Dimorphism In Shape Research Articles

Geometric morphometrics reveals sex-differential shape allometry in a spider.

Common scientific wisdom assumes that spider sexual dimorphism (SD) mostly results from sexual selection operating on males. However, testing predictions from this hypothesis, particularly male size hyperallometry, has been restricted by methodological constraints. Here, using geometric morphometrics (GMM) we studied for the first time sex-differential shape allometry in a spider (Donacosa merlini, Araneae: Lycosidae) known to exhibit the reverse pattern (i.e., male-biased) of spider sexual size dimorphism. GMM reveals previously undetected sex-differential shape allometry and sex-related shape differences that are size independent (i.e., associated to the y-intercept, and not to size scaling). Sexual shape dimorphism affects both the relative carapace-to-opisthosoma size and the carapace geometry, arguably resulting from sex differences in both reproductive roles (female egg load and male competition) and life styles (wandering males and burrowing females). Our results demonstrate that body portions may vary modularly in response to different selection pressures, giving rise to sex differences in shape, which reconciles previously considered mutually exclusive interpretations about the origins of spider SD.

Effects of Sexually Dimorphic Shape Cues on Neurophysiological Correlates of Women’s Face Processing

Sexual dimorphism (i.e., masculinity in males and femininity in females) is known to affect social perceptions that are important for both mate choice and intrasexual competition, such as attractiveness and dominance. Little is known, however, about the neurophysiological underpinnings mediating sexual dimorphism’s effects on face processing. Here we investigate the neurological correlates of processing sexually dimorphic faces using event-related potentials (ERPs). We employed image transformation techniques to enhance and reduce the sexually dimorphic shape features of male and female faces viewed by women performing a sex categorization task. Sexual dimorphism modulated superior-central N250 magnitude and the peak latency of the N170 and P200. The sex of the face further modulated the amplitude of the P200. These findings extend prior work linking the superior-central N250 to social categorization processes triggered by face shape, and strengthen its functional interpretation in terms of coarse- versus fine-grained categorical judgements. We conclude that ERPs can illuminate the cognitive mechanisms (i.e., mental processes) underlying behavioral responses to sexual dimorphism.

On the sexual dimorphism in <i>Parafossarulus manchouricus </i>(Gerstfeldt in Bourguignat, 1860) (Bithyniidae, Gastropoda, Mollusca)

On the basis of dissections and shell measurements we studied sexual dimorphism in shell shape in Parafossarulus manchouricus taken from the bay of the Bira River (Russian Far East). It is shown that there are no statistically significant differences in shells of males and females in P. manchouricus .

Sexual dimorphism and population differentiation in the Chilean Neotropical moth Macaria mirthae (Lepidoptera, Geometridae): a wing geometric morphometric example

Sexual shape dimorphism is the differentiation of male and female organisms based on their shape variation; this definition was proposed for the use of geometric morphometrics analysis where the geometric features of the shape are analyzed without the influence of the size. Macaria mirthae (Lepidoptera: Geometridae) is a moth that inhabits different valleys in the north of Chile principally associated to Acacia macracantha and lately Leucaena leucocephala both trees of the Fabaceae family. The Sexual dimorphism was analyzed in this species in order to corroborate studies on the use of wing as a sexual differentiation trait, and specific influence of localities was also evaluated. A clear shape variation was found where the male wings are more contracted compared to female wings. A climate influence is also suggested that could differentiate the wing shape from the individuals that inhabit two different valleys in the neotropical region of the north of Chile. This research supports previous studies identifying a clear Sexual shape dimorphism in the wing, as a selected trait, suggesting that oviposition and male competition of this group of moths is reflected in their wings. These differences raise the question whether Sexual shape dimorphism can be modulated by natural selection.

The ecology of sexual dimorphism in size and shape of the freshwater blenny Salaria fluviatilis.

Sexual selection is considered the major cause of sexual dimorphism, but recent observations suggest that natural selection may play a more important role in the evolution of sex differentiation than previously recognized. Therefore, studying the trade-offs between natural selection and sexual selection is crucial to a better understanding of the ecology underlying the evolution of sexual dimorphism. The freshwater blenny Salaria fluviatilis, a fish inhabiting lakes and rivers around the Mediterranean Sea, displays strong sexual dimorphism in size, shape, and behavior (i.e., larger body and head size for males and higher swimming requirements for females during the reproductive period). We tested for differences in sexual dimorphism in size and shape between the populations from lake and river habitats with the goal of identifying the trade-offs between natural and sexual selection that underlie variations in sexual dimorphism in this species. Our results show i) differences in sexual size dimorphism (SSizeD) in accordance to Rensch’s rule (i.e., larger individuals in rivers associated with higher SSizeD), and ii) a decrease in shape differentiation between males and females in lake populations. Together, this suggests that the different environmental conditions between lake and river habitats (e.g., resource limitations, predation pressure, water velocity) affect the relative importance of sexual selection in the display of sexual dimorphism within the species. This study highlights the importance of considering the environmental conditions to which populations are exposed to better understand the ecology underlying the evolution of sexual dimorphism.

