Sexual dimorphism of the canine roots in theMacaca fuscata

In situ radiographic analysis of the maxillary canines ofMacaca fuscata was conducted on 88 specimens in 44 individuals (23 dry skulls and 21 live animals) in order to examine the number of roots. The left canines were then extracted from ten female skulls for measurement, further radiographic examination, and visual morphological observation. The results showed a clear sexual dimorphism in root morphology: all male canines were clearly distinguished as single-rooted from the radiograph, whereas more than 40% of the female canines were double-rooted. Variation was also found among the single-rooted female canines, in that some of these teeth appeared to have a bifurcated canal. This sexual dimorphism in the number of maxillary canine roots and the individual variation found among the females in root and canal morphology are previously unreported for this species. No observations were attempted on mandibular canines, however, because of the incomplete nature of the sample.     

Sexual dimorphism in cuticular hydrocarbons of the Australian field cricket Teleogryllus oceanicus (Orthoptera: Gryllidae)

Sexual dimorphism is presumed to reflect adaptive divergence in response to selection favouring different optimal character states in the two sexes. Here, we analyse patterns of sexual dimorphism in the cuticular hydrocarbons of the Australian field cricket Teleogryllus oceanicus using gas chromatography. Ten of the 25 peaks found in our chromatographs, differed in their relative abundance between the sexes. The presence of sexual dimorphism in T. oceanicus is discussed in reference to a review of sexual dimorphism in cuticular hydrocarbons of other insects. We found that this trait has been examined in 103 species across seven different orders. Seventy-six of these species (73%) displayed sex specificity of cuticular hydrocarbons, the presence/absence of which does not appear to be directly linked to phylogeny. The occurrence of sexual dimorphism in cuticular hydrocarbons of some but not other species, and the extent of variation within genera, suggest that this divergence has been driven primarily by sexual selection.     

Sexual dimorphism in canine length of woolly spider monkeys (Brachyteles arachnoides,E. Geoffroy 1806)

We measured canine teeth from 28 woolly spider monkeys (Brachyteles arachnoides) to assess sexual dimorphism and population differences. The specimens are from the Brazilian states of Bahia, Minas Gerais, Espírito Santo, Rio de Janeiro, and São Paulo. We found strong sexual dimorphism in canine length for individuals belonging to populations south of 22°00 latitude but no sexual dimorphism in canine length from individuals of populations north of 21°00 latitude. Canine length did not vary among females of northern and southern populations. However, southern males had significantly longer canines than northern males. This geographical difference in canine morphology, together with the presence or absence of thumbs and published accounts of differences in genetics and social structure between northern and southern populations, suggests thatBrachyteles arachnoides may be composed of at least two subspecies, which appear to be separated by the rivers Grande and Paraiba do Sul and the Serra da Mantiqueira.     

Sexual size dimorphism,growth, and maturity of the fluvial eight-barbel loach in the Kako River,Japan

The maturation and growth pattern of the fluvial eight-barbel loach Lefua sp. (Japanese name: nagare-hotoke-dojo), an endangered species, was investigated using an individual identification-recapture method from 1995 to 1998 in an upper reach of a headwater tributary of the Kako River, Hyogo Prefecture, Japan. Based on observations of the gonads through the abdominal skin, the loach was estimated to breed mostly from May to July. All the males matured by age 1⁺, and all the females matured by age 2⁺. Gamete release in all individuals of both males and females was predicted from recaptured loaches during each breeding season. The standard length of mature females was significantly larger than that of males, showing sexual size dimorphism (SSD). The maximum sizes recorded were 75.4 mm SL for females and 61.2 mm SL for males. Both males and females of immature specimens grew mainly from May to November, including the breeding season, with no significant differences in growth rates between them. After sexual maturity, both males and females grew mainly from July to October (or November), after the breeding season, and the females exhibited higher growth rates than males. Therefore, SSD of the species seems to be attributable to the different growth rates after maturity. The longevity of the loach was estimated to exceed ten years based on individual growth patterns of various sizes during the survey period. It is likely that the loach has an iteroparous life history, breeding every year, and moderate growth rates after maturity.     

