Interaction between the X chromosome and an autosome regulates size sexual dimorphism in Portuguese Water Dogs

Size sexual dimorphism occurs in almost all mammals. In Portuguese Water Dogs, much of the difference in skeletal size between females and males is due to the interaction between a Quantitative Trait Locus (QTL) on the X-chromosome and a QTL linked to Insulin-like Growth Factor 1 (IGF-1) on the CFA 15 autosome. In females, the haplotype of CFA 15 resulting in small size is dominant. In males, the haplotype for large size is dominant. Females, homozygous at the CHM marker on the X chromosome and homozygous for the large size CFA 15 haplotype are, on average, as large as large males. However, all females that are heterozygous at the CHM marker are small, regardless of their CFA 15 genotype. This interaction suggests a genetic mechanism that in turn leads to a scenario for the evolution of size sexual dimorphism consistent with a proposal of Lande that sexual dimorphism can evolve because females secondarily become smaller than males as a consequence of natural selection for optimal size. Our results also can explain Rensch's Rule, which states that size is often positively correlated with the level of size sexual dimorphism.     

Morphometric measurements and sexual dimorphism of the piriform aperture in adults

Purpose

The aim of this study was to evaluate the dimensions (maximal width and length), the size and the shape of the PA and their sexual dimorphism.

Methods

Using 3D-CT scan reconstructions and landmarks positioning around the piriform aperture and on the face, a collective of 170 non-pathologic subjects (79 female, 91 male) from Marseille (France) was examined in classical and geometric morphometrics methods.

Results

The mean width of the piriform aperture was 24.00 mm in females and 25.32 mm in males, the mean length was 32.54 mm in females and 36.35 mm in males. The difference between males and females was significant, and our data correlates well with the previously data acquired from humans skulls. Facial measurements also showed a statistically significant dimorphism. In morphometric geometrics, the correlation between the centroïd size and PC1 in the shape space was weak, while this correlation was strong in the size and shape space. Visualization of shape differences was achieved on 2D wireframes.

Conclusion

Shape and size analysis of the piriform aperture showed the existence of a significant sexual dimorphism. These results encourage us to go further with functional and imaging correlations.     

3D analysis of sexual dimorphism in size,shape and breathing kinematics of human lungs

Sexual dimorphism in the human respiratory system has been previously reported at the skeletal (cranial and thoracic) level, but also at the pulmonary level. Regarding lungs, foregoing studies have yielded sex‐related differences in pulmonary size as well as lung shape details, but different methodological approaches have led to discrepant results on differences in respiratory patterns between males and females. The purpose of this study is to analyse sexual dimorphism in human lungs during forced respiration using 3D geometric morphometrics. Eighty computed tomographies (19 males and 21 females) were taken in maximal forced inspiration (FI) and expiration (FE), and 415 (semi)landmarks were digitized on 80 virtual lung models for the 3D quantification of pulmonary size, shape and kinematic differences. We found that males showed larger lungs than females (P < 0.05), and significantly greater size and shape differences between FI and FE. Morphologically, males have pyramidal lung geometry, with greater lower lung width when comparing with the apices, in contrast to the prismatic lung shape and similar widths at upper and lower lungs of females. Multivariate regression analyses confirmed the effect of sex on lung size (36.26%; P < 0.05) and on lung shape (7.23%; P < 0.05), and yielded two kinematic vectors with a small but statistically significant angle between them (13.22°; P < 0.05) that confirms sex‐related differences in the respiratory patterns. Our 3D approach shows sexual dimorphism in human lungs likely due to a greater diaphragmatic action in males and a predominant intercostal muscle action in females during breathing. These size and shape differences would lead to different respiratory patterns between sexes, whose physiological implications need to be studied in future research.     

