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Bilateral symmetry is quite common in animals, but in some cases, asymmetry can be altered by hereditary or developmental processes. Symmetry may be preserved, or asymmetry may increase as the developmental stages progress. This study applied geometric morphometric analyses at the juvenile and adult stages to investigate directional asymmetry and fluctuating asymmetry in turtle shells. In total, 71 turtle shells (46 adults, 25 juveniles) of Testudo hermanni boettgeri were used. These turtle shells were recorded using the Generalized Procrustes method to interpret developmental asymmetry. A covariance matrix was then applied, followed by principal component analysis. Analysis of Variance (ANOVA) was used to explain individual variation. The procedures were applied and interpreted separately to the carapace and plastron. Specific structures, such as the nuchal and neural plates, exhibited a narrower shape than the mean shape configuration in directional asymmetry. The epiplastron region showed significant enlargement in juveniles compared to adults, potentially linked to developmental growth. This study investigated fluctuating asymmetry (FA) and directional asymmetry (DA) in turtle shells by analyzing the carapace and plastron. Although wavy asymmetry was not statistically significant overall, localized shape differences between the edges of the coastal and neural plates of the carapace and the edges of the plastron were observed. The side effects showed statistical significance (p = 0.0005). Environmental or developmental factors may have influenced these differences. Directional asymmetry was statistically significant for the carapace and plastron, indicating consistent shape changes associated with developmental growth. This study revealed significant directional asymmetry in the carapace and plastron of Testudo hermanni boettgeri, reflecting consistent developmental trends.

Three FA indices showed correlations with age and magnitude of traits, but not in general. Significant correlations between magnitude of traits and their FA were more pronounced in AFA (12 traits) than in RFA (10 traits) in all age classes except yearlings. For the tray tine form (curvature), FA significantly correlated with its magnitude in young, middle-aged and ripe stags, which indicates that the trait is a reliable indicator of asymmetry. Significant differences in AFA among age classes were found in four traits (weight of dry antlers, volume of antlers, distal circumference of beams and total length of crown tines). By RFA, a significant difference among age classes was only found for the distal circumference of beams. Thus, AFA is a more vulnerable condition index. Contrary to other research findings, developmental instability was more pronounced in older age classes. In yearlings, no significant FA dependence on the trait of antler size was detected, but in certain traits, an asymmetry detected at an early age remains visible later as well, although in stags grown under relatively optimal (especially trophic) environment conditions, developmental instability was present anyway. This proposes two hypotheses for further research: Competition may be manifested even under controlled conditions, which might jeopardize the developmental stability of certain individuals, or some traits will show developmental instability regardless of relatively good environmental conditions.

Multiple indicators have been used to assess the degree of exposure of fish to anthropogenic chemicals in their stream habitats. We hypothesized that brook stickleback (Culaea inconstans) in a headwater stream receiving urban and agricultural runoff (South Fork Whitewater River, SFWR) would exhibit poorer condition, reduced reproductive fitness, and a greater left side to right side morphological asymmetry (i.e., fluctuating asymmetry or FA) than fish from a nearby headwater stream with a forested drainage basin (Garvin Brook). Male and female fish were collected from both streams just prior to spawning in 2013–2015. In 2013 and 2014, fish were assessed for overall condition (Fulton’s K), internal measures of condition (hepatosomatic index, HSI) and reproductive fitness (gonadosomatic index [GSI], total oocyte count, and oocyte mass). In 2015, measurements of head length, jaw length, eye diameter, pectoral fin length, and pelvic fin length were made on both sides of each fish for assessing degree of FA. We observed declining condition with fish size, increased liver size, and reduced oocyte counts and oocyte size in female brook stickleback in SFWR relative to those from Garvin Brook. SFWR females had significantly higher FA than Garvin females for all structures assessed, except pelvic fin length. FA also was slightly higher for all structures in SFWR males compared to Garvin males, but differences were not significant. A composite FA index combining all measurements from an individual fish into a single value displayed highly significant differences for female fish (SFWR FA >> Garvin FA), but not for male fish (SFWR FA = Garvin FA). Exposure of brook stickleback to reduced water quality in SFWR during early development appears to increase morphological asymmetry in female (but not male) fish, and continuing exposure to compromised water quality throughout life impacts both general condition and reproductive fitness of stickleback, especially older female fish, in SFWR.

This study aimed to observe the type of asymmetry exhibited by Porcellio laevis sampled from 15 sites belonging to Tunisian industrialized areas. Physicochemical parameters such as pH, organic matter and CaCO3 contents were measured in soils. Moreover, Cd, Pb, Zn, and Cu concentrations were determined in both soils and woodlice. Additionally, 10 metrical traits were measured to evaluate the type of asymmetry on individuals: the basis, the second and the third articles of the antenna, the first article of the flagellum of the antenna and the merus, the carpus, and the propodus of the sixth and the seventh pereopods. Among the 531 measured individuals, 432 exhibited fluctuating asymmetry (FA) while the remaining individuals exhibited antisymmetry or directional asymmetry. The data obtained were analyzed using a multivariate statistical analysis. Contrary to our hypothesis, the results showed that individuals from contaminated sites have a low FA level, whereas those from uncontaminated sites have a high FA level, particularly females but with some exceptions. Variations in FA level in the traits and populations studied and its usefulness as a stress indicator were discussed.