Sexual dimorphism and allometry in primate ossa coxae

Five measurements were taken on the ossa coxae of 454 adult primates representing Ceboidea, Cercopithecoidea and Hominoidea. Sex differences in these variables and their relationships to overall body size and sexual dimorphism were tested by means of Student's t-test and regression analysis. The study attempts to clarify the nature of primate pelvic sexual dimorphism, including allometric effects, and more specifically, test the assertion made by Mobb and Wood (1977) that sexual dimorphism in body size in not an important determinant in pelvic sex differences. Variables that contribute to the size of the birth canal tend to be larger in females than males in all taxa studied except two. In these, Hylobates and Alouatta, there were no significant differences between the sexes for any of the five variables. In general, sexual dimorphism in variables contributing to the size of the birth canal was correlated (r ? 0.8) with sexual dimorphism in body size. Furthermore, the coefficients of allometry underlying pelvic sex differences were shown to be moderately correlated (r ? 0.5) with sexual dimorphism in size. The influence of other adaptive factors on primate pelvic sexual dimorphism are also briefly discussed.     

Sexual dimorphism in relation to winter foraging in the white-backed woodpecker ( Dendrocopos leucotos)

Male white-backed woodpeckers (Dendrocopos leucotos) in a 250-km² study area in western Norway are significantly larger than females in bill length and depth, wing and tarsus lengths, and bodyweight. During the winters (October–March 1985–2002), most pairs were observed within their breeding territory where both sexes foraged mainly in grey alder and birch trees, and visited trees of the same tree height and stem width. However, males foraged more frequently on dead trees and on trees broken by storms. Males also used more trees with less bark cover, foraged nearer the ground and used foraging sites of larger diameter. Furthermore, males practised more deep wood-pecking and less bark-pecking than females. Unlike in other sexually dimorphic woodpecker species, the foraging niche breadth in wintering white-backed woodpeckers showed only minor sexual differences, and the sexes overlapped significantly in all parameters examined. Since previous studies in the area have shown that the sexes overlap considerably in use of their territory, it was expected, as found in other size dimorphic woodpeckers, that the larger male would displace the supposedly socially subordinate female to suboptimal feeding sites. In our area, the sexes were rarely seen together, and no sign of aggression between the sexes was observed. Despite the sex-specific differences found in the foraging behaviour of the birds, it is not obvious how the differences should be related to size dimorphism.Communicated by F. Bairlein     

Size-sex relationship and sexual dimorphism in JapaneseArisaema (Araceae)

The size-sex relationship and sexual differences of sixArisaema species native to Japan were investigated. The size-sex relationship showed almost the same pattern in all species. When the plant was small in size, the sex expression was male, and sex expression changed from male to female as the plant grew larger. Male ratios decreased rapidly around a critical size, but this critical size differed from one species to another. Sexual differences were detected in reproductive structures and behavior, although no difference was detected in vegetative structures. The stoutness, longevity and inner tissue of the scape showed remarkable differences between males and females, and this difference was represented most clearly as the size-weight relationship. Earlier initiation of flowering in males was also observed. No difference was found in resource allocation to reproductive structures between male and female plants at the flowering stage. However, a broad variation in the amount of resource allocation to reproductive structures was found at the fruiting stage in female individuals, which was attributed to differences in the setting rate of mature fruits.     

Sexual selection versus alternative causes of sexual dimorphism in teiid lizards

Summary The presence and extent of sexual dimorphisms in body form (size and shape) of adult macroteiid lizards were investigated. Males were significantly larger than females in the temperate species, Cnemidophorus tigris, and in the tropical species, Ameiva ameiva and C. ocellifer. Young adult C. tigris males grew faster than young adult females within and between reproductive seasons. Adult males of all species had larger heads than adult females of the same body size; this difference increased with body size. Moreover, male C. tigris were heavier than females of the same snout-vent length. The causes and consequences of the sexual dimorphisms were also examined. The possible causes of body size are especially numerous, and distinguishing the relative influences of the various causal selection factors on body size is problematical. Nevertheless, observational field data were used to tentatively conclude that intrasexual selection was the cause of larger body size of C. tigris males relative to females because (1) larger males won in male aggressive interactions, (2) the winning males gained access to more females by repelling competitors and by female acceptance, (3) larger males consequently had higher reproductive success, and (4) other hypothetical causes of larger male size were unsupported.     

