Dimorphism In Shape Research Articles

Obstetrical Implications of Sexual Dimorphism in Hominoid Os Coxae

Many studies have examined pelvic sexual dimorphism and its functional implications in linear analyses, but few have used three‐dimensional (3D) methods, which are ideal for complex structures such as the pelvis. This study examines human and ape os coxae using 3D geometric morphometrics (GM) to determine if patterns of sexual dimorphism relate to obstetrical and/or biomechanical requirements. Twenty‐five 3D landmarks were collected on 35 human and 116 hominoid os coxae. Generalized Procrustes and principal component analyses were performed on combined and sex‐specific species samples. Tests of male and female human os coxae demonstrate dimorphism in several pelvic traits related to increasing birth canal dimensions in females; females have a wider subpubic angle and greater sciatic notch than males, as well as a short ischial spine. Hominoids, however, did not exhibit sexual dimorphism in pelvic shape. These results confirm previous studies showing that human pelvic shape dimorphism is related to the obstetrical requirements of birthing a large fetus, rather than sexual dimorphism in locomotor biomechanics. Future 3D GM research on other primate species that have large neonates relative to maternal size may determine whether the primate pelvis exhibits similar patterns of response to obstetrical selection pressures as in humans.

Differential growth of naturally and sexually selected traits in an Anolis lizard

AbstractSexual dimorphism may be indicative of differential natural and/or sexual selection pressures acting on males and females. Although similar degrees of adult sexual dimorphism may be observed among populations and species, underlying physiological, developmental and ecological processes driving growth during the juvenile stages may vary. Unraveling how and when differences arise during ontogeny is important to our understanding of the evolutionary patterns observed among adults. In addition, growth patterns may differ among traits within a single individual. Anolis lizards vary greatly in the degree of adult sexual size and shape dimorphism. Ultimate hypotheses (e.g. sexual selection, habitat partitioning) have been put forward to explain this variation, but proximate mechanisms operating during the juvenile stages remain largely unknown. Herein, we aim at elucidating the proximate mechanisms of sexual dimorphism in head and limb shape, performance and dewlap size in Anolis baracoae, a crown‐giant anole. We used a longitudinal approach and raised 23 captive‐bred juvenile A. baracoae lizards through adulthood. By quantifying body size, head and limb dimensions, dewlap size and bite performance, we obtained growth trajectories that were compared between the sexes and among traits. Our results show that the growth of head and limb shape is similar in males and females, whereas dewlap size and bite performance diverge at a specific age. Based on these results, we hypothesize that, whereas selection favors a similar head and limb shape in males and females, selection pressures on dewlap size and bite performance likely differ between the sexes. In addition, dewlap size starts diverging around the time the animals reach sexual maturity, whereas bite performance diverges much earlier in (sexually) immature males.

Disentangling the Size and Shape Components of Sexual Dimorphism

Many organisms are sexually dimorphic, reflecting sex-specific selection pressures. But although sexual dimorphism may consist of different variables from size to shape and physiology, most research emphasizes a single aspect of sexual dimorphism, notably size, without specifying its components and their relationship. Among terrestrial animals, spiders exhibit most extreme sex-specific differences in size and abdominal shape, and therefore represent ideal models to address this question. Here, we dissect sexual dimorphism in spiders at two phylogenetic hierarchical levels. At the species level, we employ comparative phylogenetic tests to explore the association between sexual shape dimorphism (SShD) and sexual size dimorphism (SSD) in the orbweb clade Argiopinae. At the genus level, we then explore such patterns on a phylogeny of orb weavers (Araneoidea). Female argiopines had more diverse abdominal morphotypes than the males and the abdominal shape evolution was only poorly correlated between the sexes. Phylogenetic and comparative data suggested that evolution of SShD in argiopines was related to geographic history, but that sexually shape monomorphic cases arose through selection for male size, perhaps acting against fecundity selection. While in argiopines there was no clear association between SShD and SSD, we detected a significant correlation in all orb weavers at the genus level. The shape and the size components of sexual dimorphism may thus respond independently to selection pressures, but at certain phylogenetic levels SSD may be a prerequisite for SShD. Research on other animal groups is needed to establish whether the here detected patterns on spiders are general.

Ontogeny of Size and Shape Sexual Dimorphism in the Pubis: A Multislice Computed Tomography Study by Geometric Morphometry.

