Onthophagus taurus. By experimentally manipulating mating status and dung availability, we demonstrate that virgin females survive longer than mated females and that the survival of mated females was negatively associated with the number of brood masses produced. Using a novel manipulation of the mating system, we separated the effects of egg production and maternal care on female survival. Previously, we have shown that females provisioning with the assistance of a major male provide relatively less care than unassisted females. However, paternal assistance did not alter the number of brood masses produced and hence the amount of reproductive effort that was allocated to egg production. Therefore, our finding that female survival was increased when receiving paternal assistance provides, to our knowledge, the first definitive evidence that maternal care reduces female lifespan. These results are of major importance to theoretical models on the evolution of parental care.
-
status dependent selection in the dimorphic beetle Onthophagus taurus
Proceedings of The Royal Society B: Biological Sciences, 2001Co-Authors: John Hunt, Leigh W. SimmonsAbstract:The occurrence of alternative reproductive phenotypes is widespread in most animal taxa. The majority of known examples best fit the notion of alternative tactics within a conditional strategy where the fitness pay-offs depend on an individual's competitive ability or status. Individuals are proposed as "choosing" the tactic that maximizes their fitness, given their status relative to others in the population. Theoretically, status-dependent selection should determine when an animal should switch between alternative tactics. While a number of studies have demonstrated unequal fitness pay-offs associated with alternative tactics, none, to our knowledge, have examined the fitness functions necessary for predicting when individuals should switch between tactics. Here, we use a dimorphic male beetle in order to provide the first empirically derived fitness function across alternative reproductive phenotypes. Our data provide empirical support for a game-theoretic conditional strategy that has evolved under status-dependent selection.
John Hunt - One of the best experts on this subject based on the ideXlab platform.
-
optimal maternal investment in the dung beetle Onthophagus taurus
Behavioral Ecology and Sociobiology, 2004Co-Authors: John Hunt, Leigh W. SimmonsAbstract:Optimal investment theory is based on the assumption that the proximate constraint acting on parental investment is resource based. A trade-off between per offspring investment and total investment seems intuitive. Consequently, a parent’s investment strategy is expected to represent a trade-off between the benefits of investment for current offspring and the costs to future reproduction for parents. In this study, we provide clear evidence that the costs and benefits of maternal provisioning in the dung beetle Onthophagus taurus influence the amount of provisions provided by the mother. Horse dung is typically of a higher nutritional value than cow dung and females were shown to provide 20% less dung to offspring when provisioning with horse dung. By reducing their investment per offspring and exhibiting a clear preference to provision offspring with horse dung, females were able to produce significantly more offspring. Females provisioning with horse dung received greater fitness returns per unit of investment and experienced lower provisioning costs, in terms of the minimum amount of dung required to produce a surviving offspring, than females provisioning with cow dung. Females provisioning in soil of low moisture content were found to have higher tunneling costs than those provisioning in soil of high moisture content, while the fitness returns per unit of investment did not differ. We adopted a marginal value theorem (MVT) approach to calculate the theoretical optimal level of investment for each dung type and for each soil moisture. Predicted levels of provisioning were lower for horse dung than for cow dung and for moist soil than for dry soil. Therefore, the results of this study are in qualitative agreement with MVT predictions and provide empirical support for the proposal that females can adaptively adjust their level of investment in response to resource and/or habitat quality. However, the theoretically predicted optimal investment yielded a poor quantitative fit with our observed levels of investment, with females providing over twice the investment predicted by the MVT approach. We suggest that this difference may reflect either our inability in directly quantifying all the necessary costs and benefits of investment in O. taurus and/or the applicability of the underlying assumptions of MVT.
-
Behavioural dynamics of biparental care in the dung beetle Onthophagus taurus
Animal Behaviour, 2002Co-Authors: John Hunt, Leigh W. SimmonsAbstract:Abstract In the dimorphic dung beetle Onthophagus taurus major males provide assistance during offspring provisioning. We examined the behavioural dynamics of biparental care to quantify directly how males and females allocate time to parental and nonparental behaviours and to determine whether parents adjust their level of investment relative to their partner's contribution. Females allocated more of their time budget to parental behaviours than males. The proportion of time females allocated to parental behaviours increased after oviposition while that of a male decreased. Male paternity assurance behaviours were negatively associated with male and female parental behaviours. Theoretical models predict that the investment provided by the members of a cooperative pair should be negatively correlated and that any shortfall of one parent should be partially compensated for by the other. In the absence of a male, unassisted females allocated more time to parental care, and performed more parental behaviours. However, compensation was incomplete as unassisted females performed fewer parental behaviours than pairs, resulting in significantly lighter brood masses (the egg and its associated dung supply). Males performed more parental behaviours when paired with small females, and small females more than large females. Contrary to prediction, the investments provided by males and females in a cooperative pair were positively correlated. Males coordinated their parental behaviours with the females rather than acting independently. Since parental behaviours were directly related to the weight of brood masses, the observed parental interactions will have important fitness consequences in this species. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.
