Perinatal stress and increased fluctuating asymmetry of dental calcium in the laboratory rat

Recent studies have consistently reported an increased magnitude of fluctuating dental, long bone, and membranous bone asymmetry as a function of perinatal stress. The present study was designed to test the hypothesis that increases in the fluctuating asymmetry of calcium may be related to the metric changes in these calcium-dependent systems. Pregnant rats were exposed to noise stress from conception through weaning. Bilateral lower first molars were extracted from the neonates, and calcium levels were determined using a standard atomic absorption technique. Levels of fluctuating asymmetry of calcium were found to be significantly increased (p less than .01) in the audiogenic noise-stressed group compared to unstressed, normal controls. These results follow the pattern reported earlier for metric analysis of the dentition and support a stress-induced calcium-transport-disruption hypothesis.     

Fluctuating Asymmetry in Menidia beryllina before and after the 2010 Deepwater Horizon Oil Spill

Assessing the impacts of the Deepwater Horizon oil spill with a dependable baseline comparison can provide reliable insight into environmental stressors on organisms that were potentially affected by the spill. Fluctuating asymmetry (small, non-random deviations from perfect bilateral symmetry) is an informative metric sensitive to contaminants that can be used to assess environmental stress levels. For this study, the well-studied and common Gulf of Mexico estuarine fish, Menidia beryllina, was used with pre and post-oil spill collections. Comparisons of fluctuating asymmetry in three traits (eye diameter, pectoral fin length, and pelvic fin length) were made pre and post-oil spill across two sites (Old Fort Bayou and the Pascagoula River), as well as between years of collection (2011, 2012)-one and two years, respectfully, after the spill in 2010. We hypothesized that fluctuating asymmetry would be higher in post-Deepwater Horizon samples, and that this will be replicated in both study areas along the Mississippi Gulf coast. We also predicted that fluctuating asymmetry would decrease through time after the oil spill as the oil decomposed and/or was removed. Analyses performed on 1135 fish (220 pre and 915 post Deepwater Horizon) showed significantly higher post spill fluctuating asymmetry in the eye but no difference for the pectoral or pelvic fins. There was also higher fluctuating asymmetry in one of the two sites both pre and post-spill, indicating observed asymmetry may be the product of multiple stressors. Fluctuating asymmetry decreased in 2012 compared to 2011. Fluctuating asymmetry is a sensitive measure of sub lethal stress, and the observed variability in this study (pre vs. post-spill or between sites) could be due to a combination of oil, dispersants, or other unknown stressors.     

Dental asymmetry,maternal obesity,and smoking

This study examines the levels of fluctuating dental asymmetry in four samples of school children: those whose mothers were obese and had smoked during the pregnancy concerned (n = 111); those whose mothers were obese non-smokers (n = 114); those whose mothers were non-obese smokers (n = 104); and those whose mothers were lean non-smokers (n = 111). The degree of fluctuating asymmetry was assessed by means of a rescaled asymmetry measure. Obesity was defined as Quetelet's index in excess of 30, and smoking status as at least 20 cigarettes per day during the pregnancy concerned. When the magnitudes of fluctuating asymmetry in children of lean smokers were compared to the control group of lean non-smokers, no significant univariate differences were found. Children of obese mothers, whether these smoked or not, were found to have significantly raised levels of asymmetry. An analysis of variance confirmed that the combination of obesity and maternal smoking was a significant predictor of fluctuating dental asymmetry. The teeth involved tended to be the maxillary first incisor and molars. It is concluded that maternal obesity has a destabilizing effect on the developing fetus and that this effect appears to be enhanced in obese mothers who smoked. This effect was absent in lean mothers, irrespective of their smoking status. Am J Phys Anthropol 102:133–139. © 1997 Wiley-Liss, Inc.     

On the meaning of increased fluctuating dental asymmetry: a cross populational study.

