The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Armin P Moczek - One of the best experts on this subject based on the ideXlab platform.
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pupal remodeling and the evolution and development of alternative male morphologies in horned beetles
BMC Evolutionary Biology, 2007Co-Authors: Armin P MoczekAbstract:Background How novel morphological traits originate and diversify represents a major frontier in evolutionary biology. Horned beetles are emerging as an increasingly popular model system to explore the genetic, developmental, and ecological mechanisms, as well as the interplay between them, in the genesis of novelty and diversity. The horns of beetles originate during a rapid growth phase during the prepupal stage of larval development. Differential growth during this period is either implicitly or explicitly assumed to be the sole mechanism underlying differences in horn expression within and between species. Here I focus on male horn Dimorphisms, a phenomenon at the center of many studies in behavioral ecology and evolutionary development, and quantify the relative contributions of a previously ignored developmental process, pupal remodeling, to the expression of male Dimorphism in three horned beetle species.
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pupal remodeling and the development and evolution of sexual Dimorphism in horned beetles
The American Naturalist, 2006Co-Authors: Armin P MoczekAbstract:Abstract: Horns or hornlike structures in beetles have become an increasingly popular study system for exploring the evolution and development of secondary sexual trait diversity and sexual Dimorphisms. The horns of adult beetles originate during a rapid growth phase during the prepupal stage of larval development, and differential activation of growth during this time is either implicitly or explicitly assumed to be the sole mechanism underlying intra‐ and interspecific differences in adult horn expression. Here I show that this assumption is not based on developmental reality. Instead, after their initial prepupal growth phase, beetle horns are extensively remodeled during the subsequent pupal stage via sex‐ and size‐dependent resorption of horn tissue. I show that adult sexual Dimorphism in four Onthophagus species is shaped partly or entirely by such pupal remodeling rather than by differential growth. Specifically, I show that after a sexually monomorphic growth phase, differential pupal horn resorpt...
J. Michael Plavcan - One of the best experts on this subject based on the ideXlab platform.
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Sexual size Dimorphism, canine Dimorphism, and male-male competition in primates: where do humans fit in?
Human Nature, 2012Co-Authors: J. Michael PlavcanAbstract:Sexual size Dimorphism is generally associated with sexual selection via agonistic male competition in nonhuman primates. These primate models play an important role in understanding the origins and evolution of human behavior. Human size Dimorphism is often hypothesized to be associated with high rates of male violence and polygyny. This raises the question of whether human Dimorphism and patterns of male violence are inherited from a common ancestor with chimpanzees or are uniquely derived. Here I review patterns of, and causal models for, Dimorphism in humans and other primates. While Dimorphism in primates is associated with agonistic male mate competition, a variety of factors can affect male and female size, and thereby Dimorphism. The causes of human sexual size Dimorphism are uncertain, and could involve several non-mutually-exclusive mechanisms, such as mate competition, resource competition, intergroup violence, and female choice. A phylogenetic reconstruction of the evolution of Dimorphism, including fossil hominins, indicates that the modern human condition is derived. This suggests that at least some behavioral similarities with Pan associated with Dimorphism may have arisen independently, and not directly from a common ancestor.
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Scaling relationships between craniofacial sexual Dimorphism and body mass Dimorphism in primates: implications for the fossil record.
American Journal of Physical Anthropology, 2002Co-Authors: J. Michael PlavcanAbstract:Craniofacial remains (the most abundant identifiable remains in the fossil record) potentially offer important information about body size Dimorphism in extinct species. This study evaluates the scaling relationships between body mass Dimorphism and different measures of craniofacial Dimorphism, evaluating taxonomic differences in the magnitude and scaling of craniofacial Dimorphism across higher taxonomic groups. Data on 40 dimensions from 129 primate species and subspecies demonstrate that few dimensions change proportionally with body mass Dimorphism. Primates show general patterns of greater facial vs. neurocranial and orbital Dimorphism, and greater Dimorphism in lengths as opposed to breadths. Within any species, though, different craniofacial dimensions can yield very different reconstructions of size Dimorphism. There are significant taxonomic differences in the relationships between size and craniofacial Dimorphism among primate groups that can have a significant impact on reconstructions of body mass Dimorphism. Hominoids tend to show lower degrees of facial Dimorphism proportional to size Dimorphism than other primates. This in turn implies that strong craniofacial Dimorphism in Australopithecus africanus could imply very strong body size Dimorphism, conflicting with the relatively modest size Dimorphism inferred from postcrania. Different methods of estimating the magnitude of size Dimorphism from craniofacial measurements yield similar results, and yield comparatively low percent prediction errors for a number of dimensions. However, confidence intervals for most estimates are so large as to render most estimates highly tentative.
