新疆沙虎的两性异形

通过测量和比较采自新疆且末县的新疆沙虎Teratoscincus przewalskii成体的体型和口宽等6个形态特征,研究了新疆沙虎的两性异形。研究共采集64只新疆沙虎(雌性26只,雄性38只),雌雄成体最小体长(SVL)分别为63.6 mm和59.7 mm。口宽、头宽、头高、眼间距和尾长5个局部形态特征均与体长呈显著正相关。新疆沙虎体长雌雄间无差异,其它身体形态特征仅口宽具有显著的两性差异,且口宽相对于体长呈异速生长,雌性增长速率大于雄性。新疆沙虎口宽的两性异形可能与两性间食性的差异有关,而体长和其它身体形态特征无显著两性差异则可能与性选择和自然选择的综合作用有关。     

Allometry of Sexual Size Dimorphism in Domestic Dog

Background

The tendency for male-larger sexual size dimorphism (SSD) to scale with body size – a pattern termed Rensch''s rule – has been empirically supported in many animal lineages. Nevertheless, its theoretical elucidation is a subject of debate. Here, we exploited the extreme morphological variability of domestic dog (Canis familiaris) to gain insights into evolutionary causes of this rule.

Methodology/Principal Findings

We studied SSD and its allometry among 74 breeds ranging in height from less than 19 cm in Chihuahua to about 84 cm in Irish wolfhound. In total, the dataset included 6,221 individuals. We demonstrate that most dog breeds are male-larger, and SSD in large breeds is comparable to SSD of their wolf ancestor. Among breeds, SSD becomes smaller with decreasing body size. The smallest breeds are nearly monomorphic.

Conclusions/Significance

SSD among dog breeds follows the pattern consistent with Rensch''s rule. The variability of body size and corresponding changes in SSD among breeds of a domestic animal shaped by artificial selection can help to better understand processes leading to emergence of Rensch''s rule.     

Sexual Size Dimorphism,Canine Dimorphism,and Male-Male Competition in Primates

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.     

Significant Male Biased Sexual Size Dimorphism in Leptobrachium leishanensis

Sexual size dimorphism(SSD) is a widespread phenomenon among animals, and whose evolution and maintenance has been a central topic in evolutionary biology since Darwin's time. SSD varies in direction among the major taxonomic groups of animals and even within the same groups. In anurans, female biased SSD is the rule in many lineages, whereas male biased SSD is a rare phenomenon. In this paper, we analyze whether SSD exists inLeptobrachium leishanensis by comparing morphological characteristics between the sexes. Our results show that all six morphological characteristics measured are significantly different between the sexes. Males are significantly larger than females, indicating that the male biased SSD of this species is apparent. The size of the nuptial spines, a special secondary sex trait of males, is significantly and positively correlated with body size. We suggest that the resource defense polygyny mating system and parental care behavior may be explanations for the evolution of male biased SSD and nuptial spine development in this species.     

东方蝾螈性二型性特征分析

以东方蝾螈大别山种群为实验材料,随机选取162只蝾螈(雄52只,雌110只),通过单变量、双变量、多变量分析的方法,进行11项体征的测量分析.结果表明,头体长是本研究的最适单变量,且头体长与腋胯距之间的相关性最高;PCl在雄性和雌性中均与头体长密切相关,且大多数体征与头体长进行比例分析均显示出异速生长关系,东方蝾螈性二型性普遍存在.本研究中11项体征呈现符合Renseh法则的雌性依赖性二型性演化特征,这种性二型性特征可能是一系列复杂的非对称性选择的结果.     

Disentangling the Size and Shape Components of Sexual Dimorphism

Evolutionary Biology - Many organisms are sexually dimorphic, reflecting sex-specific selection pressures. But although sexual dimorphism may consist of different variables from size to shape and...     