-
a cost of maternal care in the dung beetle Onthophagus taurus
Journal of Evolutionary Biology, 2002Co-Authors: John Hunt, Leigh W. Simmons, Janne S KotiahoAbstract:Parental care theory assumes that investment in current offspring will trade against future investment. A number of field studies on birds have used clutch size manipulations to demonstrate a survival cost to chick rearing. However, such studies do not account for costs accrued during earlier stages of reproduction because not all aspects of reproductive effort are manipulated by varying the number of nestlings. In this study, we investigate the effect of reproductive effort on female survival in the dung beetle, Onthophagus taurus. By experimentally manipulating mating status and dung availability, we demonstrate that virgin females survive longer than mated females and that the survival of mated females was negatively associated with the number of brood masses produced. Using a novel manipulation of the mating system, we separated the effects of egg production and maternal care on female survival. Previously, we have shown that females provisioning with the assistance of a major male provide relatively less care than unassisted females. However, paternal assistance did not alter the number of brood masses produced and hence the amount of reproductive effort that was allocated to egg production. Therefore, our finding that female survival was increased when receiving paternal assistance provides, to our knowledge, the first definitive evidence that maternal care reduces female lifespan. These results are of major importance to theoretical models on the evolution of parental care.
-
status dependent selection in the dimorphic beetle Onthophagus taurus
Proceedings of The Royal Society B: Biological Sciences, 2001Co-Authors: John Hunt, Leigh W. SimmonsAbstract:The occurrence of alternative reproductive phenotypes is widespread in most animal taxa. The majority of known examples best fit the notion of alternative tactics within a conditional strategy where the fitness pay-offs depend on an individual's competitive ability or status. Individuals are proposed as "choosing" the tactic that maximizes their fitness, given their status relative to others in the population. Theoretically, status-dependent selection should determine when an animal should switch between alternative tactics. While a number of studies have demonstrated unequal fitness pay-offs associated with alternative tactics, none, to our knowledge, have examined the fitness functions necessary for predicting when individuals should switch between tactics. Here, we use a dimorphic male beetle in order to provide the first empirically derived fitness function across alternative reproductive phenotypes. Our data provide empirical support for a game-theoretic conditional strategy that has evolved under status-dependent selection.
-
maternal and paternal effects on offspring phenotype in the dung beetle Onthophagus taurus
Evolution, 2000Co-Authors: John Hunt, Leigh W. SimmonsAbstract:Parents often have important influences on the development of traits in their offspring. One mechanism by which parents are able to influence offspring phenotype is through the level of care they provide. In onthophagine dung beetles, parents typically provision their offspring by packing dung fragments into a brood mass. Onthophagus taurus males can be separated into two discrete morphs: Large, "major" males have head horns, whereas "minor" males are hornless. Here we show that a switch in parental provisioning strategies adopted by males coincides with the switch in male morphology. Male provisioning results in the production of heavier brood masses than females will produce alone. However, unlike females in which the level of provisioning increases with body size in a continuous manner, the level of provisioning provided by males represents an "all-or-none" tactic with all major males providing a fixed level of provisioning irrespective of their body size. Offspring size is determined largely by the quantity of dung provided to the developing larvae so that paternal and maternal provisioning affects the body size and horn size of offspring produced. The levels of provisioning by individual parents are significantly repeatable, suggesting paternal and maternal effects as candidate indirect genetic effects in the evolution of horn size in the genus Onthophagus.
Armin P. Moczek - One of the best experts on this subject based on the ideXlab platform.