Temporomandibular joint shape in anthropoid primates varies widely and is patterned by size and phylogeny

The temporomandibular joint is the direct interface between the mandible and the cranium and is critical for transmitting joint reaction forces and determining mandibular range of motion. As a consequence, understanding variation in the morphology of this joint and how it relates to other aspects of craniofacial form is important for better understanding masticatory function. Here, we present a detailed three-dimensional (3D) geometric morphometric analysis of the cranial component of this joint, the glenoid fossa, across a sample of 17 anthropoid primates, and we evaluate covariation between the glenoid and the cranium and mandible. We find high levels of intraspecific variation in glenoid shape that is likely linked to sexual dimorphism and joint remodeling, and we identify differences in mean glenoid shape across taxonomic groups and in relation to size. Analyses of covariation reveal strong relationships between glenoid shape and a variety of aspects of cranial and mandibular form. Our findings suggest that intraspecific variation in glenoid shape in primates could further be reflective of high levels of functional flexibility in the masticatory apparatus, as has also been suggested for primate jaw kinematics and muscle activation patterns. Conversely, interspecific differences likely reflect larger scale differences between species in body size and/or masticatory function. Results of the covariation analyses dovetail with those examining covariation in the cranium of canids and may be indicative of larger patterns across mammals.     

Impact of various ecological parameters on the life-history characteristics of Bufotes viridis sitibundus from Turkey

In this study, we used the skeletochronology method to estimate various growth parameters, such as age structure, minimum and maximum life span, age of sexual maturity, and the relationship between body size and weight of eight different populations of the variable toad, Bufotes viridis sitibundus, in Turkey. Further, we determined the relationship between these parameters and ecologic factors using the partial Mantel test. A significant difference was found among the populations with respect to age, body size, and body weight in both males and females. On average, the maximum life span was recorded as 10 years for males and 11 years for females. In the studied populations, the average age of sexual maturity ranged between 2 and 4 years for both sexes. Sexual dimorphism in terms of snout-vent length (SVL) was not observed between males and females in all the populations. Toads from the higher altitudes tended to be significantly larger, older, and heavier than those from lower altitudes. We concluded that altitude and temperature have an impact on the growth rate, body size, and body mass.     

Sexual size and shape dimorphism in Turkish common toads (Bufo bufo Linnaeus 1758)

Differences in male and female traits (sexual dimorphism [SD]) are widespread in animals. Dimorphism in morphological characters evolves under the effect of environmental and genetic factors and is shaped by natural and sexual selection. In this study, intersexual differences in size and shape in common toad, Bufo bufo, populations in Turkey were investigated. For this, linear measurements of 27 body-related morphometric characters in a sample of 140 individuals (70 males and 70 females) were compiled. The data were analyzed using univariate and multivariate statistical methods. The results show SD in body size with females having larger body size, a trait related with fecundity and thus probably under sexual selection. Body shape differences, which are associated with head width and dorsal head, are likely to prey size. Male-biased differences observed in nasal characters and tympanum may also be associated with sexual selection (male–male competition). Our findings are consistent with previous studies of major of Anura and support a role for selection pressures acting differentially upon individuals from both sexes, resulting in the evolution of sexually dimorphic traits.     

Cranial shape variation in mink: Separating two highly similar species

European and American minks (Mustela lutreola and Neovison vison, respectively) are very similar in their ecology, behavior, and morphology. However, the American mink is a generalist predator and seems to adapt better to anthropized environments, allowing it to outcompete the European mink in areas where it has been introduced, threatening the survival of the native species. To assess whether morphological differences may be contributing to the success of the American mink relative to the European mink, we analyzed shape variation in the cranium of both species using 3D geometric morphometrics. A set of 38 landmarks and 107 semilandmarks was used to study shape variation between and within species, and to assess how differences in size factored into that variation. Sexual dimorphism in both size and shape was also studied. Significant differences between species were found in cranial shape, but not in size. Relative to American mink, European mink have a shorter facial region with a rounder forehead and wider orbits, a longer neurocranium with less developed crests and processes, and an antero‐medially placed tympanic bullae with an anteriorly expanded cranial border. Within species, size‐related sexual dimorphism is highly significant, but sexual dimorphism in shape is only significant in American mink, not in European mink. Additionally, two trends common to both species were discovered, one related to allometric changes and another to sexual size dimorphism. Shape changes related to increasing size can be subdivided into two, probably related, groups: increased muscle force and growth. The first group somewhat parallels the differences between both mink species, while the second group of traits includes an anterodorsal expansion of the face, and the neurocranium shifting from a globous shape in small individuals to a dorsoventrally flattened ellipse in the largest ones. Finally, the sexual dimorphism trend, while also accounting for differences in muscle force, seems to be related to the observed dietary differences between males and females. Overall, differences between species and sexes, and shape changes with increasing size, seem to mainly relate to differences in masticatory‐muscle volume and therefore muscle force and bite force, which, in turn, relate to a wider range of potential prey (bigger prey, tougher shells). Thus, muscle force (and dietary range) would be larger in American mink than in European mink, in males than in females, and in larger individuals than in smaller ones.     

