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Directional Asymmetry (directional + asymmetry)
Selected AbstractsON THE ADAPTIVE ACCURACY OF DIRECTIONAL ASYMMETRY IN INSECT WING SIZEEVOLUTION, Issue 11 2008Christophe Pélabon Subtle left,right biases are often observed in organisms with an overall bilateral symmetry. The evolutionary significance of these directional asymmetries remains uncertain, however, and scenarios of both developmental constraints and adaptation have been suggested. Reviewing the literature on asymmetry in insect wings, we analyze patterns of directional asymmetry in wing size to evaluate the possible adaptive significance of this character. We found that directional asymmetry in wing size is widespread among insects, with left- and right-biased asymmetries commonly observed. The direction of the asymmetry does not appear to be evolutionarily conserved above the species level. Overall, we argue that the very small magnitude of directional asymmetry, 0.7% of the wing size on average, associated with an extremely imprecise expression, precludes directional asymmetry from playing any major adaptive role. [source] BILATERAL DIRECTIONAL ASYMMETRY OF THE APPENDICULAR SKELETON OF THE HARBOR PORPOISE (PHOCOENA PHOCOENA)MARINE MAMMAL SCIENCE, Issue 3 2005Anders Galatius Abstract Directional asymmetry (DA) of the lengths, diameters, and masses of the scapula, humerus, radius, and ulna were analyzed on a sample of 213 harbor porpoises from Denmark and West Greenland. The levels of DA were consistent across yearlings and older animals, mature and immature animals, sexes, and populations. All investigated variables showed significant DA favoring the right side. For the pooled sample, DA of lengths ranged from 0.2% SE 0.1 (ulna) to 1.2% SE 0.1 (scapula). DAs of diameters were 1.5% SE 0.2 for the humerus, 0.6% SE 0.1 for the radius, and 1.3% SE 0.2 for the ulna. DA of mass ranged from 2.8% SE 0.5 (humerus) to 4.3% SE 0.7 (ulna). The humerus and ulna had significantly larger mean diameter/ length ratios on the right side than the left, making them more robust. The large DA of scapula length indicates larger muscle mass associated with the right flipper, while the generally more robust right humerii and ulnae may be designed for higher levels of mechanical stress. These DAs and the examples of lateralized behavior recorded in cetaceans, point to the existence of lateralized use of the flippers at the population level in harbor porpoises and possibly other cetacean species. [source] Directional asymmetry of long-distance dispersal and colonization could mislead reconstructions of biogeographyJOURNAL OF BIOGEOGRAPHY, Issue 5 2005Lyn G. Cook Abstract Aim, Phylogenies are increasingly being used to attempt to answer biogeographical questions. However, a reliance on tree topology alone has emerged without consideration of earth processes or the biology of the organisms in question. Most ancestral-state optimization methods have inherent problems, including failure to take account of asymmetry, such as unequal probabilities of losses and gains, and the lack of use of independent cost estimates. Here we discuss what we perceive as shortcomings in most current tree-based biogeography interpretation methods and show that consideration of processes and their likelihoods can turn the conventional biogeographical interpretation on its head. Location, Southern hemisphere focus but applicable world-wide. Methods, The logic of existing methods is reviewed with respect to their adequacy in modelling processes such as geographical mode of speciation and likelihood of dispersal, including directional bias. Published reconstructions of dispersal of three plant taxa between Australia and New Zealand were re-analysed using standard parsimony and maximum likelihood (ML) methods with rate matrices to model expected asymmetry of dispersal. Results, Few studies to date incorporate asymmetric dispersal rate matrices or question the simplistic assumption of equal costs. Even when they do, cost matrices typically are not derived independently of tree topology. Asymmetrical dispersal between Australia and New Zealand could be reconstructed using parsimony but not with ML. Main conclusions, The inadequacy of current models has important consequences for our interpretation of southern hemisphere biogeography, particularly in relation to dispersal. For example, if repeated directional dispersals and colonization in the direction of prevailing winds have occurred, with intervening periods of speciation, then there is no need to infer dispersals against those winds. Failure to take account of directionality and other biases in reconstruction methods has implications beyond the simple misinterpretation of the biogeography of a taxonomic group, such as calibration of molecular clocks, the dating of vicariance events, and the prioritization of areas for conservation. [source] On hidden heterogeneity in directional asymmetry , can systematic bias be