-
developmental regulation and evolution of scaling novel insights through the study of Onthophagus beetles
Current opinion in insect science, 2017Co-Authors: Sofia Casasa, Daniel B Schwab, Armin P. MoczekAbstract:Scaling relationships play critical roles in defining biological shape, trait functionality, and species characteristics, yet the developmental basis of scaling and its evolution remain poorly resolved in most taxa. In the horned beetle genus Onthophagus, scaling relationships of most traits are largely comparable across many species, however, the morphology and scaling of horns, a recent evolutionary invention, has diversified dramatically, ranging from modestly to highly positively linear to more complex sigmoidal allometries. Through a series of transcriptomic screens and gene function assays, the doublesex, hedgehog, insulin, and serotonin signaling pathways have recently been implicated in the regulation of amplitude, slope, and threshold location of the highly sigmoidal horn allometry in O. taurus. These and other findings suggest that co-option of these pathways into the regulation of horn development may have been critical in the evolutionary transitions from isometric to positively allometric to sigmoidal allometries in Onthophagus, thereby contributing to the extraordinary diversification of one of the most species-rich genera in the animal kingdom.
-
diversification of doublesex function underlies morph sex and species specific development of beetle horns
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Teiya Kijimoto, Armin P. Moczek, Justen AndrewsAbstract:Sex-specific trait expression is frequently associated with highly variable, condition-dependent expression within sexes and rapid divergence among closely related species. Horned beetles are an excellent example for studying the molecular basis of these phenomena because horn morphology varies markedly among species, between sexes, and among alternative, nutritionally-cued morphs within sexes. In addition, horns lack obvious homology to other insect traits and provide a good opportunity to explore the molecular basis of the rapid diversification of a novel trait within and between species. Here we show that the sex-determination gene doublesex (dsx) underlies important aspects of horn development, including differences between sexes, morphs, and species. In male Onthophagus taurus, dsx transcripts were preferentially expressed in the horns of the large, horned morph, and RNAi-mediated knockdown of dsx dramatically altered male horn allometry by massively reducing horn development in large males, but not in smaller males. Conversely, dsx RNAi induced ectopic, nutrition-sensitive horn development in otherwise hornless females. Finally, in a closely related species (Onthophagus sagittarius) that has recently evolved a rare reversed sexual dimorphism, dsx RNAi revealed reversed as well as novel dsx functions despite an overall conservation of dsx expression. This suggests that rapid evolution of dsx functions has facilitated the transition from a regular sexual dimorphism to a reversed sexual dimorphism in this species. Our findings add beetle horns to existing examples of a close relationship between dsx and sexual trait development, and suggest that dsx function has been coopted to facilitate both the evolution of environmentally-cued intrasexual dimorphisms and rapid species divergences in a novel trait.
-
evolution and development Onthophagus beetles and the evolutionary development genetics of innovation allometry and plasticity
2011Co-Authors: Armin P. MoczekAbstract:1. the expression of horns, exaggerated and diverse secondary sexual traits lacking obvious homology to other insect traits; 2. rich phenotypic diversity including morphological, behavioural, and physiological traits; 3. the significance of environmental factors, especially nutrition, in guiding phenotype determination; 4. the fact that Onthophagus beetles stand out as the animal kingdom’s most speciose genus.
-
gene discovery in the horned beetle Onthophagus taurus
BMC Genomics, 2010Co-Authors: Jeong Hyeon Choi, Armin P. Moczek, Teiya Kijimoto, Emilie C Snellrood, Hongseok Tae, Youngik Yang, Justen AndrewsAbstract:Horned beetles, in particular in the genus Onthophagus, are important models for studies on sexual selection, biological radiations, the origin of novel traits, developmental plasticity, biocontrol, conservation, and forensic biology. Despite their growing prominence as models for studying both basic and applied questions in biology, little genomic or transcriptomic data are available for this genus. We used massively parallel pyrosequencing (Roche 454-FLX platform) to produce a comprehensive EST dataset for the horned beetle Onthophagus taurus. To maximize sequence diversity, we pooled RNA extracted from a normalized library encompassing diverse developmental stages and both sexes. We used 454 pyrosequencing to sequence ESTs from all post-embryonic stages of O. taurus. Approximately 1.36 million reads assembled into 50,080 non-redundant sequences encompassing a total of 26.5 Mbp. The non-redundant sequences match over half of the genes in Tribolium castaneum, the most closely related species with a sequenced genome. Analyses of Gene Ontology annotations and biochemical pathways indicate that the O. taurus sequences reflect a wide and representative sampling of biological functions and biochemical processes. An analysis of sequence polymorphisms revealed that SNP frequency was negatively related to overall expression level and the number of tissue types in which a given gene is expressed. The most variable genes were enriched for a limited number of GO annotations whereas the least variable genes were enriched for a wide range of GO terms directly related to fitness. This study provides the first large-scale EST database for horned beetles, a much-needed resource for advancing the study of these organisms. Furthermore, we identified instances of gene duplications and alternative splicing, useful for future study of gene regulation, and a large number of SNP markers that could be used in population-genetic studies of O. taurus and possibly other horned beetles.
