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1.
Members of the leiognathid subfamily Gazzinae, comprising approximately two‐thirds of ponyfish species, are sexually dimorphic with regard to features of the light organ system (LOS). In Gazzinae, the circumesophageal light organ (LO) of males is enlarged and varies in shape compared with similarly sized conspecific females. In association with male species‐specific translucent external patches on the head and flank, these sexually dimorphic LO features are hypothesized to be correlated with species‐specific luminescence displays. Anatomical differences in LO shape, volume, and orientation, and its association with the gas bladder and other internal structures that function in light emission, are compared to observations of luminescence displays for every major lineage within Leiognathidae. We reconstruct the character evolution of both internal and external morphological features of the LOS to investigate the evolution of LO sexual dimorphism and morphology. Both internal and external sexual dimorphism in the ponyfish LOs were recovered as most likely to have evolved in the common ancestor of Leiognathidae, and likelihood‐based correlation analyses indicate that the evolution of internal and external dimorphism in males is statistically correlated. Magnetic resonance imaging technology was applied to examine the unique internal LOs of ponyfishes in situ, which provides a new metric (LO index) for comparison of LO structure across lineages. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.  相似文献   

2.
A phylogeny was generated for Leiognathidae, an assemblage of bioluminescent, Indo‐Pacific schooling fishes, using 6175 characters derived from seven mitochondrial genes (16S, COI, ND4, ND5, tRNA‐His, tRNA‐Ser, tRNA‐Leu), two nuclear genes (28S, histone H3), and 15 morphological transformations corresponding to features of the fishes' sexually dimorphic light‐organ system (LOS; e.g., circumesophageal light organ, lateral lining of the gas bladder, transparent flank and opercular patches). Leiognathidae comprises three genera, Gazza, Leiognathus, and Secutor. Our results demonstrate that Leiognathidae, Gazza, and Secutor are monophyletic, whereas Leiognathus is not. The recovered pattern of relationships reveals that a structurally complex, strongly sexually dimorphic and highly variable species‐specific light organ is derived from a comparatively simple non‐dimorphic structure, and that evolution of other sexually dimorphic internal and external features of the male LOS are closely linked with these light‐organ modifications. Our results demonstrate the utility of LOS features, both for recovering phylogeny and resolving taxonomic issues in a clade whose members otherwise exhibit little morphological variation. We diagnose two new leiognathid genera, Photopectoralis and Photoplagios, on the basis of these apomorphic LOS features and also present derived features of the LOS to diagnose several additional leiognathid clades, including Gazza and Secutor. Furthermore, we show that five distinct and highly specialized morphologies for male‐specific lateral luminescence signaling, which exhibit species‐specific variation in structure, have evolved in these otherwise outwardly conservative fishes. Leiognathids inhabit turbid coastal waters with poor visibility and are often captured in mixed assemblages of several species. We hypothesize that the species‐specific, sexually dimorphic internal and external modifications of the leiognathid LOS provide compelling evidence for an assortative mating scheme in which males use species‐specific patterns of lateral luminescence signaling to attract mates, and that this system functions to maintain reproductive isolation in these turbid coastal environments. © The Willi Hennig Society 2005.  相似文献   

3.
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.  相似文献   

4.
Genetic differentiation arises due to the interaction between natural and sexual selection, migration and genetic drift. A potential role of sexual selection in speciation has received much interest, although comparative studies are inconsistent in finding supporting evidence. A poorly tested prediction is that species subject to a higher intensity of sexual selection should show greater genetic differentiation amongst populations because females from these populations should be more choosy in mate choice. The Goodeinae is a group of endemic Mexican fishes in which female choice has driven some species to be morphologically sexually dimorphic, whereas others are relatively monomorphic. Here, we measured population divergence, using microsatellite loci, within four goodeid species which show contrasting levels of sexual dimorphism. We found higher levels of differentiation between populations of the more dimorphic species, implying less gene flow between populations. We also found evidence of higher levels of genetic differences between the sexes within populations of the dimorphic species, consistent with greater dispersal in males. Adjusted for geographic distance, the mean F(ST) for the dimorphic species is 0.25 compared with 0.16 for the less dimorphic species. We conclude that population differentiation is accelerated in more sexually dimorphic species, and that comparative phylogeography may provide a more powerful approach to detecting processes, such as an influence of sexual selection on differentiation, than broad-scale comparative studies.  相似文献   