Sexual dimorphism in <Emphasis Type="Italic">Sebastes owstoni</Emphasis> (Scorpaenidae) from the Sea of Japan

Morphological and genetic differences between red and yellow morphotypes of Sebastes owstoni were investigated, utilizing 277 males [84.0–194.3 mm in standard length (SL)] and 542 females (92.3–251.5 mm SL) from the Sea of Japan. All males smaller than 120 mm SL were characterized by red body color. The frequency of specimens with yellow body color thereafter increased gradually with SL, all specimens larger than 170 mm SL being yellow. The specimens with yellow body color were observed throughout the year. All females smaller than 170 mm SL were characterized by red body color, the frequency of specimens with yellow body color tending to slightly increase with SL. However, most females had red body color, except for 16 specimens (177.7–241.5 mm SL) that were yellow, growth-related color change from red to yellow being uncommon. Morphological analysis of 49 males (107.6–193.3 mm SL) and 68 females (108.7–241.5 mm SL) showed the head length, orbit diameter, lower jaw length, and predorsal length to be relatively greater, but the distance between the pelvic and anal fins less, in males. A discriminant analysis using Mahalanobis distances resulted in 100% correct assignment of specimens to sex, regardless of SL and body color. In addition, no genetic differences were apparent between red and yellow individuals in mitochondrial DNA sequence analyses from the threonine tRNA to the first half of the control region (498 bp). Accordingly, the differences in body color, maximum size, and the five morphometric characters listed above were considered to represent sexual dimorphism. That evidenced by body color was considered to appear after that shown by morphometric characters, some exceptions in the former occurring in females. This is the first report of permanent sexual dimorphism in body color in Sebastes.     

Sexual dimorphism in the growth of the cranium

The major sexual dimorphisms in body size appear at puberty but, by then, 95% of the growth of the cranium is completed. As sexual dimorphism in the cranium is as great as for other parts of the body, this suggests that it must appear at an earlier age, and that cranium/body size ratios for the two sexes will vary during growth. Results from a longitudinal study of Montreal children are used to investigate this phenomenon. The effect is expressed quantitatively by proportional growth and growth velocity curves, based on the final size of boys, which show that the dimorphism indeed makes an early appearance. The data are also analyzed on an age scale relative to the ages of peak growth velocity in stature, derived from the individual growth curves. This shows that although there is a minor pubertal spurt in growth for the external cranial dimensions of boys, it contributes relatively little to the final dimorphism in cranial size. To summarize this aspect of growth, an index of cephalization is calculated: head length × head width/stature. Cross-sectional standards for the change of the mean index with age show a linear decline for boys and girls until puberty, with a constant difference between them. After puberty, the index becomes equal in the two sexes. Individual development curves for the index are however not linear.     

Sexual selection and canine dimorphism in New World monkeys

Social and ecological factors are important in shaping sexual dimorphism in Anthropoidea, but there is also a tendency for body-size dimorphism and canine dimorphism to increase with increased body size (Rensch's rule) (Rensch: Evolution Above the Species Level. London: Methuen, 1959.) Most ecologist interpret Rensch's rule to be a consequence of social and ecological selective factors that covary with body size, but recent claims have been advanced that dimorphism is principally a consequence of selection for increased body size alone. Here we assess the effects of body size, body-size dimorphism, and social structure on canine dimorphism among platyrrhine monkeys. Platyrrhine species examined are classified into four behavioral groups reflecting the intensity of intermale competition for access to females or to limiting resources. As canine dimorphism increases, so does the level of intermale competition. Those species with monogamous and polyandrous social structures have the lowest canine dimorphism, while those with dominance rank hierarchies of males have the most canine dimorphism. Species with fission-fusion social structures and transitory intermale breeding-season competition fall between these extremes. Among platyrrhines there is a significant positive correlation between body size and canine dimorphism However, within levels of competition, no significant correlation was found between the two. Also, with increased body size, body-size dimorphism tends to increase, and this correlation holds in some cases within competition levels. In an analysis of covariance, once the level of intermale competition is controlled for, neither molar size nor molar-size dimorphism accounts for a significant part of the variance in canine dimorphism. A similar analysis using body weight as a measure of size and dimorphism yields a less clear-cut picture: body weight contributes significantly to the model when the effects of the other factors are controlled. Finally, in a model using head and body length as a measure of size and dimorphism, all factors and the interactions between them are significant. We conclude that intermale competition among platyrrhine species is the most important factor explaining variations in canine dimorphism. The significant effects of size and size dimorphism in some models may be evidence that natural (as opposed to sexual) selection also plays a role in the evolution of increased canine dimorphism.     

Sexual dimorphism in the tooth-crown diameters of the deciduous teeth

Mesiodistal and buccolingual crown dimensions of the right deciduous teeth of 133 white children were analyzed for information on sexual dimorphism and sex discrimination using discriminant analysis. Even though consistent differences were found for only 15 out of 20 paired measurements, five of them significant at p = 0.05 or better, discriminant analysis showed the possibility of correctly sexing up to 75% of the juvenile sample, using a maximum of seven deciduous teeth.     

