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1,369 results for “sexual dimorphism”
Figure 8.5 in Variation and sexual dimorphism in Tyrannosaurus rex
Figure 8.5. Dorsal view of the anterior portion of the left dentary of Tyrannosaurus "x" (Samson) preserving small alveoli for DT1 and DT2 and a large alveolus for the third dentary tooth DT3.
Figure 8.2 in Variation and sexual dimorphism in Tyrannosaurus rex
Figure 8.2. Medial view of right dentary of the type Tyrannosaurus rex CM 9380. Note the incisiform first dentary tooth.
Figure 8.6 in Variation and sexual dimorphism in Tyrannosaurus rex
Figure 8.6. Lateral view of the left lachrymals of (A) Tyrannosaurus "x" AMNH 5027 and (B) Tyrannosaurus rex BHI 3033. Note the larger lateral pneumatic foramen on T. rex.
Figure 8.4 in Variation and sexual dimorphism in Tyrannosaurus rex
Figure 8.4. Dorsal view of the anterior portion of the left dentary of Tyrannosaurus rex CM 9380 preserving small first dentary tooth DT1 and large second dentary tooth DT2.
Figure 8.3 in Variation and sexual dimorphism in Tyrannosaurus rex
Figure 8.3. Left and right first dentary teeth of Tyrannosaurus rex BHI 3033. (A) Lateral view. (B) Posterior view. Note that both serrations are exposed in the posterior view, creating the typical tyrannosaurid D-shaped cross section.
FIGURE 5 in Hyperxiphia hirashimai, comb. n. (Hymenoptera, Xiphydriidae) from southern Japan: remarkable sexual dimorphism revealed by DNA barcodes and new distribution records
FIGURE 5. Distribution of Hyperxiphia hirashimai, black dots showing collection records.
Prenatal androgen exposure causes a sexually dimorphic transgenerational increase in offspring susceptibility to anxiety disorders
<p class="MsoBodyTextIndent">If and how obesity and elevated androgens in women with polycystic ovary syndrome (PCOS) affect their offspring's psychiatric health is unclear. Using data from Swedish population health registers, we showed that daughters of mothers with PCOS have a 78% increased risk of being diagnosed with anxiety disorders. We next generated a PCOS-like mouse (F<sub>0</sub>) model induced by androgen exposure during late gestation, with or without diet-induced maternal obesity, and showed that the first generation (F<sub>1</sub>) female offspring develop anxiety-like behavior, which is transgenerationally transmitted through the female germline into the third generation of female offspring (F<sub>3</sub>) in the androgenized lineage. In contrast, following the male germline, F<sub>3</sub> male offspring (mF<sub>3</sub>) displayed anxiety-like behavior in the androgenized and the obese lineages. Using a targeted approach to search for molecular targets within the amygdala, we identified five differentially expressed genes involved in anxiety-like behavior in F<sub>3</sub> females in the androgenized lineage and eight genes in the obese lineage. In mF<sub>3</sub> male offspring, three genes were dysregulated in the obese lineage but none in the androgenized lineage. Finally, we performed <i>in vitro</i> fertilization (IVF) using a PCOS mouse model of continuous androgen exposure. We showed that the IVF generated F<sub>1</sub> and F<sub>2</sub> offspring in the female germline did not develop anxiety-like behavior, while the F<sub>2</sub> male offspring (mF<sub>2</sub>) in the male germline did. Our findings provide evidence that elevated maternal androgens in PCOS and maternal obesity may underlie the risk of a transgenerational transmission of anxiety disorders in children of women with PCOS.</p>
Data from: The evolution of sexually dimorphic tail feathers is not associated with tail skeleton dimorphism
Sexual selection can influence the evolution of sexually dimorphic exaggerated display structures. Herein, we explore whether such costly ornamental integumentary structures evolve independently or if they are correlated with phenotypic change in the associated skeletal system. In birds, elongate tail feathers have frequently evolved in males and are beneficial as intraspecific display structures but impart a locomotor/energetic cost. Using the sexually dimorphic tail feathers of several passeriform species as a model system, we test the hypothesis that taxa with sexually dimorphic tail feathers also exhibit sexual dimorphism in the caudal skeleton that supports the muscles and integument of the tail apparatus. Caudal skeletal morphology is quantified using both geometric morphometrics and linear morphometrics across four sexually dimorphic passeriform species and four closely related monomorphic species. Sexual dimorphism is assessed using permutational MANOVA. Sexual dimorphism in caudal skeletal morphology is found only in those taxa that exhibit active functional differences in tail use between males and females. Thus, dimorphism in tail feather length is not necessarily correlated with the evolution of caudal skeletal dimorphism. Sexual selection is sufficient to generate phenotypic divergence in integumentary display structures between the sexes, but these change are not reflected in the underlying caudal skeleton. This suggests that caudal feathers and bones evolve semi-independently from one another and evolve at different rates in response to different types of selective pressures.
