Sexual dimorphism Research Papers - Academia.edu (original) (raw)

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- Zoology, Sexual dimorphism, Bite force, Netherlands
- by Tracey Sutton
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- Biology, Sexual dimorphism, Biological Sciences, Fishes

In this paper, we examine allometric and sexual-selection explanations for interspecific differences in the amount of sexual dimorphism among 60 primate species. Based on evidence provided by statistical analyses, we reject Leutenegger and Cheverud's [(1982). Int. J. Primatol. 3: 387-402] claim that body size alone is the major factor in the evolution of sexual dimorphism. The alternative proposed here is that sexual selection due to differences in the reproductive potential of males and females is the primary cause of sexual dimorphism. In addition, we propose that the overall size of a species determines whether the dimorphism will be expressed as size dimorphism, rather than in some other form.

- by Steven Gaulin
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- Zoology, Primatology, Sexual Selection, Sexual dimorphism

In many hummingbird species there is an opposite pattern of sexual dimorphism in bill length and other morphometric measures of body size. These differences seem to be closely related with differences in foraging ecology directly associated with a different resource exploitation strategy. The aim of this study was to assess if natural selection is acting on wing length and bill size in hummingbird males and females with different resource exploitation strategies (i.e., territorial males and non-territorial females). If competition for resources promotes sexual dimorphism as a selective pressure, males should be subjected to negative directional selection pressure for wing length and no selection pressure over bill size, while females should undergo positive directional selection pressure for both bill size and wing length. The morphometric data we collected suggests that there is no selection for wing length and bill size in male hummingbirds. In contrast, our females exhibited positive directional selection for both wing length and bill size. Although we cannot reject sexual selection acting on sexually dimorphic traits, this study suggests that natural selection may promote sexual dimorphism in traits that are closely related with hummingbird foraging ecology and resource exploitation strategies.

- by Cristian Estades
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- Zoology, Ornithology, Sexual Selection, Foraging ecology

When navigating, women typically focus on landmarks within the environment, whereas men tend to focus on the Euclidean properties of the environment. However, it is unclear whether these observed differences in navigational skill result from disparate strategies or disparate ability. To remove this confound, the present study required participants to follow either landmark-or Euclidean-based instructions during a navigation task (either in the real-world or on paper). Men performed best when using Euclidean information, whereas women performed best when using landmark information, suggesting a dimorphic capacity to use these 2 types of spatial information. Further, a significant correlation was observed between the mental rotation task and the ability to use Euclidean information, but not the ability to use landmark information.

- by Jennifer Leason
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- Psychology, Locomotion, Face recognition (Psychology), Behavioral Neuroscience

Adult males ofLytta vesicatoria (Coleopt., Meloidae) synthesize cantharidin, but females do not, although the substance is present in the females too. We developed a method for rearing larvae of this parasitic beetle in the laboratory. It is shown that there exist 7 larval stages and 4 hypermetamorphic forms (triungulinus, second larva,pseudochrysalis and fourth larva). Larvae from the second to the fifth stage (second larva) synthesize cantharidin. Therefore, we conclude that the substance present in the adult female is at least in part synthesized in the larval period. Nothing is known about the biological significance of this biochemical sexual dimorphism.

- by Dietrich Meyer
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- Physiology, Sexual dimorphism, Clinical Sciences, Biochemistry and cell biology

Because sexual selection pressures are high in sexually dimorphic organisms, morphological, physiological and performance traits are often studied in a sexual selection context. The proximate mechanisms underlying evolutionary change in these traits, however, remain largely unstudied. Here, we examined the role of steroids in shaping morphology and physiological performance in males of a sexually dimorphic lizard (Gallotia galloti). We compared morphology and physiological performance of males with experimentally elevated testosterone levels to sham-operated males. Before surgery, inter-individual variation in plasma testosterone levels correlated positively with bite force capacity. Administration of exogenous testosterone resulted in an increase of the mass of both jaw closing and locomotory muscles compared with sham-operated individuals, but the responsiveness varied considerably among muscle groups. In contrast to our expectations, the dramatic testosterone-induced changes in muscle masses did not result in concordant changes in bite force performance or sprint speed.

- by Jerry Husak and +3
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- Evolutionary Biology, Genetics, Zoology, Skeletal muscle biology

The spotted dol phin (Stenella attenuata) is found throughout much of the eastern tropical Pacific Ocean. A previous study evaluated morphological variation in skull morphology, but now specimens are available for a greater portion of the range. Also, corrections have been made in data and an assessment has been made evaluating repeatability of character measurements. We reas sessed geographic variation in 30 cranial features (26 morphometric measures and 4 tooth counts) based on 611 museum specimens. All characters except two tooth counts showed statistically signifi cant geographic variation, while 21 of the 30 characters exhibited significant sexual dimorphism. Males were larger in most charac ters; females were larger in some length measurements involving the rostrum and ramus. As in pre vious analyses, inshore S. attenu ata were found to be very distinc tive, so subsequent analyses fo cused on offshore spotted dolphins from 29 50 latitude-longitude blocks. Mantel tests ...

