共查询到20条相似文献,搜索用时 15 毫秒
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Pound N Penton-Voak IS Surridge AK 《Proceedings. Biological sciences / The Royal Society》2009,276(1654):153-159
Relationships between androgens and the size of sexually dimorphic male traits have been demonstrated in several non-human species. It is often assumed that a similar relationship exists for human male faces, but clear evidence of an association between circulating testosterone levels and the size of masculine facial traits in adulthood is absent. Here we demonstrate that, after experimentally determined success in a competitive task, men with more a masculine facial structure show higher levels of circulating testosterone than men with less masculine faces. In participants randomly allocated to a 'winning' condition, testosterone was elevated relative to pre-task levels at 5 and 20 min post-task. In a control group of participants allocated to a 'losing' condition there were no significant differences between pre- and post-task testosterone. An index of facial masculinity based on the measurement of sexually dimorphic facial traits was not associated with pre-task (baseline) testosterone levels, but was associated with testosterone levels 5 and 20 min after success in the competitive task. These findings indicate that a man's facial structure may afford important information about the functioning of his endocrine system. 相似文献
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The magnitude and direction of sexual size dimorphism (SSD) varies greatly across the animal kingdom, reflecting differential selection pressures on the reproductive and/or ecological roles of males and females. If the selection pressures and constraints imposed on body size change along environmental gradients, then SSD will vary geographically in a predictable way. Here, we uncover a biogeographical reversal in SSD of lizards from Central and North America: in warm, low latitude environments, males are larger than females, but at colder, high latitudes, females are larger than males. Comparisons to expectations under a Brownian motion model of SSD evolution indicate that this pattern reflects differences in the evolutionary rates and/or trajectories of sex‐specific body sizes. The SSD gradient we found is strongly related to mean annual temperature, but is independent of species richness and body size differences among species within grid cells, suggesting that the biogeography of SSD reflects gradients in sexual and/or fecundity selection, rather than intersexual niche divergence to minimize intraspecific competition. We demonstrate that the SSD gradient is driven by stronger variation in male size than in female size and is independent of clutch mass. This suggests that gradients in sexual selection and male–male competition, rather than fecundity selection to maximize reproductive output by females in seasonal environments, are predominantly responsible for the gradient. 相似文献
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MICHEL VEUILLE 《Biological journal of the Linnean Society. Linnean Society of London》1980,13(1):89-100
Individuals of the genus Jaera do not mate at random. In the species from the Mediterranean group, J. italica and. J. nordmanni, large males and medium sized females are at an advantage and their sizes are positively assorted. These effects are attributable to sexual competition between males. In the Ponlo-caspian species J. istri, no advantage of large males exists, but sexual selection could be the cause for a long passive phase prior to copulation and for normalizing selection upon female size at pairing. In the Atlantic species, J. albifrons, no selection can be ascertained.
Differential mating success in males appears as one of the causes of the evolution of sexual dimorphism in body size, which makes males larger, of equal size, or smaller than females according to the species. The reason for this reversal in dimorphism seems to differ in the two sexes. Sexual selection provides an explanation for the evolution of male size, while the interspecific changes in female length are more likely due to ecological factors. 相似文献
Differential mating success in males appears as one of the causes of the evolution of sexual dimorphism in body size, which makes males larger, of equal size, or smaller than females according to the species. The reason for this reversal in dimorphism seems to differ in the two sexes. Sexual selection provides an explanation for the evolution of male size, while the interspecific changes in female length are more likely due to ecological factors. 相似文献
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The use of fluctuating asymmetry (FA) for biomonitoring environmental stress is limited by the lack of work on how FA in particular traits responds to specific stresses. Here, by manipulating the number of individuals in an enclosed fallow deer (Dama dama) population, we describe, for the first time, clear density dependence in the FA of juvenile jaw morphology. The impact of high population density on FA was strong for both sexes, supporting the use of FA for indexing environmental stress. In addition, there was some indication that the change in FA was greater in males (43.6%) than females (28.5%). Finally, the ability to buffer density-dependent stress was independent of body condition. We suggest that, under highly limiting conditions, whole cohorts may be unable to buffer against developmental error, irrespective of individual quality. 相似文献
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Thomas J. Sanger Susan M. Seav Masayoshi Tokita R. Brian Langerhans Lela M. Ross Jonathan B. Losos Arhat Abzhanov 《Proceedings. Biological sciences / The Royal Society》2014,281(1784)