-
est and microarray analysis of horn development in Onthophagus beetles
BMC Genomics, 2009Co-Authors: Teiya Kijimoto, Armin P. Moczek, James C Costello, Zuojian Tang, Justen AndrewsAbstract:Background The origin of novel traits and their subsequent diversification represent central themes in evo-devo and evolutionary ecology. Here we explore the genetic and genomic basis of a class of traits that is both novel and highly diverse, in a group of organisms that is ecologically complex and experimentally tractable: horned beetles.
Claudia Palestrini - One of the best experts on this subject based on the ideXlab platform.
-
an unfinished speciation process revealed by geometric morphometrics horn allometries and biomolecular analyses the case of the fracticornis similis opacicollis species complex of the genus Onthophagus coleoptera scarabaeidae
Zoologischer Anzeiger – A Journal of Comparative Zoology, 2013Co-Authors: Astrid Pizzo, Danilo Zagaria, Claudia PalestriniAbstract:Abstract Species complexes, composed by closely related species of difficult identification for their morphological similarity, provide unique opportunity to study the early phases of morphological and genetic differentiation and the microevolutionary dynamics promoting speciation. Within the genus Onthophagus the presence of many species complexes and sibling species testify to a recent impressive adaptive radiation. We focused on the debated species-complex Onthophagus (PalaeOnthophagus) ‘fracticornis–similis–opacicollis’ as a model to study the evolution of morphology, the role of male polyphenism and the microevolutionary dynamics promoting speciation. Even if at present there is a general consensus that Onthophagus fracticornis is a good species, greater discrepancies arise on the taxonomic status of Onthophagus similis and Onthophagus opacicollis: according to some authors these are sibling species with a wide range of sympatry whilst others maintain they are morphotypes of a single, polymorphic species. To investigate the relationships within the complex and to study evolution of morphology and the dynamics of their differentiation, we studied together allopatric and sympatric populations integrating multiple approaches: the geometric morphometric analysis of the shapes of genital and non-genital morphological structures, the comparison of horn static allometries and the biomolecular analysis of a mitochondrial gene. The results provided a complex and often incongruent pattern of morphological and genetic evolution, consistent with a hypothesis of a still unfinished speciation process in sympatric areas and a fully realised speciation by means of ecological segregation in allopatry.
-
Trade-off between horns and other functional traits in two Onthophagus species (Scarabaeidae, Coleoptera)
Zoomorphology, 2012Co-Authors: Astrid Pizzo, Anna L M Macagno, Serena Dusini, Claudia PalestriniAbstract:Beetle horns are extraordinarily diversified secondary sexual structures used for mate choice and male–male combat. Due to an interaction of nutritional, hormonal and genetic factors, their polyphenic development is metabolically expensive and occurs in the virtually closed system of the pre-pupal stage, after the developing larva has stopped feeding. Previous studies showed the occurrence of resource competition resulting in a trade-off between horns and other morphological structures. These studies also revealed functional associations between autoecology and horns, as a function of their physical location (i.e. head versus pronotum), and suggested that constraints imposed by trade-offs on adult morphology may have profound evolutionary consequences, such as ecological and reproductive isolation. In this study, we compared trade-off patterns between horns and other functional traits (eyes, antennae, legs, head, epipharynges and genitalia) in two congeneric species bearing horns located in the same anatomical area, but with different morphologies. Specifically, we considered Onthophagus taurus , characterised by a pair of long, lunated cephalic horns, and Onthophagus fracticornis , expressing a single cephalic horn. We demonstrated that, even when horns are located in the same physical position on the insect’s body, differences in horn morphology can bring about differences in how functional traits respond to horn investment. These differences are interpretable in the light of the hierarchy of functions carried out by these structures and their component parts in each species.