Sexual selection has driven the evolution and elaboration of a wide variety of displays and ornaments in male nonhuman primates, including capes, cheek flanges, and sexual coloration. Among the most sexually dimorphic of all primates is the drill (Mandrillus leucophaeus), the males of which can be 3 times the mass of females, possess large canines, and exhibit extremely bright sexual skin coloration. However, the function of male coloration in this species has never been examined. Here, we present data on male color (measured objectively using digital photography), dominance rank, measures of male-female association, and key sexual behaviors, of adult male drills (n=17) living in four semi free-ranging enclosures at the Drill Rehabilitation and Breeding Center in Nigeria. We test the hypothesis that male coloration is a badge of status, indicating dominance rank, and the hypothesis that male coloration attracts females. We found that male coloration did indicate rank, and that high ranking, strongly colored males were more likely to associate with adult females, and more specifically with fully tumescent females. These males also engaged in more sexual activity. However, measures of male-female association and sexual behaviors were not related to male color once rank had been taken into consideration; i.e., for males of a given rank, females did not prefer those that were more colorful. We discuss the results in light of what is known about the wild drill social system, in which unfamiliar Int J Primatol (

- by Caroline Ross
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- Zoology, Primatology, Digital Photography, Sexual Selection

Age structure and morphology differ among Pacific salmon (Oncorhynchus spp.) populations. Sexual selection and reproductive capacity (fecundity and egg size) generally favor large (old), deep-bodied fish. We hypothesized that natural selection from physical access to spawning grounds and size-biased predation by bears, Ursus spp., opposes such large, deep-bodied salmon. Accordingly, size and shape of salmon should vary predictably among spawning habitats. We tested this hypothesis by measuring the age composition and body depth of sockeye salmon, Oncorhynchus nerka, and the intensity of predation in a range of breeding habitats in southwestern Alaska. Stream width was positively correlated with age at maturity and negatively correlated with predation level. However, salmon spawning on lake beaches were not consistently old, indicating that different factors affect age in riverine- and beach-spawning populations. Body depths of male and female salmon were positively correlated with w...

- by Lisa Wetzel
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- Zoology, Sexual dimorphism, sockeye salmon

Animals respond to novel stimuli via explorative or neophobic behavior or both. The coexistence of these responses toward novel foods may be a successful adaptive strategy for a generalist species such as Cebus apella, because it allows the gradual introduction of new foods into the diet and reduces the risk of poisoning by ingestion of large amounts of toxic compounds . Neophobia has been studied mostly in captivity. We investigated responsiveness to novelty in a group of 25-30 wild tufted capuchins (Cebus apella) in Iguazú National Park (Argentina). They had been habituated to visiting sites where bananas were provided on three elevated platforms. We presented novel stimuli on an adjacent platform. There were 4 experimental conditions with 10 sessions each: the Novel Food condition, the Novel Object condition, the Control condition, in which the platform was empty, and the Banana condition. In the Novel Food and Novel Object conditions, a new stimulus-food or object-was on the platform during each session. The Banana condition provided information on capuchin response to a familiar preferred food. Overall, capuchins were less responsive toward novel objects than toward novel foods; however, although cautious, they ate small amounts of the novel foods. Age affected individual responsiveness toward novel foods, whereas sex affected responsiveness toward novel objects. Capuchins ignored the empty platform. Our findings are in agreement with the

- by Charles Janson
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- Zoology, Primatology, Sexual dimorphism, Age

A sex-related difference in olfactory sensitivity to androstenone has been reported to occur during adolescence. More males than females exhibited anosmia to androstenone, or an increase in androstenone threshold with age. The current study addressed the question whether similar, sexually dimorphic effects of aging over puberty can also be found for androstadienone. A total of 102 subjects participated (36 females, 66 males). Similar to previous investigations, subjects were divided into a group of 47 individuals with a mean age of 13.3 years, defined as pre/peri-pubertal, and a group of 55 subjects with a mean age of 17.1 years, defined as post-pubertal. All subjects underwent tests for verbal abilities, general olfactory function, and measurements of androstadienone thresholds. The study provided the following major results: (1) Male subjects exhibited higher androstadienone sensitivity in the pre/peri-pubertal group as compared to the post-pubertal group. This difference was not observed in female subjects. Correspondingly, a negative correlation between age and androstadienone sensitivity was found for male subjects, but not for female subjects. (2) In contrast to this sex-specific change of the androstadienone odor threshold, verbal skills and odor identification abilities increased with age in all subjects regardless of their sex. In conclusion, the present observations confirm previous research on sex-differentiated effects of aging during puberty on sensitivity towards odorous steroids. While the underlying causes are unknown, it may be hypothesized that the decreased sensitivity could result from the increased endogenous levels of androstadienone in male subjects. Future studies should include both steroid and non-steroid odorants to futher explore these age-related changes. D

- by Thomas Hummel
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- Adolescent, Sexual dimorphism, Biological Sciences, Puberty

The existence of sexual dimorphism in individual elements of the human skeleton allows sex
determination and significantly enhances the identification of fragmentary skeletal material.
Traditionally, the pelvis and the skull are used for an accurate sex determination. Sometimes they
are not available and alternative methods have to be used. The aim of this work is to study the sexual
dimorphism of the proximal portion of the posterior femur by analyzing the biometric data of the
Purkait’s triangle. The studied sample comprises 203 individuals (112 males and 91 females) from the
Modern Human Skeletal Reference Collection (The Athens Collection) of the Department of Animal &
Human Physiology (National & Kapodistrian University of Athens). The biometric data were analyzed by
Discriminant Analysis and equations were generated for sex determination, which gave an overall
correct classification of 78.3%. For the right and the left femur the percentages of correct classification
were 77.8% and 75.9% respectively. These accuracy rates were compared to those of an Indian population
and were found to be lower (86.5% for males and 86.3% for females). The study of sexual dimorphism (SD)
in Greek, Indian, European-American and African-American populations gave interesting results. The AB
diameter in the Greek sample shows the lowest degree of SD while the AC diameter shows the highest. In
the other three population samples, the BC diameter shows the highest degree of SD. We assume that the
femur anatomy of the Greeks is the major cause that the Purkait method does not give high rates of
correct classification. It is therefore advisable that practitioners exercise caution when using this method
on skeletal material from Greece, especially in forensic contexts.