Suarez reports a greater magnitude of fluctuating dental asymmetry for Neandertal sample when compared with a sample of modern Ohio whites. He postulates that this greater antimeric variance could be due to a greater degree of inbreeding in the Neandertal populations. In the present investigation, the magnitude of fluctuating dental asymmetry is evaluated for Eskimo and Pueblo populations. These populations were found to exhibit dental variance of equal magnitude to that of the Neandertal population. As these populations are not highly inbred, a stress related mechanism is suggested to explain these observations and the inbreeding hypothesis is rejected. The implications of this mechanism to Brace's Probable Mutation Effect are discussed.     

Prenatal stress and increased fluctuating asymmetry in the parietal bones of neonatal rats

Recent studies have reported increased fluctuating dental and long bone asymmetry in neonates as a function of prenatal stress. The present study was designed to assess the effects of prenatal stress on a third calcium-dependent system, membranous bone. Pregnant rats were exposed to cold, heat, or noise from conception through parturition. Bilateral parietal bone lengths were measured in the term neonates. Levels of fluctuating asymmetry were found to be significantly increased (p less than .001) in all three stressed groups compared to unstressed controls. Results support the concept of a generalized stress response, and suggestions are offered for human osteological application.     

Problems of sampling and inference in the study of fluctuating dental asymmetry

Randomly distributed or “fluctuating” dental asymmetry has been accorded evolutionary meaning and interpreted as a result of environmental stress. However, except for congenital malformation syndromes, the determinants of human crown size asymmetry are still equivocal. Both a computer simulated sampling experiment using a combined sample size of N = 3000, and the requirements of adequate statistical power show that sample sizes of several hundred are needed to detect population differences in dental asymmetry. Using the largest available sample of children with defined prenatal stresses, we are unable to find systematic increases in crown size asymmetry. Given sampling limitations and the current inability to link increased human dental asymmetry to defined prenatal stresses, we suggest that fluctuating dental asymmetry is not yet established as a useful and reliable measure of general stress in human populations.     

Dental arch asymmetry in an isolated Adriatic community

Developmental stability reflects the ability of a genotype to develop in the same way under varying environmental conditions. Deviations from developmental stability, arising from disruptive effects of environmental and genetic stresses, can be measured in terms of fluctuating asymmetry, a particularly sensitive indicator of the ability to cope with these stresses during ontogeny. In an inbred Adriatic island population, we expected dental arch fluctuating asymmetry 1) to be higher than in an outbred sample from the same island, and 2) within this population, to increase with the level of inbreeding. Due to environmental stress, we also expected to find higher fluctuating asymmetry in the outbred island population than in an urban reference group from the same country. The material consisted of 506 dental casts of 253 children from 1) the island of Hvar, and 2) Zagreb, Croatia. Three-dimensional coordinates of 26 landmarks spanning the arches were digitized. The analysis partitioned the asymmetry of arch forms into components for directional and fluctuating bilateral asymmetry, using the appropriate Procrustes method (geometric morphometrics). The results corroborated the hypotheses. Fluctuating asymmetry was found to be higher on the island than in Zagreb in all groups and in both jaws, and increased significantly with endogamy level in the lower jaw. There was no significant directional asymmetry in the Zagreb sample and likewise none in the upper jaws of the outbred island group, but significant directional asymmetry in both jaws of the inbred population and also in the lower jaws of the outbred island group. These results suggest an environmental as well as a genetic influence on dental arch asymmetry. Although the lower jaws expressed these two stresses almost additively, the upper jaws appeared to be better buffered. The role of directional asymmetry as a potential indicator of craniofacial developmental instability clearly merits further attention.     

The ontogeny of fluctuating asymmetry

We tested seven hypotheses regarding the mechanisms by which fluctuating asymmetry (FA) originates. We did this by analyzing data on four bilateral characters measured repeatedly during the development of individual domestic fowl. Immediately posthatching, there was substantial directional asymmetry, which rapidly decreased. We detected FA at significant levels in all characters in the majority of our measurements over the remainder of development. We also examined the effects of known environmental stressors (food and density stress) on levels of FA. At the levels we examined, changes in these stressors did not alter the degree of asymmetry we found in fowl. Time series of asymmetry for individuals did not exhibit regular oscillations, as much of the relevant literature predicts. Asymmetry levels reflected the combined effects of developmental noise, which was random in degree and direction, and feedback processes, which decreased asymmetry by altering growth rates on both sides of the body. Our findings best fit the predictions of the residual asymmetry and compensatory growth hypotheses, which suggest that levels of asymmetry reflect only recent growth history.     