avoided?JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2006L. C. STIGE Abstract Directional asymmetry (DA) biases the analysis of fluctuating asymmetry (FA) mainly because among-individual differences in the predisposition for DA are difficult to detect. However, we argue that systematic bias mainly results from predictable associations between signed right,left asymmetry and other factors, i.e. from systematic variation in DA. We here demonstrate methods to test and correct for this, by analysing bilateral asymmetry in size and shape of an irregular sea urchin. Notably, in this model system, DA depended significantly on body length and geographic origin, although mean signed asymmetry (mean DA) was not significant in the sample as a whole. In contrast to the systematic variation in DA, undetectable, random variability in the underlying DA mainly leads to reduced statistical power. Using computer simulations, we show that this loss of power is probably slight in most circumstances. We recommend future studies on FA to routinely test and correct for not only as yet for mean DA, but also for systematic variation in DA. [source] BILATERAL DIRECTIONAL ASYMMETRY OF THE APPENDICULAR SKELETON OF THE HARBOR PORPOISE (PHOCOENA PHOCOENA)MARINE MAMMAL SCIENCE, Issue 3 2005Anders Galatius Abstract Directional asymmetry (DA) of the lengths, diameters, and masses of the scapula, humerus, radius, and ulna were analyzed on a sample of 213 harbor porpoises from Denmark and West Greenland. The levels of DA were consistent across yearlings and older animals, mature and immature animals, sexes, and populations. All investigated variables showed significant DA favoring the right side. For the pooled sample, DA of lengths ranged from 0.2% SE 0.1 (ulna) to 1.2% SE 0.1 (scapula). DAs of diameters were 1.5% SE 0.2 for the humerus, 0.6% SE 0.1 for the radius, and 1.3% SE 0.2 for the ulna. DA of mass ranged from 2.8% SE 0.5 (humerus) to 4.3% SE 0.7 (ulna). The humerus and ulna had significantly larger mean diameter/ length ratios on the right side than the left, making them more robust. The large DA of scapula length indicates larger muscle mass associated with the right flipper, while the generally more robust right humerii and ulnae may be designed for higher levels of mechanical stress. These DAs and the examples of lateralized behavior recorded in cetaceans, point to the existence of lateralized use of the flippers at the population level in harbor porpoises and possibly other cetacean species. [source] ON THE ADAPTIVE ACCURACY OF DIRECTIONAL ASYMMETRY IN INSECT WING SIZEEVOLUTION, Issue 11 2008Christophe Pélabon Subtle left,right biases are often observed in organisms with an overall bilateral symmetry. The evolutionary significance of these directional asymmetries remains uncertain, however, and scenarios of both developmental constraints and adaptation have been suggested. Reviewing the literature on asymmetry in insect wings, we analyze patterns of directional asymmetry in wing size to evaluate the possible adaptive significance of this character. We found that directional asymmetry in wing size is widespread among insects, with left- and right-biased asymmetries commonly observed. The direction of the asymmetry does not appear to be evolutionarily conserved above the species level. Overall, we argue that the very small magnitude of directional asymmetry, 0.7% of the wing size on average, associated with an extremely imprecise expression, precludes directional asymmetry from playing any major adaptive role. [source] SHAPE ANALYSIS OF SYMMETRIC STRUCTURES: QUANTIFYING VARIATION AMONG INDIVIDUALS AND ASYMMETRYEVOLUTION, Issue 10 2002Christian Peter Klingenberg Abstract., Morphometric studies often consider parts with internal left-right symmetry, for instance, the vertebrate skull. This type of symmetry is called object symmetry and is distinguished from matching symmetry, in which two separate structures exist as mirror images of each other, one on each body side. We explain a method for partitioning the total shape variation of landmark configurations with object symmetry into components of symmetric variation among individuals and asymmetry. This method is based on the Procrustes superimposition of the original and a reflected copy of each landmark configuration and is compatible with the two-factor ANOVA model customary in studies of fluctuating asymmetry. We show a fully multivariate framework for testing the effects in the two-factor model with MANOVA statistics, which also applies to shapes with matching symmetry. We apply the new methods in a small case study of pharyngeal jaws of the Neotropical cichlid fish Amphilophus citrinellus. The analysis revealed that the symmetric component of variation in the pharyngeal jaws is dominated by the contrast between two alternative trophic morphs in this species and that there is subtle but statistically significant directional asymmetry. Finally, we provide some general recommendations for