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Developmental Instability: Causes and Consequences

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Abstract

Fear lives among Everest’s mighty ice-fluted faces and howls across its razor-sharp crags. Gnawing at reason and enslaving minds, it has killed many and defeated countless others. But in 1953, Edmund Hillary and Tenzing Norgay stared into its dark eye and did not waver. On May 29, they pushed spent bodies and aching lungs past the achievable to pursue the impossible. At a terminal altitude of 29,028 feet, they stood triumphant atop the highest peak in the world. With nimble words and a straightforward style, New Zealand mountaineering legend Hillary recollects the bravery and frustration, the agony and glory that marked his Everest odyssey. From the 1951 expedition that led to the discovery of the Southern Route, through the grueling Himalayan training of 1952, and on to the successful 1953 expedition led by Colonel John Hunt, Hillary conveys in precise language the mountain’s unforgiving conditions. In explicit detail he recalls an Everest where chaotic icefalls force costly detours, unstable snow ledges promise to avalanche at the slightest misstep, and brutal weather shifts from pulse-stopping cold to fiendish heat in mere minutes. In defiance of these torturous conditions, Hillary remains enthusiastic and never hesitates in his quest for the summit. Despite the enormity of his and Norgay’s achievement, he regards himself, Norgay, and the other members of his expedition as hardworking men, not heroes. And while he never would have reached the top without practiced skill and technical competence, his thrilling memoir speaks first to his admiration of the human drive to explore, to understand, to risk, and to conquer.

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... However, in the process of natural development, small disturbances or errors occur that have cumulative effects independently on both sides, causing an asymmetry of the structure [2]. Asymmetry can occur due to the influence of genetic and environmental factors [2,3]. The study of asymmetry has many theoretical and practical applications in conservation biology, quantitative genetics, evolutionary biology, medicine, and agriculture, among others [3,4]. ...
... Asymmetry can occur due to the influence of genetic and environmental factors [2,3]. The study of asymmetry has many theoretical and practical applications in conservation biology, quantitative genetics, evolutionary biology, medicine, and agriculture, among others [3,4]. Deviations from perfect symmetry can be measured as variances (or related measures of dispersion) of linear dimensions, variation in shape involving reference points, or continuous symmetry measures [5,6]. ...
... In the present study, for the length and width of the ears and the horn perimeter of the SM creole bovines, the bilateral differences point towards a fluctuating asymmetry, biased towards right for ear width and horn perimeter, and towards left for ear and horn length. Since the development of these structures-ears and horns-is under the control of the same set of genes [3,4,14], the fluctuating asymmetry could constitute a reflection of a normal condition. It has been reported that fluctuating asymmetry may be associated with damage to the horns [35]; however, in this study, during the collection of information, no damage was observed in the horns of the animals. ...
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Simple Summary The Sanmartinero creole bovine (SM) is found in the department of Meta (Colombian Orinoquia) and derives from the bullfighting cattle introduced by the Spanish in the 15th century. Its adaptation process has allowed it to develop adaptive characteristics to live in extreme climatic environments. Although there are studies on its reproductive and productive characteristics, little is known about possible asymmetries in some biological structures. Fluctuating asymmetry allows us to detect a possible developmental instability that may be caused by stressful conditions. The aim of our study was to present the current state of developmental instability in two bilateral cephalic characters of the SM creole bovine. The results showed a fluctuating asymmetry biased to the left for ear and horn length, and to the right for ear width and horn perimeter. We consider that the environment in which it lives may have an impact on the development of cephalic structures, creating stress in the animal, which causes the detected asymmetry. However, the authors are not aware of any studies on this topic. Abstract Asymmetric studies can indicate disturbances in the developmental process. Fluctuating asymmetry (FA) is considered an indicator of stress. The Sanmartinero (SM) creole bovine is native to the department of Meta (Colombian Orinoquia) and its adaptation process has allowed it to live in extreme tropical environments. The aim of this cross-sectional and descriptive study was to present the current state of the knowledge of asymmetries in some cephalic characters of the SM creole bovine. A total of 94 animals were studied (18 uncastrated males and 76 females) from three different farms, with an age range of 0.5–10 years. For each animal, two measurements of the ear (width and length) and two measurements of the horn (perimeter and length) were obtained in vivo. The degree of asymmetry was calculated as (R − L)/(R + L). Bilateral differences pointed towards a fluctuating asymmetry (e.g., a random variation in the trait that is expected to be perfectly symmetrical) biased towards right for ear width and horn perimeter, and towards left for ear and horn length. Since the development of these structures—ears and horns—is under the control of the same set of genes, the fluctuating asymmetry could constitute a reflection of a normal condition.
... Fluctuating asymmetry (FA)-defined as random deviations from symmetry in traits that are otherwise bilaterally symmetrical-has been repeatedly demonstrated to reflect a morphological proxy for the frequency and/or magnitude of stress events experienced by an individual (Badyaev et al., 2000;Lens et al., 1999;Polak, 2003;Sherman et al., 2009;Weller & Ganzhorn, 2004). As bilateral traits share a common genome (Klingenberg, 2015;Polak, 2003), the presence of FA is a manifestation of developmental instabilities that disrupt typical developmental patterns, resulting in the phenomenon of asymmetry (Møller, 1991;Palmer & Strobeck, 1986;Waddington, 1957). ...
... Fluctuating asymmetry (FA)-defined as random deviations from symmetry in traits that are otherwise bilaterally symmetrical-has been repeatedly demonstrated to reflect a morphological proxy for the frequency and/or magnitude of stress events experienced by an individual (Badyaev et al., 2000;Lens et al., 1999;Polak, 2003;Sherman et al., 2009;Weller & Ganzhorn, 2004). As bilateral traits share a common genome (Klingenberg, 2015;Polak, 2003), the presence of FA is a manifestation of developmental instabilities that disrupt typical developmental patterns, resulting in the phenomenon of asymmetry (Møller, 1991;Palmer & Strobeck, 1986;Waddington, 1957). Though literature documenting FA is vast and variable, our understanding of how demographic factors such as age and sex influence FA-as well as when individuals may be most susceptible to developmental disruptions-remains ambiguous, particularly within the context of broad-scale ecological catastrophes. ...
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As natural disasters become more frequent due to climate change, understanding the biological impact of these ecological catastrophes on wild populations becomes increasingly pertinent. Fluctuating asymmetry (FA), or random deviations from bilateral symmetry, is reflective of developmental instability and has long been positively associated with increases in environmental stress. This study investigates craniofacial FA in a population of free‐ranging rhesus macaques ( Macaca mulatta ) that has experienced multiple Category 3 hurricanes since the colony's inception on Cayo Santiago, including 275 individuals from ages 9 months to 31 years (F = 154; M = 121). Using geometric morphometrics to quantify FA and a linear mixed‐effect model for analysis, we found that sex, age, and decade of birth did not influence the amount of FA in the individuals included in the study, but the developmental stage at which individuals experienced these catastrophic events greatly impacted the amount of FA exhibited ( p = .001). Individuals that experienced these hurricanes during fetal life exhibited greater FA than any other post‐natal developmental period. These results indicate that natural disasters can be associated with developmental disruption that results in long‐term effects if occurring during the prenatal period, possibly due to increases in maternal stress‐related hormones.
... Furthermore, these physiological and psychological fitness indicators overlap in the expected direction, where positive physiological indicators tend to correlate with positive psychological indicators [82,83], suggesting the possibility of a single factor underlying both. Note that these "fitness indicators" are themselves explained to varying degrees by the overlapping theories of classical evolution [84], sexual selection [85], and developmental instability [86,87], but here we present them only as examples of mental characteristics (such as those captured in "c"). In the present study, we do find some evidence supporting the "fitness indicator" explanation for "c". ...