Heat stress, fluctuating asymmetry and prenatal selection in the laboratory rat

Recent studies have demonstrated that stress may increase the fluctuating asymmetry of teeth and limbs in laboratory animals. The present study investigates the effects of heat on such parameters. Pregnant laboratory rats are exposed to temperatures of 33 degrees C during gestation. Increases in fluctuating asymmetry of dental dimensions as well as bone density are found for the pups of such females when compared to unstressed controls. A general increase in limb lengths is also reported for young of heat stressed animals. Prenatal selection with differential survival is suggested as a possible explanation for differences found between the experimental and control animals.     

Stress and dental asymmetry in a population of Japanese children

We studied the significance of the magnitude of fluctuating dental asymmetry in 489 Japanese children by regression analysis. The search was for the predictability of asymmetry from levels of five factors assumed to be relevant parameters of prenatal stress. The five factors were derived by principal components analysis to simplify the interrelationships between birth weight, gestational age, maternal age, parity, sex, year of birth, socioeconomic status, and F, the coefficient of inbreeding. Only the regression of asymmetry on a factor representing a secular effect related to sex ratio was statistically significant; however, the relationship was too small to be biologically meaningful. The significance of individual asymmetry is thus equivocal, and this is discussed in terms of the meaning of asymmetry vis à vis overall fitness and developmental homeostasis. We conclude that experimental research will be necessary to elucidate not only the determinants of dental asymmetry but the relationship between these determinants and mortality and morbidity.     

Variables affecting dental fluctuating asymmetry in human isolates

The aims of the present study are to 1) determine and describe levels of dental fluctuating asymmetry (FA) in a highly endogamous human group; 2) evaluate the effects of various FA measures on perceived FA levels and their interrelationships; 3) study the connections between dental variables (tooth size, class, position, type, location and dimension) and FA levels; and 4) estimate the interrelationships between dental FA measures. The study was carried out on 242 Bedouin boys aged 5 to 14 years. The results demonstrate that the main variables influencing dental FA levels within this population are tooth class (incisors, canine, premolars, molars) and position (mesial, distal) and that the interaction between the two is significant. When sample sizes are large enough and individual measures are needed for the statistical analysis, the use of a computational method based on absolute values is legitimate. Clear relationships between some FA dental traits are discerned though principal-components analysis. © 1993 Wiley-Liss, Inc.     

Bite Force Performance,Fluctuating Asymmetry and Antisymmetry in the Mandible of Inbred and Outbred Wild-Derived Strains of Mice (<Emphasis Type="Italic">Mus musculus domesticus</Emphasis>)

Developmental instability, as measured by fluctuating asymmetry is generally considered to increase with genetic and environmental stresses. Few studies have, however, addressed the role of asymmetry in altering organism performance. Here, we measured bite force performance in three strains of inbred and outbred mice derived from wild ancestors. We quantified size and shape directional, and fluctuating asymmetry, as well as inter-individual variation of their mandibles using geometric morphometrics. We also developed a way to estimate shape antisymmetry, to filter it out of the fluctuating asymmetry component. Contrary to our expectations, we found no significant link between bite force and asymmetry levels. Inbreeding did not produce any clear and significant increase or decrease in neither inter-individual variance, nor fluctuating asymmetry. Furthermore, fluctuating asymmetry levels were unrelated to inter-individual variance levels, although these two types of variation affected the same areas of the mandible. We did not highlight any impact of inbreeding depression on bite force. Fluctuating asymmetry was reduced in the mandible, which we argue may be linked to its functional relevance. We found some significant but very reduced antisymmetry possibly linked to lateralization. This lateralization did not relate to any bite force difference. Our results show that neither inbreeding, nor asymmetry (combining fluctuating, directional asymmetry and antisymmetry) significantly affect bite force performance in mice, and that despite affecting the same morphological regions, developmental stability and canalization are independent.     