Sexual shape dimorphism and selection pressure on males in fossil ostracodes

AbstractSexual dimorphism is thought to have evolved via selection on both sexes. Ostracodes display sexual shape dimorphism in adult valves; however, no previous studies have addressed temporal changes on evolutionary timescales or examined the relationships between sexual shape dimorphism and selection pressure and between sexual shape dimorphism and juvenile shape. Temporal changes in sexually dimorphic traits result from responses of these traits to selection pressure. Using the Gaussian mixture model for the height/length ratio, a valve-shape parameter, we identified sexual differences in the valve shape ofKrithe dolichodeiras.l. from deep-sea sediments of the Paleocene (62.6–57.6 Ma) and estimated the proportion of females in the fossil populations at 11 time intervals. Because the proportion of females in a population is altered by the mortality rate of adult males, it is reflective of selection pressure on males. We attempted to correlate the height/length ratios between the sexes with the proportion of females, taking into consideration that the valve shape was not linked with the selection pressure on males. In time-series data of the height/length ratio, both sexes indicate no significant changes on evolutionary timescales, even though the sex ratio of the population changed from female skewed to male skewed during the late Paleocene. The sexual shape dimorphism was not driven by sexual selection. The static allometry between the height/length ratio and length indicates that the sexual shape dimorphism did not function for sexual display. The absence of change over time in the female allometric slope suggests that the evolution of valve shape was constrained by stasis.

Differential gene expression in narrow- and broad-headed European glass eels (Anguilla anguilla) points to a transcriptomic link of head shape dimorphism with growth rate and chemotaxis.

One of the major challenges in evolutionary biology is to understand the mechanisms underlying morphological dimorphism and plasticity, including the genomic basis of traits and links to ecology. At the yellow eel stage of the European eel (Anguilla anguilla), two morphotypes are found: broad- and narrow-heads. This dimorphism has been linked to dietary differences, with broad-heads feeding on harder, larger prey than narrow-heads. However, recent research showed that both morphotypes could be distinguished at the glass eel stage, the nonfeeding predecessor of the yellow eel stage, implying that nondietary factors play a role in the development of this head shape dimorphism. Here, we used transcriptome profiling (RNAseq) to identify differentially expressed genes between broad- and narrow-headed glass eels. We found 260 significantly differentially expressed genes between the morphotypes, of which most were related to defence and immune responses. Interestingly, two genes involved in growth (soma and igf2) were significantly upregulated in narrow-heads, while nine genes involved in chemotaxis showed significant differential expression. Thus, we found support for the observation that head shape is associated with somatic growth, with fast-growing eels developing a narrower head. Additionally, observations in the wild have shown that slow-growers prefer freshwater, while fast-growers prefer brackish water. The differential expression of genes involved in chemotaxis seems to indicate that glass eel growth rate and habitat choice are linked. We hypothesize that two levels of segregation could take place in the European eel: first according to habitat choice and second according to feeding preference.

A complete survey of normal pores on a smooth shell ostracod (Crustacea): Landmark-based versus outline geometric morphometrics.

Pores and sensilla on ostracod shell have often been used in studies of ontogeny, taxonomy, and phylogeny of the group. However, an analysis of sexual dimorphism and variation between valves in the number and distribution of pores is lacking. Also, such studies have never been done on a widely distributed, morphologically variable, and weakly ornamented freshwater ostracod. Here, we survey pores in one such species, Physocypria kraepelini. We choose 27 homologous pores as landmarks for 2D-geometric morphometric analysis, with the aim to assess intersexual and between valves variation in size and shape relative to the Fourier outline analysis. This species has only simple (Type A) pores with and without a lip, and each pore carries an undivided sensory seta. Our results show that the total number of pores varies (from 270 to 296), but this is not associated with a specific valve. Males carry fewer pores than females, however no sex specific pores are found. Small intrapopulation divergence of the Cyt b molecular marker (1%) indicates that morphological variability is not species related. We found that P. kraepelini exhibits directional asymmetry of size and shape, sexual size dimorphism (SSD) but lacks sexual shape dimorphism (SShD). Two geometric morphometrics methods were congruent in the estimation of SSD, SShD, and directional asymmetry of shape but differ in the statistical evaluation of directional asymmetry of size. Contrary to other animal groups, our study suggests that ostracods have more pronounced directional asymmetry of shape compared to directional asymmetry of size.