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While both psychopathology and cognitive deficits manifest in mental health disorders, the nature of their relationship remains poorly understood. Recent research suggests a potential common factor underlying both domains. Using data from the Philadelphia Neurodevelopmental Cohort (N = 9494, ages 8–21), we estimated and validated a “c” factor representing overall cerebral functioning through a structural model combining cognitive and psychopathology indicators. The model incorporated general factors of psychopathology (“p”) and cognitive ability (“g”), along with specific sub-domain factors. We evaluated the model’s criterion validity using external measures, including parent education, neighborhood socioeconomic status, global functioning, and intracranial volume, and assessed its predictive utility for longitudinal psychosis outcomes. The model demonstrated acceptable fit (CFI = 0.98, RMSEA = 0.021, SRMR = 0.030), and the “c” factor from this model showed stronger associations with parent education (r = 0.43), neighborhood SES (r = 0.47), and intracranial volume (r = 0.39) than “p” and “g” factors alone. Additionally, baseline “c” factor scores significantly predicted psychosis spectrum outcomes at follow-up (d = 0.30–0.57). These findings support the utility of a “c” factor in capturing overall cerebral function across cognitive and psychopathology domains, with potential implications for understanding brain function, improving clinical assessment, and optimally focusing interventions.
... The eco-evolutionary theory of developmental instability posits that (i) minor, non-directional deviations from perfect symmetry in morphological traits-known as fluctuating asymmetry (FA)arise when an individual is unable to buffer against environmental or genetic stress during development and (ii) lower developmental stability, reflected by greater FA, signals an individual's 'lower quality', leading to reduced mate attraction and diminished genetic fitness (Gavrikov et al., 2023;Møller & Swaddle, 1997;Polak, 2003;Waddington, 1942). This theory is straightforward, intuitively appealing, internally coherent, and thus compelling; it meets all the criteria that Fagerström (1987) outlined as characteristics of a successful ecological theory. ...
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Májeková et al. (2024) demonstrated that leaf fluctuating asymmetry (FA) is not a reliable indicator of stress. I broaden the perspective on the findings by these authors. High prevalence of confirmation bias could explain why as much as 39% of 131 unique entries (plant species × stress type) in the database of published studies compiled by these authors showed the significant increase in FA with stress. The use of blind methods should be considered obligatory for any study addressing environmental or genetic impacts on FA. Both data and conclusions from FA‐related studies that did not report blinding should only be used when proof of negligible impact from confirmation bias can be provided. It is essential that all measures taken against biases are described in each submitted manuscript, and that the need to check for these requirements is included in instructions for reviewers. Read the free Plain Language Summary for this article on the Journal blog.
... At the same time, asymmetries in the structure of various body segments can be observed in phylogeny and ontogeny [7]. Estimating the symmetry or asymmetry of anatomical structures can indicate "developmental stability" at different stages of ontogeny [17]. The variation of both right and left measurements and descriptive characteristics indicates the existence of fluctuating asymmetry. ...
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Background: The leg interosseous membrane (LIM) stabilises the tibia and the fibula. These two bones articulate at the proximal and distal tibiofibular joints. In addition, the LIM is the place of attachment of tibialis anterior muscle, extensor digitorum longus muscle, fibularis tertius muscle (anatomical variant), tibialis posterior muscle and flexor hallucis longus muscle. The specific structure of the collagen fibre network of the LIM provides durability comprising collagenous fibres that are predominately projected longitudinally, obliquely, and often transversely. Materials and methods: 222 human foetuses (Male: 120, Female: 102) between 117 and 197 (median 177) days of foetal life were available for the study. The material derived from the foetal collection is stored in the Department of Human Morphology and Embryology, Division of Anatomy of the Medical University of Wroclaw. In this study, we assessed the variability of the foetal LIM using a novel dyeing technique to identify the LIM syndesmotic structure. Results: Overall, the study of the three types of interosseous fibres (transverse, oblique, longitudinal) of the right/left leg revealed that the fibres run in all three directions with frequencies approximating 60-70%. However, there were differences in the frequency of fibre directions and in the size of LIM between sexes. Conclusions: After consideration of the directions and size of fibres of LIM, parts of it can be used for reconstruction of the upper limb interosseous membrane. Sexually dimorphic features of the LIM in the studied material confirm the different dynamics of lower limb growth in each sex.
... Variation often presents in the form of distinct phenotypes which are not present in normal individuals. It can also manifest in subtle ways due to developmental instability (Polak, 2003). Developmental instabilities are deviations from normal morphological development due to epigenetic disturbance (Zakharov, 1992). ...
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Trait functionality can act as a constraint on morphological development. Traits that become vestigialized can exhibit unstable developmental patterns such as fluctuating asymmetry (FA) and variation in populations. We use clearing and staining along with morphometric analyzes to compare FA and allometry of limbs in Western lesser sirens ( Siren nettingi ) to Ouachita dusky salamanders ( Desmognathus brimleyorum ) . Our results describe new carpal phenotypes and carpal asymmetry in our sample of S. nettingi . However, we found no significant evidence of limb length asymmetry in S. nettingi . The degree of relative limb asymmetry correlates inversely with body size in both of our samples. This work provides strong evidence of increased mesopodal variation within a population of S. nettingi . Our work provides a basis for further study of a broader range of morphological traits across salamanders.
... Because FA results from random events during development, scholars have found it useful to generate a measure of the magnitude of FA for each individual to evaluate developmental imprecision by proxy (e.g., Møller & Swaddle, 1997;Polak, 2003). ...
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Objectives Historical evidence from 18th‐ and 19th‐century England suggests that industrialization's impacts on health were largely negative, especially among marginalized groups. However, available documentary evidence is often biased toward adult men and rarely sheds light on the experiences of other members of the population, such as women and children. Craniofacial fluctuating asymmetry (FA) can serve as a proxy measurement of developmental instability and stress during development. This study examines the associations among age, sex, socioeconomic status (SES), and FA in skeletal samples from industrial‐era England. Materials and Methods The sample for this study comes from four industrial‐era cemeteries from England (A.D. 1711–1857). Geometric morphometric analyses of three‐dimensional landmark coordinate data were used to generate a measure of FA for each individual (Mahalanobis distance). A three‐way ANOVA was used to evaluate the impacts of sex, SES, and FA scores on adult age at death ( n = 168). Results Significant associations existed between age at death and SES ( p = 0.004) and FA scores ( p = 0.094). Comparisons of the estimated means indicated that age at death was consistently higher among high SES individuals and individuals with FA scores less than one standard deviation from the mean. Conclusions This study supports findings from previous studies that have suggested that the differences in resource access and environmental buffering generated by socioeconomic inequality can impact longevity and patterns of mortality among socioeconomic status groups. Likewise, stress in early life—evinced by craniofacial fluctuating asymmetry—can influence observed patterns of longevity in adults decades later.
... Fluctuating asymmetry is the result of the influence of exogenous factors during embryogenesis and is strongly dependent upon the growth speed of the developing fetus. It is represented by random deviations from perfect symmetry between the left and right sides of bilateral traits (Polak, 2003;Zakharov & Graham, 1992). According to Wertheim (2011), the asymmetry of volar pads observed during the critical developmental stage leads to asymmetrical ridge configurations of the terminal (permanent) pattern type. ...
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Dermatoglyphic patterns are permanently established and matured before the 24th week of gestation. Their frequencies and localization might be a good indicator of developmental instability in individuals with an altered neurodevelopment and show potential as biomarkers of autism spectrum disorder (ASD). In this study, fingerprint pattern counts and fluctuating asymmetry in the distribution of patterns are compared between 67 boys diagnosed with ASD (aged 5.11 ± 2.51 years) and 83 control boys (aged 8.58 ± 3.14 years). Boys with ASD had a higher rate of discordance in their fingerprint patterns ( p = .0026), showing more often bilateral differences in the occurrence of certain patterns. A chi‐square test revealed that the difference in pattern frequencies between boys with ASD and the control group is the most significant in frequencies of whorls, tented arches, and ulnar loops. Boys with ASD have significantly fewer ulnar loops, significantly more whorls, and tented arches in the right hand. The achieved results are in favor of the suggestion that prenatal influences, which play a role in the development of bilateral differences in fingerprint patterns up to the 24th week of gestation, may be a potential cause of an altered neurodevelopment in ASD individuals.
... A AF diz respeito à diferença entre os lados direito e esquerdo de características que sob condições ideais deveriam apresentar simetria bilateral, porém, são afetadas pelo estresse epigenético durante o desenvolvimento do indivíduo (Anciães & M a r i n i , 2000). Acredita-se que a AF reflita a incapacidade dos organismos de minimizar o efeito de perturbações aleatórias sobre o seu desenvolvimento e, consequentemente, o nível de estresse a que são submetidos (Polak, 2003). Dessa forma, a existência de AF em todos os grupos genéticos para aves de ambos os sexos e sistemas intensivo e semi-intensivo demonstrou que esses animais foram submetidos a estresse durante o desenvolvimento, fato que pode afetar a produtividade. ...