5.
Colour signalling traits are often lost over evolutionary time, perhaps because they increase vulnerability to visual predators or lose relevance in terms of sexual selection. Here, we used spectrometric and phylogenetic comparative analyses to ask whether four independent losses of a sexually selected blue patch are spectrally similar, and whether these losses equate to a decrease in conspicuousness or to loss of a signal. We found that patches were lost in two distinct ways: either increasing reflectance primarily at very long or at very short wavelengths, and that species with additional colour elements (UV, green and pink) may be evolutionary intermediates. In addition, we found that patch spectral profiles of all species were closely aligned with visual receptors in the receiver's retina. We found that loss of the blue patch makes males less conspicuous in terms of chromatic conspicuousness, but more conspicuous in terms of achromatic contrast, and that sexual dimorphism often persists regardless of patch loss. Dorsal surfaces were considerably more cryptic than were ventral surfaces, and species in which male bellies were the most similar in conspicuousness to their dorsal surfaces were also the most sexually dimorphic. These results emphasize the consistent importance of sexual selection and its flexible impact on different signal components through evolutionary time.  相似文献   

6.
雌雄异株植物对环境胁迫响应的性别差异与性别比例 雌雄异株植物在性特征(繁殖器官)和次级性特征(植物的特征)均表现出性二态。形态、生理与生态特征等次级性特征的性别差异,通常在繁殖成本和其他功能性状之间存在着权衡。尽管有证据表明性二态对环境胁迫的响应不一定存在于所有植物中,但次级性特征的权衡可能受到环境胁迫的影响。当植物表现出性二态时,不同的物种与胁迫因子可以导致性别特异性的响应。因此,胁迫作用对雌雄异株植物影响的概括性研究是必须的。另外,性二态可能会影响雌雄异株植物沿着环境梯度的频率和分布,引起生态位分化与性别空间分异。目前,控制性别比例偏差的原因和机制还知之甚少。本综述旨在讨论不利环境下的性别特异性响应与性别比例偏差,有利于深入的理解性二态对环境胁迫的响应。  相似文献   

7.
Species in which the sexes equally exhibit colourful ornaments are an issue for evolutionary theory. Among several hypotheses, sexual selection for mutual mate choice and social selection for signals of behavioural dominance are most commonly supported. We examined the previously documented sex‐similar size of yellow‐orange ear patches in the king penguin, Aptenodytes patagonicus. This species is monogamous and pairs just before reproduction. Raising a chick requires considerable effort by both parents, as they alternate care of their single offspring with foraging at sea. The size of the ear patches appears to signal aggressive territoriality in the breeding colony for both sexes. However, experiments suggest that females prefer large patch size during mate choice, and males do not prefer this trait. We tested whether the size of the coloured ear patch was influenced by sexual selection for couples that had recently paired. We used analyses of covariance to compare the size of the ear patch to a measure of body size and then tested for the difference between males and females. Males were 6.2% larger in ear patch width and 7.7% larger in ear patch area than females, and the distance between the ear patches over the head was 7.5% smaller in males, with all differences highly significant. Consequently, sexual selection appears to favour larger ear patches in males, possibly because of an excess of males that promotes female choice. Social selection also appears to favour the evolutionary maintenance of ear patches of males, and thus both types of selection may contribute to enlarged ear patches.  相似文献   

8.
Podarcis bocagei and Podarcis carbonelli are two lacertid species endemic to the western Iberian Peninsula, and both show head size and shape sexual dimorphism. We studied immature and adult head sexual dimorphism and analysed ontogenetic trajectories of head traits with body and head size, aiming to shed light on the proximate mechanisms involved. Immatures were much less dimorphic than adults, but geometric morphometric techniques revealed that head shape sexual differences are already present at this stage. Males and females differed in allometry of all head characters with body size, with males showing a disproportionate increase of head size and dimensions. On the other hand, head dimensions and head shape changed with increasing head size following similar trends in both sexes, possibly indicating developmental restrictions. Consequently, adult sexual dimorphism for head characters in these species is the result of both shape differences in the immature stage and hypermetric growth of the head in relation to body size in males.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 111–124.  相似文献   

9.
10.
Gymnotiform electric fish emit an electric organ discharge that, in several species, is sexually dimorphic and functions in gender recognition. In addition, some species produce frequency modulations of the electric organ discharge, known as chirps, that are displayed during aggression and courtship. We report that two congeneric species (Apteronotus leptorhynchus and A. albifrons) differ in the expression of sexual dimorphism in these signals. In A. leptorhynchus, males chirp more than females, but in A. albifrons chirping is monomorphic. The gonadosomatic index and plasma levels of 11-ketotestosterone were equivalent in both species, suggesting that they were in similar reproductive condition. Corresponding to this difference in dimorphism, A. leptorhynchus increases chirping in response to androgens, but chirping in A. albifrons is insensitive to implants of testosterone, dihydrotestosterone or 11-ketotestosterone. Species also differ in the sexual dimorphism and androgen sensitivity of electric organ discharge frequency. In A. leptorhynchus, males discharge at higher frequencies than females, and androgens increase electric organ discharge frequency. In A.␣albifrons, males discharge at lower frequencies than females, and androgens decrease electric organ discharge frequency. Thus, in both chirping and electric organ discharge frequency, evolutionary changes in the presence or direction of sexual dimorphism have been accompanied and perhaps caused by changes in the androgen regulation of the electric organ discharge. Accepted: 18 February 1998  相似文献   