Changes in Size and Age of Chinook Salmon Oncorhynchus tshawytscha Returning to Alaska

The average sizes of Pacific salmon have declined in some areas in the Northeast Pacific over the past few decades, but the extent and geographic distribution of these declines in Alaska is uncertain. Here, we used regression analyses to quantify decadal trends in length and age at maturity in ten datasets from commercial harvests, weirs, and spawner abundance surveys of Chinook salmon Oncorhynchus tshawytscha throughout Alaska. We found that on average these fish have become smaller over the past 30 years (~6 generations), because of a decline in the predominant age at maturity and because of a decrease in age-specific length. The proportion of older and larger 4-ocean age fish in the population declined significantly (P < 0.05) in all stocks examined by return year or brood year. Our analyses also indicated that the age-specific lengths of 4-ocean fish (9 of 10 stocks) and of 3-ocean fish (5 of 10 stocks) have declined significantly (P < 0.05). Size-selective harvest may be driving earlier maturation and declines in size, but the evidence is not conclusive, and additional factors, such as ocean conditions or competitive interactions with other species of salmon, may also be responsible. Regardless of the cause, these wide-spread phenotypic shifts influence fecundity and population abundance, and ultimately may put populations and associated fisheries at risk of decline.     

Sexual Size Dimorphism and Body Condition in the Australasian Gannet

Sexual size dimorphism is widespread throughout seabird taxa and several drivers leading to its evolution have been hypothesised. While the Australasian Gannet (Morus serrator) has previously been considered nominally monomorphic, recent studies have documented sexual segregation in diet and foraging areas, traits often associated with size dimorphism. The present study investigated the sex differences in body mass and structural size of this species at two colonies (Pope’s Eye, PE; Point Danger, PD) in northern Bass Strait, south-eastern Australia. Females were found to be 3.1% and 7.3% heavier (2.74 ± 0.03, n = 92; 2.67 ± 0.03 kg, n = 43) than males (2.66 ± 0.03, n = 92; 2.48 ± 0.03 kg, n = 43) at PE and PD, respectively. Females were also larger in wing ulna length (0.8% both colonies) but smaller in bill depth (PE: 2.2%; PD: 1.7%) than males. Despite this dimorphism, a discriminant function provided only mild accuracy in determining sex. A similar degree of dimorphism was also found within breeding pairs, however assortative mating was not apparent at either colony (R² < 0.04). Using hydrogen isotope dilution, a body condition index was developed from morphometrics to estimate total body fat (TBF) stores, where TBF(%) = 24.43+1.94*(body mass/wing ulna length) – 0.58*tarsus length (r² = 0.84, n = 15). This index was used to estimate body composition in all sampled individuals. There was no significant difference in TBF(%) between the sexes for any stage of breeding or in any year of the study at either colony suggesting that, despite a greater body mass, females were not in a better condition than males. While the driving mechanism for sexual dimorphism in this species is currently unknown, studies of other Sulids indicate segregation in foraging behaviour, habitat and diet may be a contributing factor.     

Sexual Dimorphism Increases Evolvability in a Genetic Regulatory Network

The majority of work on genetic regulatory networks has focused on environmental and mutational robustness, and much less attention has been paid to the conditions under which a network may produce an evolvable phenotype. Sexually dimorphic characters often show rapid rates of change over short evolutionary time scales and while this is thought to be due to the strength of sexual selection acting on the trait, a dimorphic character with an underlying pleiotropic architecture may also influence the evolution of the regulatory network that controls the character and affect evolvability. As evolvability indicates a capacity for phenotypic change and mutational robustness refers to a capacity for phenotypic stasis, increases in evolvability may show a negative relationship with mutational robustness. I tested this with a computational model of a genetic regulatory network and found that, contrary to expectation, sexually dimorphic characters exhibited both higher mutational robustness and higher evolvability. Decomposition of the results revealed that linkage disequilibrium within sex and linkage disequilibrium between sexes, two of the three primary components of additive genetic variance and evolvability in quantitative genetics models, contributed to the differences in evolvability between sexually dimorphic and monomorphic populations. These results indicate that producing two pleiotropically linked characters did not constrain either the production of a robust phenotype or adaptive potential. Instead, the genetic system evolved to maximize both quantities.     