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Fluctuating asymmetry (FA) is a technique that, based on the measurement of discrete or continuous characteristics on both sides of the individual, aims to assess whether ontogenetic development has been affected by external stressors. Stress in chickens can trigger several problems, from cannibalism to premature termination of laying, affecting animal welfare and productivity. Thus, the objective was to investigate the existence of FA in the shape and size of the head of native birds of the Peloco, Caneludo do Catolé and Canela Preta genetic groups and commercial lineage CBC, as well as to identify whether the environment and the rearing system can be considered stressors for birds. Birds from the three native genetic groups, as well as birds from the commercial lineage CBC showed FA in head shape and size, probably related to the environment, especially to chronic heat stress, given the high temperatures of the rearing environment. As for the birds of the Peloco genetic group, there was a greater sensitivity to stress when kept in confinement, as the males of this group raised in an intensive system showed undesirable social behavior, such as cannibalism.
... Calvarial development aims to achieve a symmetric paired structure (Elliot, 2010), and deviations from this "target" morphology could result from individual or population developmental stress/noise (ecologic input) (Urbanova et al., 2014) and could be profoundly consequential in both brain and behavior of the species. Useful inferences about such biological processes may be made since morphological asymmetry may provide information on a variety of biological mechanisms such as developmental stability devoid of congenital malformations occurring as dorsal and ventral notches which substrates in neurological disorders such as syringomelia and cerebellar protrusions (Polak, 2003). There is a lack of documented evidence on the development of the skull relative to cognition in this species, thus making accurate taxonomic classification and discrimination among similar extant species conjectural, especially for trafficked Pangolin. ...
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We present a postnatal evaluation of skull developmental signaling in small African pangolin emphasizing structural, and cognitive trend in ontogeny for assessment of developmental instability, proper identification and classification, forty digitally processed skulls and foramen magnum from different geo-locations were assessed for asymmetry, foramen magnum shape and modularity using geometric and Elliptical Fourier analyses. Multivariate analysis of regression demonstrated low (p < 0.5) but directional fluctuating asymmetry (F1539 = 3.4045, F882 = 3.2665, dorsal and ventral views). Allometric trajectories followed rostrocaudal, caudolateral directions; Intercepts for shape/size predictions were parallel. Mahalanobis distances between centroids (2.42) were significant (p < 0.01). The variance-covariance matrix in ontogeny lies between 0.0017 and 0.56. Foramen magnum outline descriptors by incremental harmonics revealed first 4 effective PCs defined 96.98% of shape properties and 3.02% constituted finerdetails. 74.1% accuracy decline after size factor elimination. Modulation PCA of covariance matrix and asymmetry component was 88.38% and 7.48% (PC1 and 2), respectively, the variance % predicted 10.08%. The studied samples confirmed 'handedness' and fluctuating asymmetries. Foramen magnum shape assumed priority over size in ontogeny with profound asymmetry (from the 5th harmonic), suggestive of compensations to lateralization in neural integration modules.
... (2) this inability to sustain stress indicates the "low quality" of an organism and results in its low genetic fitness [1][2][3][4]. This theory is simple, easily grasped, internally consistent, and, therefore, attractive; that is, it fully meets the conditions which, according to Fagerström [5], define the success of an ecological theory. ...
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The eco-evolutionary theory of developmental instability predicts that small, non-directional deviations from perfect symmetry in morphological traits (termed fluctuating asymmetry, FA) emerge when an individual is unable to buffer environmental or genetic stress during its development. Consequently, FA is widely used as an index of stress. The goal of the present study was to experimentally test a seemingly trivial prediction derived from the theory of developmental instability—and from previous observational studies—that significant growth retardation (which indicates stress) in plants is accompanied by an increase in FA of their leaves. We induced stress, evidenced by a significant decrease in biomass relative to control, in cucumber (Cucumis sativus), sweet pepper (Capsicum annuum), and common bean (Phaseolus vulgaris) by applying water solutions of copper and nickel to the soil in which plants were grown. Repeated blind measurements of plant leaves revealed that leaf FA did not differ between stressed and control plants. This finding, once again, demonstrated that FA cannot be seen as a universal indicator of environmental stress. We recommend that the use of FA as a stress index is discontinued until the scope of the developmental instability theory is clarified and its applicability limits are identified.
... Randomness in asymmetry, fluctuating asymmetry, has been of interest to biologists for a long while [115][116][117][118][119], not merely because of its asymmetry as such, but also as an indirect index of developmental stability resulting from developmental buffering [120]. Comprehensive reviews are available of the origins and nature of fluctuating asymmetry and its applications [121][122][123]. ...
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Recent fMRI and fTCD studies have found that functional modules for aspects of language, praxis, and visuo-spatial functioning, while typically left, left and right hemispheric respectively, frequently show atypical lateralisation. Studies with increasing numbers of modules and participants are finding increasing numbers of module combinations, which here are termed cerebral polymorphisms—qualitatively different lateral organisations of cognitive functions. Polymorphisms are more frequent in left-handers than right-handers, but it is far from the case that right-handers all show the lateral organisation of modules described in introductory textbooks. In computational terms, this paper extends the original, monogenic McManus DC (dextral-chance) model of handedness and language dominance to multiple functional modules, and to a polygenic DC model compatible with the molecular genetics of handedness, and with the biology of visceral asymmetries found in primary ciliary dyskinesia. Distributions of cerebral polymorphisms are calculated for families and twins, and consequences and implications of cerebral polymorphisms are explored for explaining aphasia due to cerebral damage, as well as possible talents and deficits arising from atypical inter- and intra-hemispheric modular connections. The model is set in the broader context of the testing of psychological theories, of issues of laterality measurement, of mutation-selection balance, and the evolution of brain and visceral asymmetries.
... When developmental noise is stronger than developmental stability in the developing organism, small accidental errors can occur in the pre-set parameters of cellular, biochemical and physiological processes (Mc Adams & Arkin, 1999). The result of developmental noise is the formation of a phenotype with characteristics fluctuating above the level of natural variations (Palmer & Strobeck, 1986;Polak, 2003). Ontogenetic disturbances in developmental stability can be caused by various genetic (Frankham, 2005;Garrido & Perez-Mellado, 2014) or environmental stressors (Anciães & Marini, 2000;Wright & Zamudio, 2002;Schmeller et al., 2011). ...
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This paper summarizes and presents the results from our years-long in situ analyses of the populations of the Marsh frog P. ridibundus and the Green toad B. viridis inhabiting freshwater ecosystems in South Bulgaria with different degrees of anthropogenic transformation. It covers the period 2009-2017 with tests of the application of fluctuating asymmetry in meristic morphological traits as a marker for deviation assessment of the developmental stability of individuals of both species as well as for parallel and independent from physicochemical analyses assessment of the quality of their living environment. The analyses held on the territory of South Bulgaria are divided into three phases: first (2009-2010), second (2011-2015) and third (2016-2017). The results of our investigations conducted over a period of 9 years, show that changes in asymmetry levels in meristic morphological traits in adult and sexually mature representatives of P. ridibundus and B. viridis are a very good bioindication method.
... Fluctuating asymmetry (FA), i.e. small, random deviations from perfect symmetry in otherwise bilaterally symmetrical traits, is widely regarded as an individual-based proxy of environmental and genetic stressors in a variety of taxa [1][2][3][4][5]. As both sides of bilateral traits develop under control of an identical genome, FA is assumed to reflect the inability of organisms to buffer their development against random perturbations, known as developmental instability (DI), and thereby mirror the level of stress to which they are imposed (reviewed in [6,7]. Despite a strong theoretical framework on FA-stress relationships, the observed associations are often weak, species-, population-, or trait-specific [8][9][10], all of which hamper the use of FA as bioindicator in evolutionary ecology and conservation biology [11,12]. ...