Sexual dimorphisms vary widely among species. This variation must arise through sex-specific evolutionary modifications to developmental processes. Anolis lizards vary extensively in their expression of cranial dimorphism. Compared with other Anolis species, members of the carolinensis clade have evolved relatively high levels of cranial dimorphism; males of this clade have exceptionally long faces relative to conspecific females. Developmentally, this facial length dimorphism arises through an evolutionarily novel, clade-specific strategy. Our analyses herein reveal that sex-specific regulation of the oestrogen pathway underlies evolution of this exaggerated male phenotype, rather than the androgen or insulin growth factor pathways that have long been considered the primary regulators of male-biased dimorphism among vertebrates. Our results suggest greater intricacy in the genetic mechanisms that underlie sexual dimorphisms than previously appreciated. 相似文献
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Raúl Cueva del Castillo;Salomón Sanabria-Urbán;Ricardo Mariño-Pérez;Hojun Song; 《Ecology and evolution》2024,14(8):e70188
In many animal species, larger body size is positively correlated with male mating success and female fecundity. However, in the case of insects, in high seasonality environments, natural selection favors a faster maturation that decreases the risk of pre-reproductive death. However, this advantageous adaptation comes at a tradeoff, resulting in a reduction in body size. Maturation time is influenced by environmental factors, such as temperature, season length, and food availability during the rains. The geographic variation in these parameters provides an opportunity to study their impact on the adaptive evolution of body size in Pyrgomorphidae grasshoppers. These grasshoppers exhibit remarkable variation in body size and wing development and can be found in diverse plant communities across Africa, Asia, Australia, and tropical America. In this study, we utilized a phylogenetic approach to examine the evolution of body size, considering climatic factors, and the influence of sexual selection on size differences between males and females. We found a positive correlation between mean annual temperature and sexual size dimorphism (SSD). Remarkably, species exhibiting a strong bias toward larger females were found to be adapted to regions with higher temperatures. In the Pyrgomorphidae family, an intermediate body size was identified as the ancestral trait. Additionally, winged male and female grasshoppers were observed to be larger than their wingless counterparts. Despite the potential conflicting pressures on body size in males and females, these grasshoppers adhere to Rench's Rule, suggesting that sexual selection on males' body size may explain the evolution of SSD. 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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Carlos Lorenzo Jos Miguel Carretero Juan Luis Arsuaga Ana Gracia Ignacio Martínez 《American journal of physical anthropology》1998,106(1):19-33
A sexual dimorphism more marked than in living humans has been claimed for European Middle Pleistocene humans, Neandertals and prehistoric modern humans. In this paper, body size and cranial capacity variation are studied in the Sima de los Huesos Middle Pleistocene sample. This is the largest sample of non-modern humans found to date from one single site, and with all skeletal elements represented. Since the techniques available to estimate the degree of sexual dimorphism in small palaeontological samples are all unsatisfactory, we have used the bootstraping method to asses the magnitude of the variation in the Sima de los Huesos sample compared to modern human intrapopulational variation. We analyze size variation without attempting to sex the specimens a priori. Anatomical regions investigated are scapular glenoid fossa; acetabulum; humeral proximal and distal epiphyses; ulnar proximal epiphysis; radial neck; proximal femur; humeral, femoral, ulnar and tibial shaft; lumbosacral joint; patella; calcaneum; and talar trochlea. In the Sima de los Huesos sample only the humeral midshaft perimeter shows an unusual high variation (only when it is expressed by the maximum ratio, not by the coefficient of variation). In spite of that the cranial capacity range at Sima de los Huesos almost spans the rest of the European and African Middle Pleistocene range. The maximum ratio is in the central part of the distribution of modern human samples. Thus, the hypothesis of a greater sexual dimorphism in Middle Pleistocene populations than in modern populations is not supported by either cranial or postcranial evidence from Sima de los Huesos. Am J Phys Anthropol 106:19–33, 1998. © 1998 Wiley-Liss, Inc. 相似文献
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In crustacean species with precopulatory mate-guarding, sexual size dimorphism has most often been regarded as the consequence of a large male advantage in contest competition for access to females. However, large body size in males may also be favoured indirectly through scramble competition. This might partly be the case if the actual target of selection is a morphological character, closely correlated with body size, involved in the detection of receptive females. We studied sexual selection on body size and antennae length in natural populations of Asellus aquaticus, an isopod species with precopulatory mate guarding. In this species, males are larger than females and male pairing success is positively related to body size. However, males also have longer antennae, relative to body size, than females, suggesting that this character may also be favoured by sexual selection. We used multivariate analysis of selection to assess the relative influences of body size and antennae length in five different populations in the field. Selection gradients indicated that overall body size was a better predictor of male pairing success than antennae length, although some variation was observed between sites. We then manipulated male antennae length in a series of experiments conducted in the laboratory, and compared the pairing ability of males with short or long antennae. Males with short antennae were less likely to detect, orient to and to pair with a receptive female compared to males with long antennae. We discuss the implications of our results for studies of male body size and sexual dimorphism in relation to sexual selection in crustaceans. 相似文献