The Proximate Causes of Sexual Size Dimorphism in Phrynocephalus przewalskii

Sexual size dimorphism (SSD) is a common phenomenon and is a central topic in evolutionary biology. Recently, the importance of pursuing an ontogenetic perspective of SSD has been emphasized, to elucidate the proximate physiological mechanisms leading to its evolution. However, such research has seldom focused on the critical periods when males and females diverge. Using mark-recapture data, we investigated the development of SSD, sex-specific survivorship, and growth rates in Phrynocephalus przewalskii (Agamidae). We demonstrated that both male and female lizards are reproductively mature at age 10–11 months (including 5 months hibernation). Male-biased SSD in snout-vent length (SVL) was only found in adults and was fully expressed at age 11 months (June of the first full season of activity), just after sexual maturation. However, male-biased SSD in tail length (TL), hind-limb length (LL), and head width (HW) were fully expressed at age 9–10 months, just before sexual maturation. Analysis of age-specific linear growth rates identified sexually dimorphic growth during the fifth growth month (age 10–11 months) as the proximate cause of SSD in SVL. The males experienced higher mortality than females in the first 2 years and only survived better than females after SSD was well developed. This suggests that the critical period of divergence in the sizes of male and female P. przewalskii occurs between 10 and 11 months of age (May to June during the first full season of activity), and that the sexual difference in growth during this period is the proximate cause. However, the sexual difference in survivorship cannot explain the male-biased SSD in SVL. Our results indicate that performance-related characteristics, such as TL, HW, and LL diverged earlier than SVL. The physiological mechanisms underlying the different growth patterns of males and females may reflect different energy allocations associated with their different reproductive statuses.     

根田鼠身体大小的性二型

在雌雄异体的有性生物中 ,反映身体结构和功能特征的某些变量在两性之间常常出现固有的和明显的差别 ,使得人们能够以此为根据判断一个个体的性别 ,这种现象被称为性二型 (ｓｅｘｕａｌｄｉｍｏｒ ｐｈｉｓｍ)。国外大量研究表明 ,哺乳动物性二型现象十分普遍 ,并且 ,在大多数情况下 ,雄性个体大于雌性个体[1] ;国内同类研究还不多 ,仅见周立等[2 ] 、盛和林[3] 、陈国芳[4 ] 、杜铭章[5] 分别对高原鼠兔(Ｏｃｈｏｔｏｎａｃｕｒｚｏｎｉａｅ)、黄鼬 (Ｍｕｓｔｅｌａｓｉｂｉｒｉｃａ)、摇蚊和海蛇的性二型现象作过报道 ,但均未分析其产生原…     

Identification of Genetic Determinants of the Sexual Dimorphism in CNS Autoimmunity

Multiple sclerosis (MS) is a debilitating chronic inflammatory disease of the nervous system that affects approximately 2.3 million individuals worldwide, with higher prevalence in females, and a strong genetic component. While over 200 MS susceptibility loci have been identified in GWAS, the underlying mechanisms whereby they contribute to disease susceptibility remains ill-defined. Forward genetics approaches using conventional laboratory mouse strains are useful in identifying and functionally dissecting genes controlling disease-relevant phenotypes, but are hindered by the limited genetic diversity represented in such strains. To address this, we have combined the powerful chromosome substitution (consomic) strain approach with the genetic diversity of a wild-derived inbred mouse strain. Using experimental allergic encephalomyelitis (EAE), a mouse model of MS, we evaluated genetic control of disease course among a panel of 26 consomic strains of mice inheriting chromosomes from the wild-derived PWD strain on the C57BL/6J background, which models the genetic diversity seen in human populations. Nineteen linkages on 18 chromosomes were found to harbor loci controlling EAE. Of these 19 linkages, six were male-specific, four were female-specific, and nine were non-sex-specific, consistent with a differential genetic control of disease course between males and females. An MS-GWAS candidate-driven bioinformatic analysis using orthologous genes linked to EAE course identified sex-specific and non-sex-specific gene networks underlying disease pathogenesis. An analysis of sex hormone regulation of genes within these networks identified several key molecules, prominently including the MAP kinase family, known hormone-dependent regulators of sex differences in EAE course. Importantly, our results provide the framework by which consomic mouse strains with overall genome-wide genetic diversity, approximating that seen in humans, can be used as a rapid and powerful tool for modeling the genetic architecture of MS. Moreover, our data represent the first step towards mechanistic dissection of genetic control of sexual dimorphism in CNS autoimmunity.     