Sexual dimorphism and age of Mediterranean salamanders

We analysed sexual size dimorphism (SSD) for two Mediterranean species of the “true” salamander clade possessing distinct life histories (Salamandra algira and Mertensiella caucasica) and equilibrated the morphometric approach to individual age by using skeletochronology. For species that have a short breeding season and live at high altitudes, such as Mediterranean amphibians, the fecundity advantage hypothesis predicts female-biased SSD to maximise reproductive success. Our results showed no SSD in either species; however, morphometric data indicated a male-biased dimorphism in limb (arm and leg) dimensions in both species when compared to body size. Limb dimorphisms are likely related to the particular mating system, which involves an amplexus during spermatophore transfer. Arm length appeared sexually dimorphic during ontogeny both in viviparous S. algira and oviparous M. caucasica. A review on SSD indicated monomorphy of body size as a common lineage-specific pattern among the “true” salamander clade, but also the common presence of other traits such as sexually dimorphic limb proportions.     

Numerical analysis of sexual dimorphism inSaguinus dentition

Among New World monkeys, more or less sexual dimorphism exists in the dentition, especially in the Cebidae. On the other hand, the Callitrichidae includingSaguinus are said to be characterized by a broad lack of sexual dimorphism with the exception of the reproductive organs. In the present article, sexual dimorphism in the dentition of someSaguinus species was reconfirmed using univariate and multivariate analytical methods. The results of the analysis were as follows: (1) there is no sexual dimorphism in the canine tooth size, except for the upper canine ofS. geoffroyi and lower canine ofS. mystax; (2) the overall tooth size difference between males and females is slight or none inS. geoffroyi, S. leucopus, andS. fuscicollis, relatively small inS. oedipus andS. mystax, and rather larger inS. midas; (3) an overall difference in shape factor between both sexes exists in all species ofSaguinus to a greater or lesser extent; (4) although only slight sexual dimorphism is recognized in the canine tooth itself, sexual dimorphism does exist in some adjacent teeth of the canine in a few species; and (5) there are some interspecific differences in the magnitude of the sexual dimorphism of theSaguinus dentition and these differences are more evident in species inhabiting the peripheral regions of the distribution areas of this genus. Taking all the evidence obtained into account, the sexual dimorphism in theSaguinus dentition must be re-investigated in comparison with other genera of the Callitrichidae.     

Sexual dimorphism and mechanics of the human hip: A multivariate assessment

The present research was undertaken to determine the effects of sexual dimorphism in the human pelvis and femur on the mechanics of human locomotion. The analysis was based on six biomechanical variables determined from 25 male and 32 female skeletal remains from the Dickson Mound site. Discriminant function analysis indicates that the mechanical variables which primarily contribute to dimorphism are the moment arm of the gluteus medius and the torque produced by the abductors at the hip. These mechanical aspects of hip function produce greater pressure on the femoral head in females.     

Environmental influences on the sexual dimorphism in body size of western bobcats

Sexual size dimorphism might be influenced by environmental constraints on sexual selection or by intraspecific competition between males and females. We studied bobcats (Lynx rufus) in collections of museum specimens from western North America to examine these hypotheses. Structural body size was estimated from several measurements of the skull, ln-transformed and indexed through principal components analysis. Sexual dimorphism in body size was estimated from the difference in size index of males and females, and compared to geographic and climatic variables associated with biotic provinces (ecoregions). Of several climatic variables that were associated with bobcat body size, only seasonality of climate was associated with sexual dimorphism. Sexual size dimorphism, longitude, elevation, and seasonality were intercorrelated. As longitude decreased (moving inland from west-coastal ecoregions), sexual dimorphism decreased with the increased elevation and seasonality of continental climates of the Rocky Mountains. We suggest that increased seasonality and the need for fasting endurance by females may place constraints on the degree of sexual dimorphism in bobcats. Sexual dimorphism of body size and sexual size dimorphism of trophic structures (teeth) exhibited a strong positive association over geography, thus indirectly supporting the hypothesis that intrasexual competition for prey could account for the geographic variation in sexual size dimorphism. Thus, both environmental constraints on sexual selection of body size and intersexual competition were supported as possible explanations of the degree of sexual size dimorphism that occurs in populations of bobcats.     

