Sexually Dimorphic Neurons in the Ventromedial Hypothalamus Govern Mating in Both Sexes and Aggression in Males
Cindy F. YangMichael C. ChiangDaniel C. GrayMahalakshmi PrabhakaranMaricruz AlvaradoScott A. JunttiElizabeth K. UngerJames A. WellsNirao M. Shah
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Sexual dimorphism
In many polygynous mammals, sexual size dimorphism (SSD) is thought to have evolved through sexual selection, because larger males prevail in male–male combat and secure access to estrous females. SSD is often correlated with higher age-specific mortality of males than of females, possibly because males have higher nutritional requirements and riskier growth and reproductive tactics. In adult chamois Rupicapra rupicapra, sexual dimorphism in skeletal size was about 5%, but dimorphism in body mass was highly seasonal. Males were about 40% heavier than females in autumn but only 4% heavier in spring. For a given skeletal size, males were heavier than females only in autumn. Chamois sexual dimorphism appears mainly due to greater summer accumulation of fat and muscle mass by males than by females. Male mass declines rapidly during the rut. Limited dimorphism in skeletal size combined with substantial but seasonal dimorphism in mass has not been reported in other sexually dimorphic ungulates. Seasonal changes in mass allow males to achieve large size for the rut by accumulating body resources during summer. The use of these resources over the rut may reduce mortality associated with sustaining a large size over the winter.
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Sexual dimorphism (ancient Greek dis : twice; morphē : form) denotes any situation where, on average, the male and the female members of a species differ. Though often used to mark simple size differences between the sexes, the same phrase can also refer to specific anatomical, physiological, psychological, or behavioral sex differences. In any given species, sexual dimorphism can vary greatly across traits. For example, Homo sapiens shows low levels of sexual dimorphism in eye color, moderate sexual dimorphism in height, and high levels of sexual dimorphism in muscle mass. Modern evolutionary theory offers explanations for the diverse patterns of sexual dimorphism observed in nature.
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The term "sexual dimorphism" refers to any differences in form, whether those differences be morphological, chemical, or physiological in nature. Sexual dimorphism may be manifested as differences in size, morphological appearance, metabolic activities, responses to hormones, drug sensitivity, rates of maturation, etc. The first report, in 1940, of a sexual dimorphism of salivary glands was that of morphological differences between the submandibular glands (SMG) of male and female mice. The sexual dimorphism of the mouse SMG is probably the most widely studied sexual dimorphism of salivary glands. The sexual dimorphism of the mouse SMG has been examined using nearly all methods of study--from neuroanatomical studies of the adrenergic stimulation of secretion by these glands to electrophoretic analysis yielding zymograms of enzymes present in mouse SMG extracts. In addition to a brief review of the sexual dimorphism of the mouse SMG, this report will examine some less well-known examples of salivary gland sexual dimorphism.
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Sexual dimorphism in the genus Sceloporus has historically been relatively well studied; however, there is little understanding of how patterns of sexual size dimorphism might vary within species and how that might affect our ability to generalize about the evolution of sexual size-dimorphism in Sceloporus and other organisms. We examined sexual size-dimorphism in a population of Sceloporus spinosus from Guadalcázar, San Luis Potosí, Mexico. Males (n = 85) and females (n = 63) showed no significant sexual dimorphism in size of the body, head, or legs. In combination with the results of other studies on sexual dimorphism in S. spinosus and closely related species of Sceloporus, our results suggest that there can be variation in sexual size-dimorphism within and among species that can limit the ability to make broad generalizations about the phylogenetic patterns of sexual dimorphism in Sceloporus.
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This paper reviews the patterns of sexual dimorphism in the living higher primates and suggests criteria for sex determination in the australopithecines. Using the bimodal distribution for australopithecine canine breadths, sex determination for individual specimens is attempted. The pattern of sexual dimorphism in the australopithecines differs from that in other higher primates: posterior-tooth dimorphism, mandibular-corpus dimorphism, and probably, therefore, body-size dimorphism are at the extreme of the higher-primate range, while canine dimorphism is considerably less than in most living primates, although greater than in living humans. It is suggested that the primary cause of the difference between hominid and pongid trends in the evolution of sexual dimorphism is the increasing importance of tools as a supplement and replacement for the canines in hominid evolution.
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A new species of Nilgirius , N. pygoprominulus sp. n. (male and female) in the family Assamiidae from Yunnan Province, China, is described and illustrated herein. Sexual size dimorphism (male larger than female) is inconsistent with most assamiids. Other sexually dimorphic features (body shape, leg IV and pseudonychium) are reported. Nilgirius pygoprominulus sp. n. is described as a new species of Trionyxellinae. Information about sexual dimorphism of the species is reported.
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Comparison of sexual dimorphism between G1 and G2 in Brithys crini Fabricius(Lepidoptera: Noctuidae)
To understand the sexual dimorphism of Brithys crini Fabricius and effects of different generations on the sexual dimorphism,the body weight and size of generation 1(G1) and generation 2(G2) were compared under the laboratory conditions.The results showed:(1)There was sexual dimorphism in G1 and G2 of B.crini reared in the laboratory.The female was larger than the male.(2)Sexual dimorphism differed between G1 and G2.Sexual dimorphism in G1 was more obvious than that in G2.These results indicated that the sexual dimorphism in B.crini maybe different from different generations reared in the laboratory.
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Abstract Sexual behavior in the two species of Cysteodemus LeConte consists of: (1) a simple form of courtship that lacks an elaborate tactual display, (2) a prolonged mating period during which the male remains mounted on the female, (3) high levels of female receptivity regardless of previous mating, and (4) postcopulatory behavior. This behavior represents a condition intermediate between that found in the Meloinae and Nemognathinae, the two major subfamilies of blister beetles.
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The degree of morphological variability in different groups of Baikal amphipods is different; sexual dimorphism among Baikal amphipods is described in approximately 30% of species by a limited number of morphological characters. There are very few works based on a large number of specimens and many morphological characters. The widespread species Gmelinoides fasciatus (Stebbing, 1899) is known from its morphological heterogeneity, but no detailed studies have been carried out. Study of sexual dimorphism of the species G. fasciatus is based on a large number of quantitative characters. The purpose of this work is to investigate sexual dimorphism and identify the most significant features. The study revealed the variability of the morphological features of G. fasciatus and pronounced sexual dimorphism, as well as the features that characterize it. Comparative analysis of morphological characters showed that in the study of sexual dimorphism it is necessary to use a greater number of characters than previously used.
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Morphological Analysis
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This paper reviews the patterns of sexual dimorphism in the living higher primates and suggests criteria for sex determination in the australopithecines. Using the bimodal distribution for australopithecine canine breadths, sex determination for individual specimens is attempted. The pattern of sexual dimorphism in the australopithecines differs from that in other higher primates: posterior-tooth dimorphism, mandibular-corpus dimorphism, and probably, therefore, body-size dimorphism are at the extreme of the higher-primate range, while canine dimorphism is considerably less than in most living primates, although greater than in living humans. It is suggested that the primary cause of the difference between hominid and pongid trends in the evolution of sexual dimorphism is the increasing importance of tools as a supplement and replacement for the canines in hominid evolution.
Sexual dimorphism
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