-
combination of geometric morphometric and genetic approaches applied to a debated taxonomical issue the status of Onthophagus massai coleoptera scarabaeidae as an endemic species vicarious to Onthophagus fracticornis in sicily
Zoology, 2011Co-Authors: Astrid Pizzo, Antonio Rolando, Fabio Mazzone, Claudia PalestriniAbstract:Abstract The present study deals with the phenomenon of insular speciation and discusses, as a case study, the debated taxonomical issue of the status of Onthophagus massai (Coleoptera, Sarabaeidae) as an endemic species vicarious to Onthophagus fracticornis in Sicily. The authors investigated the differentiation patterns between an insular population belonging to the supposed species O. massai (collected in its locus typicus , Piano Battaglia) and three Italian O. fracticornis populations (collected along a N–S latitudinal gradient). These patterns are described and analysed using multiple approaches: the qualitative inspection of the microsculpture of elytral surfaces, considered a diagnostic character for O. massai identification; the comparison of horn static allometries, known to be a good indicator of divergence processes between closely related species or isolated populations of the same species; the comparison of the patterns of shape and size difference of the head, epipharynx and genitalia attained with a combination of traditional and geometric (landmark and semilandmark) morphometric methods; and, finally, the estimation of the genetic relationships between Sicilian and continental populations obtained by analysing cytochrome oxidase subunit 1 mitochondrial gene sequences. The integration of the results of these approaches indicates that there is not sufficient evidence to vindicate the species status for O. massai , which should more likely be considered a small-sized version of O. fracticornis (a possible case of insular dwarfism). However, the complex pattern of shape, size and genetic variation observed between the populations analysed hinted at the possibility that a diversification process is ongoing, but not only between insular and continental populations; each population showed a tendency to evolve as an evolutionarily independent unit.
-
size and shape interspecific divergence patterns partly reflect phylogeny in an Onthophagus species complex coleoptera scarabaeidae
Zoological Journal of the Linnean Society, 2011Co-Authors: Anna L M Macagno, Astrid Pizzo, Antonio Rolando, Claudia PalestriniAbstract:Polyphenism has been suggested as an accelerator for morphological evolution and speciation. In the dung beetles of the genus Onthophagus, horn expression is polyphenic: large males develop horns whereas smaller males express greatly reduced or no horns. Horn static allometries seem to diverge rapidly amongst extant taxa, a process which might trigger changes in the male genital morphology, thus possibly promoting speciation as a by-product. It can therefore be hypothesized that interspecific distances in allometries and, possibly, in other morphological traits mirror phylogenetic distances. In this study we first assessed the phylogenetic relationships amongst three closely related taxa belonging to the so-called ‘Onthophagus fracticornis-similis-opacicollis’ species-complex by sequencing the mitochondrial gene cytochrome oxidase subunit 1 (cox1). Biomolecular results indicated three independent lineages, the closest relationships being found between Onthophagus similis and Onthophagus opacicollis. Then we assessed the extent to which divergence pattern of horn static allometries and size and shape divergence patterns of one genital (paramere) and two nongenital (head and epipharynx) structures mirrored the phylogenetic relationships. Interspecific divergence patterns of horn static allometries, paramere, and head shape were found to be congruent with the evolutionary relationships inferred from biomolecular data. Nevertheless, paramere size and epipharynx shape showed patterns not consistent with the phylogeny. Furthermore, the relative size of nongenital structures showed little interspecific divergence compared to their shapes. Our results suggest that size and shape interspecific divergence mirror phylogeny only in part; they also indicate that distinct morphological traits may differ in their tendency to evolve in concert, and that size and shape of the same trait can evolve independently across species. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162, 482–498.
-
epipharynx shape as a tool to reveal differentiation patterns between insect sister species insights from Onthophagus taurus and o illyricus insecta coleoptera scarabaeidae
Organisms Diversity & Evolution, 2009Co-Authors: Astrid Pizzo, Anna L M Macagno, Antonio Rolando, Angela Roggero, Claudia PalestriniAbstract:We evaluated the potential of the adult epipharynx to reveal interspecific differentiation patterns in closely related Onthophagus species. Although easy to analyse, this structure has received little attention in Scarabaeidae taxonomy, probably because a qualitative inspection of its shape often does not yield differences between congeneric species. The polyphenic sister species Onthophagus taurus Schreber, 1759 and O. illyricus Scopoli, 1763 were chosen as a case study. They are extremely similar, to the extent that in some cases they cannot be identified unambiguously without the help of biomolecular analysis. In this study, a combination of linear measurements and a landmark-based approach was employed to quantify inter- and intraspecific shape variation in the epipharynx of specimens sampled at the same study site. Our results showed that the epipharynx is a monomorphic structure: its shape does not vary as a function of sex or male phenotype. In males, epipharynx shape does not change with head shape or horn length. The close proximity of the epipharynx to the horns and the synchronous developmental patterns of these two structures suggest that a developmental trade-off may act between them. Despite these predisposing conditions, however, our results suggest that epipharynx size is not subject to costs associated with horn development, and that the trait is highly canalised. Surprisingly, when using geometric morphometrics the epipharynx appears to be a better tool than genitalia for discriminating between the two sister species.