- by Sotiris Manolis and +1
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- Sexual dimorphism

... Data table »View table. Table 3. Frequencies of the main type of dives of thick-billed murres (Uria lomvia) and razorbills (Alca torda) at Gannet Islands, Labrador. ... 1993; Jones et al. 2002) differently. ... Clair et al. 2001;... more

- by Martin Renner and +1
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- Zoology, Sexual dimorphism, Sex Difference, Foraging behaviour

Ammonites of the Middle Tithonian An ammonite fauna from an isolated outcrop of the Upper Jurassic Vaca Muerta Formation is described from Barda Negra in the southern part of the Neuquén-Mendoza Basin. It comprises several macroconch specimens of the species Aspidoceras cf. euomphalum Steuer, 1897 besides macroconchs and microconchs of Windhauseniceras internispinosum (Krantz, 1926), the index species of the Andean Middle Tithonian Internispinosum Zone. Morphological and taxonomic relationships of the studied aspidoceratids with previously described species and the sexual dimorphism in W. internispinosum are discussed.

- by Guenter Schweigert
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- Biostratigraphy, Sexual dimorphism

Although researchers have suggested that adult women who experienced early puberty may demonstrate particularly strong preferences for masculine men, evidence for such an association is equivocal. Here we show that adult women's preferences for masculinized male voices (i.e., male voices with lowered pitch) are negatively associated with the age at which they experienced first menses (i.e., age at menarche). Moreover, this relationship was independent of women's stated preference for long-versus short-term relationships, suggesting that the relationship does not necessarily reflect individual differences in women's preferred type of relationship. We discuss alternative mechanisms for the relationship between early puberty and women's masculinity preferences, focusing on the possibility that girls who experience early puberty might learn to associate masculinity with desirable mates because of exposure to particularly masculine males during adolescence.

- by Lynda Boothroyd
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- Psychology, Cognitive Science, Mate Choice, Mate selection

This study describes the morphology of the nematode cysts and larvae found in Achatina fulica (giant African snail) in Brazil. Sixty snails were collected in Mesquita, Rio de Janeiro State. Fourteen of the snails were naturally infected. The cysts were spherical, pink colored and measured 0.97 to 1.57 mm in diameter. In the majority of cases they had a single larvae involved in amorphous material. A total of 222 encysted larvae were recovered. Of these, 30 were utilized in the morphological study. The length of the larvae varied from 2.57 to 5.8 mm and they were classified as small -up to 3.5 mm; medium -from 3.53 to 4.5 mm; and large -greater than 4.52 mm. The average length of the larvae in the three groups was 2.85, 3.87 and 5.23 mm, respectively. The larval cuticle was white, shiny and transversally striated until the posterior end of the body. At the anterior end there is a mouth with three lips, with amphids and papillae, followed by a muscular esophagus with average length of 0.61 mm, terminating in an esophageal bulb and having a nerve ring in the middle third of the esophagus, and an intestine with an opening near the posterior end. The tail begins from this opening and has two types of ends: short and abrupt or long and gradually tapering. The difference in the tail end can suggest sexual dimorphism, although no primordial reproductive structures were observed. These characteristics were not sufficient to identify the larvae, so there is a need for further study.

- by Solange Brandolini
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- Zoology, Scanning Electron Microscopy, Sexual dimorphism, Rio de Janeiro
- by Vineeta Saini
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- Forensic Anthropology, Forensic Science, FORENSIC, India

Genetic modifications causing germ cell death during meiotic prophase in the mouse frequently have sexually dimorphic phenotypes where oocytes reach more advanced stages than spermatocytes. To determine to what extent these dimorphisms are due to differences in male versus female meiotic prophase development, we compared meiotic chromosome events in the two sexes in both wild-type and mutant mice. We report the abundance and time course of appearance of structural and recombinationrelated proteins of fetal oocyte nuclei. Oocytes at successive days post coitus show rapid, synchronous meiotic prophase development compared with the continuous spermatocyte development in adult testis. Consequently, a genetic defect requiring 2-3 days from the onset of prophase to reach arrest registers pachytene as the developmental endpoint in oocytes. Pachytene spermatocytes, on the other hand, which normally accumulate during days 4-10 after the onset of prophase, will be rare, giving the appearance of an earlier endpoint than in oocytes. We conclude that these different logistics create apparent sexually dimorphic endpoints. For more pronounced sexual dimorphisms, we examined meiotic prophase of mice with genetic modifications of meiotic chromosome core components that cause male but not female sterility. The correlations between male sterility and alterations in the organization of the sex chromosome cores and X-Y chromatin may indicate that impaired signals from the XY domain (XY chromosome cores, chromatin, dense body and sex body) may interfere with the progression of the spermatocyte through prophase. Oocytes, in the absence of the X-Y pair, do not suffer such defects.

