Skull morphological variation in a British stranded population of false killer whale (Pseudorca crassidens): a three-dimensional geometric morphometric approach

The false killer whale (Pseudorca crassidens (Owen, 1846)) is a globally distributed delphinid that shows geographical differentiation in its skull morphology. We explored cranial morphological variation in a sample of 85 skulls belonging to a mixed sex population stranded in the Moray Firth, Scotland, in 1927. A three-dimensional digitizer (Microscribe 2GX) was used to record 37 anatomical landmarks on the cranium and 25 on the mandible to investigate size and shape variation and to explore sexual dimorphism using geometric morphometric. Males showed greater overall skull size than females, whereas no sexual dimorphism could be identified in cranial and mandibular shape. Allometric skull changes occurred in parallel for both males and females, supporting the lack of sexual shape dimorphism for this particular sample. Also, fluctuating asymmetry did not differ between crania of males and females. This study confirms the absence of sexual shape dimorphism and the presence of a sexual size dimorphism in this false killer whale population.

Clasp and dance: Mating mode promotes variable sexual size and shape dimorphism trajectories in crocodile newts (Caudata: Salamandridae)

Sexual dimorphism (SD) is a main source of intraspecific morphological variation, however sexual shape dimorphism (SShD) was long time neglected in evolutionary research. Especially in cold-blooded animal groups only subtle shape differences are expressed between males and females and the selective forces behind it are poorly understood. Crocodile newts of the genera Echinotriton and Tylototriton are highly polymorphic in their reproductive ecology and hence, are a highly suitable model system to investigate potential evolutionary forces leading to SShD differences. We applied 3D geometric morphometrics to the cranial and humerus morphology of nine species of crocodile newts to investigate patterns of SShD in relation to the different mating modes. Trajectories of shape differences between males and females differ in both, cranium and humerus but mating mode does explain differences in SShD trajectories between species only in cranial morphology. Nevertheless, cranial morphology shape differed between the amplecting and circle dancing species. Hence, other selective forces must act here. Variable interspecific allometric trajectories are a potential source of shape differences whereas these trajectories are quite stable for the sexes irrespective of the species.

Unraveling the Morphological Variation of Triatoma infestans in the Peridomestic Habitats of Chuquisaca Bolivia: A Geometric Morphometric Approach

Morphometrics has been used on Triatomines, a well-known phenotypically variable insect, to understand the process of morphological plasticity and infer the changes of this phenomenon. The following research was carried out in two regions of the inter-Andean valleys and two Chaco regions of Chuquisaca-Bolivia. Triatoma infestans adults were collected from the peridomestic (pens and chicken coops) along a geographic gradient in order to evaluate the morphological differentiation between groups and their pattern of sexual shape dimorphism. Geometric morphometric methods were applied on the wings and heads of T. infestans. The main findings include that we proved sexual dimorphism in heads and wings, determined the impact of environmental factors on size and shape and validated the impact of nutrition on head shape variation. These results show that geometric morphometric procedures can be used to provide key insight into the biological adaptation of T. infestans on different biotic (nutrition) and abiotic (environment) conditions, which could serve in understanding and evaluating infestation processes and further vector control programs.

Environmental convergence in facial preferences: a cross-group comparison of Asian Vietnamese, Czech Vietnamese, and Czechs

It has been demonstrated that sociocultural environment has a significant impact on human behavior. This contribution focuses on differences in the perception of attractiveness of European (Czech) faces as rated by Czechs of European origin, Vietnamese persons living in the Czech Republic and Vietnamese who permanently reside in Vietnam. We investigated whether attractiveness judgments and preferences for facial sex-typicality and averageness in Vietnamese who grew up and live in the Czech Republic are closer to the judgements and preferences of Czech Europeans or to those of Vietnamese born and residing in Vietnam. We examined the relative contribution of sexual shape dimorphism and averageness to the perception of facial attractiveness across all three groups of raters. Czech Europeans, Czech Vietnamese, and Asian Vietnamese raters of both sexes rated facial portraits of 100 Czech European participants (50 women and 50 men, standardized, non-manipulated) for attractiveness. Taking Czech European ratings as a standard for Czech facial attractiveness, we showed that Czech Vietnamese assessments of attractiveness were closer to this standard than assessments by the Asian Vietnamese. Among all groups of raters, facial averageness positively correlated with perceived attractiveness, which is consistent with the "average is attractive" hypothesis. A marginal impact of sexual shape dimorphism on attractiveness rating was found only in Czech European male raters: neither Czech Vietnamese nor Asian Vietnamese raters of either sex utilized traits associated with sexual shape dimorphism as a cue of attractiveness. We thus conclude that Vietnamese people permanently living in the Czech Republic converge with Czechs of Czech origin in perceptions of facial attractiveness and that this population adopted some but not all Czech standards of beauty.