Data from: Sexual selection on male size drives the evolution of male-biased sexual size dimorphism via the prolongation of male development
Sexual size dimorphism (SSD) arises when the net effects of natural and sexual selection on body size differ between the sexes. Quantitative SSD variation between taxa is common, but directional intraspecific SSD reversals are rare. We combined micro- and macroevolutionary approaches to study geographic SSD variation in closely related black scavenger flies. Common garden experiments revealed stark intra and interspecific variation: Sepsis biflexuosa is monomorphic across the Holarctic, while S. cynipsea (only in Europe) consistently exhibits female-biased SSD. Interestingly, S. neocynipsea displays contrasting SSD in Europe (females larger) and North America (males larger), a pattern opposite to the geographic reversal in SSD of S. punctum documented in a previous study. In accordance with the differential equilibrium model for the evolution of SSD, the intensity of sexual selection on male size varied between continents (weaker in Europe) whereas fecundity selection on female body size did not. Subsequent comparative analyses of 49 taxa documented at least six independent origins of male-biased SSD in Sepsidae, which is likely caused by sexual selection on male size and mediated by bimaturism. Therefore, reversals in SSD and the associated changes in larval development might be much more common and rapid and less constrained than currently assumed.
Data from: Sexual dimorphism explains residual variance around the survival-reproduction tradeoff in lizards: implications for sexual conflict over life-history evolution
The tradeoff between survival and reproduction is a central feature of life-history variation, but few studies have sought to explain why females of some species exhibit relatively lower survival than expected for a given level of reproductive effort. Intralocus sexual conflict theory proposes that sex differences in selection on survival and reproductive effort may, by virtue of shared genes underlying these components of fitness, prevent females from optimizing this life-history tradeoff. To test this hypothesis, we used a phylogenetically based comparative analysis of published estimates for mean annual survival and reproductive effort from females of 82 lizard species to (1) characterize the tradeoff between survival and reproduction, and (2) test whether variation around this tradeoff is explained by sexual size dimorphism (SSD), a potential proxy for sexual conflict over life-history traits. Across species, we found a strong negative correlation between mean annual survival and reproductive effort, confirming this classic life-history tradeoff. Although residual variance around this tradeoff is unrelated to the absolute magnitude of SSD, it is strongly related to the direction of SSD. Specifically, we found that females have lower survival than expected for a given level of reproductive effort in female-larger species, whereas they have higher survival than expected in male-larger species. Given that female-larger SSD is thought to reflect selection for increased fecundity, our results suggest that intralocus sexual conflict may be particularly likely to constrain female life-history evolution in situations where increased reproductive effort is favored, but the phenotypes that facilitate this increase (e.g., body size) are constrained by antagonistic selection on males.