Life history traits and patterns of sexual dimorphism in the freshwater crab Potamon ibericum (Bieberstein, 1809) (Decapoda: Brachyura: Potamidae) from the western Alborz Mountains, Iran

The assessment of life history traits can help to better understand the population dynamics of the respective species. We present some life history traits of the freshwater crab Potamon ibericum (Bieberstein, 1809) from the western Alborz Mountains, Iran. Carapace size at the onset of morphometric maturity was estimated using the breakpoint of the relative growth of the chela and abdomen in males and females, respectively, by implementing piecewise linear regressions. In order to quantify variations in the estimated breakpoint, a bootstrap resampling method was applied. Allometric trajectories of chelar dimensions were also applied to juveniles and adults. Sexual size dimorphism was evaluated using the dimensions of the carapace and chelae, and patterns of the carapace shape dimorphism were investigated by implementing geometric morphometric analysis. The results showed that females reach morphometric maturity at smaller sizes than males, which could be of advantage in the fluctuating environment of their freshwater habitat in order to mate as soon as possible and increase fecundity. Positive allometric trends in the length of the major chela was observed in adults of both sexes, and the possible adaptive forces on the evolution of this pattern are discussed. Results of sexual dimorphism analyses confirmed male-biased sexual size dimorphism and functional adaptation of carapace shape in both sexes.

Sexual dimorphism in size and shape of traits related to locomotion in nine anuran species from Serbia and Montenegro

Sexual dimorphism in size and shape of traits related to locomotion in nine anuran species from Serbia and Montenegro

Reproductive Biology of Three Sympatric Species of Gymnophthalmid Lizards from the Sand Dunes of the Middle São Francisco River, Bahia, Brazil

Abstract. Gymnophthalmidae is a Neotropical family that comprises small- to medium-sized lizards and a huge diversity of morphologies and habitats. Although they have been broadly targeted in several systematics studies, the knowledge of their reproductive biology is still poorly known, especially for fossorial species like Calyptommatus leiolepis, Nothobachia ablephara, and Procellosaurinus tetradactylus, sympatric species from the dune fields at Sao Francisco River, Bahia, Brazil. We analyzed gonads of 388 specimens of C. leiolepis, 180 of N. ablephara, and 47 of P. tetradactylus from Alagoado sand dunes, Bahia. Females are larger than males in all species and there is no sexual dimorphism in head shape. The three species undergo extended, possibly continuous, reproduction. Variation of testes volume was observed only in C. leiolepis, with lower values between August and December; however, sperm production was detected within this period. Clutch size always comprised two eggs and there was no correlatio...

Sexual dimorphism and associated population characteristics in the benthopelagic shrimp <em>Pasiphaea sivado</em> (Crustacea: Caridea: Pasiphaeidae)

Morphological and size dimorphism between genders of the benthopelagic shrimp Pasiphaea sivado are reported for the first time in the present work. All five pleopod protopods of females are thinner and more elongated than the male pleopod protopods, which in turn are anteriorly rounded and have robust shapes. The shape variability of the second pleopod protopods was also analysed using geometric morphometrics techniques which clearly differentiated between the thinner, elongated shape of the females and the robust shape of males. An important application of the observations of sexual dimorphism in pleopod shape in adult P. sivado is, from now on, the ability to quickly assess the gender of individuals when fisheries and population biology studies are carried out in the field unaided by a magnifying. A critical size from which the population sex ratio biases changed from female to male dominance was found in all studied western Mediterranean populations of P. sivado. This critical size different and became progressively smaller from populations in the Alboran Sea to populations in the Catalan Sea. Concerning sex ratio, no significant tendency of gender segregation was found across the bathymetric distribution range of the species, suggesting that this species does not perform differential depth distribution by gender.