11.
This study examines statistical correlations between socioecological variables (including measures of group composition, intermale competition, and habitat preference) and the ontogeny of body size sexual dimorphism in anthropoid primates. A regression-based multivariate measure of dimorphism in body weight ontogeny is derived from a sample of 37 species. Quantitative estimates of covariation between socioecological variables and this multivariate measure are evaluated. Statistically significant covariation between the ontogeny of dimorphism and socioecological variables, with the possible exception of habitat preference, is observed. Sex differences in ontogeny are lacking in species that exhibit low levels of intermale competition and are classifiable as species with monogamous/polyandrous mating systems. Among dimorphic species, two modes of dimorphic growth are apparent, which seem to be related to different kinds of group compositions. Multimale/multifemale species tend to become dimorphic through bimaturism (sex differences in duration of growth) with minimal sex differences in growth rate. Single-male/multifemale species tend to attain dimorphism through differences in rate of growth, often with limited bimaturism. Measures of intermale competition may also covary with these modes of dimorphic growth, but the relations among these variables are sometimes ambiguous. Correlations between dimorphic growth and behavioral variables may reflect alternative life history strategies in primates. Specifically, the ways in which risks faced by subadult males are distributed and the relations of these risks to growth rates seem to influence the evolution of size ontogenies. The absence of dimorphic ontogeny in some species can be tied to similar distributions of risk in each sex. In taxa that become dimorphic primarily through rate differences in growth, the lifetime distribution of risks for males may change rapidly. In contrast, males may face a pattern of uniformly changing or stable risk in species that become dimorphic through bimaturism. Finally, much variation recorded by this study remains unexplained, providing additional evidence of the need to specially examine female ontogeny before primate body size dimorphism can be satisfactorily explained. © 1995 Wiley-Liss, Inc.  相似文献   

12.
Why are American mink sexually dimorphic? A role for niche separation   总被引:3,自引:0,他引:3  
American mink are highly sexually dimorphic, with males being up to twice the size of females. Sexual dimorphism may arise for several reasons, including intra- or inter-sexual selection, inter-sexual competition, or divergent reproductive roles. Whether or not dimorphism arises from competition, a degree of niche separation is expected in dimorphic species. Sexual divergence in feeding niche has been reported for many species, including mink. This is likely to be manifested in a greater degree of dimorphism in those structures, such as teeth, that are used for the acquisition of prey. We tested the hypothesis that teeth and other trophic structures of male mink would be significantly larger than those of females, after controlling for underlying skeletal size differences. Canine and carnassial teeth, and several skull dimensions, were larger than predicted in males. There is good evidence that sexual dimorphism in mink trophic apparati is greater than predicted from allometry. We examined the development of dimorphism in various features with age and found that it was not consistent. Several trophic features were dimorphic amongst juveniles, and the degree of dimorphism remained relatively constant with age. Dimorphism in canines, and in relative body mass, was less apparent amongst juveniles and increased with increasing age. We discuss our results in the light of contemporary theories on the evolution and maintenance of sexual size dimorphism and argue that niche separation as a result of dimorphism in trophic features, while probably not the driving force behind sexual size dimorphism, may play a role in its maintenance.  相似文献   

13.
The swimbladder plays an important role in buoyancy regulation but is typically reduced or even absent in benthic freshwater fishes that inhabit fast flowing water. Here, we document, for the first time, a remarkable example of swimbladder sexual dimorphism in the highly rheophilic South Asian torrent minnows (Psilorhynchus). The male swimbladder is not only much larger than that of the female (up to five times the diameter and up to 98 times the volume in some cases), but is also structurally more complex, with multiple internal septa dividing it into smaller chambers. Males also exhibit a strange organ of unknown function or homology in association with the swimbladder that is absent in females. Extreme sexual dimorphism of non-gonadal internal organs is rare among vertebrates and the swimbladder sexual dimorphisms that we describe for Psilorhynchus are unique among fishes.  相似文献   