Justen Andrews - One of the best experts on this subject based on the ideXlab platform.
-
diversification of doublesex function underlies morph sex and species specific development of beetle horns
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Teiya Kijimoto, Armin P. Moczek, Justen AndrewsAbstract:Sex-specific trait expression is frequently associated with highly variable, condition-dependent expression within sexes and rapid divergence among closely related species. Horned beetles are an excellent example for studying the molecular basis of these phenomena because horn morphology varies markedly among species, between sexes, and among alternative, nutritionally-cued morphs within sexes. In addition, horns lack obvious homology to other insect traits and provide a good opportunity to explore the molecular basis of the rapid diversification of a novel trait within and between species. Here we show that the sex-determination gene doublesex (dsx) underlies important aspects of horn development, including differences between sexes, morphs, and species. In male Onthophagus taurus, dsx transcripts were preferentially expressed in the horns of the large, horned morph, and RNAi-mediated knockdown of dsx dramatically altered male horn allometry by massively reducing horn development in large males, but not in smaller males. Conversely, dsx RNAi induced ectopic, nutrition-sensitive horn development in otherwise hornless females. Finally, in a closely related species (Onthophagus sagittarius) that has recently evolved a rare reversed sexual dimorphism, dsx RNAi revealed reversed as well as novel dsx functions despite an overall conservation of dsx expression. This suggests that rapid evolution of dsx functions has facilitated the transition from a regular sexual dimorphism to a reversed sexual dimorphism in this species. Our findings add beetle horns to existing examples of a close relationship between dsx and sexual trait development, and suggest that dsx function has been coopted to facilitate both the evolution of environmentally-cued intrasexual dimorphisms and rapid species divergences in a novel trait.
-
gene discovery in the horned beetle Onthophagus taurus
BMC Genomics, 2010Co-Authors: Jeong Hyeon Choi, Armin P. Moczek, Teiya Kijimoto, Emilie C Snellrood, Hongseok Tae, Youngik Yang, Justen AndrewsAbstract:Horned beetles, in particular in the genus Onthophagus, are important models for studies on sexual selection, biological radiations, the origin of novel traits, developmental plasticity, biocontrol, conservation, and forensic biology. Despite their growing prominence as models for studying both basic and applied questions in biology, little genomic or transcriptomic data are available for this genus. We used massively parallel pyrosequencing (Roche 454-FLX platform) to produce a comprehensive EST dataset for the horned beetle Onthophagus taurus. To maximize sequence diversity, we pooled RNA extracted from a normalized library encompassing diverse developmental stages and both sexes. We used 454 pyrosequencing to sequence ESTs from all post-embryonic stages of O. taurus. Approximately 1.36 million reads assembled into 50,080 non-redundant sequences encompassing a total of 26.5 Mbp. The non-redundant sequences match over half of the genes in Tribolium castaneum, the most closely related species with a sequenced genome. Analyses of Gene Ontology annotations and biochemical pathways indicate that the O. taurus sequences reflect a wide and representative sampling of biological functions and biochemical processes. An analysis of sequence polymorphisms revealed that SNP frequency was negatively related to overall expression level and the number of tissue types in which a given gene is expressed. The most variable genes were enriched for a limited number of GO annotations whereas the least variable genes were enriched for a wide range of GO terms directly related to fitness. This study provides the first large-scale EST database for horned beetles, a much-needed resource for advancing the study of these organisms. Furthermore, we identified instances of gene duplications and alternative splicing, useful for future study of gene regulation, and a large number of SNP markers that could be used in population-genetic studies of O. taurus and possibly other horned beetles.
-
est and microarray analysis of horn development in Onthophagus beetles
BMC Genomics, 2009Co-Authors: Teiya Kijimoto, Armin P. Moczek, James C Costello, Zuojian Tang, Justen AndrewsAbstract:Background The origin of novel traits and their subsequent diversification represent central themes in evo-devo and evolutionary ecology. Here we explore the genetic and genomic basis of a class of traits that is both novel and highly diverse, in a group of organisms that is ecologically complex and experimentally tractable: horned beetles.
