Low Fluctuating Asymmetry Research Articles

Differences in otolith shape and fluctuating-asymmetry between reared and wild gilthead seabream (Sparus aurata Linnaeus, 1758).

Otolith structure is a useful tool in discrimination among fish populations as it is a permanent record of the influence of endogenous and exogenous factors. In the present study we examined otolith morphology and fluctuating asymmetry (FA) for differences between wild-caught (by bottom trawl) and reared specimens of Gilthead seabream (Sparus aurata). Based on the frequency of regenerated scales (degree of scale regeneration, SRD) on each specimen, a threshold of 30% SRD was used to assign wild-caught fish individuals as wild (≤30% SRD, LR group) or as possible aquaculture escapees (>30% SRD, HR group). Based on the analysis of elliptic Fourier descriptors, significant differences were found in otolith shape between reared (Rr) and the wild-caught groups (LR, HR). Reared fish had otoliths with significantly larger perimeter (OP ) than wild-caught fish. Furthermore, FA was significantly higher in the Rr than the LR group for OP and all except one shape descriptors (harmonics 2-7). The HR group exhibited intermediate levels of FA between the low and high FA levels observed in the LR and Rr groups. Results are discussed in terms of the value of combining otolith and scale morphology for the identification of escapees in wild Gilthead seabream stocks.

Relationships between mating tactics and male traits such as body size and fluctuating asymmetry in the Japanese scorpionfly

Fluctuating asymmetry (FA) is defined as small, random deviations from perfect bilateral symmetry in a morphological trait. It has sometimes been used as an indicator of male quality because it affects male mating success. In the Japanese scorpionfly, Panorpa japonica, males are known to use two mating tactics, donation of nuptial gifts and forced mating. In P. japonica, low FA males are more likely to win a competition with another male, and females prefer low FA male sex pheromones. However, no studies have been conducted on the effect of FA on the mating tactics adopted by males. In the present study, we first observed the mating behaviors of P. japonica and classified these into three patterns: (1) nuptial gifting, (2) forced mating, and (3) feeding mating. Second, we investigated the relationships between mating tactics and male traits, including body size, FA, and weapon size. The results showed a positive correlation between absolute FA and mating duration only in the case of feeding mating. We discuss the reasons why this significant correlation was found in P. japonica.

The Face of Early Cognitive Decline? Shape and Asymmetry Predict Choice Reaction Time Independent of Age, Diet or Exercise

Slower reaction time is a measure of cognitive decline and can occur as early as 24 years of age. We are interested if developmental stability predicts cognitive performance independent of age and lifestyle (e.g., diet and exercise). Developmental stability is the latent capacity to buffer ontogenetic stressors and is measured by low fluctuating asymmetry (FA). FA is random—with respect to the largest side—departures from perfect morphological symmetry. The degree of asymmetry has been associated with physical fitness, morbidity, and mortality in many species, including humans. We expected that low FA (independent of age, diet and exercise) will predict faster choice reaction time (i.e., correct keyboard responses to stimuli appearing in a random location on a computer monitor). Eighty-eight university students self-reported their fish product consumption, exercise, had their faces 3D scanned and cognitive performance measured. Unexpectedly, increased fish product consumption was associated with worsened choice reaction time. Facial asymmetry and multiple face shape variation parameters predicted slower choice reaction time independent of sex, age, diet or exercise. Future work should develop longitudinal interventions to minimize early cognitive decline among vulnerable people (e.g., those who have experienced ontogenetic stressors affecting optimal neurocognitive development).

Measure of environmental stress on Porcellio laevis Latreille, 1804 sampled near active Tunisian industrial areas

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

Do defoliating insects distinguish between symmetric and asymmetric leaves within a plant?

