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Sexual dimorphism in body size (sexual size dimorphism) is common in many species. The sources of selection that generate the independent evolution of adult male and female size have been investigated extensively by evolutionary biologists, but how and when females and males grow apart during ontogeny is poorly understood. Here we use the hawkmoth, Manduca sexta, to examine when sexual size dimorphism arises by measuring body mass every day during development. We further investigated whether environmental variables influence the ontogeny of sexual size dimorphism by raising moths on three different diet qualities (poor, medium and high). We found that size dimorphism arose during early larval development on the highest quality food treatment but it arose late in larval development when raised on the medium quality food. This female-biased dimorphism (females larger) increased substantially from the pupal-to-adult stage in both treatments, a pattern that appears to be common in Lepidopterans. Although dimorphism appeared in a few stages when individuals were raised on the poorest quality diet, it did not persist such that male and female adults were the same size. This demonstrates that the environmental conditions that insects are raised in can affect the growth trajectories of males and females differently and thus when dimorphism arises or disappears during development. We conclude that the development of sexual size dimorphism in M. sexta occurs during larval development and continues to accumulate during the pupal/adult stages, and that environmental variables such as diet quality can influence patterns of dimorphism in adults. 相似文献
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The physiological basis of reaction norms: the interaction among growth rate, the duration of growth and body size 总被引:4,自引:1,他引:3
The general effects of temperature and nutritional quality ongrowth rate and body size are well known. We know little, however,about the physiological mechanisms by which an organism translatesvariation in diet and temperature into reaction norms of bodysize or development time. We outline an endocrine-based physiologicalmechanism that helps explain how this translation occurs inthe holometabolous insect Manduca sexta (Sphingidae). Body sizeand development time are controlled by three factors: (i) growthrate, (ii) the timing of the cessation of juvenile hormone secretion(measured by the critical weight) and (iii) the timing of ecdysteroidsecretion leading to pupation (the interval to cessation ofgrowth [ICG] after reaching the critical weight). Thermal reactionnorms of body size and development time are a function of howthese three factors interact with temperature. Body size issmaller at higher temperatures, because the higher growth ratedecreases the ICG, thereby reducing the amount of mass thatcan accumulate. Development time is shorter at higher temperaturesbecause the higher growth rate decreases the time required toattain the critical weight and, independently, controls theduration of the ICG. Life history evolution along altitudinal,latitudinal and seasonal gradients may occur through differentialselection on growth rate and the duration of the two independentlycontrolled determinants of the growth period. 相似文献
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G Davidowitz HF Nijhout DA Roff 《Evolution; international journal of organic evolution》2012,66(9):2916-2928
A great deal is known about the evolutionary significance of body size and development time. They are determined by the nonlinear interaction of three physiological traits: two hormonal events and growth rate (GR). In this study we investigate how the genetic architecture of the underlying three physiological traits affects the simultaneous response to selection on the two life-history traits in the hawkmoth Manduca sexta. The genetic architecture suggests that when the two life-history traits are both selected in the same direction (to increase or decrease) the response to selection is primarily determined by the hormonal mechanism. When the life-history traits are selected in opposite directions (one to increase and one to decrease) the response to selection is primarily determined by factors that affect the GR. To determine how the physiological traits affect the response to selection of the life-history traits, we simulated the predicted response to 10 generations of selection. A total of 83% of our predictions were supported by the simulation. The main components of this physiological framework also exist in unicellular organisms, vertebrates, and plants and can thus provide a robust framework for understanding how underlying physiology can determine the simultaneous evolution of life-history traits. 相似文献
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H. Frederik Nijhout Derek A. Roff Goggy Davidowitz 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2010,365(1540):567-575