Few studies have been conducted to determine sex differences in the immature coxal bone and the results were often contradictory. The authors studied sexual dimorphic differences of the pubis using geometric morphometric analysis of five osteometric landmarks recorded by multislice computed tomography (MSCT), based on three-dimensional reconstructions of 188 children (95 boys, 93 girls) living in the region of Toulouse, southwestern France, ranging in age from 1 to 18years old. They used geometric morphometric methodology first to test sexual dimorphism in size (centroid size) and shape (Procrustes residuals) and second to examine patterns of shape change with age (development) and size change with age (growth). Based on statistical significance test results, the pubic shape became sexually dimorphic at 13years old, although visible shape differences were observed as early as 9years old. This work showed that the trajectories of pubis shape (development) and size (growth) differed throughout ontogeny and between sexes.

Selective pressures in the human bony pelvis: Decoupling sexual dimorphism in the anterior and posterior spaces.

Sexual dimorphism in the human bony pelvis is commonly assumed to be related to the intensity of obstetrical selective pressures. With intense obstetrical selective pressures, there should be greater shape dimorphism; with minimal obstetrical selective pressures, there should be reduced shape dimorphism. This pattern is seen in the nondimorphic anterior spaces and highly dimorphic posterior spaces. Decoupling sexual dimorphism in these spaces may in turn be related to the differential influence of other selective pressures, such as biomechanical ones. The relationship between sexual dimorphism and selective pressures in the human pelvis was examined using five skeletal samples (total female n = 101; male n = 103). Pelvic shape was quantified by collecting landmark coordinate data on articulated pelves. Euclidean distance matrix analysis was used to extract the distances that defined the anterior and posterior pelvic spaces. Sex and body mass were used as proxies for obstetrical and biomechanical selective pressures, respectively. MANCOVA analyses demonstrate significant effects of sex and body mass on distances in both the anterior and the posterior spaces. A comparison of the relative contribution of shape variance attributed to each of these factors suggests that the posterior space is more influenced by sex, and obstetrics by proxy, whereas the anterior space is more influenced by body mass, and biomechanics by proxy. Although the overall shape of the pelvis has been influenced by obstetrical and biomechanical selective pressures, there is a differential response within the pelvis to these factors. These results provide new insight into the ongoing debate on the obstetrical dilemma hypothesis.

Sexual dimorphism in bite force in the grey mouse lemur

AbstractSexual dimorphism is thought to be the result of sexual selection, food competition and/or niche differentiation, or simply the result of differential growth between the sexes. Despite the fact that sexual dimorphism is common among primates, lemurs are thought to be largely monomorphic. Yet, females of the species Microcebus are known to be larger than males. Here, we investigate if dimorphism in head dimensions is present in a colony of captive grey mouse lemurs Microcebus murinus. Moreover, we test whether any observed shape dimorphism is associated with differences in bite force between the sexes. Our results show that male and female grey mouse lemurs are indeed sexually dimorphic in head dimensions, with females having taller and wider heads than males. Moreover, we confirm previous observations that females are heavier than males. Bite force was principally determined by head dimensions and age in our dataset, and differed between sexes, with females biting harder than males. These data suggest a potential role for niche dimorphism in driving the observed shape and performance dimorphism as female reproductive output may depend upon the ability of animals to obtain resources that are difficult to ingest.

The morphometrics of "masculinity" in human faces.

In studies of social inference and human mate preference, a wide but inconsistent array of tools for computing facial masculinity has been devised. Several of these approaches implicitly assumed that the individual expression of sexually dimorphic shape features, which we refer to as maleness, resembles facial shape features perceived as masculine. We outline a morphometric strategy for estimating separately the face shape patterns that underlie perceived masculinity and maleness, and for computing individual scores for these shape patterns. We further show how faces with different degrees of masculinity or maleness can be constructed in a geometric morphometric framework. In an application of these methods to a set of human facial photographs, we found that shape features typically perceived as masculine are wide faces with a wide inter-orbital distance, a wide nose, thin lips, and a large and massive lower face. The individual expressions of this combination of shape features—the masculinity shape scores—were the best predictor of rated masculinity among the compared methods (r = 0.5). The shape features perceived as masculine only partly resembled the average face shape difference between males and females (sexual dimorphism). Discriminant functions and Procrustes distances to the female mean shape were poor predictors of perceived masculinity.