Shape variation of the prawn Macrobrachium jelskii (Palaemonidae: Decapoda) in the Neotropical semiarid drainages: an intra- and inter-basin investigation

The present study aims to show the intra- and inter-basin body-shape variations of the freshwater prawn Macrobrachium jelskii (Miers, 1877) in Brazilian Neotropical semiarid basins, quantifying relations to address if its occurrence is old and natural or recent and artificial (anthropic). We used a geometric-morphometric tool to explore patterns of shape variation of the cephalothorax, abdomen and cheliped regarding eco-evolutionary traces (sexual dimorphism, hydrodynamism and geographical isolation) among the drainages. The sexual shape dimorphism was observed in cephalothorax and abdomen of females, which presented more horizontally stretched than in males, possibly favouring gonadal development, vitellogenesis and egg attachment. No apparent hydrodynamic trend was observed in the morpho-space. Moreover, no consensus was shown in the morpho-space about the geographic isolation in semiarid basins regarding the three body-structure planes. However, the abdominal plane indicates a low population/basin structure, which can be an indirect reflection of variations of vitellogenesis in eggs modulated by environmental factors. Furthermore, morphometric variations show low phenotypic plasticity, which is supported by the literature, indicating a scenario of non-natural distribution.

Measuring the Inter and Intraspecific Sexual Shape Dimorphism and Body Shape Variation in Generalist Ground Beetles in Russia

Ground beetles in multiple species vary greatly in the expression of the shape on sexual traits, resulting in a sexual shape dimorphism as a consequence of sexual selection differences. The present research focuses on the study of inter and intrasexual sexual shape dimorphism of two generalist genera of ground beetles Pterostichus and Carabus. Geometric morphometric methods were applied to five generalist species of ground beetles Carabus exaratus, C. granulatus, Pterostichus melanarius, P. niger, and P. oblongopunctatus and several multivariate analyses were applied for two different traits, abdomen and elytra. Three of the five species analyzed showed high levels of sex-based shape dimorphism. However, the most generalist species, P. melanarius and P. oblongopunctatus, did not evidence shape-based sexual dimorphism differentiation in both of the analyzed traits, as statistically confirmed based on the permutation of pairwise comparison of the Mahalanobis distances of a sex–species classifier. It is generally known that environmental stress in natural populations can affect the fitness expression, principally related to sexual fecundity, being that this pattern is more evident in non-generalist species. In our results, the contrary pattern was found, with the absence of sexual shape dimorphism for two of the three generalist species analyzed. On the other hand, the interspecies shape variation was clearly identified using principal component analysis of both of the analyzed traits. Finally, this research is the first to analyze the relationship between sexual shape dimorphism in Russian ground beetles, evidencing the lack of understanding of the mechanism underlying the sexual dimorphism, especially in species living in extreme environments.

Cues for facial attractiveness and preference of sexual dimorphism: A comparison across five cultures

It has been hypothesised that the strength of association between sex typicality and attractiveness follows an adaptive pattern across cultures. Such pattern allows for adjustment of individual preferences for facial cues associated with direct (parenting) and indirect (biological quality) benefits from mating with a potential mate according to environmental conditions. To test this hypothesis, we examined associations among intra-culturally perceived sex typicality, attractiveness, measured skin lightness, measured averageness, and sexual dimorphism of shape from facial images, while controlling for age, body mass, and facial width, in five distinct cultures with different environmental and socioeconomic conditions (Cameroon, N of facial stimuli = 200, 100 women; Colombia, N = 138, 66 women; Czechia, N = 100, 50 women; Iran, N = 87, 43 women; and Turkey, N = 185, 93 women). Our results suggest that measured sexual shape dimorphism and averageness are not significantly associated with neither perceived sex typicality nor attractiveness across the cultures. In all samples of female faces, however, perceived sex typicality was positively related to facial attractiveness. Women found perceived sex typicality in men as more attractive only in the Czech environment, with its relatively abundant resources, and in Colombia, which is a highly socioeconomically heterogeneous and competitive culture. Lighter skin raised the ratings of both attractiveness and sex typicality only in Cameroonian women. Darker men were perceived significantly more sex-typical but not more attractive in Cameroonian, Colombian, and Iranian samples. Altogether, our results highlight the need to control for which measure of sexual dimorphism is used (perceived or measured) and make a detailed description of the local environment. It is the perceived, rather than measured, sexual dimorphism that is associated with perceived attractiveness, and wealth distribution, rather than public, health that seems to affect masculinity preferences.