大山雀身体大小的性二态及其季节变化

动物中普遍存在雌雄个体身体大小的性二态现象。了解近缘种之间身体大小性二态现象的差异,可为深入探讨身体大小性二态现象的潜在驱动机制提供证据。国外对欧亚大山雀(Parus major)的研究发现,其喙长、跗跖长、翅长等6项身体大小指标存在着明显的性二态,且喙长的性二态存在季节间差异。大山雀(P.cinereus)曾被作为欧亚大山雀的一个亚种,其形态和行为与欧亚大山雀存在着诸多相似之处。为探讨大山雀是否也存在身体大小性二态及季节性差异,本研究分析了2018至2020年间在河南董寨国家级自然保护区捕捉的226只(雌性96只和雄性130只)大山雀的喙长、头喙长、跗跖长、翅长、尾长和体长这6项体征指标的两性差异及其季节变化。结果显示,大山雀上述6项身体大小指标均存在不同程度的性二态现象,且雄性个体仅喙长与雌性的差异不显著,其余5项指标均显著大于雌性。此外,身体大小指标的两性差异不随季节显著变化,但两性的跗跖长在秋季均显著短于冬季和繁殖季,尾长在繁殖季均显著长于秋季和冬季。上述结果表明,大山雀身体大小的性二态及其季节性差异与欧亚大山雀并不完全相似。无论其身体大小存在性二态和季节变化的原因,还是其与欧亚大山雀在身体大小性二态模式上的差别,都有待今后进一步研究。     

Sex-Specific Weight Loss Mediates Sexual Size Dimorphism in Drosophila melanogaster

The selective pressures leading to the evolution of Sexual Size Dimorphism (SSD) have been well studied in many organisms, yet, the underlying developmental mechanisms are poorly understood. By generating a complete growth profile by sex in Drosophila melanogaster, we describe the sex-specific pattern of growth responsible for SSD. Growth rate and critical size for pupariation significantly contributed to adult SSD, whereas duration of growth did not. Surprisingly, SSD at peak larval mass was twice that of the uneclosed adult SSD with weight loss between peak larval mass and pupariation playing an important role in generating the final SSD. Our finding that weight loss is an important regulator of SSD adds additional complexity to our understanding of how body size is regulated in different sexes. Collectively, these data allow for the elucidation of the molecular-genetic mechanisms that generate SSD, an important component of understanding how SSD evolves.     

Inverse of Rensch's Rule of Allometry for Sexual Size Dimorphism in Bufo andrewsi

Difference in body size between males and females(sexual size dimorphism:SSD) and its variation are a common phenomenon in animal kingdom.Rensch’s rule predicts that the degree of SSD variation increases with the enlarged mean body size when males are larger than females and decreases when females are larger than males.Here,whether the patterns of variations in SSD in the Andrew’s toad(Bufo andrewsi)follow Rensch’s rule was tested using unpublished data from 14 populations and published data fro...     

Sexual Size Dimorphism in the Color Pattern Elements of Two Mimetic Heliconius Butterflies

Sexual dichromatism and sexual dimorphism of body size are reasonably well studied in butterflies. Sexual size dimorphism of color pattern elements, however, is much less explored. The object of this study is Heliconius, a genus of butterflies well known for the coevolution between mate color preferences and mimicry. Given the sexual role of wing coloration, we investigated the existence of sexual size dimorphism in the wing color elements of a mimetic pair—Heliconius erato phyllis Fabricius and Heliconius besckei Ménétriés—and analyzed the allometric patterns of these traits. Correlation between size of elements in the dorsal and ventral wing surfaces were also estimated. In both species, three out of four elements were larger in males, but the non-dimorphic element was not the same. With regard to the allometric patterns, our most important finding was that smaller males of one species have proportionally larger yellow bars. This is the first study specifically concerning quantitative sexual dimorphism in the coloration of this well-known genus of butterflies and it opens new prospects to investigate sex-related natural selection and sexual selection of color pattern elements.     

猕猴颊齿大小的性差研究初报

对28例太行山成年猕猴(♂10,♀18)的上、下颌颊齿齿冠面积进行测量。运用SPSS 10.0统计软件的多变量分析,选择有关颊齿变量建立性别判别函数。结果表明:猕猴颊齿具有明显的性差。选择不同的变量和选择不同的判别函数其性别正确判别率不同。上、下颌颊齿的性差有一定差异。使用逐步判别法建立判别函数,其性别正确判别率上颌颊齿为89.3%,下颌颊齿为92.3%。