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Fluctuating asymmetry (FA) is used to reveal environmental or genetic stress, but the results of some studies are inconsistent. We aimed to give some explanations of possible controversial conclusions, when FA was employed. We measured FA (one dimensional and one – meristic traits) in the recognized bioindicators – ground beetles (Coleoptera, Carabidae). Beetles were sampled in vast area (four provinces of Russia with the spectrum of the studied sites, which differed in antropogenic impact, vegetation, landscape features). On the basis of such measurements (4673 specimen) we performed the data base. Subsequent ANOVA showed, that FA was species-specific (out of 6 species investigated it was expressed in 5 ones), sex-biased (males had higher levels of FA) and were affected practically by all environmental factors. Besides significant species:sex and factors:sex interactions were found. So when employing FA as an indicator of stress, overall biological and ecological variation in species-indicator must be investigated before. Sometimes FA (or its absence) may not be due to pollution or another disturbing factor, but be the result of the effect of unaccounted but FA determinative factors.
... However, whereas FA derives from the variation of two parallel but separate developmental pathways, MI is linked to developmental interactions among traits [13,22]. A high degree of FA can be expected in populations that have undergone severe bottlenecks and experienced high levels of inbreeding, owing to the breakup of regulating gene networks [6,12,14,24]. Conversely, MI has been associated with the variation introduced by developmental interactions and environmental factors at different developmental stages [25]. MI may be driven by bottlenecks and inbreeding, and loss of MI might accelerate evolutionary adaptive shifts of morphological traits, hence facilitating phenotypic evolvability [26][27][28][29][30][31][32]. ...
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We explored fluctuating asymmetry (FA) and morphological integration (MI) in the skull of the small, highly inbred and divergent Apennine bear ( Ursus arctos marsicanus ), to explore its uniqueness and investigate any potential effects of inbreeding depression. We used 3D geometric morphometrics contrasting Apennine bears with other two large outbred bear populations from Scandinavia and Kamchatka as controls. Shape divergence and variability were explored by a principal component analysis on aligned coordinates of 39 landmarks. Procrustes ANOVA, morphological disparity and the global integration index were used to explore FA, shape variance and MI. By remarking Apennine bears as a highly divergent phenotype, we recorded the highest FA and deviation from self-similarity compared with the other two control populations. We conclude that Apennine bears are likely facing developmental instability as a consequence of inbreeding depression, whereas the divergent trait covariance pattern may represent a potential source of evolutionary novelties. We discuss the implications for the conservation and management of this imperiled taxon.
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Variations in plant genotypes and phenotypes are expressed in ways that lead to the development of defensive abilities against herbivory. Induced defenses are mechanisms that affect herbivore insect preferences and performance. We evaluated the performance of resistant and susceptible phenotypes of Bauhinia brevipes (Fabaceae) against attacks by the gall-inducing insect Schizomyia macrocapillata (Diptera). We hypothesized that there is a positive relationship between resistance to S. macrocapillata and host plant performance because resistance can have a high adaptive value. We evaluated plant architecture, nutritional leaf quality, leaf fluctuating asymmetry, and reproductive capacity between phenotypes. Plant performance was evaluated at three ontogenetic stages: seed, seedling, and juvenile. Overall, there were no differences in vegetative and reproductive performance or asymmetry between the resistant and susceptible mature plants. We found no relationship between leaf nutritional quality and resistance to S. macrocapillata. Plant performance was consistent across ontogeny for both phenotypes, except for five variables. Contrary to our expectations, the susceptible plants performed equally well or better than the resistant plants, suggesting that tolerance and overcompensation to herbivory in B. brevipes may be mediated by induced defense. Our study highlights the importance of multiple layers of plant defense against herbivory, where plant tolerance acts as a secondary barrier in plants susceptible to gall-inducing insects.
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Simple Summary As concerns over animal welfare grow, individuals working in animal husbandry need easier ways to assess the psychological wellbeing of livestock. Recent research in lateralisation and stress has helped scientists find links between stress and the sides of the body animals use to inspect new objects and people or engage in new experiences. Research has shown that the left side of the brain processes familiar conditions, while the right side of the brain is more often used for new situations. These sides of the brain correspond to behaviours expressed with the opposite side of the body. Animals often use a specific eye or leg when initiating behavioural responses or interactions which can be assumed to link to the opposite side of the brain. This article summarised the existing literature for lateralisation in common livestock species in addition to advocating for increased use of thermography when assessing welfare in livestock. Abstract Lateralised behavioural responses to environmental stressors have become more frequently used as indicators of social welfare in animals. These lateralised behavioural responses are under the control of asymmetrical brain functions as part of the primary functions of most vertebrates and assist in primary social and survival functions. Lateralised behavioural responses originating from the left hemisphere are responsible for processing familiar conditions, while the right hemisphere is responsible for responding to novel stimuli in the environment. The forced lateralisation and side preference tests have been used to determine the visual lateralised behavioural responses in livestock to environmental stressors. Limb preference during movement has also been used to determine motor lateralisation. Although behavioural investigations in livestock have recorded lateralised behavioural responses to environmental stressors, there are still limitations in the implication of lateralisation to other conditions, such as restraint and invasive procedures. Thus, it is important to have a non-invasive measure for these lateralised behavioural responses. Recently, lateralised behavioural responses have been correlated with the use of infrared temperature of external body surfaces, such as the eyes and coronary bands of limbs. This review summarised the different forms of the lateralised behavioural responses in livestock, especially cattle and horses, to environmental stressors, and the association between these responses and the relevant external body surfaces’ infrared temperature, with the purpose of improving the use of non-invasive measures in assessing welfare conditions in animals. The combination of the lateralised behavioural responses and infrared temperature of external body surfaces to environmental stressors could improve the assessment strategies of welfare conditions and the related additional husbandry interventions that could be applied to improve the welfare of farm animals.
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Small African pangolins (genus Phataginus) presently face a general decline in population due to reduced survivability resulting from captive breeding failure and trafficking. We here present a postnatal evaluation of skull developmental signaling in a small African pangolin, emphasizing evolutionary trends in ontogeny. Forty digitally processed skulls and foramina magna from different geographic locations were assessed for asymmetry, foramen magnum shape and modularity using geometric and elliptical Fourier analyses. Multivariate regression of log transformed centroid size and the asymmetric component of shape suggested significant asymmetry through ontogeny where size accounted for 81.34% of asymmetric shape changes. Analysis of variance demonstrated low but directional fluctuating asymmetry in dorsal and ventral views. Allometric trajectories followed rostro-caudal and caudo-lateral directions; intercepts for shape/size predictions were parallel. Mahalanobis distances between centroids were significant. Foramen magnum outline descriptors by incremental harmonics revealed that the first four effective PCs defined 96.98% of shape properties, and 3.02% constituted finer details. The studied samples confirmed directional “handedness” and fluctuating asymmetries. Foramen magnum shape assumed priority over size in ontogeny with profound asymmetry (from the 5th harmonic), suggestive of attenuated ability of paired symmetric bilaterality of cranial integration modules. Our observation postulates a rapid cranial evolution in the small African pangolin due to natural selection constraints occasioned by population inconsistencies.
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Host- and habitat-induced morphological shape and size variations are common in phytophagous and parasitic taxa. Several integrated morphological and molecular techniques have been commonly used to understand host-induced morpho-cryptic species forms. Compared to other arthropods, cryptic speciation was more common in Acari. This study focused on the host-specific morphological cryptic shape and size variations of Tetranychus neocaledonicus, collected from moringa and cassava hosts. We used geometric morphometric analysis to uncover the shape and size of inter-and intra-spider mite populations and discovered that host-specific shape and size variations existed in spider mites regardless of sex. Interestingly, there was no phylogenetic signal in spider mites, implying that the morpho-cryptic speciation of T. neocaledonicus is solely based on the host-induced selection. The molecular clock hypothesis was accepted in our CO1 and 18s rRNA phylogeny analyses, and spider mites collected from both hosts were genetically less diverse. We conclude that T. neocaledonicus exhibited morphologically detectable cryptic population diversity in each host but that these populations are evolutionarily young form. Apart from these host-induced variations, we also monitored the impact of the clearing agent (lactic acid) on the shape and size of T. neocaledonicus; from this study, we proved that the clearing agent significantly alters the taxonomically important morphological traits of spider mites irrespective of the mites’ sex, as confirmed by multivariate statistical analysis. This is the first study report to investigated the host-induced morphological variations of spider mites and the impact of a clearing agent.