1. Plants represent a highly heterogeneous resource for herbivores. One dimension of this heterogeneity is reflected by the within‐plant variation in the leaf fluctuating asymmetry (FA), i.e. in the magnitude of the random deviations from the symmetry in leaf shape.2. This study is the first to test experimentally the hypothesis that variation in the quality of individual leaves for defoliating insects (11 species) within a plant (seven tree and shrub species) is associated with the FA of these leaves.3. It was demonstrated that specialist defoliators generally distinguish between nearly symmetric (low FA) and highly asymmetric (high FA) leaves, but do not distinguish between discs cut from these leaves. Low‐FA leaves of Salix caprea, Salix myrsinifolia and Populus tremula were of better quality for insects than high‐FA leaves, as demonstrated by both preference tests and performance trials. By contrast, high‐FA leaves of Betula pubescens were of better quality for insects than low‐FA leaves, whereas insects feeding on Alnus incana showed similar responses to high‐ and low‐FA leaves.4. It is concluded that insect herbivores can distinguish between leaves with high and low FA, and that FA may be associated with the quality of an individual leaf for insects, although the direction and strength of the effect of leaf FA on insect preference and performance vary among study systems. The ecological significance of substantial within‐plant variation in leaf FA remains to be explored.

Factors Associated with Developmental Instability in the Dental Arches of Children

Dental arch asymmetry is often associated with malocclusion and is implicated in numerous functional deficiencies including speaking and mastication. While the existence of asymmetric dental arch shape has been well documented in malocclusion, less is known about the potential factors tied to its expression. Developmental instability refers to the suite of epigenetic factors that can disrupt the normal growth pattern of an individual and cause an increase in asymmetry. In this study, we examine the relationship of numerous health and dietary factors with developmental instability in the dental arches of children.A sample of 406 dental casts of children at age 5 from the Iowa Fluoride Study were digitized with 22 landmarks along the gingival papillae and then submitted to a Procrustes ANOVA to quantify dental arch Fluctuating Asymmetry (FA). Using FA as a metric of developmental instability, we separated individuals into low and high FA groups and then ran a series of two sample T‐Tests to see if individuals with high FA had poorer dietary or health related factors when compared to individuals with low FA.Results indicate that antibiotic usage was higher on average in children in the high FA group when compared to children with low dental arch FA (p=0.037), indicating that higher instances of childhood infection and disease may result in more asymmetric dental arches. Likewise, children with lower Vitamin D consumption had increased FA compared to children with higher levels of Vitamin D in their diet (p=0.039).These results confirm that infectious disease and diet can play a role in the normal development of the dental arches. Deficits in important nutrients, like Vitamin D, as well as elevated exposure to infectious disease, can be tied to increased dental arch asymmetry. These factors should be considered not only for the general health of a growing child, but also with regard to their proper masticatory development.Support or Funding InformationSupported by a Carver Charitable Trust Grant #12‐4058 and the NIH through Grants 2 UL1 TR000442, 1T90DE023520, R01‐DE09551 and U01‐DE018903.

Fluctuating asymmetry in an extreme morphological adaptation in the Chilean bee Xeromelissa rozeni (Hymenoptera: Colletidae)

Fluctuating asymmetry (FA), random deviations from perfect symmetry in bilateral traits, is a common inverse measure of developmental stability (DS), which is related to one’s ability to buffer against environmental and genetic perturbations. There is a widespread hypothesis that heterozygosity grants an increased ability to compensate for developmental errors caused by genetic and environmental factors, rendering homozygous individuals less symmetric than heterozygous ones. In addition, if natural selection on FA is common, nonessential traits should exhibit higher asymmetry than functionally essential traits. This is especially well tested in haplodiploid organisms, which present a clear distinction between “homo”zygosity (males) and heterozygosity (females). Relatively few FA studies looked at this relationship in hymenopterans or in haplodiploid organisms in general and the results are rather inconsistent. This study compares FA measurements of seven parts of the maxillary palpus, with sclerotized and membranous parts scored separately, and two wing venation characters for males and females of the Chilean bee Xeromelissa rozeni (Toro and Moldenke, 1979). The results of this study suggest that there is an equally strong selection force for maxillary palp symmetry in both males and females leading to a relatively low FA in both sexes, and that less functional traits exhibit higher FA due to relaxation of selection. Lastly, we stress the importance of testing a larger number of independent traits.