Maternal environment and craniofacial growth: geometric morphometric analysis of mandibular shape changes with in utero thyroxine overexposure in mice

An estimated 3% of US pregnancies are affected by maternal thyroid dysfunction, with between one and three of every 1000 pregnancies being complicated by overactive maternal thyroid levels. Excess thyroid hormones are linked to neurological impairment and excessive craniofacial variation, affecting both endochondral and intramembranous bone. Using a geometric morphometric approach, this study evaluates the role of in utero thyroxine overexposure on the growth of offspring mandibles in a sample of 241 mice. Canonical variate analysis utilized 16 unilateral mandibular landmarks obtained from 3D micro‐computed tomography to assess shape changes between unexposed controls (n = 63) and exposed mice (n = 178). By evaluating shape changes in the mandible among three age groups (15, 20 and 25 days postnatal) and different dosage levels (low, medium and high), this study found that excess maternal thyroxine alters offspring mandibular shape in both age‐ and dosage‐dependent manners. Group differences in overall shape were significant (P < 0.001), and showed major changes in regions of the mandible associated with muscle attachment (coronoid process, gonial angle) and regions of growth largely governed by articulation with the cranial base (condyle) and occlusion (alveolus). These results compliment recent studies demonstrating that maternal thyroxine levels can alter the cranial base and cranial vault of offspring, contributing to a better understanding of both normal and abnormal mandibular development, as well as the medical implications of craniofacial growth and development.     

Endocrine mechanisms of primate life history trade‐offs: Growth and reproductive maturation in vervet monkeys

Life history theory predicts that the timing of maturation will result from a trade‐off between growth and the age of first reproduction. This trade‐off and its mechanisms of action are still poorly understood in many species and have not been well studied at the individual level. This study examined hypothesized trade‐offs between growth and reproductive maturation in wild populations of vervet monkeys (Cercopithecus aethiops) from Kenya, East Africa. Individuals were sampled from four populations in widely separated sites differing in temperature, altitude, and rainfall. Biological samples and morphometric measures were collected from 50 adult males, 83 adult females, and 225 juveniles. Gonadal steroids and leptin levels were analyzed by radioimmunoassay of sera from 136 juvenile males and 90 juvenile females. Cross‐sectional profiles of morphometric and endocrine data were used to assess the onset and cessation of growth in relation to sexual maturation. Gonadal steroids were used to assess sexual maturation and breeding onset. Leptin was used as an index of nutritional state. Estimates of mortality were derived from population age‐structure. Across populations, higher resource productivity and nutrient status were associated with more rapid growth. Shorter growth duration was associated with earlier reproductive onset. These findings provide support for models of trade‐offs between the timing of growth completion and reproductive onset, but they are contradicted by the evidence that reproduction precedes the cessation of growth in these populations. The biphasic actions of estradiol provide an alternative model and mechanism for the growth‐reproduction trade‐off. Am. J. Hum. Biol., 2009. © 2009 Wiley‐Liss, Inc.     