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To gain insight into the evolution of flower traits in the generalized food-deceptive plant Iris pumila, we assessed the color, size, shape, and fluctuating asymmetry (FA) of three functionally distinct floral organs—outer perianths (‘falls’), inner perianths (‘standards’), and style branches—and estimated pollinator-mediated selection on these traits. We evaluated the perianth color as the achromatic brightness of the fall, measured the flower stem height, and analyzed the floral organ size, shape, and FA using geometric morphometrics. Pollinated flowers had significantly higher brightness, longer flower stems, and larger floral organs compared to non-pollinated flowers. The shape and FA of the floral organs did not differ, except for the fall FA, where higher values were found for falls of pollinated flowers. Pollinator-mediated selection was confirmed for flower stem height and for subtle changes in the shape of the fall and style branch—organs that form the pollination tunnel. This study provides evidence that, although all analyzed flower traits play significant roles in pollinator attraction, flower stem height and pollination tunnel shape evolved under the pollinator-mediated selection, whereas achromatic brightness, size, and symmetry of floral organs did not directly affect pollination success.
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The horns and antlers borne by the males of many species of ungulate are considered to be both badges of quality, and armaments for use during intraspecific combat. Underpinning arguments concerning their dual utility is the idea that these structures should be costly to produce in order that the signal value of the structure is maintained. In agreement with such theorising is the belief that fluctuating asymmetry (FA), small deviations from symmetry around a mean of zero, measures individual quality as it represents the ability of the individual to withstand stress. We investigated whether the antlers of fallow deer indicated something of the quality of the bearer by assessing whether the degree of antler FA was associated with breakage (i.e., badge of quality) or with tactical investment in fighting (i.e., armament). We show the anticipated relationship between FA and antler damage, however, there was no relationship between FA and contest tactics. The present study, therefore, shows partial support for the idea that the magnitude of fluctuating asymmetry expressed by weaponry is related to individual quality.
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This study addresses the problem of concordance in fluctuating asymmetry (FA) across traits by analyzing the relationship between FAs and the mean values of character measurements in a set of morphological traits. Regression slopes vary in natural populations, thus, revealing discordance in FA across traits among these populations. Hence, commonly accepted techniques for measuring developmental instability with FA result in uncertainties. Here, I relate FA to mean as a two-dimensional complex to demonstrate the uniformly negative slopes of standardized FA vs. mean value regressions for sets of morphological traits from eighteen distinct natural marine and aquatic populations. Comprehensive analysis of the FA–mean complex cannot be recommended for wide use in assessing stress and fitness, but it offers promise to improve FA measuring methodologies and to better understand the nature of developmental instability.
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Size and shape are important determinants of fitness in most living beings. Accordingly, the capacity of the organism to regulate size and shape during growth, containing the effects of developmental disturbances of different origin, is considered a key feature of the developmental system. In a recent study, through a geometric morphometric analysis on a laboratory-reared sample of the lepidopteran Pieris brassicae, we found evidence of regulatory mechanisms able to restrain size and shape variation, including bilateral fluctuating asymmetry, during larval development. However, the efficacy of the regulatory mechanism under greater environmental variation remains to be explored. Here, based on a field-reared sample of the same species, by adopting identical measurements of size and shape variation, we found that the regulatory mechanisms for containing the effects of developmental disturbances during larval growth in P. brassicae are also effective under more natural environmental conditions. This study may contribute to better characterization of the mechanisms of developmental stability and canalization and their combined effects in the developmental interactions between the organism and its environment.
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Directional asymmetry in testes size is commonly documented in vertebrates. The degree of testes size asymmetry has been confirmed to be associated with natural and sexual selection. However, the role of natural and sexual selection driving variations in testes size asymmetry among species of anurans are largely unknown. Here, we studied the patterns of variations in testes size asymmetry and the factors shaping its variations among 116 anuran species. The results indicated that the left size-biased testes in 110 species (94.83% of 116 species) is more common than the right size-biased testes in six species. For all studied species, the degree of testes size asymmetry was positively associated with relative livers and body fat mass, following the prediction of the packaging hypothesis. We also found that the postcopulatory sperm competition (e.g., residual testes size) was positively associated with the degree of testes asymmetry. However, environmental stress (e.g., high latitude, precipitation seasonality and temperature seasonality) did not promote more symmetrical testes for all species. Our findings suggest that both natural selection for larger livers in body space and sexual selection for rapid increase in testis mass for most species during the breeding season can play key roles in driving in testes size asymmetry across anuran species.
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Variation of the meristic characteristics of pholidosis in the sand lizard, Lacerta agilis, was studied both in laboratory experiments and in natural populations. The total phenotypic variability was assessed by the variation of the sum of the number of scales on the left and on the right sides of the body (l + r), while the measure of developmental stability, providing insight into the degree of fluctuating asymmetry, or developmental variability, was assessed by the variation of the difference in the character values on the left and on the right (l − r). Experimental incubation of eggs at different temperatures demonstrates that the minimal level of both kinds of variability corresponds to a certain temperature, which can be characterized as an optimal one, increasing both with an increase and with a decrease in the temperature from this regime. The data demonstrate the crucial role of the temperature impact for the phenotypic variation under study. An increase in the level of developmental variability to the north and to the south from the center part of the species range, in the absence of an obvious trend in geographic variation of the level of total phenotypic variability, assumes an increase in the role of developmental variability in the observed phenotypic diversity at the periphery of the species range. The results obtained indicate the importance of a population phenogenetic approach, based on the developmental stability study in natural populations, to provide certain information supposing the possible nature of phenotypic diversity in a species range.
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Developmental noise is a variety that is not related to the usually distinguished sources of phenotypic diversity, i.e., differences in the genotype and in the environment. This variation arises in the process of the realization of genetic information and reflects the imperfection of ontogenetic processes. The most common measure of it is the value of fluctuating asymmetry as slight deviations from the symmetry. Developmental noise proves to be one of the main sources of intrapopulation phenotypic diversity. The magnitude of this variability is an ontogenetic response to environmental or genetic stress, and its assessment, in fact, provides a unique opportunity to estimate the developing system condition. The level of developmental noise, characterizing an organism’s condition, acts as another population parameter that allows to approach the evaluation of the community condition. Initial deviations in the system condition can be detected even against the background of optimal estimates of abundance, biodiversity, and ecosystem functioning.
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Bringing together a variety of accomplished dental researchers, this book covers a range of topics germane to the study of human and other primate teeth. The chapters encompass work on individuals to samples, ranging from prehistoric to modern times. The focus throughout the book is the methodology required for the study of modern dental anthropology, comprising the scientific methods in use today - ranging from simple observation to advanced computer-based analyses - which can be utilized by the reader in their own dental research. Originating from the 20th anniversary meeting of the Dental Anthropology Association, this is a valuable reference source for graduate students, academic researchers and professionals in the social and life sciences, as well as clinicians.
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This study aimed to evaluate and measure the occurrence of jaw and palate asymmetry based on 3D-printed stereolithographic models of edentulous elderly people. The analyses were performed on 3D models of the jaws, which were printed using the data (CT) obtained from the CBCT center. The control group consisted of 10 modern adult skulls (7 male and 3 female skulls) owned by the Department of Anthropology of the Wrocław University of Environmental and Life Sciences. The small size of the studied groups did not allow for the performance of the analysis indicating the form of the observed morphological asymmetry—it was impossible to differentiate to indicate whether the examined features showed directional or fluctuating asymmetry. However, it was possible to determine the direction of the morphological asymmetry of the analyzed features. Both in the test group and the control group, it was a right-sided asymmetry. The analysis of the significance of differences in mean values of the asymmetry index showed that the intensity of asymmetry of the anterior part of the superior alveolar arch was significantly greater in the test group. The severity of the asymmetry of the lateral part of the alveolar arch in the tested groups did not differ significantly. The authors concluded that adequate maxillary height does not only influence proper dental prosthesis adhesion but also corresponds with a potential source for correct dental implant placement. We also concluded that the vertical height of the edentulous alveolar process of the mandible is important for adequate prosthesis fixing. In some cases, the bone atrophy and the bone itself are asymmetrical, so planning a prosthesis might be challenging. The adequate placement of implants should include the symmetry of jaw bones because of future masticatory force impact on the bone and the entire masticatory system, including the temporomandibular joint.