Facial asymmetry is negatively related to assertive personality but unrelated to dominant personality in men

Fluctuating asymmetry (FA) is a putative indicator of development instability in humans and other species, and some literature supports a women’s preference for low degree of FA in opposite sex (e.g., symmetrical face). Also some personality traits associated to social status (e.g., dominance and assertiveness) are attractive to women due to direct and indirect benefits associated to high status. The aim of this work was to study the relationship between facial FA and dominant and assertive personalities. We found a negative correlation between facial FA and assertive personality but not between facial FA and dominant personality. Moreover, we found a positive correlation between assertive and dominant personality. Our results suggest that a low facial FA and assertive personality can be related to be advertising desirable traits and high status in men in order to be more attractive to women. This study supports the evidence shown by previous works which shows that a low facial FA is related with socially desirable and attractive aspects of personality.

The ecological context of bilateral symmetry of organ and organisms

A particular phenotype is generated through numerous networks of interactions from within the cell to the whole ecosystem. The level of the environmental noise and the ability of a given genotype to render different phenotypes under different environmental conditions, called phenotypic plasticity, determine survival or death at individual and/or population level. It is important to highlight that non-lethal environmental changes are important for generating genetic variability and promoting biological adaptations. However, when the level of environmental noise starts to be stressed, the developmental stability (DS) of the organism can be perturbed. The DS has been analysed through the symmetry deviations in organs or organisms with bilateral structure. The symmetry deviations occur due to inability to contain disorders from environmental or endogenous conditions during its development. This deviation is called fluctuating asymmetry (FA) when is a non-directional deviation in the symmetry of a bilateral structure normally distributed in a population. Low FA has been associated with greater DS. The analysis of FA has often been used to measure the effects of environmental perturbations. In this review, I discuss the concept of plant stress and phenotypic plasticity connecting both to the generation of an asymmetry phenotype, highlighting the usefulness of FA as an indicator of the level of stress which the organism is subjected to. Further, although this review explores mainly the connection between FA and stress in plants, the ecological context of symmetry in animals and plant-insect interaction is also discussed. Finally, I provided some methodologies used to detect symmetry variations in organs or organisms with bilateral structure.

The effect of fluctuating asymmetry and leaf nutrients on gall abundance and survivorship

Fluctuating asymmetry (FA) is defined as small and random deviations from perfect symmetry in otherwise bilaterally symmetrical traits. Usually, plants under stress have a higher nutritional quality and are preferred by insect herbivores. Here, we examined the relationship among leaf FA of Bauhinia brevipes (Fabaceae), nutrients and the occurrence of Schizomyia macrocapillata (Cecidomyiidae: Diptera). We evaluated whether: (i) FA was related to S. macropillata abundance and survivorship; (ii) FA correlated with the levels of foliar nutrients (macro- and micronutrients, and organic carbon); and (iii) S. macropillata abundance was related to leaf nutrients. The results showed a positive relationship between FA and gall abundance. S. macrocapillata survivorship was five times higher in B. brevipes individuals with high FA levels, but this difference was not significant. The influence of nutrients in B. brevipes FA was negligible, except for foliar nitrogen, which was 7.3% higher in plants with low FA levels. The abundance of S. macrocapillata was negatively related to nitrogen levels, but gall survivorship was not affected by this nutrient. We found evidence for a causal relationship between FA and gall occurrence, since S. macropillata gall oviposition occurs in young undeveloped leaves, thus mature leaves show an increase in FA. Nonetheless, in this system, neither FA nor nitrogen influenced gall survivorship.