Context-dependent expression of sexual dimorphism in island populations of the common wall lizard (Podarcis muralis)

The condition-dependent sexual dimorphism model explains the evolution and maintenance of sexual dimorphism in traits targeted by sexual selection, and predicts that the magnitude of sexual dimorphism depends on the variability of individual condition, male traits being more variable than female corresponding traits. Most convincing examples concern insects, while studies among vertebrates are scanty because manipulating condition often is not possible, and the time to reach sexual maturity may be too long. Islands offer a unique opportunity to compare how the environment affects the expression of sexual dimorphism, since they represent ‘natural experimental sets’ in which different populations of the same species may experience alternative environmental constraints. We investigated the occurrence of context-dependent expression in sexual dimorphism of head shape in insular populations of the common wall lizards (Podarcis muralis) inhabiting the Tuscan Archipelago (Tyrrhenian Sea). Alternative models were formulated: H0 assumes that the sexual dimorphism is uninfluenced by islands, H1 assumes the only effect of phylogeny, H2A and H2B account for the biogeography of the archipelago (island size and distance from the mainland), while H3 assumes island-specific effects on sexual dimorphism. Models were compared using Akaike's information criterion adjusted for multivariate analyses. All hypotheses performed better than H0, but H3 largely outperformed all other alternative hypotheses, indicating that environmental features of islands play an additive effect to ontogenetic, biogeographic and genetic factors in defining variation in head shape sexual dimorphism. Our results support the hypothesis of a context-dependent sexual dimorphism in common wall lizards. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114, 552–565.

Allometry of head size and shape dimorphism in the grass snake (Natrix natrix L.)

This study was conducted to investigate allometry of head growth patterns in the grass snake (Natrix natrix (Linnaeus, 1758)). Although male and female grass snakes differ in relative head size, their head growth patterns follow similar trajectories. The sexual differences are roughly constant during ontogeny. Most head dimensions grow with negative allometry or isometry with respect to the snout?vent length except head width, which grows with positive allometry in both sexes.

Eucypris fontana(Graf, 1931) (Crustacea, Ostracoda) in permanent environments of Patagonia Argentina: a geometric morphometric approach

Fil: Ramos, Lorena Yesica. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Patagonia Norte. Instituto de Investigacion En Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue; Argentina

Sexual dimorphism in Trachylepis vittata (Olivier, 1804) (Sauria: Scincidae) in the Zagros Mountains, western Iran

We describe sexual dimorphism in coloration, size, and shape in 48 specimens (19 males and 29 females) of the bridled skink, Trachylepis vittata (Olivier, 1804), collected from western regions of the Iranian Plateau. For the analyses, we used 29 metric and 9 meristic characters. Our study showed the existence of slight sexual size dimorphism in body and head size between the sexes. Males had significantly smaller heads and narrower bodies than females. Furthermore, males and females were different in the structure of the cloaca. The possible scenarios behind sexual dimorphism in this lizard are discussed.

Sexual Dimorphism and Allometric Effects Associated With the Wing Shape of Seven Moth Species of Sphingidae (Lepidoptera: Bombycoidea).

Sexual dimorphism is a pronounced pattern of intraspecific variation in Lepidoptera. However, moths of the family Sphingidae (Lepidoptera: Bombycoidea) are considered exceptions to this rule. We used geometric morphometric techniques to detect shape and size sexual dimorphism in the fore and hindwings of seven hawkmoth species. The shape variables produced were then subjected to a discriminant analysis. The allometric effects were measured with a simple regression between the canonical variables and the centroid size. We also used the normalized residuals to assess the nonallometric component of shape variation with a t-test. The deformations in wing shape between sexes per species were assessed with a regression between the nonreduced shape variables and the residuals. We found sexual dimorphism in both wings in all analyzed species, and that the allometric effects were responsible for much of the wing shape variation between the sexes. However, when we removed the size effects, we observed shape sexual dimorphism. It is very common for females to be larger than males in Lepidoptera, so it is expected that the shape of structures such as wings suffers deformations in order to preserve their function. However, sources of variation other than allometry could be a reflection of different reproductive flight behavior (long flights in search for sexual mates in males, and flight in search for host plants in females).