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Developmental instability (DI) is an individual's inability to produce a specific developmental outcome under a given set of conditions, generally thought to result from random perturbations experienced during development. Fluctuating asymmetry (FA) — asymmetry on bilateral features that, on average, are symmetrical (or asymmetry deviating from that arising from design) — has been used to measure DI. Dating to half a century ago, and accelerating in the past three decades, psychological researchers have examined associations between FA (typically measured on bodily or facial features) and a host of outcomes of interest, including psychological disorders, cognitive ability, attractiveness, and sexual behavior. A decade ago, a meta-analysis on findings from nearly 100 studies extracted several conclusions. On average, small but statistically reliable associations between FA and traits of interest exist. Though modest, these associations are expected to greatly underestimate the strength of associations with underlying DI. Despite the massive sample size across studies, we still lack a good handle on which traits are most strongly affected by DI. A major methodological implication of the meta-analysis is that most studies have been, individually, woefully underpowered to detect associations. Though offering some intriguing findings, much research is the past decade too has been underpowered; hence, the newer literature is also likely noisy. Several large-scale studies are exceptions. Future progress depends on additional large-scale studies and researchers’ sensitivity to power issues. As well, theoretical assumptions and conceptualizations of DI and FA driving psychological research may need revision to explain empirical patterns.
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There are many environmental and genetic factors that disrupt the stable structure of development in organisms. Although the strength of these vary, they leave certain signs in the body structure. Fluctuating asymmetry is a widely used population-level index of developmental instability, developmental noise, and robustness. Many bilateral traits are used in fluctuating asymmetry studies in humans. These traits include dermatoglyphics, limb lengths and widths, bilateral facial characters, and teeth. In this review, I evaluate the measurement methods of many bilateral anthropometric characters, taken from the bodies of living individuals with classical digital calipers.
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The symmetry of a human organism’s structure is an expression of the general law of development regarding organic life. Assessing the symmetry of the face and its individual components is one of the most important factors when it comes to the overall assessment of a patient’s stomatognathic system and is essential in the planning of orthodontic and prosthetic treatment. The aim of this study is to assess the symmetry of the occurrence and the measurement parameters of the pre-angular notch of the mandible. The study included computed tomography scans of 187 patients who all exhibited a visible pre-angular notch in the mandible. There was a noticeable and measurable asymmetry in the length of the angle of the notches as well as in the area of the notch angles. The differentiation of the right- and left-side measurements points to the existence of a fluctuating asymmetry. Other measurements which describe the pre-angular notch of the lower jaw do not show asymmetry.
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Fluctuating asymmetry (FA) may serve as a reliable indicator of the functional importance of structures within an organism. Primary locomotor structures often display lower levels of FA than other paired structures, highlighting that selection can maintain symmetry in fitness-enhancing traits. Polyphenic species represent an attractive model for studying the fine-scale relationship between trait form and function, because multiple morphs exhibit unique life history adaptations that rely on different traits to maximize fitness. Here, we investigated whether individuals of the wing polyphenic sand field cricket (Gryllus firmus) maintain higher levels of symmetry in the bilateral structures most vital for maximizing fitness based on their specific life history strategy. We quantified FA and directional asymmetry (DA) across a suite of key morphological structures indicative of investment in somatic growth, reproduction, and flight capability for males and females across the flight-capable longwing (LW) and flight-incapable shortwing (SW) morphs. Although we did not find significant differences in FA across traits, hindwings lacked DA that was found in all other structures. We predicted that functionally important traits should maintain a higher level of symmetry; however, locomotor compensation strategies may reduce the selective pressures on symmetry or developmental constraints may limit the optimization between trait form and function.
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Fluctuating asymmetry as a special kind of asymmetry can be defined as deviations from a known predetermined ratio of the parts of morphological structure under study. As a special type of phenotypic variability fluctuating asymmetry is a manifestation of ontogenetic noise or developmental variability. This type of variability is ubiquitous and plays a significant role in the observed phenotypic diversity. The level of fluctuating asymmetry turns out to be an indicator of optimal developmental conditions and genetic coadaptation. It is also considered as a parameter of fitness. Thus, fluctuating asymmetry acts as a measure of developmental stability in developmental biology and as a measure of population condition in population biology.
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Studies of shape asymmetry have become increasingly abundant as the methods of geometric morphometrics have gained widespread use. Most of these studies have focussed on fluctuating asymmetry and have largely obtained similar results as more traditional analyses of asymmetry in distance measurements, but several notable differences have also emerged. A key difference is that shape analyses provide information on the patterns, not just the amount of variation, and therefore tend to be more sensitive. Such analyses have shown that apparently symmetric structures in animals consistently show directional asymmetry for shape, but not for size. Furthermore, the long-standing prediction that phenotypic plasticity in response to environmental heterogeneity can contribute to fluctuating asymmetry has been confirmed for the first time for the shape of flower parts (but not for size). Finally, shape analyses in structures with complex symmetry, such as many flowers, can distinguish multiple types of directional asymmetry, generated by distinct direction-giving factors, which combine to the single component observable in bilaterally symmetric structures. While analyses of shape asymmetry are broadly compatible with traditional analyses of asymmetry, they incorporate more detailed morphological information, particularly for structures with complex symmetry, and therefore can reveal subtle biological effects that would otherwise not be apparent. This makes them a promising tool for a wide range of studies in the basic and applied life sciences.
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The integration of complex structures is proportional to the intensity of the structural fusion; its consequences are better known than the covariational effects under less restrictive mechanisms. The synthesis of a palimpsest model based on two early parallel pathways and a later direct pathway explains the cephalothoracic complexity of decapod crustaceans. Using this model, we tested the evolvability of the developmental modularity in Aegla araucaniensis, an anomuran crab with an evident adaptive sexual dimorphism. The asymmetric patterns found on the landmark configurations suggest independent perturbations of the parallel pathways in each module and a stable asymmetry variance near the fusion by canalization of the direct pathway, which was more intense in males. The greater covariational flexibility imposed by the parallel pathways promotes the expression of gonadic modularity that favors the reproductive output in females and agonistic modularity that contributes to mating success in males. Under these divergent expressions of evolvability, the smaller difference between developmental modularity and agonistic modularity in males suggests higher levels of canalization due to a relatively more intense structural fusion. We conclude that: (1) the cephalothorax of A. araucaniensis is an evolvable structure, where parallel pathways promote sexual disruptions in the expressions of functional modularity, which are more restricted in males, and (2) the cephalothoracic palimpsest of decapods has empirical advantages in studying the developmental causes of evolution of complex structures.
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Empirical studies of phenotypic variation show that genetic and environmental heterogeneity account for only part of it. Usually, the magnitude of the residual variation is comparable with that of the genetic component, while notably exceeding the magnitude of the environmental component. This can be interpreted in two ways. A deterministic interpretation associates it with artifacts such as measurement error and genetic and environmental heterogeneity that is unaccounted for. An indeterministic interpretation argues that it is random or stochastic phenotypic variation (SPV) resulting from developmental instability - a developing organism's inability to produce a consistent phenotype in a given environment. Classical example of debates between determinists and indeterminists took place about a century ago in quantum physics. In discussing Heidelberg's Uncertainty Principle, Einstein metaphorically expressed his deterministic position: 'God does not play dice with universe'. The indeterministic Uncertainty Principle, however, was eventually widely accepted. Currently, most biologists implicitly or explicitly support deterministic interpretations of phenotypic variation patterns. Here, a wide range of data on morphological traits (studied with analysis of fluctuating asymmetry) and non-morphological traits are analyzed to provide evidence that SPV is not an artifact, but a valid phenomenon. This evidence supports conclusions that observed associations between SPV and stress can be analyzed in the framework of dynamic energy budget theory, and are inextricably linked through energy homeostasis.