14.
Body coloration is sexually dimorphic in many vertebrate species, including lizards, in which males are often more conspicuous than females. A detailed analysis of the relative size of coloured patches and their reflectance, including the ultraviolet (UV) range, has rarely been performed. In the present work we quantified sexual dimorphism in body traits and surface area of all lateral patches from adult females and males of two subspecies of Gallotia galloti (G. g. galloti and G. g. eisentrauti). We also analysed the magnitude of sexual dichromatism in the UV‐visible reflectance of such patches and the changes in patch size and brightness during the reproductive season (April–July). Males had significantly larger patch areas (relative to their snout‐vent length) and higher brightness (mainly in the UV‐blue range) than did females in both subspecies. The comparison of relative patch areas among months did not reach statistical significance. However, patch brightness significantly changed during the breeding season: that of the UV‐blue (300–495 nm) range from lizards of the two subspecies was significantly larger in June than in April, while brightness in the 495–700 nm range in G. g. galloti was larger in May, June, and July than in April. A different pattern of dichromatism was also detected in the two populations, with G. g. eisentrauti being more sexually dichromatic than G. g. galloti. We discuss the results in terms of possible evolutionary causes for the sexual dichromatism related to different ecological characteristics of the habitats where each subspecies live. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 556–569.  相似文献   

15.
Abstract.— As commonly observed among closely related species within a variety of taxa, Drosophila species differ considerably in whether they exhibit sexual dimorphism in coloration or morphology. Those Drosophila species in which male external sexual characters are minimal or absent tend, instead, to have exaggerated ejaculate traits such as sperm gigantism or seminal nutrient donations. Underlying explanations for the interspecific differences in the presence of external morphological sexual dimorphism versus exaggerated ejaculate traits are addressed here by examining the opportunity for sexual selection on males to occur before versus after mating in 21 species of Drosophila . Female remating frequency, an important component of the operational sex ratio, differs widely among Drosophila species and appears to dictate whether the arena of sexual selection is prior to, as opposed to after, copulation. Infrequent female mating results in fewer mating opportunities for males and thus stronger competition for receptive females that favors the evolution of male characters that maximize mating success. On the other hand, rapid female remating results in overlapping ejaculates in the female reproductive tract, such that ejaculate traits which enhance fertilization success are favored. The strong association between female remating frequency in a given species and the presence of sexually selected external versus internal male characters indicates that the relationship be examined in other taxa as well.  相似文献   

16.
Asian colobines exhibit a wide range of sexual dimorphism in body mass. Some species are monomorphic, whereas others are strongly dimorphic. Strong sexual dimorphism is generally viewed as the consequence of intense male contest competition over access to mates, but this idea appears not to explain variation in sexual dimorphism in Asian colobines. Our results show that modular colobines, i.e. species in which social units aggregate into higher‐level bands or often associate, have significantly higher levels of sexual dimorphism in body mass than the nonmodular ones. This finding was corroborated by means of phylogenetically controlled methods and multiple regression analyses. The results suggest that living in a modular society intensifies the contest competition among males, which is further exacerbated by the continuous presence of all‐male units. Am. J. Primatol. 71:609–616, 2009. © 2009 Wiley‐Liss, Inc.  相似文献   

17.
Sexual segregation in Soay sheep (Ovis aries) was investigated using an experimental approach in order to test the sexual dimorphism-body size hypothesis. Two corollaries of the sexual dimorphism-body size hypothesis were tested: (1) in dimorphic species males, the larger sex, have relatively smaller bite sizes on short swards because of the scaling of incisor arcade with body weight, and (2) they move off earlier to feed on taller but poorer-quality swards when such swards are patchily distributed on a scale which enables the spatial segregation of individuals. Patch choice between sexes was estimated using a matrix of grass patches which differed in both quality and biomass of grass on offer (HQ: high-quality-low-biomass; LQ: low-quality-high-biomass). Sex differences in patch choice and grazing behaviour were tested in short-term preference trials. Incisor breadth showed no significant difference between sexes. On the other hand, muzzle width was dimorphic, with females having a narrower muzzle than males. Bite size was significantly different between the sexes, being smaller in females than in males, although it was not significantly different between sward types. Females had a higher bite rate than males and the bite rate was higher in the HQ sward type than the LQ sward type. When the effect of body mass was removed, no sex differences in muzzle size, bite size or bite rate were found. The intake rate did not differ between the sexes or between sward types. Whilst both sexes preferred the HQ sward type, females spent a significantly longer time feeding on the LQ sward type than did males. The difference detected between the sexes in patch choice was not consistent directly with the sexual dimorphism-body size hypothesis. Alternative explanations based on sex differences in foraging behaviour in relation to body mass sexual dimorphism are discussed to explain the result. Received: 1 February 1999 / Accepted: 12 May 1999  相似文献   