Data from: Ecological divergence and sexual selection drive sexual size dimorphism in new world pitvipers (Serpentes: Viperidae)
Hypotheses for the origin and maintenance of sexual size dimorphism (SSD) fall into three primary categories: (i) sexual selection on male size, (ii) fecundity selection on female size and (iii) ecological selection for gender-specific niche divergence. We investigate the impact of these forces on SSD evolution in New World pitvipers (Crotalinae). We constructed a phylogeny from up to eight genes (seven mitochondrial, one nuclear) for 104 species of NW crotalines. We gathered morphological and ecological data for 82 species for comparative analyses. There is a strong signal of sexual selection on male size driving SSD, but less evidence for fecundity selection on female size across lineages. No support was found for allometric scaling of SSD (Rensch's rule), nor for directional selection for increasing male size (the Fairbairn–Preziosi hypothesis) in NW crotalines. Interestingly, arboreal lineages experience higher rates of SSD evolution and a pronounced shift to female-biased dimorphism. This suggests that fecundity selection on arboreal females exaggerates ecologically mediated dimorphism, whereas sexual selection drives male size in terrestrial lineages. We find that increasing SSD in both directions (male- and female-biased) decreases speciation rates. In NW crotalines, it appears that increasing magnitudes of ecologically mediated SSD reduce rates of speciation, as divergence accumulates within species among sexes, reducing adaptive divergence between populations leading to speciation.
Data from: Differential investment in pre- versus post-copulatory sexual selection reinforces a cross-continental reversal of sexual size dimorphism in Sepsis punctum (Diptera: Sepsidae)
Theory predicts that males have a limited amount of resources to invest in reproduction, suggesting a trade-off between traits that enhance mate acquisition and those enhancing fertilization success. Here we investigate the relationship between pre- and post-copulatory investment by comparing the mating behavior and reproductive morphology of four European and five North American populations of the dung fly Sepsis punctum (Diptera) that display a reversal of sexual size dimorphism (SSD). We show that the geographic reversal in SSD between the continents (male-biased in Europe, female-biased in North America) is accompanied by differential investment in pre- versus post-copulatory traits. We find higher re-mating rates in European populations, where larger males acquire more matings and consequently have evolved relatively larger testes and steeper hyper-allometry with body size. American populations, in sharp contrast, display much reduced, if any, effect of body size on those traits. Instead, North American males demonstrate an increased investment in mate acquisition prior to copulation, with more mounting attempts and a distinctive abdominal courtship display that is completely absent in Europe. When controlling for body size, relative female spermathecal size is similar on both continents, so we find no direct evidence for the co-evolution of male and female internal reproductive morphology. By comparing allopatric populations of the same species that apparently have evolved different mating systems and consequently SSD, we thus indirectly demonstrate differential investment in pre- vs. post-copulatory mechanisms increasing reproductive success.
Data from: Resource availability and sexual size dimorphism: differential effects of prey abundance on the growth rates of tropical snakes
1. Broad phylogenetic patterns in sexual size dimorphism (SSD) are shaped by sex differences in net selection pressures (e.g., sexual selection, fecundity selection, survival selection), but environmental and ecological factors can also affect the expression of SSD. 2. Discussions of proximate ecological influences on SSD have focused on niche divergence; for example, increase in a prey type used by only one sex can elevate growth rates of that sex but not the other. Food limitation also can generate spatial and temporal variation in SSD. Under restricted prey abundance, curtailed growth may mask SSD even if the optimal size is greater for one sex than the other. Because an increase in food availability then elicits increased feeding and growth by the sex that benefits more from increased body size, variation in prey abundance can generate variation in SSD. 3. We used mark-recapture methods to study growth rates relative to prey (frog) abundance in two species of sexually dimorphic colubrid snake species in tropical Australia. 4. In Slatey-grey snakes (Stegonotus cucullatus), a species in which larger body size enhances reproductive output in both sexes (because larger males win combat bouts, and larger females produce more / heavier eggs), increased abundance of frogs caused equivalent increases in growth rates in both sexes, and hence did not affect SSD. In Keelbacks (Tropidonophis mairii), a species in which larger size enhances reproductive output in females more than males (reflecting a lack of male-male combat), increased abundance of frogs elicited higher growth rates of females only. Thus, SSD in Keelbacks was modified by prey abundance. 5. Our results show that the magnitude of sex differences in adult body size can be influenced by proximate environmental factors, and support the hypothesis of sex-specific targets for maximum feeding rates.