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Background: Morphological integration refers to the tendency of anatomical structures to show correlated variations because they develop in response to shared developmental processes or function in concert with other structures. The objective of this study was to determine the relationships between the dimensions of different cranial-cervical-facial structures in patients with Down syndrome (DS). Methodology: The study group consisted of 41 individuals with DS who had undergone cone-beam computed tomography (CBCT) at the Dental Radiology Unit of the University of Santiago de Compostela (Spain). In the historical archive of this same unit, 41 CBCTs belonging to individuals with no known systemic disorders or severe malformations of the maxillofacial region were selected, forming an age and sex-matched control group. Twenty-nine measurements were performed on each participant's CBCT images, which were grouped into three blocks: atlantoaxial dimensions, craniovertebral dimensions and cephalometric dimensions. To determine whether there were significant differences between the dimensions obtained in the DS and control groups, we applied multiple analysis of variance and linear discriminant analysis tests. The analysis of the association between blocks (in pairs) was performed with the canonical correlation analysis test. Results: The dimensions evaluated in the three blocks of variables of individuals with DS differ significantly from those of nonsyndromic controls (p < 0.001). The highest discriminative capacity to identify controls and patients with DS was obtained with the cephalometric dimensions (87.5%). With regard to the association between blocks (two-by-two measurements), we found no significant relationship in the DS group. However, we confirmed a statistically significant correlation between all pairs of blocks of variables in the controls, especially between the atlantoaxial and cephalometric dimensions (p < 0.001) and between the craniovertebral and cephalometric dimensions (p < 0.001). Conclusions: Our results confirm a very poor morphological integration of the cranial-cervical-maxillary complex in individuals with DS. This finding reinforces the proposal that gene overload enhances the channeling process.
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Significance Theoretically, symmetry in bilateral animals is subject to sexual selection, since it can serve as a proxy for genetic quality of competing mates during mate choice. Here, we report female preference for symmetric males in Drosophila , using a mate-choice paradigm where males with environmentally or genetically induced wing asymmetry were competed. Analysis of courtship songs revealed that males with asymmetric wings produced songs with asymmetric features that served as acoustic cues, facilitating this female preference. Females experimentally evolved in the absence of mate choice lost this preference for symmetry, suggesting that it is maintained by sexual selection.
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Fluctuating asymmetry (FA) is a morphometric tool used to measure developmental instability in organisms which have been exposed to stress or other adverse conditions. Phenotypic variability in response to stressors are the result of interactions between genomes and the environment, acting in a noisy developmental system. Most of the organisms have bilateral symmetry with a repetition of structures in different positions or orientations; asymmetrical variation has been a morphological response associated with insecticide application inducing disturbances in endocrinal system product of the chemicals. Triatoma infestans (is the main vector of Chagas disease in South America. The availability of food sources varies for populations of T. infestans living in different habitats; insects that inhabit the intradomicile feed preferentially on human blood, whereas insects that develop in the peridomicile feed on the blood of the other mammals and birds. The following research evaluate the FA to the different ecotopes in two geographical areas of Chuquisaca Bolivia; Yamparáez/Sotomayor of the high inter-Andean valleys and Huacaya/Imbochi of the boreal Chaco and a CIPEIN laboratory strain population. A combination of advanced morphometrics tools and multivariate analysis were used to quantify the levels of asymmetry produced by pyretroid near to the peridomiciles in Bolivia. Populations from Yamparáez/Sotomayor were found to have higher levels of FA which the combination of environmental conditions such as low temperatures avoid greater permanence in the habitat and more exposition to insecticide. A better understanding of the combination of these tools will allow researchers to implement better public policies to regulate insecticide applications and to understand how certain organisms adapt to multiple stressors.
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Understanding how environmental variation influences even cryptic traits is important to clarify the roles of selection and developmental constraints in past evolutionary divergence and to predict future adaptation under environmental change. Female yellow dung flies (Scathophaga stercoraria) typically have three sperm storage compartments (3S), but occasionally four (4S). More spermathecae are thought to be a female adaptation facilitating sperm sorting after mating, but the phenotype is very rare in nature. We manipulated the flies' developmental environment by food restriction, pesticides, and hot temperatures to investigate the nature and extent of developmental plasticity of this trait, and whether spermatheca expression correlates with measures of performance and developmental stability, as would be expected if 4S expression is a developmental aberration. The spermathecal polymorphism of yellow dung fly females is heritable, but also highly developmentally plastic, varying strongly with rearing conditions. 4S expression is tightly linked to growth rate, and weakly positively correlated with fluctuating asymmetry of wings and legs, suggesting that the production of a fourth spermatheca could be a nonadaptive developmental aberration. However, spermathecal plasticity is opposite in the closely related and ecologically similar Scathophaga suilla, demonstrating that overexpression of spermathecae under developmental stress is not universal. At the same time, we found overall mortality costs as well as benefits of 4S pheno‐ and genotypes (also affecting male siblings), suggesting that a life history trade‐off may potentially moderate 4S expression. We conclude that the release of cryptic genetic variation in spermatheca number in the face of strong environmental variation may expose hidden traits (here reproductive morphology) to natural selection (here under climate warming or food augmentation). Once exposed, hidden traits can potentially undergo rapid genetic assimilation, even in cases when trait changes are first triggered by random errors that destabilize developmental processes. Female yellow dung flies (Scathophaga stercoraria) express 3 or 4 sperm storage organs, the related S. suilla 2 or 3 (right). Is this a developmental aberration, or an adaptive trait for sperm sorting? Environmental change (heat, pesticides, abundant food) augments developmental errors and induces spermathecal variation in proportion to growth rate, which can expose previously hidden traits to natural selection to produce a new beneficial function. Female yellow dung flies naturally vary in number of sperm storage compartments (3S or 4S). This spermathecal polymorphism is strongly heritable but also developmentally plastic. 4S expression is linked to growth rate and weakly correlated with fluctuating asymmetry, so potentially a developmental aberration. There are mortality costs as well as benefits for 4S phenotypes, suggesting adaptive life‐history trade‐offs. Spermathecal plasticity differs in the closely related and ecologically similar Scathophaga suilla. Environmental changes can expose hidden traits with initially no function to natural selection. Female yellow dung flies naturally vary in number of sperm storage compartments (3S or 4S). This spermathecal polymorphism is strongly heritable but also developmentally plastic. 4S expression is linked to growth rate and weakly correlated with fluctuating asymmetry, so potentially a developmental aberration. There are mortality costs as well as benefits for 4S phenotypes, suggesting adaptive life‐history trade‐offs. Spermathecal plasticity differs in the closely related and ecologically similar Scathophaga suilla. Environmental changes can expose hidden traits with initially no function to natural selection.
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We are interested here in the central organ of our thoughts: the brain. Advances in neuroscience have made it possible to obtain increasing information on the anatomy of this organ, at ever-higher resolutions, with different imaging techniques, on ever-larger samples. At the same time, paleoanthropology has to deal with partial reflections on the shape of the brain, on fragmentary specimens and small samples in an attempt to approach the morphology of the brain of past human species. It undeniably emerges from the perspective we propose here that paleoanthropology has much to gain from interacting more with the field of neuroimaging. Improving our understanding of the morphology of the endocast necessarily involves studying the external surface of the brain and the link it maintains with the internal surface of the skull. The contribution of neuroimaging will allow us to better define the relationship between brain and endocast. Models of intra- and inter-species variability in brain morphology inferred from large neuroimaging databases will help make the most of the rare endocasts of extinct species. We also conclude that exchanges between these two disciplines will also be beneficial to our knowledge of the Homo sapiens brain. Documenting the anatomy among other human species and including the variation over time within our own species are approaches that offer us a new perspective through which to appreciate what really characterizes the brain of humanity today.
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Key message Leaf symmetry and leaf size are explained by genetic variation between and within lineages and to a lesser extent by climatic factors, while leaf asymmetry can only be partly explained by geographic factors in Quercus aquifolioides Rehder & E.H. Wilson. ContextLeaves are the primary photosynthetic organs of plants, and their morphology affects various crucial physiological processes potentially linked to fitness.AimsWe explored the variation in leaf morphology of an alpine oak, Quercus aquifolioides, in order to examine its relationship to genetic, geographic, and climatic factors.Methods We conducted a genetic survey using 25 nuclear microsatellites. Based on Bayesian clustering analysis, 273 sampled trees from 29 populations of Q. aquifolioides were assigned to two lineages that correspond to the Western Sichuan Plateau-Hengduan Mountains (WSP-HDM) and Tibet geographic areas, with some individuals showing mixed ancestry. To undertake morphological analyses, we collected 1435 leaves from these trees and characterized them in terms of 13 landmarks. The metric dimensions of these leaves were digitally captured in the two-dimensional coordinates of these landmarks, then divided into leaf size and symmetric and asymmetric components of leaf shape. To analyze how different components of leaf morphology vary across lineages, we employed Procrustes Analysis of Variance (ANOVA), two-block partial least-square analysis (2B-PLS), and several other multivariate analysis approaches. We also applied distance-based redundancy analysis (dbRDAs) to explore relations between leaf morphology and genetic, geographic, and climatic factors.ResultsMultivariate analysis indicated significant differentiation in leaf symmetric shape components and leaf size between the WSP-HDM and Tibet lineages, while the mixed individuals were morphologically intermediate. The dbRDA analysis showed that most of the variation in symmetric components and leaf size was explained by genotypic effects, with the symmetric components of leaf shape being also significantly explained by geography and climate; however, variation in asymmetric components is only very weakly explained by geography.Conclusion Our results demonstrated that leaf morphological variation in shape and size across Q. aquifolioides geographic range is related to both its genetic differentiation and to a lesser extent to climatic factors. We discuss how these patterns could be interpreted in terms of both geographical isolations among and within lineages, and possible adaptive responses for particular traits, in contrast to asymmetric variation.