Sexual selection,sexual dimorphism and plant phylogeny

Summary Darwin examined sexual dimorphism in animals, arguing that sexual selection was important in the evolution of such dimorphism. Sexual dimorphism in plants may have parallel causes and costs.The processes that contribute to sexual dimorphism may also lead to speciation and morphological differences among related species, as argued originally by Darwin. Where sexes are separate and dimorphism is well-developed, males of related animal species (both vertebrate and invertebrate) are often strikingly different from each other, while females may be virtually indistinguishable. A similar pattern may exist in plants: it is frequently the males (of dioecious taxa) or the male portions of the flower (in co-sexual flowers) that apparently have diversified. I suggest that the similarity of pattern may be accounted for by a similarity of process.In addition, sexual selection may have contributed to certain evolutionary trends within the angiosperms and, indeed, to angiosperm radiation.     

Sexual dimorphism in clonal growth forms and ramet distribution patterns in <Emphasis Type="Italic">Rumex acetosella</Emphasis> (Polygonaceae)

We investigated clonal traits in the dioecious herb Rumex acetosella to characterize sexual dimorphism in clonal forms and to correlate below-ground clonal patterns and above-ground ramet distributions. We recorded creeping root length, branching patterns, ramet and clump (caespitose ramets from the same position on the root) sprouting patterns, and biomass allocations in three females and males. We also estimated the patch size of flowering ramets within a quadrat. No sexual dimorphism was detected in the frequencies of branches and flowering ramets per root length. Male plants allocated proportionally more biomass to below-ground organs. Total root length did not differ between the sexes. Females sprouted more clumps with fewer flowering ramets per root length than males, which sprouted fewer clumps with more flowering ramets, which meant that clump sprouting patterns were phalanx-like in females and guerrilla-like in males. Flowering ramets were aggregately distributed in both females and males and patch sizes were similar between sexes, indicating that the spreader propagations were not found in the guerrilla-like males. We assumed that sexual dimorphism occurred in response to physiological integration for higher reproductive effort in females.     

蝙蝠体型性别二态性研究现状与展望

动物体型性别二态性(Sexual size dimorphism,SSD)是存在于动物界的普遍现象,作用于某一性别体型的选择压力与作用于另一性别体型的选择压力大小或方向的不同被认为是SSD 产生的原因。伦施法则认为,在雄性体型比雌性体型大的动物类群中,SSD 随体型增大而增大,相反地,在雌性体型比雄性体型大的生物类群中随体型增大而减小。本文从动物体型性别二态性产生的原因及规律方面概述了其研究现状,以及蝙蝠性别二态性研究的进展,并提出关于蝙蝠体型性别二态性尚未解决的科学问题及未来的研究展望。     

端黑萤和边褐端黑萤两性异形和雌性个体生育力

检测了端黑萤(Abscondita chinensis)和边褐端黑萤(Abscondita terminalis)繁殖期个体大小和形态特征的两性异形以及雌性繁殖输出。两因素方差分析表明,端黑萤的全长显著小于边褐端黑萤的全长,雌性个体显著大于雄性个体。以全长为协变量的两因素协方差分析显示,端黑萤的前胸背板宽、鞘翅长、复眼宽、胸长、腹宽、发光器面积及体重均显著小于边褐端黑萤,而腹长显著大于边褐端黑萤,触角长物种间差异不显著;雌性的前胸背板宽、腹长、腹宽及体重均显著大于雄性,而鞘翅长、复眼宽、胸长、触角长、发光器面积均显著小于雄性;物种和性别的交互作用对前胸背板宽、复眼宽、腹长、触角长及发光器面积影响显著,对其余的鞘翅长、胸长、腹宽及体重影响不显著。端黑萤和边褐端黑萤的两性异形指数分别为0.144和0.091。9个形态特征变量的主成分分析(Eigenvalue ≥ 1)发现,前2个主成分共解释56.8%的变异;复眼宽和发光器面积在第一主成分有较高的负负载系数,腹长有较高的正负载系数(解释31.3%变异);前胸背板宽和鞘翅长在第二主成分有较高的负负载系数(解释25.5%变异)。端黑萤和边褐端黑萤的平均窝卵数分别为28.9粒和18粒。线性回归显示,端黑萤和边褐端黑萤的窝卵数均与母体的全长及体重呈显著的正相关。单因素方差分析表明,特定全长的端黑萤的窝卵数显著大于边褐端黑萤。端黑萤和边褐端黑萤均属于雌性偏大的两性异形,是生育力选择、能量分配和运动综合影响的结果。雌萤腹腔容量等关键局部特征的增大是对生育力选择的适应,且生育力大小与两性异形差异程度成正相关。