Latitudinal Influence on the Sexual Dimorphism of the Marine Fish Bathygobius soporator (Gobiidae: Teleostei)

Environmental gradients in a marine setting may have significant effects on morphological variations and evolutionary patterns, including sexual dimorphism variations within and between fish populations. We analyzed sexual shape and size dimorphism in accordance with Rensch and Bergmann’s rules in five coastal populations of the gobiid Bathygobius soporator along 4000 km of the Brazilian coastline. The populations differ significantly in sexual body shape dimorphism, with a tendency toward reduced intrapopulation dimorphism, increasing with latitude. Body size variation was significant between populations and population vs. sex, and inverse to Bergmann’s rule. Moreover, size dimorphism among populations of B. soporator does not follow Rensch’s rule. These data represent a rare example of inter and intrapopulation spatial variation in sexual dimorphism associated with latitude in marine fish. This suggests a complex and particularized scenario of biotic and abiotic interactions acting on local populations of B. soporator in extensive coastal areas of the Western Atlantic, with profound implications for species evolution.

Geometric morphometric and traditional methods for sex assessment using the posterior ilium.

The human hip bone is generally accepted as the most reliable bone for sex estimation in forensic and bioarchaeological disciplines. However, it is seldom completely preserved. The best preserved region is typically around the sacroiliac joint and its auricular surface; it is therefore surprising that this surface has not been involved in standard sexing methods. The aim of this study was to explore the shape and size sexual dimorphism of the auricular surface in detail and to compare its sex estimation accuracy using the geometric morphometric (GM) and traditional methodological approach. Our sample consisted of 121 specimens from 3 European osteological collections. The GM part of the study was based on 2D sliding semilandmarks that covered the outline of the auricular surface. Furthermore, several linear measurements and visual features (e.g. auricular surface elevation, postauricular sulcus) were chosen to test sex estimation accuracy using support vector machines. Concerning the GM analysis, the most notable sexual differences in the auricular surface outline relate to size. The best accuracy was achieved using form variables reaching 81.0%. Comparable accuracy (80.2%) was achieved using the metric approach, but combined with visual features the accuracy was increased to 93.4%. The GM approach was not very efficient in sexing the auricular surface outline, but the combination of visual features from the posterior ilium and metric variables of the auricular surface could be useful in sex estimation. Therefore, we provide a further testable linear discriminant equation based on this combination of variables.

Allometry and Sexual Dimorphism in the Human Pelvis.

Sexual dimorphism in the human pelvis has evolved in response to several jointly acting selection regimes that result from the pelvis' multiple roles in locomotion and childbirth, among others. Because human males are, on average, taller than females, some aspects of sexual dimorphism in pelvis shape might result from allometry, the association between stature and pelvis shape across individuals. In this study, they aimed to disentangle and quantify the two components contributing to pelvic sex differences: the allometric component, which emerges as a consequence of dimorphism in stature, and the remaining non-allometric sexual dimorphism component. A geometric morphometric analysis of a dense set of 3D landmarks, measured on 99 female and male adult individuals was conducted. While pelvis size was similar in both sexes, the average differences in pelvis shape reflected the well-documented pattern of sexual dimorphism. There was almost no overlap between females and males in shape space. Their analysis showed that pelvis size and shape were similarly associated with stature in both sexes. It was found that dimorphism in the height-to-width ratio of the pelvis and in the orientation of the iliac blades was largely allometric, whereas dimorphism in the subpubic angle and the relative size and distance of the acetabula was largely non-allometric. It was concluded that, in contrast to the overall pelvic proportions, sexual dimorphism in the birth-relevant pelvic dimensions was mainly of non-allometric origin and was presumably mediated via steroid hormone secretion during puberty. Anat Rec, 300:698-705, 2017. © 2017 Wiley Periodicals, Inc.

Cranial variability of the Serbian red fox

We used geometric morphometric techniques to examine variability in Serbian red fox (Vulpes vulpes) crania. Male crania are about 5% larger than female ones and sexual size dimorphism (SSD) was significant. Also, significant cranial shape differences were found between the sexes. Males are characterized by reduced basicranial, but broader rostral and zygomatic regions. Although a slight and significant allometric effect was detected and larger specimens are smaller in the region of basicranium, cranial sexual shape dimorphism (SShD) pattern is not influenced by SSD. As small to moderate SSD in canid species is a general characteristics of the family, additional studies are needed to determine whether basicranial reduction in males, i.e. its enlargement in females, could be an important feature in characterizing cranial SShD patterns in other Canidae members. While uniform considering size, the shape of Serbian red fox crania varies geographically, as well as depending on proportion of agricultural habitats. In comparison to those from central and eastern Serbia, specimens from the northern Serbian region Vojvodina (with higher proportions of agricultural areas) have more robust crania with shorter snouts and maxillae, larger palatine bones accompanied with anteriorly moved posterior edges of the canine alveolus and laterally expanded zygomatic arches. Encompassing mostly facial and temporal cranial regions these shape changes are probably related to diet differences, although genetic diversification cannot be excluded as a possible contributing factor.