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Taxonomic variation in the patterns of craniofacial Dimorphism in primates.
Journal of Human Evolution, 2002Co-Authors: J. Michael PlavcanAbstract:Understanding sexual Dimorphism in living primates is important for interpreting the biological and taxonomic significance of variation in the primate fossil record. In the past two decades, there has been an increasing emphasis on the fact that sexual Dimorphism varies in both magnitude and pattern among species. Several studies have suggested that distinct patterns of Dimorphism may assist in species recognition and perhaps phylogenetic analysis. This study evaluates patterns of craniofacial Dimorphism in samples of 82 anthropoid primates. Dimensions of the viscerocranium tend to be more dimorphic than those of the neurocranium and orbits. Principal components analysis of phylogenetically controlled data demonstrates a basic pattern of Dimorphism in overall skull proportions, and a distinction between length and breadth measurements. For any given species there can be substantial variation in the magnitude of Dimorphism among dimensions, and different species can show substantially different patterns of Dimorphism within and between regions of the skull and jaws. Patterns of Dimorphism are clearly associated with phylogeny. Pattern similarity is not dependent on the overall magnitude of craniofacial Dimorphism, or body mass Dimorphism. Among all anthropoids, there are few combinations of characters that consistently show greater or lesser degrees of Dimorphism. Such "stability" of patterns increases within genera. Patterns of Dimorphism are likely to be useful for interpreting the taxonomic significance of variation in the fossil record. However, phylogenetic propinquity alone is not reason to use an extant species as a model for variation in an extinct species. Rather, care must be taken to identify stable patterns of Dimorphism within a group of closely related extant species.
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Sexual Dimorphism in primate evolution.
American Journal of Physical Anthropology, 2002Co-Authors: J. Michael PlavcanAbstract:Sexual Dimorphism is a pervasive phenomenon among anthropoid primates. Comparative analyses over the past 30 years have greatly expanded our understanding of both variation in the expression of Dimorphism among primates, and the underlying causes of sexual Dimorphism. Dimorphism in body mass and canine tooth size is familiar, as is pelage and “sex skin” Dimorphism. More recent analyses are documenting subtle differences in the pattern of skeletal Dimorphism among primates. Comparative analyses have corroborated the sexual selection hypotheses, and have provided a more detailed understanding of the relationship between sexual selection, natural selection, and mating systems in primates. A clearer picture is emerging of the relative contribution of various selective and nonselective mechanisms in the evolution and expression of Dimorphism. Most importantly, recent studies have shown that Dimorphism is the product of changes in both male and female traits. Developmental studies demonstrate the variety of ontogenetic pathways that can lead to Dimorphism, and provide additional insight into the selective mechanisms that influence Dimorphism throughout the lifetime of an animal. Evidence from the fossil record suggests that Dimorphism probably evolved in parallel twice, and the Dimorphism in some extinct hominoids probably exceeded that of any living primate. Our advances in understanding the behavioral/ecological correlates of Dimorphism in living primates have not improved our ability to reconstruct social systems in extinct species on the basis of Dimorphism alone, beyond the inference of polygyny or intense male-male competition. However, our understanding of the behavioral/ecological correlates of growth and development, and of the expression of Dimorphism as a function of separate changes in male and female traits, offers great potential for inferring evolutionary changes in behavior over time. Yrbk Phys Anthropol 44:25–53, 2001. © 2001 Wiley-Liss, Inc.
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Inferring social behavior from sexual Dimorphism in the fossil record.
Journal of Human Evolution, 2000Co-Authors: J. Michael PlavcanAbstract:Sexual Dimorphism is commonly used as evidence of the behavior of extinct species. Even so, few analyses scrutinize whether extant comparative data support inferences of mating systems or behavior in extinct species. This analysis evaluates the relations between measures of Dimorphism and several estimates of mating system and intrasexual competition. Dimorphism alone provides poor resolution for reconstructing behavior. Many behavioral inferences based on perceived Dimorphism are not supported by extant comparative data. This reflects the large standard errors of relations between Dimorphism estimates and behavioral classifications. Used with caution, Dimorphism can provide a hint of the behavior of extinct species in some cases. However, in many cases inferred Dimorphism allows little more than an inference of polygyny, without any indication of specific types of mating systems.
Matthew C. Mihlbachler - One of the best experts on this subject based on the ideXlab platform.