Facial fluctuating asymmetry (FA), presumably a proxy measure of developmental instability, has been proposed to inversely relate to vocal attractiveness, which may convey information on heritable fitness benefits. Using an improved method of measuring facial FA, we sought to replicate two recent studies that showed an inverse correlation of facial FA with vocal attractiveness. In two samples of men ( N = 165) and women ( N = 157), we investigated the association of automatically measured facial FA based on 3D face scans with male and female observer-rated attractiveness of voice recordings. No significant associations were found for men or women, also when controlling for facial attractiveness, age, and body mass index. Equivalence tests show that effect sizes were significantly smaller than previous meta-analytic effects, providing robust evidence against a link of facial FA with vocal attractiveness. Thus, our study contradicts earlier findings that vocal attractiveness may signal genetic quality in humans via an association with FA.

This paper formulates the problem of measuring bilateral symmetry of objects analytically for landmark data, and develops various new testing procedures and exploratory data analyses. The development is linked with the fundamental biological problem of measuring directional asymmetry and fluctuating asymmetry. We distinguish two types of symmetry, object symmetry and matching symmetry, and provide tests under assumptions of isotropic landmark variability as well as non-isotropy. The tests require novel statistical and geometrical analyses of the Procrustes shape manifold. For describing components of symmetry and asymmetry within samples, an extension of principal component analysis is introduced and illustrated by appropriate deformation techniques. Various real examples are used to illustrate the practical relevance of this work.

Disturbance from the normal developmental trajectory of a trait during growth—the so-called developmental instability—can be observed morphologically through phenodeviants and subtle deviations from perfect symmetry (fluctuating asymmetry). This study investigates the relationship between phenodeviance in the human vertebral column (as a result of axial patterning defects) and limb fluctuating asymmetry. Since both types of markers of developmental instability have been found associated with congenital abnormalities in humans, we anticipate a relationship between them if the concept of developmental instability, measured through either phenodeviants or asymmetry, would reflect an organism-wide process. Yet we did not find any support for this hypothesis. We argue that the vast differences in the developmental processes involved in both systems renders these two markers of developmental instability unrelated, in spite of their associations with other congenital abnormalities. Our results thus contribute to the growing awareness that developmental instability is not an organism-wide property.

Fluctuating asymmetry (FA) represents small, non-directional deviations from perfect symmetry in morphological characters. FA is generally assumed to increase in response to stress; therefore, FA is frequently used in ecological studies as an index of environmental or genetic stress experienced by an organism. The values of FA are usually small, and therefore the reliable detection of FA requires precise measurements. The reproducibility of fluctuating asymmetry (FA) was explored by comparing the results of measurements of scanned images of 100 leaves of downy birch (Betula pubescens) conducted by 31 volunteer scientists experienced in studying plant FA. The median values of FA varied significantly among the participants, from 0.000 to 0.074, and the coefficients of variation in FA for individual leaves ranged from 25% to 179%. The overall reproducibility of the results among the participants was rather low (0.074). Variation in instruments and methods used by the participants had little effect on the reported FA values, but the reproducibility of the measurements increased by 30% following exclusion of data provided by seven participants who had modified the suggested protocol for leaf measurements. The scientists working with plant FA are advised to pay utmost attention to adequate and detailed description of their data acquisition protocols in their forthcoming publications, because all characteristics of instruments and methods need to be controlled to increase the quality and reproducibility of the data. Whenever possible, the images of all measured objects and the results of primary measurements should be published as electronic appendices to scientific papers.

Fluctuating asymmetry (FA), in contrast with other asymmetries, is the bilateral asymmetry that represents small, random developmental differences between right and left sides. After nearly a century of using traditional morphometrics in the estimation of FA, geometric morphometrics (GM) now provides new insights into the use of FA as a tool, especially for assessing environmental and developmental stress. Thus, it will be possible to assess adaptation to various environmental stressors as particular triggers for unavoidable selection pressures. In this review, we describe measures of FA that use geometric morphometrics, and we include a flow chart of the methodology. We also describe how this combination (GM + FA) has been tested in several agroecosystems. Nutritional stress, temperature, chemical pollution, and population density are known stressors experienced by populations in agroecosystems.

The prevalence of inter-limb strength differences is well documented in the literature however, there are inconsistencies related to measurement and reporting, and the normative values and effects associated with inter-limb asymmetry. Therefore, the aims of this systematic review were to: 1) assess the appropriateness of existing indices for the calculation of asymmetry, 2) interrogate the evidence basis for literature reported thresholds used to define asymmetry and 3) summarise normative levels of inter-limb strength asymmetry and their effects on injury and performance. To conduct this systematic review, scientific databases (PubMed, Scopus, SPORTDiscus and Web of Science) were searched and a total of 3,594 articles were retrieved and assessed for eligibility and article quality. The robustness of each identified asymmetry index was assessed, and the evidence-basis of the identified asymmetry thresholds was appraised retrospectively using the references provided. Fifty-three articles were included in this review. Only four of the twelve identified indices were unaffected by the limitations associated with selecting a reference limb. Eighteen articles applied a threshold to original research to identify “abnormal” asymmetry, fifteen of which utilised a threshold between 10-15%, yet this threshold was not always supported by appropriate evidence. Asymmetry scores ranged between and within populations from approximate symmetry to asymmetries larger than 15%. When reporting the effects of strength asymmetries, increased injury risk and detriments to performance were often associated with larger asymmetry, however the evidence was inconsistent. Limitations of asymmetry indices should be recognised, particularly those that require selection of a reference limb. Failure to reference the origin of the evidence for an asymmetry threshold reinforces doubt over the use of arbitrary thresholds, such as 10-15%. Therefore, an individual approach to defining asymmetry may be necessary to refine robust calculation methods and to establish appropriate thresholds across various samples and methodologies that enable appropriate conclusions to be drawn.