Condition dependence and the origins of elevated fluctuating asymmetry in quality signals

Developmental stability is the ability of organisms to buffer development against perturbations. Different classes of traits typically have different levels of fluctuating asymmetry (FA), a measure of developmental instability. In particular, elevated FA in sexually selected quality signals has attracted a great deal of attention. There are 3 main hypotheses to explain elevated developmental instability in quality signals. Developmental instability may be related to the cost of trait production, a trait’s condition dependence, or the levels of interindividual trait variation. Here we test these 3 hypotheses by comparing FA in structural traits, nonsignaling color traits, and 2 signaling color traits: a condition-dependent quality signal in Polistes dominulus wasps and noncondition-dependent identity signals in P. fuscatus wasps. Overall, color traits have higher FA than structural traits, though FA differs among the 3 classes of color traits. The clypeal identity signal in P. fuscatus has the highest interindividual trait variation, yet shows relatively low FA, indicating that interindividual trait variation does not explain heightened FA. The quality signal in P. dominulus has the highest FA, though it is not costly to produce. Therefore, the elevated FA in quality signals cannot be attributed to costs of signal production. The quality signal in P. dominulus is condition dependent, however, so our results indicate that increased developmental instability in quality signaling traits can be attributed to their condition-dependent development. A link between developmental stability and condition dependence provides a mechanism through which quality signals may integrate information about overall condition in the absence of costly trait development. Key words: badge of status, condition dependence, fluctuating asymmetry, identity signal, Polistes, quality signal, sexual selection. [Behav Ecol]

Fluctuating Asymmetry and personality

The relationship between Fluctuating Asymmetry (FA) and personality can cast light on the fitness consequences and selective benefits underlying personality. However few studies have investigated the topic and these have rendered inconsistent findings. Theoretically predicted relationships of FA to personality include linear associations and curvilinear associations (with low FA leading to average—not extreme—personality trait levels). Evidence for no association would suggest that personality has no consequences for general fitness. We summarise the findings to date, adding two new studies, testing each of the hypothesised models with well-validated measures of FA, and personality traits. No consistent associations were found. Though it remains possible that low FA is weakly related to conscientiousness and openness to experience, the major personality domains seem unrelated to FA.

Testosterone, facial symmetry and cooperation in the prisoners' dilemma

Recent research has analyzed how individual characteristics, like the exposure to different hormones and symmetry, affect decision-making and strategic behaviour. The present article investigates the effect of symmetry, of exposure to testosterone (T) in utero and during puberty and of current T on cooperation in a Prisoners' Dilemma Game (PDG). T is a hormone with well known effect on males' behaviour, and that promotes activities that seek to increase reproductive success. Fluctuating Asymmetry (FA) reflects the ability of the organism to maintain a stable development and it is usually employed as a variable reflecting genetic quality (low FA values are thought to signal higher genetic quality). Our results show that subjects with intermediate levels of second to fourth digit ratio (a proxy of exposure to T in utero) and with high FA cooperate more often in the PDG. We also observe that the latter effect is due to the fact that FA has an impact on subjects' expectations about the behaviour of their counterpart in the game. These results reinforce the described link between markers related to genetic quality and cooperative behaviour. This possible linkage of individual condition and pro-social behaviour in humans clearly merits further attention.

Neonatal exposure to short days and low temperatures blunts stress response and yields low fluctuating asymmetry in Siberian hamsters

Fluctuating asymmetry (FA) refers to small, non-directional deviations from perfect bilateral symmetry in morphological characters. Individuals with low FA presumably either developed in a relatively stable environment and/or were better able to buffer against developmental stressors. The present study investigated the effects of seasonal factors measured by day length and ambient temperature manipulations on the development of bilateral characters and concomitant changes in stress responses. Siberian hamsters were exposed to either long days (16 h of light per day) or short days (8 h of light per day) combined with either standard temperatures (21 ± 2 °C) or low temperatures (8 ± 2 °C) on the day of birth until weaning. Cortisol concentrations at baseline and following acute restraint stress, and FA values were measured in adulthood. Females reared in winter-like conditions with short day lengths and low temperatures had low FA and low cortisol concentrations following restraint stress compared to other females. Females reared in long day lengths and standard temperatures had the highest rate of increase in cortisol concentrations after restraint among other female groups. No group effects were observed in males regarding day length and temperature manipulations. Baseline and post-restraint cortisol concentrations were higher in females than males for all groups except in animals reared in short day lengths and low temperatures. Our results suggest that winter-like conditions during neonatal period evoke hyposensitivity to stress in adult females and this blunted response to stress is a key factor in achieving ideal growth patterns.