Developmental morphology of the cervical vertebrae and the emergence of sexual dimorphism in size and shape: A computed tomography study

Cervical vertebral bodies undergo substantial morphological development during the first two decades of life that are used clinically to visually determine skeletal maturation with the cervical vertebral maturation index (CVMI). CVMI defines six stages that capture the morphological transformations from 6 years to 18 years. However, CVMI has poor reproducibility given its qualitative nature and does not account for sexual dimorphism. This study aims to quantify the morphological development of the cervical vertebral bodies C2–C7 in size (height and depth) and shape and examine the emergence of sexual dimorphism. Using 115 (70 M;45F) computed tomography studies from typically developing individuals ages 6 months to 20 years, landmarks were placed at the margins of the C2–C7 cervical vertebral bodies in the midsagittal plane for size and shape analysis. Findings revealed a dichotomy in the growth trends of height versus depth. The C2–C7 growth in depth gained the majority of the adult size by age 5 years, while the C3–C7 growth in height displayed two periods of accelerated growth during early childhood and puberty. Significant sex differences were found in height and depth growth trends and the form-space ontogenetic trajectories during puberty, with minor but evident differences emerging at age 3 years. Female C2–C7 depth measures were smaller than males at all ages. However, sex differences in height became evident due to males continuing to grow after females reach maturity. Findings quantify the morphological developmental stages of CVMI and emphasize the need to account for sex differences when assessing skeletal maturation.     

Cervical vertebral body growth and emergence of sexual dimorphism: a developmental study using computed tomography

The size and shape of human cervical vertebral bodies serve as a reference for measurement or treatment planning in multiple disciplines. It is therefore necessary to understand thoroughly the developmental changes in the cervical vertebrae in relation to the changing biomechanical demands on the neck during the first two decades of life. To delineate sex‐specific changes in human cervical vertebral bodies, 23 landmarks were placed in the midsagittal plane to define the boundaries of C2 to C7 in 123 (73 M; 50 F) computed tomography scans from individuals, ages 6 months to 19 years. Size was calculated as the geometric area, from which sex‐specific growth trend, rate, and type for each vertebral body were determined, as well as length measures of local deformation‐based morphometry vectors from the centroid to each landmark. Additionally, for each of the four pubertal‐staged age cohorts, sex‐specific vertebral body wireframes were superimposed using generalized Procrustes analysis to determine sex‐specific changes in form (size and shape) and shape alone. Our findings reveal that C2 was unique in achieving more of its adult size by 5 years, particularly in females. In contrast, C3–C7 had a second period of accelerated growth during puberty. The vertebrae of males and females were significantly different in size, particularly after puberty, when males had larger cervical vertebral bodies. Male growth outpaced female growth around age 10 years and persisted until around age 19–20 years, whereas females completed growth earlier, around age 17–18 years. The greatest shape differences between males and females occurred during puberty. Both sexes had similar growth in the superoinferior height, but males also displayed more growth in anteroposterior depth. Such prominent sex differences in size, shape, and form are likely the result of differences in growth rate and growth duration. Female vertebrae are thus not simply smaller versions of the male vertebrae. Additional research is needed to further quantify growth and help improve age‐ and sex‐specific guidance in clinical practice.     

Age‐dependent changes of the mandible bone throughout the lifespan in female F344/N rat

Age‐dependent changes of the mandible bone in female F344/N rats, aged 22–1196 days, were analyzed using physiological bone properties and morphology. Bone weight, bone area, bone mineral components, and bone mineral density were assessed using dual‐energy X‐ray absorptiometry. The bone weight, bone area, bone mineral components, and bone mineral density increased rapidly until approximately 150 days of age, increased gradually thereafter, and then stabilized or decreased after 910 days of age. The ratio of bone mineral components to bone weight (bone mineral ratio) increased rapidly until approximately 43 days of age and stabilized thereafter. Size of the mandible, which was measured at 13 points on mandible surface, increased with age, and the rate of change showed a similar pattern to the other parameters. From a principal component analysis on morphometric measurements, principal component 1 (size factor) increased proportionally with age, whereas principal component 2 (shape factor) decreased until approximately 88 days of age and then increased after 365 days of age. As a result, the scatter plots for principal component 1 and principal component 2 were V‐shaped, which indicates that the mandible developed in size, with deformation at younger ages, and recovered its original shape later in life. Our results revealed the occurrence of inflection points at approximately 43, 88, 150, 365, and 910 days of age. Some of these ages corresponded to transition points revealed by the age‐dependent changes of the occlusal mandibular condyle and tooth wear in the same rat.     