Fluctuating asymmetry of morphometric characters in house mice: the effects of age, sex, and phenotypical extremeness in a randombred population

Fluctuating asymmetry (FA) was calculated for nine paired morphometric characters in a randombred population of house mice in order to assess the effects of age, sex, and phenotypical extremeness. FA did not significantly vary between sexes for any of the characters, and age proved to be significant only for innominate length. Additionally, FA values in high extreme individuals and low extreme individuals were compared to those for intermediate individuals to discover whether extreme individuals showed increased fluctuating asymmetry (decreased developmental stability) due to increased levels of homozygosity. Differences in fluctuating asymmetry magnitudes were found between the groups, although the extreme individuals did not consistently show increased fluctuating asymmetry and FA differences also showed no significant association with the level of heritability of each character. Potential reasons for these findings are discussed.     

Canalization and developmental instability of the fetal skull in a mouse model of maternal nutritional stress

Nutritional imbalance is one of the main sources of stress in both extant and extinct human populations. Restricted availability of nutrients is thought to disrupt the buffering mechanisms that contribute to developmental stability and canalization, resulting in increased levels of fluctuating asymmetry (FA) and phenotypic variance among individuals. However, the literature is contradictory in this regard. This study assesses the effect of prenatal nutritional stress on FA and among‐individual variance in cranial shape and size using a mouse model of maternal protein restriction. Two sets of landmark coordinates were digitized in three dimensions from skulls of control and protein restricted specimens at E17.5 and E18.5. We found that, by the end of gestation, maternal protein restriction resulted in a significant reduction of skull size. Fluctuating asymmetry in size and shape exceeded the amount of measurement error in all groups, but no significant differences in the magnitude of FA were found between treatments. Conversely, the pattern of shape asymmetry was affected by the environmental perturbation since the angles between the first eigenvectors extracted from the covariance matrix of shape asymmetric component of protein restricted and control groups were not significantly different from the expected for random vectors. In addition, among‐individual variance in cranial shape was significantly higher in the protein restricted than the control group at E18.5. Overall, the results obtained from a controlled experiment do not support the view of fluctuating asymmetry of cranial structures as a reliable index for inferring nutritional stress in human populations. Am J Phys Anthropol 154:544–553, 2014. © 2014 Wiley Periodicals, Inc.     

Inbreeding reduces power-law scaling in the distribution of fluctuating asymmetry: an explanation of the basis of developmental instability

The study of fluctuating asymmetry has been controversial because of conflicting results found in much of the primary literature. It has been suggested that the source of this conflict is the fact that the basis of fluctuating asymmetry is poorly understood and that, as a consequence, methodology of fluctuating asymmetry studies may be flawed. A new model for the phenomenological basis of fluctuating asymmetry, that variation in fluctuating asymmetry is in large part due to the random exponential growth of cell populations (geometric Brownian motion) that are terminated randomly around a genetically programmed development time, is presented here. If termination of development has a genetic component, then scaling effects and kurtosis in the distribution of fluctuating asymmetry should increase with genetic redundancy of the population. This model prediction was tested by comparing the distribution of multivariate size and shape fluctuating asymmetry in large samples collected from both wild populations and four moderately inbred lines of Drosophila simulans. It was found that while wild populations were best described by a lognormal distribution with power-law scaled tails, the inbred lines derived from the wild stock were dramatically normalized (half-normal) in three of four cases. As predicted, the scaling exponent of the upper tail of the distribution of fluctuating asymmetry increased with inbreeding while the kurtosis and mean fluctuating asymmetry decreased with inbreeding. The model suggests an additional explanation of leptokurtosis in fluctuating asymmetry. Kurtosis and scaling of the statistical distribution of fluctuating asymmetry in a population is related directly to genetic differences between individuals and these differences affect their ability to buffer the process of development against random perturbations.     