Sexual Dimorphism and Diet ofPseudis tocantins(Anura, Hylidae, Pseudae)

Abstract. The genus Pseudis (Hylidae) includes aquatic frogs distributed throughout South America east of the Andes. Few papers have been published on the ecology of these species, despite the great interest their gigantic larvae raise among herpetologists. Pseudis tocantins has a widespread distribution along the Tocantins-Araguaia hydrographic basin in Brazil and virtually nothing has been published about its natural history and ecology. The present work aimed to evaluate, based on 159 specimens from 13 populations, sexual dimorphism in size and shape and diet composition of P. tocantins along most of its known distribution. Females were significantly larger than males and body shape differed significantly between sexes, with tibia length and tympanum diameter as the variables contributing the most to this difference. We found 13 prey categories in frog’s stomachs, with Araneae, Odonata, and Orthoptera being the most important items, respectively. Aquatic animals were also part of the species diet (even...

A Morphological Analysis of the Subtribe Pegylina Lacroix, 1989 (Scarabaeidae: Melolonthinae: Melolonthini) Reconstitutes Its Generic Composition

Phylogenetic analysis using six outgroup and 26 ingroup taxa and 18 external adult morphological characters resulted in a paraphyletic Pegylina as composed by Lacroix (1989). To maintain the Pegylina as a monophyletic subtribe, the genus Stenopegylis Arrow, 1943 is removed from the Pegylina and placed in the Melolonthini sensu lato, pending further cladistic analyses of the Afrotropical melolonthines. Following the analyses presented here, eight character areas (antennomere number, labrum form, protarsal claw shape, protibial spur, pronotum, mesosternum and mesosternal process, body shape and sexual dimorphism) are discussed with reference to differentiating Hypopholis Erichson, 1847 syn. nov. from Pegylis Erichson, 1847. Consequently, the former is synonymized with the latter, resulting in the following new combinations: Pegylis sommeri (Burmeister, 1855) comb. nov.; P. uelensis (Burgeon, 1946) comb. nov. and P. vittata (Fåhraeus in Boheman, 1857) comb. nov. An appended checklist for the subtribe Pegylina as presently composed includes 37 species in two genera, Eupegylis Duvivier, 1892 (1 sp.) and Pegylis Erichson, 1847 (36 spp.). During outgroup selection for this analysis it became aparent that the monotypic Wernerophylla nigra Lacroix, 2001 syn. nov. is conspecific with Stenopegylis cylindrica Arrow, 1943 and consequently this synonymy is implemented here.

Sex and sex steroids: impact on the kinetics of fatty acids underlying body shape.

Adult humans have a remarkable sexual dimorphism in body shape. Men tend to store relatively more fat in the upper body whereas women store more fat in the lower body. We do not have a complete understanding of the mechanisms underlying these differences, but we know that people who preferentially store abdominal fat are at greater risk of metabolic disease. It is also known that the changes in sex steroid concentrations during puberty and again with advancing age are accompanied by changes in body fat distribution. The objective of this review is to describe what has been learned regarding the mechanisms underlying changes in regional body fat distribution that occur as a result of changes in sex hormones and to delineate effects of sex steroids in modulating body composition.

Pollination Ecology ofArnebia szechenyi(Boraginaceae), a Chinese Endemic Perennial Characterized by Distyly and Heteromorphic Self-Incompatibility

Heterostyly, a genetically controlled floral polymorphism, includes both distyly and tristyly. In Boraginaceae, distyly was reported in several genera but it was rarely studied quantitively in the genus Arnebia. We experimentally studied the pollination ecology of Arnebia szechenyi, a perennial herb native to China. It exhibited precisely reciprocal herkogamy and marked between-morph pollen number and pollen shape dimorphism, and the ratio between the two morphs in each of the four populations studied was nearly equal to 1. This indicates an equilibrium ratio in distylous species with heteromorphyic self-incompatibility, which was further supported by the fact that no fruit was produced in flowers subjected to self-pollination or intra-morph pollination. In comparison with naturally pollinated flowers, hand inter-morph pollination increased both fruit set and seed set significantly, indicating pollen limitation in both morphs under natural conditions. Bombylius sp. and Nomia femoralis were the main visitors and could efficiently pollinate between the morphs of A. szechenyi. Overall, our results indicate that A. szechenyi is a typically distylous species with heteromorphic self-incompatibility, and the pollen limitation of seed production might suggest that distyly in A. szechenyi could be selected via male fitness.

Shape, size, and maturity trajectories of the human ilium.