Is the Pelvis Sexually Dimorphic in Turtles?

Variation in the pelvis is intrinsically linked to life history evolution. This is perhaps best exemplified by sexually dimorphic pelvic variation in bipedal primates. Yet, whether this trend is applicable to other taxa is unclear. Using turtle anatomy as a model, I tested the hypothesis that the pelvis is also sexually dimorphic in egg‐laying tetrapods. I sampled a natural turtle population with female‐biased sexual size dimorphism (i.e., larger females). I show that the area of the egg canal (pelvic aperture) is greater in females. Morphological differences between sexes were predicted by body size, such that skeletal shape deformation of the female ilium increased proportionally with pelvic aperture area. These results suggest that sexual pelvic dimorphism might be indirectly maintained by selection for large female size, consistent with the pelvic constraint hypothesis in reptiles. However, subsampling of similarly sized individuals revealed that pelvic aperture area and shape may vary in disproportion to body size. Comparisons of pelvic ontogenetic trajectories across multiple lineages are needed to clarify the occurrence of sexual pelvic dimorphism in turtles and other egg‐laying tetrapods. My findings provide impetus to further explore how sex‐specific functional demands influence the architecture of the pelvic girdle. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.     

Anthropometric and craniofacial sexual dimorphism in obstructive sleep apnea patients: is there male–female phenotypical convergence?

Obstructive sleep apnea (OSA) is more common in men than women. Body size is greater in males (sexual dimorphism), but large body habitus is associated with OSA for both genders. We speculated that male–female phenotypical convergence (reduced sexual dimorphism via identical phenotype acquisition) occurs with OSA and tested hypotheses: (1) phenotypical features pathogenic for OSA differ between OSA and healthy subjects irrespective of gender; and (2) such characteristics exhibit phenotypical convergence. Utilizing an existing database, we calculated male–female (group average) ratios for eight anthropometric and 33 surface cephalometric variables from 104 Caucasian OSA patients [72 males; apnea–hypopnea index (events h^?1): males: 42.3 ± 24.7 versus females: 42.6 ± 26.1 (P > 0.9)] and 85 Caucasian, healthy, non‐OSA, community volunteers (36 males). Log‐transformed data were analysed using a general linear model with post‐hoc unpaired t‐tests and significance at P < 0.0012 (Bonferroni multiple‐comparison correction). OSA patients were older (56.9 ± 14.4 versus 38.0 ± 13.8 years), but there were no within‐group gender‐based age differences. All anthropometric variables (except height), plus cranial base width, mandibular breadth and retromandibular width diagonal were larger in gender‐matched OSA versus healthy comparisons; thus satisfying hypothesis (1). Male–female ratios were mostly >1.0 across groups, but with no significant group × gender interactions no variable satisfied hypothesis (2). Thus, in this exploratory study, OSA patients had gender‐common phenotypical differences to healthy subjects, but sexual dimorphism was preserved. Lack of complete phenotypical convergence may indicate gender‐based critical phenotype‐level attainment for OSA and/or gender‐based OSA prevalence arises from factors other than those in this study.     

Morphometric variations of the 7th cervical vertebrae of Zulu,White, and Colored South Africans

The 7th cervical vertebrae of 240 cadavers of South African Zulu, White, and Colored population groups were examined to determine morphometric variation. White and Colored females had statistically significant narrower cervical anteroposterior diameters than their male counterparts, whereas no statistically significant difference between sexes of the Zulu population group was observed in this variable. In addition, although Zulu and Colored females had statistically significant narrower cervical transverse diameters than their male counterparts, there was no statistically significant variation between South African white males and females in this respect. The findings indicate that sexual dimorphism is more apparent in the vertebral centrum, across the three population groups, where males had significantly larger dimensions in centrum anteroposterior diameter, height, and width than their female counterparts. The study further reveals that sexual dimorphism is more apparent when one compares aspects of the 7th cervical vertebra between sexes within the same population group. Overall, the dimensions of the various variates of the vertebra are substantially smaller in women than in men. The smaller dimensions, particularly of the centrum, may be the result of lower skeletal mass in women and render them more vulnerable to fractures resulting from compression forces. Clin. Anat. 23:399–406, 2010. © 2010 Wiley‐Liss, Inc.     