morphometric studies of symmetric shapes. [source] Limb bones asymmetry and stress in medieval and recent populations of Central EuropeINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 5 2008M. Kujanová Abstract Monitoring the degree of asymmetry in different parts of the human body can contribute to population studies, as it may be connected indirectly with the social structure, living conditions, and also with biomechanical stress affecting the person. Analysis of asymmetry may also assess preferential use of the right or left of the body during specific activities. This study is based on the measurements of bones of the upper and lower limbs of skeletons derived from the remarkable medieval cemeteries of Mikul,ice-Kostelisko (78 male, 132 female) and Pru,ánky (66 male, 69 female) (9th,12th centuries AD), and a series of skeletons representing a recent population from Bohemia (143 male, 157 female). The objective was to assess directional asymmetry (DA), fluctuating asymmetry (FA) and antisymmetry (AS) of the dimensions of the evaluated bones, and to use these data to compare the characteristics of the medieval and recent populations. DA was recorded in most dimensions. In the upper limb, the humerus exhibited the greatest expression of asymmetry, and, with the exception of the clavicle, DA was always more pronounced on the right side. Conversely, DA was less prevalent in the lower limb bones. It was more pronounced on the transverse, sagittal and circumferential dimensions of the diaphyses and epiphyses than on the length, and in most cases it was on the left side. The FA values were very low, and almost negligible in relation to the size. Nevertheless, FA was markedly more frequent on the lower than on the upper limb. In contrast to the medieval population, the recent population had higher FA and DA values. Thus, we propose that people from this medieval population were subjected to lower developmental stress than the recent sample. Copyright © 2008 John Wiley & Sons, Ltd. [source] Lifestyle, occupation, and whole bone morphology of the pre-Hispanic Maya coastal population from Xcambó, Yucatan, MexicoINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 3 2007Isabel S. Wanner Abstract The present bioarchaeological study examines the external diaphyseal geometric properties of humeri, radii, femora and tibiae of the Classic period skeletal population of Xcambó, Yucatan, Mexico. The diaphysial proportions are evaluated using a biomechanical approach together with data from the material context and other osteological information. Our intent is to provide new answers to questions concerning lifestyle, domestic labour division and subsistence strategies of this coastal Maya settlement that was inhabited from the Late and Terminal Preclassic (300 BC,350 AD) to the Postclassic Period (900,1500 AD). Our results provide evidence for a marked sexual division of labour when compared with values from contemporaneous inland populations. The overall male and female loading patterns differ remarkably in terms of form and in bilateral comparison. A high directional asymmetry in the upper limbs is evident among males, a condition related to maritime transportation and trading activities. On the other hand, female upper limbs are characterized by very low side differences. Forces on the arms of women were probably dominated by food processing, in particular the grinding of grains or seeds. In the lower limbs, males show significantly higher anteroposterior bending strengths, which can be explained by greater engagement in transportation tasks and carrying heavy loads. In the course of the Classic period (350,900 AD), diachronic changes affect the male sample only, which suggests a shift of occupational pattern and physical demands. This shift, in turn, reflects Xcambó's changing role as the centre of a densifying settlement area and its place in the trading activities of northern Yucatan. Other topics of discussion relate to general regional trends and local prehispanic subsistence strategies. Our conclusions emphasize the value of geometric long bone analysis in the reconstruction of activity patterns and lifestyles in ancient coastal settlements. Copyright © 2007 John Wiley & Sons, Ltd. [source] Response of fluctuating and directional asymmetry to selection on wing shape in Drosophila melanogasterJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2006C. PÉLABON Abstract We tested whether directional selection on an index-based wing character in Drosophila melanogaster affected developmental stability and patterns of directional asymmetry. We selected for both an increase (up selection) and a decrease (down selection) of the index value on the left wing and compared patterns of fluctuating and directional asymmetry in the selection index and other wing traits across selection lines. Changes in fluctuating asymmetry across selection lines were predominantly small, but we observed a tendency for fluctuating asymmetry to decrease in