Sexual Wing Shape Dimorphism in Piophila casei (Linnaeus, 1758 Diptera: Piophilidae)

The Piophilidae are synanthropic flies that grow and develop on cheese, fish, cured meat, among others substrates. Some species represents an important forensic indicator associated to carcasses, because the adults are common during the bloat stage, and the larvae are associated to the advanced to dry stages. Recently, the geometric morphometrics has been used to quantified the sexual shape dimorphism in medical important insects. We proposed to evaluate the shape sexual dimorphism in Piophila casei through the wing geometric morphometrics. Were collected 34 P. casei specimens and sorted by sex (17 females and 17 males), later the wing was dissected and slide mounted for digitalizing eight landmarks. The x, y coordinates were aligned by Generalized Procrustes Analysis to extract the matrix configurations and centroid size. The sexual shape dimorphism differences were evaluated by means a Discriminant Analysis (DA), and the size with non-parametric ANOVA. We didn't found differences in centroid size between females and males; however, the shape was significantly different between sex. In the cross-validation DA, 82% specimens were correctly classified into females and 88% males. Our study represents the first investigation that quantifies the sexual shape and size dimorphism in Piophila casei, and this could be a basis for further studies that combines geometric morphometrics tools and forensic entomology.

Sexual size and shape dimorphism in the Near Eastern fire salamander, Salamandra infraimmaculata (Caudata: Salamandridae)

Sexual dimorphism, phenotypic difference between males and females of the same species, has been demonstrated in many invertebrates and vertebrates. In many of these studies, which were especially conducted on amphibians, female individuals were reported to be larger than males. However, this does not necessarily mean that this also applies to body shapes. Therefore, in this study, a total of 31 characters of body size and body shape were measured and analyzed in the Near Eastern fire salamander, in order to understand whether these characters differ between female and male individuals. The results suggest that there is a significant difference between the sexes in terms of both body size and some body shapes (e.g. arm and leg length, arm diameter, cloacal proportions) in this fire salamander. I conclude that both sexual size and shape dimorphism need to be taken into account to help understand an organism’s life-history traits, ecology, population dynamics and behavior.

Sexual dimorphism in the carapace shape and length of the freshwater palaemonid shrimp Macrobrachium potiuna (Müller, 1880) (Decapoda: Caridea: Palaemonidae): geometric and traditional morphometric approaches

Sexual dimorphism is characterized by morphological, physiological, or behavioral differences between males and females. The genus Macrobrachium is a diverse group of freshwater shrimps distributed throughout tropical and subtropical regions. They have a great intra- and interspecific morphological variation, with some species showing sexual dimorphism. We investigated the sexual dimorphism of the size and shape of the carapace and body weight of Macrobrachium potiuna (Müller, 1880) in three populations of the State of Paraná through traditional and geometric morphometric techniques. The populations were sampled from three rivers: the Pombas River, Coastal Basin, the Piraquara River, First Plateau, and the Guabiroba River, Second Plateau. Morphometric analyses indicated that male shrimps showed differences in carapace length and body weight: the higher the distance from the sea, the smaller and lighter the shrimps. Carapace shape also differed significantly between the sexes in all three populations, with males having a less robust carapace, but a more elongated rostrum than females. The morphological differences between the genders seem to reflect the reproductive roles of males and females in this environment.

Morphological variation among populations of Hemigrammus coeruleus (Characiformes: Characidae) in a Negro River tributary, Brazilian Amazon

ABSTRACT We explored patterns of phenotypic variation in Hemigrammus coeruleus from the Unini River basin, a blackwater river in the Brazilian Amazon. Geometric morphometrics was used to evaluate variation in body shape among populations from four tributaries (UN2-UN5). We found no evidence for sexual dimorphism in body size and shape. However, morphological differences among populations were detected as the analyses recovered significant groups corresponding to each sub-basin, with some overlap among them. The populations from UN2, UN3 and UN5 had more elongate bodies than fish from UN4. The most morphologically divergent population belonged to UN4, the tributary with the most divergent environmental conditions and the only one with seasonally-muddy waters. The morphological variation found among these populations is likely due to phenotypic plasticity or local adaptation, arising as a product of divergent ecological selection pressures among sub-basins. This work constitutes one of the first to employ a population-level geometric morphometric approach to assess phenotypic variation in Amazonian fishes. This method was able to distinguish subtle differences in body morphology, and its use with additional species can bring novel perspectives on the evaluation of general patterns of phenotypic differentiation in the Amazon.