Data from: Sexual, fecundity, and viability selection on flower size and number in a sexually dimorphic plant
The evolution of sexual dimorphism will depend on how sexual, fecundity and viability selection act within each sex, with the different forms of selection potentially operating in opposing directions. We examined selection in the dioecious plant Silene latifolia using planted arrays of selection lines that differed in flower size (small vs. large). In this species a flower size/number tradeoff exists within each sex, and males produce smaller and more numerous flowers than females. Moreover, floral traits are genetically correlated with leaf physiology. Sexual selection favoring males in the small-flower line occurred via greater overlap in the timing of flower output between males from this line and females. Fecundity selection favored males with high flower production, as siring success was proportionate to pollen production. Viability selection opposed sexual selection, favoring males from the large-flower line. In females, fecundity and viability selection operated in the same direction, favoring those from the large-flower line via greater seed production and survival. These results concur with the pattern of floral sexual dimorphism. Together with previous results they suggest that the outcome of the different forms of selection will be environmentally dependent, and therefore help to explain variation among populations in sexually dimorphic traits.
Data from: Phylogeny suggests non-directional and isometric evolution of sexual size dimorphism in argiopine spiders
Sexual dimorphism describes substantial differences between male and female phenotypes. In spiders, sexual dimorphism research almost exclusively focuses on size, and recent studies have recovered steady evolutionary size increases in females, and independent evolutionary size changes in males. Their discordance is due to negative allometric size patterns caused by different selection pressures on male and female size (converse Rensch's rule). Here, we investigated macroevolutionary patterns of sexual size dimorphism (SSD) in Argiopinae, a global lineage of orb weaving spiders with varying degrees of SSD. We devised a Bayesian and maximum likelihood molecular species level phylogeny, then used it to reconstruct sex specific size evolution, to examine general hypotheses and different models of size evolution, to test for sexual size coevolution, and to examine allometric patterns of SSD. Our results, revealing ancestral moderate sizes and SSD, failed to reject the Brownian motion model, which suggests a non-directional size evolution. Contrary to predictions, male and female sizes were phylogenetically correlated, and SSD evolution was isometric. We interpret these results to question the classical explanations of female-biased SSD via fecundity, gravity, and differential mortality. In argiopines, SSD evolution may be driven by these or additional selection mechanisms, but perhaps at different phylogenetic scales.
Data from: Interactive effects of competition and social environment on the expression of sexual dimorphism
The expression of sexual dimorphism is expected to be influenced by the acquisition of resources available to allocate to trait growth, combined with sex-specific patterns of resource allocation. Resource acquisition in the wild may be mediated by a variety of ecological factors, such as the density of interspecific competitors. Allocation may in turn depend on social contexts, such as sex ratio, that alter the payoff for investment in sexual traits. How these factors interact to promote or constrain the expression and evolution of sexual dimorphism is poorly understood. We manipulated sex ratio and interspecific resource competition over the growing season of red-spotted newts (Notophthalmus viridescens) in artificial ponds. Fish competitors had a stronger effect on female than male growth, which effectively eliminated the expression of sexual size dimorphism. In addition, newt sex ratio influenced fish growth, leading to reduction in fish mass with an increase in female newt frequency. Fish also reduced the expression of male tail height, a sexually selected trait, but only in tanks with a female-biased sex ratio. This suggests males alter their resource allocation pattern in response to the strength of sexual selection. Our results demonstrate that ecologically and socially mediated interactions between sex-specific resource acquisition and allocation can contribute to variation in the expression of sexual dimorphism.