the up-selected lines in both replicates. Because changes in fluctuating asymmetry depended on the direction of selection, and were not related to changes in trait size, these results fail to support existing hypotheses linking directional selection and developmental stability. Selection also produced a pattern of directional asymmetry that was similar in all selected lines whatever the direction of selection. This result may be interpreted as a release of genetic variance in directional asymmetry under selection. [source] On hidden heterogeneity in directional asymmetry , can systematic bias be avoided?JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2006L. C. STIGE Abstract Directional asymmetry (DA) biases the analysis of fluctuating asymmetry (FA) mainly because among-individual differences in the predisposition for DA are difficult to detect. However, we argue that systematic bias mainly results from predictable associations between signed right,left asymmetry and other factors, i.e. from systematic variation in DA. We here demonstrate methods to test and correct for this, by analysing bilateral asymmetry in size and shape of an irregular sea urchin. Notably, in this model system, DA depended significantly on body length and geographic origin, although mean signed asymmetry (mean DA) was not significant in the sample as a whole. In contrast to the systematic variation in DA, undetectable, random variability in the underlying DA mainly leads to reduced statistical power. Using computer simulations, we show that this loss of power is probably slight in most circumstances. We recommend future studies on FA to routinely test and correct for not only as yet for mean DA, but also for systematic variation in DA. [source] Fluctuating and directional asymmetry in young human males: Effect of heavy working condition and socioeconomic status,AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010Özener Abstract Many adverse environmental and genetic factors can affect stability of development during human growth. Although the level of fluctuating asymmetry (FA) may be influenced by environmental and genetic stress encountered during this period, directional asymmetry (DA) is largely attributable to differential mechanical loading during bone growth, for example, handedness. I assessed the effects of heavy working conditions and socioeconomic conditions on asymmetry levels in three groups of young human males: 1) individuals employed in the heavy industry sector (n = 104, mean age = 18.48 ± 0.61 years), 2) individuals who had the same socioeconomic status as the laborers (n = 102, mean age = 18.39 ± 0.58 years) but were not laborers, and 3) nonlaborers from the higher socioeconomic levels of society (n = 103, mean age = 18.43 ± 0.67). For all subjects, hand length, hand width, elbow width, wrist width, knee width, ankle width, foot length, foot width, ear length, and ear width were measured. All measurements of the upper extremities in the labor group appeared to exhibit DA; in the other two groups only hand measurements exhibited DA. According to analysis of FA, subjects living in poor conditions exhibited more FA than their nonlaborer peers living in better conditions. In addition, biomechanical pressures due to heavy working conditions of the labor group appeared to cause increased DA in the upper extremities: DA increased with an increase in the number of years working. Am J Phys Anthropol 143:13,20, 2010. © 2010 Wiley-Liss, Inc. [source] Age estimation from stages of union of the vertebral epiphyses of the ribsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2009Luis Ríos Abstract This study attempts to fill a persistent gap in the literature by documenting the timing of epiphyseal union at the vertebral end of the ribs in a sample of modern Portuguese skeletons. The skeletal remains of 53 females and 45 males, between the ages of 11 and 30, were taken from the Lisbon documented skeletal collection. Individuals in the sample have been previously described as being representative of a middle-to-low socioeconomic segment of the early 20th century Lisbon population. Three anatomical locations were examined for epiphyseal union: the head, the articular tubercle and the nonarticular tubercle. The first epiphysis to show partial union is that of the nonarticular tubercle (females, 11,19 years; males, 11,19 years), followed by the epiphysis of the articular tubercle (females, 11,20 years; males, 16,20 years), and finally by the head epiphysis (females, 15,24 years; males, 16,22 years), which can still show incomplete epiphyseal closure at 25 and 24 years for females and males, respectively. A trend for earlier female maturation was observed, but the statistical tests only confirmed this result for some ribs and age groups. No directional asymmetry was found, but a significant fluctuating asymmetry was observed in all three epiphyses. A preliminary analysis showed that the asymmetric group of individuals in the study sample includes all the rural-to-urban migrants, relative to the symmetric group. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source] Asymmetry of the os pubis: Implications for the Suchey-Brooks methodAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2009Rebecca S. Overbury Abstract Studies of skeletal development frequently document populational incidences of bilateral asymmetry. Degenerative morphological skeletal changes, attributed to age related and irregular ossification, may also progress asymmetrically, either as the result of asymmetric biomechanical factors expressed over the lifespan, asymmetric expression of physiological processes, or progressive magnification of asymmetry acquired previously during development. This study illustrates the effects of bilateral asymmetry on age at death estimates obtained from human skeletal remains. The Suchey-Brooks method, which uses the pubic symphyseal face for age estimation (Katz and Suchey, Am J Phys Anthropol 69 1986 427,435), was selected for the study based on its widespread use. Asymmetry in the Suchey-Brooks symphyseal age phases was found in over 60% of a sample composed of 20th century White male individuals from 18 to 86 years of age (N = 130). However, results suggest that the presence of asymmetry does not compromise the accuracy of the Suchey-Brooks method if the morphologically older symphyseal face of an asymmetric individual is used to estimate age at death. In addition, weak directional asymmetry and a correlation between age and asymmetry were found. This suggests that a comparison of asymmetry in this area with that in other skeletal areas, where the factors originating and influencing asymmetry are better understood, may be useful in better understanding the biological processes which underlie the age markers used in the Suchey-Brooks method. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc. [source] Bilateral asymmetry in the limb bones of the chimpanzee (Pan troglodytes),AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2005L.A. Sarringhaus Abstract There is much debate in behavioral primatology on the existence of population-level handedness in chimpanzees. The presence or absence of functional laterality in great apes may shed light on the origins of human handedness and on the evolution of cerebral asymmetry. The plasticity of long bone diaphyses in response to mechanical loading allows the functional interpretation of differences in cross-sectional geometric. While left-right asymmetry in upper limb diaphyseal morphology is a known property in human populations, it remains relatively unexplored in apes. We studied bilateral asymmetry in 64 skeletons of wild-caught chimpanzee using the humerus, second metacarpal, and femur. The total subperiosteal area (TA) of the diaphyses was measured at 40% of maximum humeral length and at the midshaft of the metacarpals and femora using external silicone molds. Overall, the TA values of the left humeri were significantly greater than the right, indicating directional asymmetry. This effect was even greater when the magnitude of difference in TA between each pair of humeri was compared. The right second metacarpals showed a tendency toward greater area than did the left, but this did not reach statistical significance. The lack of asymmetry in the femur serves as a lower limb control, and suggests that the upper limb results are not a product of fluctuating asymmetry. These findings imply behavioral laterality in upper limb function in chimpanzees, and suggest a complementary relationship between precision and power. Am J Phys Anthropol 2005., © 2005 Wiley-Liss, Inc. [source] Dominance relationships among one-male units in a provisioned free-ranging band of the Sichuan snub-nosed monkeys (Rhinopithecus roxellana) in the Qinling Mountains, ChinaAMERICAN JOURNAL OF PRIMATOLOGY, Issue 7 2008Peng Zhang Abstract We studied the dominance relationships among one-male units (OMUs) in a provisioned free-ranging band of the Sichuan snub-nosed monkeys (Rhinopithecus roxellana) in the Qinling Mountains of central China from 2001 to 2005. The band was composed of 6,8 OMUs that stayed in the band for several years. Linear dominance orders could be detected using displacement interactions with directional asymmetry among OMUs in 82.3±5% of interactions, and ambiguous and reversed interactions in 17.7±5%. The dominance rank of OMUs was positively related with the duration of their stay in the band, and this may be attributed to the association of the resident male with adult females, rather than the fighting ability of resident males, as males do not fight seriously with each other. Subordinate units were observed to merge with dominant units resulting in an elevation of their rank order. The linear dominance relationship among OMUs in the Sichuan snub-nosed monkeys may have evolved as a result of competition for preferred food trees. Am. J. Primatol. 70:634,641, 2008. © 2008 Wiley-Liss, Inc. [source] | ||||||||||