下颌骨若干测量性状的时代间比较

目的 分析全新世人群下颌骨若干测量性状及性别差异率的时代间变化。方法 以中国考古遗址520例下颌骨为研究材料,用SPSS18.0软件进行同一时代内男女测量性状的比较,不同时代间测量性状、测量指数的比较（独立样本t检验）,并计算了性别差异率、测量指数时代变化率。结果 不同时代男性颏孔、下颌孔横径的比较中,现代人群最大,而女性颏孔、下颌孔不同时代间差异不显著。相比新石器时代与青铜铁器时代,颏孔、下颌孔横径的性别差异率在现代人群中最大。截面周长比指数、颏孔垂直位置指数在不同时代间的大小关系都为：新石器>青铜铁器>现代。结论 相比新石器时代与青铜铁器时代,下颌骨大多测量性状在现代人群中的性别差异率最大。新石器时代以来,下颌第一磨牙（M₁）处的下颌体粗壮程度相对下颌第一前磨牙（P₃）处而言在降低,颏孔垂直位置在持续上升。     

Effect of controlled dietary consistency and cage environment on the rat mandibular growth

Forty Fischer strain inbred albino rats, evenly divided by sex, were obtained at 9 days of age. The animals were weaned at 21 days and randomly divided into the four experimental groups. Two variations on dietary consistency, hard and soft diet, as well as two variations on cage environment, normal and no biting surfaces, constituted the experimental groupings. The experimental period consisted of 16 weeks during which the animals were raised under the designated conditions. At the end of the experimental period the animals were killed with carbon dioxide, and the entire mandible, and both femurs, were dissected free. Weight and volumetric analysis were carried out in a standard fashion on the cleaned specimens. Area and linear measurements were performed and analyzed with a specially designed computer program. The results showed that there was sexual dimorphism in the Fischer rat both with respect to body weight and the weight, volume, area, and linear measurements of the mandible. The effects of dietary consistency had a greater influence on mandibular ramus size and form than did those caused by alteration in cage environment. The posterior region of the mandible, in association with the heavy muscles of mastication, was affected more by dietary consistency than was the anterior region. The entire region of the mandibular ramus acted as an area of adaptation and growth. The findings of this study indicate that dietary consistency has a small but significant effect on mandibular size in specific measurements. The cage environment used in this experiment did not limit function to the extent necessary to see measurable changes in mandibular measurements.     

Digit ratio (2D:4D), sex differences,allometry, and finger length of 12–30‐year olds: Evidence from the British Broadcasting Corporation (BBC) internet study

Many studies have reported digit ratio (2D:4D) to be sexually dimorphic, (males lower 2D:4D than females). However, Kratochvíl and Flegr ([ 2009 ]: Biol Lett 5:643‐646) have suggested that 2D regressed on 4D has an allometric regression line with nonzero Y‐intercept that is shared by males and females. Thus, 2D is shorter than expected when 4D is long, and males have lower 2D:4D than females because they have longer fingers. In this study, it is shown that this suggestion may be incorrect because sex differences in slope were not considered. Participants were recruited in an Internet study and had an age range of 12–30 years. The expected sex difference in 2D:4D was found, and the regression of 2D on 4D showed a significant sex difference in slope (males lower than females). A comparison of 10 age groups (12 years, 13 years…, 21–30 years) showed that sexual dimorphism for fingers was age dependent, varying from monomorphic to very dimorphic. Changes in sexual dimorphism of 2D:4D were much less marked, but there was a significant reduction in mean 2D:4D with age. The tendency for slopes of 2D regressed on 4D to be lower in males compared with females was significant in eight age groups. Sex difference in 2D:4D varied across the age groups and was positively related to the magnitude of the difference in female and male slopes. In contrast to the report of Kratochvíl and Flegr, it was found that the regression of 2D on 4D showed sex differences in slope, and such differences gave rise to the sexual dimorphism in 2D:4D. Am. J. Hum. Biol. 22:604–608, 2010. © 2010 Wiley‐Liss, Inc.