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Fluctuating Asymmetry (FA) in morphology is used as a proxy for developmental instability in response to stress factors. FA has important implications for understanding the impact of differential environments and stressors on the skeletal phenotype. Here, we explore FA in the mandibular morphology of wild and captive Macaca fuscata to detect differences induced by the captive environment. We use two different approaches in Geometric Morphometrics to characterise the degree and patterns of FA and Directional Asymmetry (DA) based on 3D mandibular landmarks. Our results show that the wild and captive groups exhibit morphological dissimilarities in the symmetric component of shape while no significant degree of asymmetry (fluctuating or directional) was detected. Based on our results and on previous literature on the subject, we suggest that (I) captivity is likely to affect the mandibular morphology of M. fuscata; (II) FA may not be a suitable indicator to detect stress in the conditions analysed; and that (III) the mandible may not be the ideal region to study asymmetry because of its functional nature.
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Background Developmental instability in archaeological samples can be detected through analysis of skeletal and dental remains. During life, disruptions to biological internal homeostasis that occur during growth and development redirect bodily resources to returning to homeostasis and away from normal processes such as symmetrical development. Because dental enamel does not remodel in life, any deviations from normal development are left behind. Even subtle disturbances to developmental trajectory may be detected in asymmetrical development of traits, specifically a random variation in sides termed fluctuating asymmetry. Human dental fluctuating asymmetry studies are common, but here we investigate the permanent dentition of a non-human primate Papio anubis , for potential fluctuating asymmetry relative to sex, weaning, and reproductive maturity. The sample stems from an outlier population that lives in the wettest and most humid habitat of any studied baboon group. Methods The skulls of adult baboons were collected after their natural death in Gashaka Gumti National Park, Nigeria. The permanent dentition of antimeric teeth (paired) were measured for maximum length and breadth using standard methods. The metrics were analyzed to assess the presence of fluctuating asymmetry in adult permanent mandibular and maxillary dentition. Measurement error and other forms of asymmetry (antisymmetry, directional asymmetry) were considered and dental measures expressing true fluctuating asymmetry were used to address three research questions. Results Males exhibit greater fluctuating asymmetry than females, suggesting that males experience greater overall instability during the developmental period. While weaning is not more stressful than other life history stages for males and females (using the first molar fluctuating asymmetry index as a proxy compared to other teeth), it is more stressful for females than males. The onset of reproduction is also not more stressful than other life history stages for males and females (using the third molar fluctuating asymmetry index as a proxy compared to other teeth), but it is more stressful for males than females. We explore possible explanations for these findings in the discussion.
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Fluctuating asymmetry (FA) is an indicator of developmental instability referred to random deviations from mean asymmetry. That average asymmetry is the directional asymmetry (DA), which, in the particular case of adolescent idiopathic scoliosis (AIS), corresponds to a right thoracic and left lumbar curves. Investigating the presence of FA and DA in AIS has never been done, and it is a key element of the pathophysiology of the scoliotic condition. Thirty‐six X‐rays of patients with AIS were digitized and analysed using Geometric Morphometric analyses to test for both statistical effects. The individual FA score for each patient was calculated using Procrustes ANOVA and a methodology based on the components of shape was used to estimate the individual DA score. DA is a stronger effect than FA (2.12 to 1), as it has been found in other clinical conditions. The individual DA score, with an effect size of 0.58, is a better predictor of the Cobb angle than FA score. The methodology presented in this paper to estimate DA score is a valid approach in the study of asymmetries in AIS. FA should be correlated in future studies with environmental covariates to serve as a variable in the medical prognosis, while DA will serve as a good predictor of the Cobb angle during the course of the condition, avoiding the abuse of X‐rays. This potential use of DA should be tested on 3D shape due to the three‐dimensional clinical presentation of AIS. A new methodology has been developed that measures directional and fluctuating asymmetry, and these individual scores make it possible to predict the Cobb angle (from the DA score) and measure developmental instability (from the FA score) in patients with adolescent idiopathic scoliosis.
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Phenotypic variation arises from genetic and environmental variation, as well as random aspects of development. The genetic (nature) and environmental (nurture) components of this variation have been appreciated since at least 1900. The random developmental component (noise) has taken longer for quantitative geneticists to appreciate. Here, I sketch the historical development of the concepts of random developmental noise and developmental instability, and its quantification via fluctuating asymmetry. The unsung pioneers in this story are Hugo DeVries (fluctuating variation, 1909), C. H. Danforth (random variation between monozygotic twins, 1919), and Sewall Wright (random developmental variation in piebald guinea pigs, 1920). The first pioneering study of fluctuating asymmetry, by Sumner and Huestis in 1921, is seldom mentioned, possibly because it failed to connect the observed random asymmetry with random developmental variation. This early work was then synthesized by Boris Astaurov in 1930 and Wilhelm Ludwig in 1932, and then popularized by Drosophila geneticists beginning with Kenneth Mather in 1953. Population phenogeneticists are still trying to understand the origins and behavior of random developmental variation. Some of the developmental noise represents true stochastic behavior of molecules and cells, while some represents deterministic chaos, nonlinear feedback, and symmetry breaking.
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The rapid and selective responses to changes in habitat structure and climate have made butterflies valuable environmental indicators. In this study, we asked whether the decline in butterfly populations near the copper-nickel smelter in Monchegorsk in northwestern Russia is accompanied by phenotypic stress responses to toxic pollutants, expressed as a decrease in body size and an increase in fluctuating asymmetry. We measured the concentrations of nickel and copper, forewing length, and fluctuating asymmetry in two elements of wing patterns in Boloria euphrosyne, Plebejus idas, and Agriades optilete collected 1–65 km from Monchegorsk. Body metal concentrations increased toward the smelter, confirming the local origin of the collected butterflies. The wings of butterflies from the most polluted sites were 5–8% shorter than those in unpolluted localities, suggesting adverse effects of pollution on butterfly fitness due to larval feeding on contaminated plants. However, fluctuating asymmetry averaged across two hindwing spots did not change systematically with pollution, thereby questioning the use of fluctuating asymmetry as an indicator of habitat quality in butterfly conservation projects.
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Background: Fluctuating asymmetry is often used as an indicator of developmental instability, and is proposed as a signal of genetic quality. The display of prominent masculine phenotypic features, which are a direct result of high androgen levels, is also believed to be a sign of genetic quality, as these hormones may act as immunosuppressants. Fluctuating asymmetry and masculinity are therefore expected to covary. However, there is lack of strong evidence in the literature regarding this hypothesis. Materials and methods: In this study, we examined a large dataset of high-density 3D facial scans of 1260 adults (630 males and 630 females). We mapped a high-density 3D facial mask onto the facial scans in order to obtain a high number of quasi-landmarks on the faces. Multi-dimensional measures of fluctuating asymmetry were extracted from the landmarks using Principal Component Analysis, and masculinity/femininity scores were obtained for each face using Partial Least Squares. The possible correlation between these two qualities was then examined using Pearson's coefficient and Canonical Correlation Analysis. Results: We found no correlation between fluctuating asymmetry and masculinity in men. However, a weak but significant correlation was found between average fluctuating asymmetry and masculinity in women, in which feminine faces had higher levels of fluctuating asymmetry on average. This correlation could possibly point to genetic quality as an underlying mechanism for both asymmetry and masculinity; however, it might also be driven by other fitness or life history traits, such as fertility. Conclusions: Our results question the idea that fluctuating asymmetry and masculinity should be (more strongly) correlated in men, which is in line with the recent literature. Future studies should possibly focus more on the evolutionary relevance of the observed correlation in women.
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