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Sexual Dimorphism and Mortality Bias in a Small Miocene North American Rhino, Menoceras arikarense: Insights into the Coevolution of Sexual Dimorphism and Sociality in Rhinos
Journal of Mammalian Evolution, 2007Co-Authors: Matthew C. MihlbachlerAbstract:Rhinos are the only modern perissodactyls that possess cranial weapons similar to the horns, antlers and ossicones of modern ruminants. Yet, unlike ruminants, there is no clear relationship between sexual Dimorphism and sociality. It is possible to extend the study of the coevolution of sociality and sexual Dimorphism into extinct rhinos by examining the demographic patterns in large fossil assemblages. An assemblage of the North American early Miocene (∼22 million years ago) rhino, Menoceras arikarense , from Agate Springs National Monument, Nebraska, exhibits Dimorphism in incisor size and nasal bone size, but there is no detectible Dimorphism in body size. The degree of Dimorphism of the nasal horn is greater than the degree of sexual Dimorphism of any living rhino and more like that of modern horned ruminants. The greater degree of sexual Dimorphism in Menoceras horns may relate to its relatively small body size and suggests that the horn had a more sex-specific function. It could be hypothesized that Menoceras evolved a more gregarious type of sociality in which a fewer number of males were capable of monopolizing a larger number of females. Demographic patterns in the Menoceras assemblage indicate that males suffered from a localized risk of elevated mortality at an age equivalent to the years of early adulthood. This mortality pattern is typical of living rhinos and indicates that young males were susceptible to the aggressive behaviors of dominant individuals in areas conducive to fossilization (e.g., ponds, lakes, rivers). Menoceras mortality patterns do not suggest a type of sociality different from modern rhinos although a group forming type of sociality remains possible. Among both living and extinct rhinos, the severity of socially mediated mortality seems unrelated to the degree of sexual Dimorphism. Thus, sexual Dimorphism in rhinos is not consistent with traditional theories about the co-evolution of sexual Dimorphism and sociality.
Peter M Kappeler - One of the best experts on this subject based on the ideXlab platform.
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the evolution of sexual size Dimorphism in prosimian primates
American Journal of Primatology, 1990Co-Authors: Peter M KappelerAbstract:: The four major hypotheses advanced to explain the evolution of sexually dimorphic characters invoke sexual selection, natural selection, allometry, and phylogenetic inertia. In this paper, each of these hypotheses is examined for its usefulness in explaining the inter-specific variation in sexual size Dimorphism among prosimian primates. Data on body weight and the degree of sexual Dimorphism were obtained for 32 prosimian and 95 simian species. Although prosimians exhibited significantly less sexual Dimorphism than simians, there was nevertheless significant variation in Dimorphism among them. The degree of sexual Dimorphism in prosimians did not show significant variance at any taxonomic level, but the majority of variance occurred within genera. Thus, sexual Dimorphism in size among prosimians is probably not constrained by phylogeny at the generic level and above. There was no significant correlation between body size and the degree of sexual Dimorphism in prosimians, suggesting the absence of an allometric effect. Similarly there was no relationship between body size and sexual Dimorphism among simians in this size range. This result suggested that the expression of sexual Dimorphism may nevertheless be influenced by absolute size. In prosimians, inter-specific differences in sexual Dimorphism were not correlated with variance in male reproductive success. It is suggested that speed and agility of males, rather than size and strength, might have been favored by intra-sexual selection in most prosimians. It seems also plausible that the relative monomorphism of most prosimians, especially in the Lemuriformes, might be a result of increased female size favored by natural selection. Consideration of all natural and sexual selective pressures that affect size in both sexes separately is required to understand the adaptive function and evolution of primate size Dimorphism.
F. Thomas - One of the best experts on this subject based on the ideXlab platform.
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Human fertility variation, size-related obstetrical performance and the evolution of sexual stature Dimorphism
Proceedings of the Royal Society B: Biological Sciences, 2000Co-Authors: J.-f. Guégan, A. Teriokhin, F. ThomasAbstract:In several animal species, change in sexual size Dimorphism is a correlated response to selection on fecundity. In humans, different hypotheses have been proposed to explain the variation of sexual Dimorphism in stature, but no consensus has yet emerged. In this paper, we evaluate from a theoretical and an empirical point of view the hypothesis that the extent of sexual Dimorphism in human populations results from the interaction between fertility and size-related obstetric complications. We first developed an optimal evolutionary model based on extensive simulations and then we performed a comparative analysis for a total set of 38 countries worldwide. Our optimization modelling shows that size-related mortality factors do indeed have the potential to affect the extent of sexual stature Dimorphism. Comparative analysis using generalized linear modelling supports the idea that maternal death caused by deliveries and complications of pregnancy (a variable known to be size related) could be a key determinant explaining variation in sexual stature Dimorphism across populations. We discuss our results in relation to other hypotheses on the evolution of sexual stature Dimorphism in humans.