18.
Allometric and heterochronic approaches to sexual dimorphism have contributed much to our understanding of the evolutionary morphology of the primate skull and dentition. To date, however, extensive studies of sexual dimorphism have been carried out only on the great apes and a few cercopithecine monkeys. To fill this gap, representative dimensions of the skull were collected among ontogenetic series of two dimorphic Old World monkeys:Macaca fascicularis (Cercopithecinae) andNasalis larvatus (Colobinae). The ontogeny of cranial sexual dimorphism was evaluated with least-squares bivariate regression, analysis of covariance (ANCOVA), and analysis of variance (ANOVA). Results indicate that within each species the sexes typically exhibit nonsignificant differences in ANCOVAs of ontogenetic trajectories, except for bivariate comparisons with bicanine breadth. AmongMacaca fascicularis, ANOVAs between males and females of common dental ages show that adult, and frequently subadult, males are significantly larger than females, i.e., sexual dimorphism develops via time and rate hypermorphosis (males primarily grow for a longer time period as well as faster). AmongNasalis larvatus, however, comparisons between males and females of common dental ages indicate that only adult males are significantly larger than females, i.e., sexual dimorphism develops primarily via time hypermorphosis (males grow for a longer time period). Within both species, females appear to exhibit an early growth spurt at dental age 2; that is, many cranial measures for females tend to be larger than those for males. Measures of the circumorbital region (e.g., browridge height), body weight, and bicanine breadth exhibit typically the highest sexual dimorphism ratios. The fact that postcanine toothrow length and neurocranial volume (less so inNasalis) demonstrate very low dimorphism ratios generally supports assertions that postnatal systemic growth (and associated selective pressures thereon) exerts a greater influence on facial, but not neural, dental, or orbital, development (Cochard, 1985, 1987; Shea, 1985a,b, 1986; Shea and Gomez, 1988; Sheaet al., 1990). Additional consideration of ontogenetic differences between species generally supports previous functional interpretations of subfamilial differences in cranial form related to agonistic displays in cercopithecine monkeys (Ravosa, 1990).  相似文献   

19.
Sexual dimorphism is founded upon a resource allocation trade‐off between investments in reproduction versus other life‐history traits including the immune system. In species with conventional parental care roles, theory predicts that males maximize their lifetime reproductive success by allocating resources toward sexual selection, while females achieve this through prolonging their lifespan. Here, we examine the interrelation between sexual dimorphism and parental care strategies in closely related maternal and biparental mouthbrooding cichlid fishes from East African Lake Tanganyika. We measured cellular immune parameters, examined the relative expression of 28 immune system and life history‐related candidate genes and analyzed the microbiota composition in the buccal cavity. According to our predictions, maternal mouthbrooders are more sexually dimorphic in immune parameters than biparental mouthbrooders, which has possibly arisen through a differential resource allocation into parental care versus secondary sexual traits. Biparental mouthbrooders, on the other hand, which share the costs of parental care, feature an upregulated adaptive immune response and stronger antiviral properties, while their inflammation response is reduced. Overall, our results suggest a differential resource allocation trade‐off between the two modes of parental investment.  相似文献   

20.
Sexual dimorphism (SD) is a common feature of animals, and selection for sexually dimorphic traits may affect both functional morphological traits and organismal performance. Trait evolution through natural selection can also vary across environments. However, whether the evolution of organismal performance is distinct between the sexes is rarely tested in a phylogenetic comparative context. Anurans commonly exhibit sexual size dimorphism, which may affect jumping performance given the effects of body size on locomotion. They also live in a wide variety of microhabitats. Yet the relationships among dimorphism, performance, and ecology remain underexamined in anurans. Here, we explore relationships between microhabitat use, body size, and jumping performance in males and females to determine the drivers of dimorphic patterns in jumping performance. Using methods for predicting jumping performance through anatomical measurements, we describe how fecundity selection and natural selection associated with body size and microhabitat have likely shaped female jumping performance. We found that the magnitude of sexual size dimorphism (where females are about 14% larger than males) was much lower than dimorphism in muscle volume, where females had 42% more muscle than males (after accounting for body size). Despite these sometimes-large averages, phylogenetic t-tests failed to show the statistical significance of SD for any variable, indicating sexually dimorphic species tend to be closely related. While SD of jumping performance did not vary among microhabitats, we found female jumping velocity and energy differed across microhabitats. Overall, our findings indicate that differences in sex-specific reproductive roles, size, jumping-related morphology, and performance are all important determinants in how selection has led to the incredible ecophenotypic diversity of anurans.  相似文献   

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