Body size and development time of Manduca sexta are both determined by the same set of three developmental–physiological factors. These define a parameter space within which it is possible to analyse and explain how phenotypic change is associated with changes in the underlying factors. Body size and development time are determined by the identical set of underlying factors, so they are not independent, but because the mechanisms by which these factors produce each phenotype are different, the two phenotypes are only weakly correlated, and the correlation is context dependent. We use a mathematical model of this mechanism to explore the association between body size and development time and show that the correlation between these two life-history traits can be positive, zero or negative, depending entirely on where in parameter space a population is located, and on which of the underlying factors has a greater variation. The gradient within this parameter space predicts the unconstrained evolutionary trajectory under directional selection on each trait. Calculations of the gradients for body size and development time revealed that these are nearly orthogonal through much of the parameter space. Therefore, simultaneous directional selection on body size and development time can be neither synergistic nor antagonistic but leads to conflicting selection on the underlying developmental parameters. 相似文献
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Critical weight in the development of insect body size 总被引:6,自引:0,他引:6
Body size is one of the most important life history characters of organisms, yet little is known of the physiological mechanisms that regulate either body size or variation in body size. Here, we examined one of these mechanisms, the critical weight, which is defined as the minimal mass at which further growth is not necessary for a normal time course to pupation. The critical weight occurred at 55% of peak larval mass in laboratory-reared larvae of the tobacco hornworm Manduca sexta. We examined the effects of genetic and environmental variation in the critical weight on body size. As in many other insects, Manduca larvae reared on poor diets were smaller and those reared at lower temperatures were larger than control animals. We demonstrated that the critical weight was lower on low quality diets but did not change with temperature. There was significant genetic variation for body size, for plasticity of body size, and for critical weight, but not for plasticity of critical weight. Variation in the critical weight accounted for 73% of between-family variance in peak larval size, whereas plasticity of critical weight was not significantly correlated with plasticity of body size. Our results suggest that although critical weight is an important factor in determining body size and enabling the evolution of body size, it may, at the same time, act as a constraint on the evolution of plasticity of body size. Thus, the determinants of body size and the determinants of plasticity of body size do not need to be identical. 相似文献
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R. Craig Stillwell Goggy Davidowitz 《Proceedings. Biological sciences / The Royal Society》2010,277(1690):2069-2074
Males and females of almost all organisms exhibit sexual differences in body size, a phenomenon called sexual size dimorphism (SSD). How the sexes evolve to be different sizes, despite sharing the same genes that control growth and development, and hence a common genetic architecture, has remained elusive. Here, we show that the genetic architecture (heritabilities and genetic correlations) of the physiological mechanism that regulates size during the last stage of larval development of a moth, differs between the sexes, and thus probably facilitates, rather than hinders, the evolution of SSD. We further show that the endocrine system plays a critical role in generating SSD. Our results demonstrate that knowledge of the genetic architecture underlying the physiological process during development that ultimately produces SSD in adults can elucidate how males and females of organisms evolve to be of different sizes. 相似文献
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R. Craig Stillwell Goggy Davidowitz 《Proceedings. Biological sciences / The Royal Society》2010,277(1701):3819-3826
The degree and/or direction of sexual size dimorphism (SSD) varies considerably among species and among populations within species. Although this variation is in part genetically based, much of it is probably due to the sexes exhibiting differences in body size plasticity. Here, we use the hawkmoth, Manduca sexta, to test the hypothesis that moths reared on different diet qualities and at different temperatures will exhibit sex-specific body size plasticity. In addition, we explore the proximate mechanisms that potentially create sex-specific plasticity by examining three physiological variables known to regulate body size in this insect: the growth rate, the critical weight (which measures the cessation of juvenile hormone secretion from the corpora allata) and the interval to cessation of growth (ICG; which measures the time interval between the critical weight and the secretion of the ecdysteroids that regulate pupation and metamorphosis). We found that peak larval mass of males and females did not exhibit sex-specific plasticity in response to diet or temperature. However, the sexes did exhibit sex-specific plasticity in the mechanism that controls size; males and females exhibited sex-specific plasticity in the growth rate and the critical weight in response to both diet and temperature, whereas the ICG only exhibited sex-specific plasticity in response to diet. Our results suggest it is important for the sexes to maintain the same degree of SSD across environments and that this is accomplished by the sexes exhibiting differential sensitivity of the physiological factors that determine body size to environmental variation. 相似文献
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Judith L. Bronstein Travis Huxman Brianna Horvath Michael Farabee Goggy Davidowitz 《Annals of botany》2009,103(9):1435-1443