Fluctuating dental asymmetry: A measure of developmental instability in Down syndrome

Subjects with Down syndrome provide a useful model for investigating the effect of chromosomal aneuploidy on developmental pathways. Studies suggest that a major effect of trisomy is a decrease in developmental stability. The present study examines fluctuating dental asymmetry in Down syndrome. Mesiodistal crown diameters were measured from dental casts of 114 Down syndrome subjects. Correlation coefficients for antimeric permanent teeth served as an index of dental asymmetry. These values were compared with normal values obtained from the literature. Fluctuating dental asymmetry is thought to reflect the relative success of developmental homeostasis in countering developmental disturbances. Down syndrome subjects have significantly increased dental asymmetry. In addition, they show a disproportionate increase in dental asymmetry for those teeth reported to have the least developmental stability. These results support the contention that the chromosomal imbalance in Down syndrome results in amplified developmental instability.     

FLUCTUATING ODONTOMETRIC ASYMMETRY,MORPHOLOGICAL VARIABILITY,AND GENETIC MONOMORPHISM IN THE CHEETAH ACINONYX JUBATUS

The magnitudes of dimensional variability and fluctuating asymmetry in dental dimensions are reported for a sample of South African cheetah Acinonyx jubatus. To test the hypothesis that elevated levels of variability and asymmetry are associated with the increased developmental instability reported for this species, our results were contrasted to those for two other felids: Felis lybica and F. caracal. These findings suggest that dental dimensions in cheetahs are not significantly more variable or asymmetric. Hence, it is concluded that the cheetah may not be as developmentally unstable as was previously supposed.     

Fluctuating asymmetry inMacaca fascicularis: A study of the etiology of developmental noise

Fluctuating asymmetry was determined for six cranial measurements in an age-diverse sample of 138 individuals ofMacaca fascicularis. These data were used to choose among four hypotheses concerning the etiology of developmental noise. The hypotheses considered are (1) that developmental noise represents asymmetry in the causal history of a developing organism's interaction with the environment, (2) that it represents stochasticity in the mechanics of growth and induction, (3) that it reflects variation in the initial conditions of a developmental process, and (4) that it represents the random accumulation of noise at a level below that of morphogenetic mechanism. These hypotheses were tested against predictions concerning the intraspecific patterning of fluctuating asymmetry against age and size and the covariation of asymmetry values. Only the predictions of the fourth hypothesis were confirmed by results of this study. These results provide evidence for the view that developmental noise, as reflected by fluctuating asymmetry, is an intrinsic property of developmental systems, and not merely produced by the complexity of the organism's interaction with the environment.     

Response of fluctuating and directional asymmetry to selection on wing shape in Drosophila melanogaster

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.     

Genetic and phenotypic correlation between fluctuating asymmetry and two measurements of fear and stress in chickens

The purpose of the present study was to estimate the genetic and phenotypic correlation between fluctuating asymmetry and two measurements of fear and stress in chickens which had not deliberately stressed in any way, using the restricted maximum likelihood procedure. A total of 1073 36-week-old birds from two generations with complete pedigree of the Quail Castellana breed was used. Fluctuating asymmetry of several traits (leg, wing, and feather lengths, and ear-lobe and wattle areas), tonic immobility duration (indicator of fear), and heterophil to lymphocyte ratio (indicator of stress) were measured. The estimated genetic relationship between relative fluctuating asymmetry for the different traits and tonic immobility tended to be positive, that between the combined relative asymmetry of all traits and tonic immobility being near to +1; no significant phenotypic relationship was found between relative fluctuating asymmetry and tonic immobility. The genetic relationship between relative fluctuating asymmetry and heterophil to lymphocyte ratio was not consistent across the traits, ranging from +1 to −1, although the genetic correlation between the combined relative asymmetry and the heterophil to lymphocyte ratio was near to +1 too; no significant phenotypic relationship was found between relative fluctuating asymmetry and heterophil to lymphocyte ratio either. Relative fluctuating asymmetry and body weight were genetically negatively correlated for leg length and ear-lobe area but positively for feather length; the genetic correlation between the combined relative asymmetry and the body weight being near to −1; phenotypic relationships were not significantly different from zero. A significant negative genetic correlation between tonic immobility and heterophil to lymphocyte ratio was found, although the phenotypic association between these two measurements was zero. Phenotypic correlations always near to zero suggest that fluctuating asymmetry was not associated with duration of tonic immobility and heterophil to lymphocyte ratio in birds that have not been deliberately stressed.