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X. BONNET F. LAGARDE B. T. HENEN J. CORBIN K. A. NAGY G. NAULLEAU K. BALHOUL O. CHASTEL A. LEGRAND R. CAMBAG 《Biological journal of the Linnean Society. Linnean Society of London》2001,72(3):357-372
Selective forces shape sexes differently, with male body proportions facing strong selection to enhance mate searching and male-to-male combat traits, and female fitness being influenced by the ability to assimilate large amounts of nutrients necessary for vitellogenesis (and/or gestation), and their ability to carry the eggs or embryos. We evaluated the sexual dimorphism of body proportion of more than 800 wild steppe tortoises (Testudo horsfieldii) in Uzbekistan. The thick, well-developed shell offers protection from predators but pronounced digging habits probably also constrain body shape (e.g. a shell that is dorso-ventrally flattened, although round from a dorsal view helps to penetrate into, and move within the soil). Thus, in this species, natural selection might favour a heavy and flat shell that is 'closed' with small openings for appendages. In males, these environmental influences appear to be countered by sexual selection. Compared to females, they weigh less (absolutely and relative to shell dimensions), have longer legs, have shell structure allowing wider movements for their legs, and they walk faster. Males were also able to right themselves more quickly than females did in experimental tests. This quick righting ability is critical because intra-sexual combats frequently result in males being flipped onto their backs and becoming prone to hyperthermia or predation. Females are heavily built, with wide shells (relative to male shells), which may provide space for carrying eggs. From our results, a number of simple hypotheses can be tested on a wide range of chelonian species. 相似文献
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In crustacean species with precopulatory mate-guarding, sexual size dimorphism has most often been regarded as the consequence of a large male advantage in contest competition for access to females. However, large body size in males may also be favoured indirectly through scramble competition. This might partly be the case if the actual target of selection is a morphological character, closely correlated with body size, involved in the detection of receptive females. We studied sexual selection on body size and antennae length in natural populations of Asellus aquaticus, an isopod species with precopulatory mate guarding. In this species, males are larger than females and male pairing success is positively related to body size. However, males also have longer antennae, relative to body size, than females, suggesting that this character may also be favoured by sexual selection. We used multivariate analysis of selection to assess the relative influences of body size and antennae length in five different populations in the field. Selection gradients indicated that, overall, body size was a better predictor of male pairing success than antennae length, although some variation was observed between sites. We then manipulated male antennae length in a series of experiments conducted in the lab, and compared the pairing ability of males with short or long antennae. Males with short antennae were less likely to detect, orient to, and to pair with a receptive female compared with males with long antennae. We discuss the implications of our results for studies of male body size and sexual dimorphism in relation to sexual selection in crustaceans. 相似文献
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横斑锦蛇Euprepiophis perlacea是中国西部特有种,《中国濒危动物红皮书》极危物种,研究成果相对匮乏。本研究采用样带法和样方法在横斑锦蛇分布区内采集到标本20号,测量其鳞片特征、体长、尾长等形态学性状,结合文献资料中已有的5号标本数据,进行统计分析。结果表明,鳞片特征是有效的分类依据,尤其背鳞(19-19-17行)、左上唇鳞数(7)和右上唇鳞数(7)在所有标本中无任何变化,是鉴定该物种的最重要特征。对尾下鳞、体长、尾长、头长、头宽、头高、眼间距共7个形态学性状数据进行方差分析,性别间的差异均无统计学意义,未发现蛇类中普遍存在的两性异形现象。横斑锦蛇体色靓丽、无毒、性情温和、行动迟缓、分布区狭窄、种群数量稀少,分布区内人口密度高,人为干扰严重,急需加强科学研究、法制宣传和科普教育,以保障该物种种群延续。 相似文献
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The average thickness of soft tissues on parts of the face is known, but its variation has not been related to cranial morphology. To investigate this relationship, measurements of facial soft-tissue depths and craniometric dimensions were taken on adult, white Australian cadavers (17 male and 23 female). Significant correlations between many soft-tissue depths and craniometric dimensions were found, suggesting a relationship between the amount of soft tissue present on the face and the size of the underlying bony skeleton. Soft-tissue depths were highly positively correlated with each other; craniometric dimensions were correlated but to a lesser extent. Males had thicker soft tissues and larger craniometric dimensions than females; considerable overlap of ranges was also noted. Multiple regression analysis was used to produce equations predicting the soft-tissue depth at specified areas of the face from craniometric dimensions. A subsample of nine cadavers was examined for the effects of tissue embalming. Embalming caused significant initial increases in facial soft-tissue depths. Cadavers embalmed for less than 6 months had soft-tissue depths significantly greater than for fully embalmed cadavers. The evidence that facial soft-tissue thicknesses vary with craniofacial dimensions has implications for forensic identification, facial aesthetic surgery, and approximation of the facial features of extinct individuals. 相似文献