- by B Spyropoulos
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- Genetics, Sexual dimorphism, Mice, Genetic modification

Behavioral tests of vision in squirrel monkeys (Suimirisciureus) reveal that there are widespread individual variations in color vision in this species. The variation has a sex-related component: whereas both trichromatic and dichromatic color vision occurs among female monkeys, males appear exclusively dichromatic. This finding suggests that, unlike humans, squirrel monkeys have only a single photopigment locus on the X chromosome. Squirrel monkeys (Soimiri sciureus)

- by Jay Neitz
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- Genetics, Color Perception, Sexual dimorphism, Vision

The estuarine grapsid crabs Chasmagnathus granulata and Cyrtograpsus angulatus belong to the most typical and dominant inhabitants of brackish coastal lagoons in southeastern South America. In a combined laboratory and field investigation of juvenile growth, we measured the increase in body size in these species under controlled conditions as well as in field experiments (in Mar Chiquita lagoon, Argentina), seasonal changes in size frequency distribution of a natural population, and growth related changes in selected morphometric traits of male and female juveniles (relations between carapace width, carapace length, propodus height and length of the cheliped, and pleon width). At 24°C, Cy. angulatus grew faster than Ch. granulata; it reached the crab-9 instar (C9; 13 mm carapace width) after 92 days, while Ch. granulata required 107 days to reach the C8 instar (7.4 mm). At 12°C, growth ceased in both species. The pleon begins to show sexual differences in the C5 (Cy. angulatus) and C8 instar (Ch. granulata), respectively, while the chelae differentiate earlier in Ch. granulata than in Cy. angulatus (in C4 vs C6). In the field, growth was maximal in summer, and was generally faster than in laboratory cultures. However, there is great individual variability in size (about 25% even in the first crab instar) and in size increments at ecdysis, increasing throughout juvenile growth. Our data indicate that, in the field, small-scale and shortterm variations in feeding conditions, temperature, and salinity account for an extremely high degree of variability in the absolute and relative rates of growth as well as in the time to sexual differentiation.

- by Tomas Luppi
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- Oceanography, Sexual dimorphism, Relative Growth Rate, Field Experiment

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 a t the hip. These mechanical aspects of hip function produce greater pressure on the femoral head in females.

- by Dennis Van Gerven
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- Evolutionary Biology, Archaeology, Paleontology, Anthropology

From a comparison of the photoresponses and membrane properties of photoreceptors from 20 species of Diptera, we conclude that coding in the time domain is matched to the dictates of visual ecology. This matching involves the dynamics of phototransduction and the use of an appropriate mix of potassium conductances to tune the photoreceptor membrane. Rapidly flying, manoeuvrable diurnal Diptera from several families have fast photoreceptors, with corner frequencies (the frequency at which signal power falls by a half) of between 50 and 107 Hz. The ponderous and predominantly nocturnal tipulids have slow photoreceptors with fully light adapted corner frequencies of 16 to 19 Hz. Dark adapted fast photoreceptors have a lower gain (as indicated by lower noise levels), a lower sensitivity, and light adapt more rapidly than dark adapted slow photoreceptors. Fast cells also have much lower input resistances and shorter time constants. Fast photoreceptors rectify more strongly in the steady state because of a weakly inactivating delayed rectifier potassium conductance with fast and slow components of activation. Slow photoreceptors rectify less strongly in the steady state because their membrane properties are dominated by strongly inactivating outward currents with reversal potentials in the range — 80 to -90 mV. The differences between potassium conductances match the differing functional requirements of fast and slow photoreceptors. The non-inactivating delayed rectifier promotes the rapid response of fast cells by reducing the membrane time constant. This is an expensive strategy, involving large conductances and currents. Slowly flying nocturnal insects do not require a high speed of response. The potassium conductances in their slow photoreceptors inactivate to avoid costly and unnecessary ion fluxes. Both the dynamics of the photoresponse and photoreceptor membrane properties exhibit sexual dimorphism. Light adapted photoreceptors in the enlarged male dorsal eye of Bibio markii have a corner frequency of 42 Hz, compared with 27 Hz for cells in the smaller female eye. This difference in frequency response correlates with the male's higher spatial acuity and is accompanied by consistent differences in potassium conductance activation rate. We conclude that the divison between fast and slow cells is the product of cellular constraints, metabolic costs and the requirements of coding efficiency at different light levels and retinal image velocities.

- by Matti Weckstrom
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- Electrophysiology, Comparative Physiology, Sexual dimorphism, Biological Sciences

The olfactory system (accessory) implicated in reproductive physiology and behavior in mammals is sexually dimorphic. These brain sex differences present two main characteristics: they are seen in neural circuits related to sexual behavior and sexual physiology and they take one of two opposite morphological patterns (male > female or female > male). The present work reports sex differences in the olfactory system in a large homogeneous sample of men (40) and women using of voxel-based morphology. Gray matter concentration showed sexual dimorphism in several olfactory regions. Women have a higher concentration in the orbitofrontal cortex involving Brodmann's areas 10, 11 and 25 and temporomedial cortex (bilateral hippocampus and right amygdala), as well as their left basal insular cortex. In contrast, men show a higher gray matter concentration in the left entorhinal cortex (Brodmann's area 28), right ventral pallidum, dorsal left insular cortex and a region of the orbitofrontal cortex (Brodmann's area 25)

- by Santiago Segovia and +1
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- Cognitive Science, Magnetic Resonance Imaging, Adolescent, Sexual dimorphism