Morphological traits of the ilium have consistently been more successful for juvenile sex determination than have techniques applied to other skeletal elements, however relatively little is known about the ontogeny and maturation of size and shape dimorphism in the ilium. We use a geometric morphometric approach to quantitatively separate the ontogeny of size and shape of the ilium, and analyze interpopulation differences in the onset, rate and patterning of sexual dimorphism. We captured the shape of three traits for a total of 191 ilia from Lisbon (Portugal) and London (UK) samples of known age and sex (0-17 years). Our results indicate that a) there is a clear dissociation between the ontogeny of size and shape in males and females, b) the ontogeny of size and shape are each defined by non-linear trajectories that differ between the sexes, c) there are interpopulation differences in ontogenetic shape trajectories, which point to population-specific patterning in the attainment of sexual dimorphism, and d) the rate of shape maturation and size maturation is typically higher for females than males. Male and female shape differences in the ilium are brought about by trajectory divergence. Differences in size and shape maturation between the sexes suggest that maturity may confound our ability to discriminate between the sexes by introducing variation not accounted for in age-based groupings. The accuracy of sex determination methods using the ilium may be improved by the use of different traits for particular age groups, to capture the ontogenetic development of shape in both sexes.

Cranial variation of the greater horseshoe bat Rhinolophus ferrumequinum (Chiroptera: Rhinolophidae) from the central Balkans

Cranial size and shape variation of the greater horseshoe bat Rhinolophus ferrumequinum from territories in Serbia and Montenegro was examined using geometric morphometric methods. Statistically significant size and shape differences among specimens from distinct geographic regions (the Carpatho–Balkanides, the Internal and External Dinarides) were observed. Bats from the Carpatho–Balkanides have the smallest crania, while those from the External Dinarides have the largest ones. Compared to specimens from the Carpatho–Balkanides, bats from the other two regions have crania wider in the temporal and elongated in the facial region, while the basicranial region is smaller. Our analysis of sexual size dimorphism revealed no statistically significant differences between males and females. Even though significant sexual shape dimorphism was observed, cranial shape differences among bats from different geographic regions exceeded those between sexes. We also found that size and shape vary with climatic factors. Allometry has statistically significant effect on cranial shape variation and somehow contributes to covariation between cranial shape and environmental variables. Although the examined bats were from a relatively small territory, we have provided new insights into important issues like geographic variation, sexual dimorphism and allometry in this species.

Sexual Dimorphism in the Parasitoid Wasps Aphidius balcanicus, Aphidius rosae, and Aphidius urticae (Hymenoptera: Braconidae: Aphidiinae)

Abstract In this study, we explored variations in the magnitude and the direction of sexual dimorphism in three parasitoid species from the genus Aphidius Nees (Aphidius balcanicus Tomanović and Petrović, Aphidius rosae Haliday, and Aphidius urticae Haliday). We also explored the variation in sexual dimorphism within one of these species, A. urticae, which parasitizes and develops in three different hosts that belong to three aphid genera. To estimate sexual size dimorphism, we selected two developmentally and functionally unrelated morphological structures: the mesoscutum and the wing. Our results showed that sexual dimorphism in mesoscutum and wing size differ (sexual dimorphism in mesoscutum size appears to be insignificant, whereas the wings are larger in males). We found a high level of variation in sexual dimorphism in wing shape within and between species. We also found that the observed shape changes are not due to size-related, allometric changes in wing shape. These results indicate that sexual dimorphism in wing size and wing shape is highly variable and could be influenced by various factors, including host effects, whereas mesoscutum size appears to be a conserved trait in aphid parasitoids.

Three new species of free-living marine nematodes from East China Sea.

Three new species of free-living marine nematodes from intertidal sands in Xiamen, Fujian province are described and illustrated. Bathylaimus denticulatus sp. n. can be distinguished by a relatively small buccal cavity with its second part armed with two distinct teeth, short 2-3 μm labial and 12-16 μm cephalic setae and amphids of 0.8-0.9 turns. Oncholaimus minor sp. n. is characterized by its relatively small body size and the sexual dimorphism in tail shape. Oncholaimus xiamenense sp. n. is identified by pronounced sexual dimorphism in tail shape, the location of postcloacal tubercle (3/4 of the distance from cloaca to tip of tail), the location of female ovary as well as the demanian system (on the right side of the intestine), the number of circumanal genital setae (12). The types are deposited in the Third Institute of Oceanography, SOA, Xiamen.