Data from: Selection on learning performance results in the correlated evolution of sexual dimorphism in life history
The evolution of learning can be constrained by trade-offs. As male and female life-histories often diverge, the relationship between learning and fitness may differ between the sexes. However, because sexes share much of their genome, intersexual genetic correlations can prevent males and females from reaching their sex-specific optima resulting in intralocus sexual conflict (IaSC). To investigate if IaSC constraints sex-specific evolution of learning we selected Caenorhabditis remanei nematode females for increased or decreased olfactory learning performance and measured learning, lifespan (in mated and virgin worms), reproduction and locomotory activity in both sexes. Males from downward-selected female lines had higher locomotory activity and longer virgin lifespan but sired fewer progeny than males from upward-selected female lines. In contrast, we found no effect of selection on female reproduction and downward-selected females showed higher locomotory activity but lived shorter as virgins than upward-selected females. Strikingly, selection on learning performance led to the reversal of sexual dimorphism in virgin lifespan. We thus show sex-specific trade-offs between learning, reproduction and lifespan. Our results support the hypothesis that selection on learning performance can shape the evolution of sexually dimorphic life-histories via sex-specific genetic correlations.
Data from: Sexual size dimorphism is not associated with the evolution of parental care in frogs
Sex differences in parental care are thought to arise from differential selection on the sexes. Sexual dimorphism, including sexual size dimorphism (SSD), is often used as a proxy for sexual selection on males. Some studies have found an association between male-biased SSD (i.e., males larger than females) and the loss of paternal care. While the relationship between sexual selection on males and parental care evolution has been studied extensively, the relationship between female-biased SSD (i.e., females larger than males) and the evolution of parental care has received very little attention. Thus, we have little knowledge of whether female-biased SSD coevolves with parental care. In species displaying female-biased SSD, we might expect dimorphism to be associated with the evolution of paternal care or perhaps the loss of maternal care. Here, drawing on data for 99 extant frog species, we use comparative methods to evaluate how parental care and female-biased SSD have evolved over time. Generally, we find no significant correlation between the evolution of parental care and female-biased SSD in frogs. This suggests that differential selection on body size between the sexes is unlikely to have driven the evolution of parental care in these clades and questions whether we should expect sexual dimorphism to exhibit a general relationship with the evolution of sex differences in parental care.
Data from: Cross-cultural variation in men's preference for sexual dimorphism in women's faces
Both attractiveness judgements and mate preferences vary considerably cross-culturally. We investigated whether men's preference for femininity in women's faces varies between 28 countries with diverse health conditions by analysing responses of 1972 heterosexual participants. Although men in all countries preferred feminized over masculinized female faces, we found substantial differences between countries in the magnitude of men's preferences. Using an average femininity preference for each country, we found men's facial femininity preferences correlated positively with the health of the nation, which explained 50.4% of the variation among countries. The weakest preferences for femininity were found in Nepal and strongest in Japan. As high femininity in women is associated with lower success in competition for resources and lower dominance, it is possible that in harsher environments, men prefer cues to resource holding potential over high fecundity.
Data from: Hormonally mediated increases in sex-biased gene expression accompany the breakdown of between-sex genetic correlations in a sexually dimorphic lizard
The evolution of sexual dimorphism is predicted to occur through reductions in between-sex genetic correlations (rmf) for shared traits, but the physiological and genetic mechanisms that facilitate these reductions remain largely speculative. Here, we use a paternal half-sibling breeding design in captive brown anole lizards (Anolis sagrei) to show that the development of sexual size dimorphism is mirrored by the ontogenetic breakdown of rmf for body size and growth rate. Using transcriptome data from the liver (which integrates growth and metabolism), we show that sex-biased gene expression also increases dramatically between ontogenetic stages bracketing this breakdown of rmf. Ontogenetic increases in sex-biased expression are particularly evident for genes involved in growth, metabolism, and cell proliferation, suggesting that they contribute to both the development of sexual dimorphism and the breakdown of rmf. Mechanistically, we show that treatment of females with testosterone stimulates the expression of male-biased genes while inhibiting the expression of female-biased genes, thereby inducing male-like phenotypes at both organismal and transcriptomic levels. Collectively, our results suggest that sex-specific modifiers such as testosterone can orchestrate sex-biased gene expression to facilitate the phenotypic development of sexual dimorphism while simultaneously reducing genetic correlations that would otherwise constrain the independent evolution of the sexes.
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