The intermediate nucleus (InM) in the preoptic area of the human brain, also known as the sexually dimorphic nucleus of the preoptic area (SDN-POA) and the interstitial nucleus of the anterior hypothalamus-1 (INAH-1) is explored here. We investigated its population of galanin-immunoreactive (Gal-Ir) neurons in relation to sex, age, and gender identity in the postmortem brain of 77 subjects. First we compared the InM volume and number of Gal-Ir neurons of 22 males and 22 females in the course of aging. In a second experiment, we compared for the first time the InM volume and the total and Gal-Ir neuron number in 43 subjects with different gender identities: 14 control males (M), 11 control females (F), 10 male-to-female (MtF) transsexual people, and 5 men who were castrated because of pros-

- by Alicia Garcia Falgueras
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- Zoology, Aging, Adolescent, Gender Identity

Conrado Zuluaga schrieb 1989 dass der Protagonist in José Eustasio Riveras Roman 'La Vorágine' (1924) nicht Arturo Cova sei, der verhinderte Poet, der seine entführte Alicia im kolumbianischen Urwald verfolgt, sondern dieser Wald selbst. Der Naturraum des Romans entwickelt verschiedene Naturdimensionen, die in Wechselwirkung zur Figurenkonzeption stehen. In dieser Arbeit wurde ein geschlechtlich belegter Naturraum in Bezug auf den Maskulinitätskonflikt Arturo Covas untersucht. Hierbei werden Inhalte der Gender Studies, der Raumtheorie und der direkten Textanalyse verwendet.

- by Fabian Daldrup
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- Gender Studies, Nature, Nature/culture Dichotomization, Sexual dimorphism

Although many accounts of facial attractiveness propose that femininity in women's faces indicates high levels of oestrogen, there is little empirical evidence in support of this assumption. Here, we used assays for urinary metabolites of oestrogen (oestrone-3-glucuronide, E1G) and progesterone (pregnanediol-3glucuronide, P3G) to investigate the relationship between circulating gonadal hormones and ratings of the femininity, attractiveness and apparent health of women's faces. Positive correlations were observed between late follicular oestrogen and ratings of femininity, attractiveness and health. Positive correlations of luteal progesterone and health and attractiveness ratings were marginally significant. Ratings of facial attributions did not relate to hormone levels for women wearing make-up when photographed. There was no effect of sex of rater on the relationships between oestrogen and ratings of facial appearance. These findings demonstrate that female facial appearance holds detectable cues to reproductive health that are considered attractive by other people. for assistance with data collection. We also thank the Reproductive Medicine Laboratory Staff of the University of Edinburgh and Martha Urquhart for assistance in hormone analysis.

- by Lynda Boothroyd
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- Aging, Face, Adolescent, Sexual dimorphism

The bill is a sexually dimorphic structure in many bird species and implicated in numerous functions. Sexual differences may arise from sexual selection or ecological divergence. Here, we examined differences in bill size and shape between males and females and explored to what extent these relate to feeding ecology of each sex in Cory's shearwater (Calonectris diomedea). We applied linear measurements and geometric morphometric methods to examine sexual differences in bill size and shape. We investigated feeding ecology by tracking foraging movements during the breeding period and by analysing stable isotope signatures in blood during the breeding period and in feathers grown during the non-breeding period. Bill traits were all sexually dimorphic, both in absolute and relative terms, and scaled hypermetrically with body mass in several characters in males. However, males and females did not differ in their feeding areas or isotopic signatures and no significant correlation was observed between these traits and bill dimorphism. Therefore, we discard the foraging-niche divergence hypothesis, and suggest that sexual dimorphism in bill size in this species is more likely driven by sexual selection related to antagonistic interactions.

- by Antigoni Kaliontzopoulou
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- Zoology, Sexual Selection, Natural Selection, Sexual dimorphism

Background: Essential in dopamine degradation, it was suggested that catechol-O-methyltransferase (COMT) might be involved in the action of antidepressants and may therefore be a promising candidate for antidepressant pharmacogenetic studies. Methods: COMT Val158met polymorphism was genotyped in 334 Chinese major depressive disorder (MDD) patients who were treated with fluoxetine for at least 4 weeks. Clinical response was evaluated using the 21-item Hamilton Rating Scale for Depression (HAM-D 21 ). In the analysis of association, response was defined as ≥50% decrease in HAM-D 21 score after treatment and then further clarified by intra-individual changes in HAM-D 21 score. Results: We found that the COMT val158met polymorphism was not associated with 4-week fluoxetine therapeutic response; however, association analysis showed that patients with the COMT Val/Val genotype had poorer responses in the eighth week (CLUMP T1 P = 0.020) and consistently showed significantly smaller reductions in HAM-D 21 scores in the eighth week (P = 0.027). Further stratification based on gender revealed an isolated effect of the COMT genotype in males (P = 0.035) but not in females (P = 0.650) in percent reduction in HAM-D 21 scores in the eighth week. Limitations: There was a lack of placebo control and the serum fluoxetine concentration was not taken into account. Conclusions: This identified association between the COMT genetic variation and antidepressant response may be useful either as a clinical predictor in the future.

- by Shih-jen Tsai and +1
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- Polymorphism, Sexual dimorphism, Dopamine, Affective Disorders

The European green crab Carcinus maenas is a widely spread invasive species. Studying the most recently introduced population of the species in the Atlantic coast off Patagonia, it became apparent to us that carapaces (the dorsal cover of the visceral-cavity detaching from the rest of the exoskeleton after ecdysis) accumulated on the intertidal may be used as a valuable complementary material to analyze the size structure of crabs. However, since growth rate (and consequently size at instar) of crabs differs between males and females, finding a method to distinguish crab sex by observation of carapace morphology was necessary to allow the construction of independent size frequency distributions for each sex. In this work, we examined the shape of the carapaces from both sexes of C. maenas, and using Elliptical Fourier Analysis successfully identified sexual dimorphism. Thus, a reliable method to identify sexes by visual observation of the carapace was developed. Based on our results, we discuss the evolutionary significance of carapace form differentiation of both sexes.

- by Silvina Van Der Molen and +1
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- Oceanography, Invasive Species, Sexual dimorphism, Fourier Analysis

Subsequent to the initial description of two Aethomys species (Aethomys adamanticola and Aethomys modernis) at the Early Pliocene site of Langebaanweg (LBW), an increase in sample size led to the secure identification of a third, as yet, undescribed species. In addition to this new species, three morphs of existing species, or possibly three new species, were also recognized. Geometric morphometrics was used to explore the relationship of fossil species and morphs with extant Aethomys species, and to assess the intra and inter-specific variation in the size and shape of modern, as well as the LBW, Aethomys specimens. Geometric morphometrics indicates a marked similarity in the upper first molar (M 1 ) shape between all the analyzed species, extant and extinct, and suggests the persistence, over a significant period of time, of a prototype Aethomys M 1 shape. The relative warp analyses indicate some overlap in shape between the two modern species, Aethomys chrysophilus and Aethomys namaquensis, as well as some interspecific variation. These two species differ significantly from one another in terms of size. Variability in terms of size and to a minor extent, shape, was also evident in the fossil Aethomys, and it was concluded that the various fossil morphs investigated did not represent new species, or intra-specific sexual dimorphism, but rather, intra-specific variability in size and shape. Interestingly, the newly-identified LBW Aethomys species, which is similar in appearance to the extant east African Aethomys kaiseri, also showed a similarity in shape and size to A. adamanticola. These results indicate that geometric morphometrics has limitations when differentiating between morphologically similar species. The presence of Aethomys in Namibia at around 10.5 to 9.5 Ma, the degree of speciation of Aethomys at LBW, and the similarity of the LBW fossil species to the modern ones (including an East African species), provides good evidence for a southern African origin for modern Aethomys.

- by Thalassa Matthews
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- Evolutionary Biology, Paleobiology, Geology, Paleoecology

Dale J, Lank DB and Reeve HK 2001. Signaling individual identity versus quality: a model and case studies with ruffs, queleas, and house finches. American Naturalist 158: 75-86 Doucet SM 2002. Structural plumage coloration, male body... more

- by Geoffrey Hill
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- Zoology, Mate selection, Sexual dimorphism, Ostrich
- by Nubia E Matta Camacho
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- Sexual dimorphism, Dimorfismo Sexual, Cromosomas

South Africa currently has a high homicide rate. This results in a large number of unidentified bodies being recovered each year, many of which are referred to the forensic examiner. This situation has resulted in considerable growth of forensic anthropological research devoted to devising standards for specific application in South African medico-legal investigations. The standards suitable for Black South Africans now encompass a wide variety of skeletal elements (e.g. cranium, humerus, pelvis, femur, patella, talus, calcaneus), each with differing degrees of accuracy. Apart from a preliminary investigation of the Zulu local population, however, we note that there appears to be no established metric mandible discriminant function standards for sex determination in this population.

- by charles oxnard
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- Forensic Anthropology, Forensic Science, Adolescent, Multidisciplinary

We hypothesized that sexual and interspecific differences in jumping performance of fleas found in our previous study are correlated with differences in resting metabolic rate (RMR) between sexes and among species. To test this hypothesis, we measured RMR of seven flea species (Xenopsylla conformis mycerini, Xenopsylla ramesis, Xenopsylla dipodilli, Parapulex chephrenis, Synosternus cleopatrae pyramidis, Nosopsyllus iranus theodori and Stenoponia tripectinata medialis). We compared RMR between sexes and among species and examined whether there is intra-and interspecific correlation between RMR and jumping ability. Both mass-specific and mass-independent RMR were the highest in female S. t. medialis, whereas mass-specific RMR was the lowest in male X. dipodilli and mass-independent RMR was the lowest in three Xenopsylla species and P. chephrenis. Mass-specific and mass-independent RMR were significantly higher in females than in males in all fleas except S. t. medialis. Differences in jumping ability between males and females were found to be correlated with sexual differences in mass-specific or mass-independent RMR. Interspecific comparison showed that the length of jump in both male and female fleas was strongly affected by their mass-specific and mass-independent RMR. #

- by Irina Khokhlova
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- Physiology, Zoology, Locomotion, Insect Physiology

Females and males differ in several features of their spindle oscillations, as well as in the hemispheric lateralization of their neurocognitive processes. In addition, the hemispheric lateralization of cognitive functions was shown to vary in an age-dependent manner. In spite of the above knowledge, data on the hemispheric lateralization of these oscillatory phenomena are scarce and no sex differences or age effects in the hemispheric lateralization of sleep spindles were reported. Here, we aim to fill this gap by the description of the hemispheric lateralization of sleep spindles in healthy human subjects. Data sets from three research groups were unified (N = 251, age range: 4−69 years, 122 females) in this retrospective multicenter study. The amplitude, density, and duration of slow (frontally dominant) and fast (centroparietally dominant) spindles were analyzed using the individual adjustment method. Hemispheric lateralization was quantified by the (L − R)/mean (L, R) index. Orbitofronto-temporo-occipital and parietal fast sleep spindle measures are left lateralized, while prefrontal spindle amplitude is characterized by right hemispheric dominance. Left lateralization of fast spindle density and duration in the temporal and orbitofrontal regions, respectively, increases as a function of age in males, but not in females. In turn, females are characterized by higher left hemispheric dominance in occipitally measured fast spindle durations as compared with males. Sleep spindles are asymmetrically distributed over the two hemispheres. This phenomenon is sexually dimorphic and region-specific perhaps indexing sex differences in neurocognitive architectures.

Sex differences in human brain structure have repeatedly been described, but results are inconsistent. However, these studies hardly controlled for cycle phase of women or the use of hormonal contraceptives. Our study shows that these factors are not negligible, but have a considerable influence on human brain structure. We acquired high-resolution structural images from the brains of 14 men, 14 women, who did not use, and 14 women, who did use hormonal contraceptives. Women, who did not use hormonal contraceptives, were scanned twice, once during their early follicular and once during their mid-luteal cycle-phase.

- by Belinda Pletzer
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- Cognitive Science, Magnetic Resonance Imaging, Sex Hormones, Prefrontal Cortex
- by Lorena Madrigal
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- Evolutionary Biology, Geography, Archaeology, Anthropology

The current study reports our findings of the relationship between cross-sectional area of the corpus callosum and brain mass in over 100 eutherian mammal species. We were specifically interested in determining whether the elephant had a corpus callosum the size that would be expected for eutherian mammal with a brain mass of approximately 5000 g, or whether a different morphology had evolved. To answer this question we first analysed data from primates, other eutherian mammals and cetaceans, finding that primates and other eutherian mammals showed a positive allometric relationship between the two variables, such that larger brains had a relatively larger corpus callosum. Interestingly, primates have a slightly larger corpus callosum than other eutherian mammals, but showed a similar allometric scaling to this group. The cetaceans had a both absolutely and relatively small corpus callosum compared to other mammals and showed isometric scaling with brain mass. The six elephants studied herein had the largest absolute corpus callosums recorded to date; however, relative to the mass of their brain, the size of the corpus callosum was what would be expected of a typical eutherian mammal with a brain mass of approximately 5000 g. The data for elephants hinted at sexual dimorphism in size of the corpus callosum, with female elephants having both an absolute and relatively larger callosum than the males. If this observation is supported in future studies, the elephants will be the first non-primate species to show sexual dimorphism in this neural character. The results are discussed in both an evolutionary and functional context.

- by Jason Hemingway
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- Comparative Anatomy, Neuroscience, Psychology, Intelligence

Many chemicals introduced into the environment by humans adversely affect embryonic development and the functioning of the male reproductive system. It has been hypothesized that these developmental alterations are due to the endocrine-disruptive effects of various environmental contaminants. The endocrine system exhibits an organizational effect on the developing embryo. Thus, a disruption of the normal hormonal signals can permanently modify the organization and future function of the male reproductive system. A wide range of studies examining wildlife either in laboratories or in natural settings have documented alterations in the development of males. These studies have begun to provide the causal relationships between embryonic contaminant exposure and reproductive abnormalities that have been lacking in pure field studies of wild populations. An understanding of the developmental consequences of endocrine disruption in wildlife can lead to new indicators of exposure and a better understanding of the most sensitive life stages as well as the consequences of exposure during these periods. r 2005 Elsevier Inc. All rights reserved.

- by Brandon Moore
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- Endocrinology, Animal Behavior, Reproduction, Fertility

Size, growth and sexual dimorphism of nine skull traits was studied in 300 East Greenland and 391 Svalbard polar bears (Ursus maritimus). Two traits were significantly larger in bears from East Greenland compared to Svalbard bears, and trait size was smaller after 1960 in five traits. For both localities and both age groups (subadult, adult), mean trait size values were higher in males than females (all: P \ 0.05). Gompertz growth models showed trait size increasing with age in seven traits. Depending on the trait, males reached 95% asymptotic trait size at age 3-10, females at age 2-6. The females of both localities matured at approximately the same age, whereas the Svalbard males generally matured years later than their East Greenland peers. The differences found in the present study between the two polar bear subpopulations support the notion that East Greenland and Svalbard polar bears probably should be managed as separate units.

- by Christian Sonne
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- Sexual dimorphism, Biological Sciences, Polar Biology, Ursus maritimus

Human beings can distinguish between a male and a female face without much difficulty. The science of recognizing and differentiating different faces by humans is not completely understood and is still under research. Sexual dimorphism is common in humans and indeed in other species of animals as well. Significant differences between males and females exist in many aspects like size, color, body shapes, and weight. In this research, we characterize and analyze the sexual dimorphism in the human face as a function of age and of face features. Features are grouped into six categories: head, eyes, orbits, nose, lips, and mouth, and ears. We demonstrate that the face of adult males is significantly different from adult females. We also identify the features that significantly contribute to the dimorphism of the face. This provides a basis for gender-based classification of faces.

- by David Marx
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- Face Recognition, Visual Communication, Sexual dimorphism, Body Shape

Males of the giant freshwater prawn Macrobrachium rosenbergii grow faster and reach higher weights at harvest than females a fact which makes the culture of all-male populations desirable. All-male populations were produced by mating sex-reversed males, i.e., neofemales, with normal males. Neofemales capable of mating and spawning were produced by removal of the androgenic gland (AG) from immature M. rosenbergii males. The main obstacle to developing a technology based on this type of manipulation is the difficulty of identifying males at a sufficiently early stage of development. To overcome this problem, we developed a novel two-step scheme for large-scale microsurgical andrectomy. Phase I post larvae were andrectomized at ages 25-60 days after metamorphosis (PL 25-60). A low success rate of functional sex reversal, resulting with all male progeny was obtained (1.3%). In the light of the low success rate and a number of cases of abnormal reproductive development, a second phase was introduced in which the progeny (presumed males) of neofemales from phase I were andrectomized at earlier ages (PL 20-30). This two-phase protocol enabled a large quantity of juvenile males to be andrectomized. In phase II there was a significant increase in the number of sexreversed animals (developed ovaries) and a significant shortening of the time to maturation. Comparison of the all-male progeny with a normal mixed population showed higher growth performance of the all-male population. This advantage together with the shorter maturation time in phase II opens the possibility to scale-up the system to field conditions. Since sexual dimorphic growth patterns are common among decapod crustaceans, it is obvious that the results of this study will have applied significance for many aquacultured species.

- by Amir Sagi
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- Zoology, Aquaculture, Sexual dimorphism, Scaling up
- by Thomas E. Schlaepfer
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- Cognitive Science, Psychiatry, Magnetic Resonance Imaging, Sexual dimorphism

We describe the sexual dimorphism in coloration, body shape, and body size in Tropidurus torquatus, a widely distributed lizard species in central Brazil. Adult males have colored patches varying from yellow to yellow-and-black, and black on the abdomen, ventral aspect of the thighs, and pre-cloacal flap. Adult females lack ventral colored patches. During ontogeny, there is a gradual darkening of the patches, but no modification either in patch size or color is associated with the reproductive cycle. Adult males have wider heads and thinner bodies than females of the same body size. Males and females grow at the same rate prior to sexual maturity, but males take longer to reach sexual maturity, maturing at a larger body size than females.

- by Guarino Colli
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- Zoology, Sexual dimorphism

Sexual dimorphism has been a special concern in human origins studies. Not only must sexual dimorphism be considered in attempts to determine sex ratios in archaeological faunal materials and prehistoric human population samples, but assessing the nature and degree of sexual dimorphism in various hominid species in the past can be crucial for understanding the nature and rate of hominid evolutionary change and sometimes to a certain degree for making species designations among (hominid or other) specimens. Obtaining sex ratio in a population is easy if each individual in the population can be accurately sexed through the use of one or more objective variables. But this is often impossible, due to the incompleteness of the osteological record. One does not, however, have to sex each individual in a population in order to ''sex the population''. Mixture analysis is a statistical method that can be used to deal with the problem of sexing the population without knowing the sex of any individual member. This paper introduces some basic concepts and procedures of mixture analysis, gives a brief review of its development and previous applications in various fields, discusses some preliminary results of its application to the tooth metric data of African early hominids, of the Lufeng hominoids and of the two cervid species (Megaloceros pachyosteus and Pseudaxis grayi) from the Homo erectus site at Zhoukoudian Locality 1. The quantitative results of this research are compared to previous qualitative assessments of the same materials. A control study to test the power of mixture analysis to discriminate sexual dimorphism was conducted on metric dental data from modern great apes, the results compared to the known metric patterns. Analysis of hominid/hominoid tooth data indicates that there are more males than females in A. robustus and more females than males in A. afarensis; there appears to be more than one species of hominoid represented at the site of Lufeng in China; and there are more females than males in the alleged smaller species among the Lufeng hominoids. The analysis of cervids from Zhoukoudian Locality 1 suggests that there are more females than males for the Megaloceros pachyosteus and more males than females for the Pseudaxis grayi; Pseudaxis grayi is dentally more sexual dimorphic than Megaloceros pachyosteus. The analysis shows that mixture analysis has great potential for determining sex ratios and the degree of sexual dimorphism for zooarchaeological and palaeontological researches.

- by Zhuan Dong
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- Demography, Archaeology, Geochemistry, Anthropology
- by Gilbert Herdt
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- Anthropology, Sexual dimorphism, American Ethnologist

One reason why the gaur Bos gaurus is a poorly understood
species is because there are no reliable data to age and sex
individuals. We studied captive gaur for two years in Mysore
Zoo, India and Omaha Zoo, USA, and determined age-specific
differences in morphological features and physical growth, by measuring shoulder height, of male and female gaur. We fitted von Bertalanffy growth functions to the shoulder height data and found maximum shoulder heights of 175 cm and 147 cm for males and females, respectively. This study ascertained for the first time that the greater the amount of white on the horns of a gaur, the older it is, and that the sexes can be distinguished based on horn shape and size differences. We found that gaur aged 15 months and below can be classified into three age classes, but are difficult to sex. The sex of gaur aged 15–36 months is best determined by a study of their horns. Adult gaur, greater than three years, are easy to sex, but are difficult to classify into single-year age classes and are reliably classified only into two age classes for females and three for males.

- by Farshid Ahrestani
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- Sexual dimorphism, Bovidae