Symmetrical women have higher potential fertility

Fluctuating asymmetry (FA) is believed to reflect developmental stability and thus may serve as a marker of the biologic quality of individuals. To test the hypothesis that degree of FA is related to a woman's potential fertility, we measured finger length together with levels of estradiol in saliva samples collected daily for an entire menstrual cycle in 171 Polish urban and rural women. We show that women who are more symmetrical, as assessed by the degree of inequality in the fourth-digit length of their right and left hands, have 13% higher average levels of estradiol over the menstrual cycle than less symmetrical women (19.4 and 17.1 pmol/l, respectively; p=.0001). Among urban women, mid-cycle levels of estradiol were 28% higher in the symmetrical group than in the asymmetrical group. Because higher hormone levels in women may lead to a substantial rise in the probability of conception, low FA may therefore be associated with increased fertility.

Antler size and fluctuating asymmetry in red deer (Cervus elaphus) stags and probability of becoming a harem holder in rut

Red deer hinds play a significant role in selecting stags for mating. We tested the hypotheses that in red deer (Cervus elaphus) the probability of becoming a harem holder (and hence achieving reproductive success) occurs in stags bearing larger, branched antlers and showing low fluctuating asymmetry (FA). Eleven antler characteristics were measured; absolute and relative FA were calculated on 51 cast antler sets from 19 individually recognized stags. Probability of becoming a harem holder (PBHH) was originally analysed separately, i.e. for antler size and FA of each antler characteristic and calculated factors for both antler size and FA. If analysed separately, large antler size and low relative but high absolute FA increased PBHH. When we combined antler size and FA of antler characteristics in one model using antler size and FA factors, however, PBHH and achieving reproductive success were mainly dependent on increasing antler size and enhanced antler branching rather than on FA. We conclude that in contrast to antler size, FA is unlikely to play any significant role in sexual selection as an indicator of individual quality. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87, 59–68.

Lack of response to selection for lower fluctuating asymmetry of mutant eyespots in the butterfly Bicyclus anynana.

Fluctuating asymmetry (FA) is claimed both to provide a means of evaluating developmental stability, and to reflect an individual's quality or the stress experienced during development. FA refers to the nondirectional variation between left and right sides, whereas directional asymmetry (DA) refers to a significant directional variation between the sides. We studied four eyespots on the dorsal forewing of the tropical butterfly, Bicyclus anynana. Two of the eyespots were specified by a mutant allele, Spotty, that was fixed in the stock. These eyespots showed higher FA than the two flanking, wild-type eyespots, although they are all formed by the same developmental pathway. We applied artificial selection for lower FA of the novel eyespots in an attempt to increase their developmental stability. There was significant variation present in individual FA in our study. However, this did not change as a result of the artificial selection. Most of the variation in FA can be accounted for by individual differences in developmental stability rather than by the applied selection or by environmental variation. Thus, it was not possible to produce any increased developmental stability of the novel eyespots by selecting for low FA. The estimates of realized heritability for both FA and DA of each eyespot were not significantly different from zero. The results suggest that FA provides little, if any, potential for exploring the mechanistic basis of developmental stability.

Female choice depends on size but not symmetry of dorsal eyespots in the butterfly Bicyclus anynana.

The eyespots on the ventral wings of Bicyclus anynana butterflies are exposed when at rest and interact with predators. Those on the dorsal surface are not exposed in this way, and may be involved in courtship and mate choice. In this study, we examined whether the size and fluctuating asymmetry (FA) of dorsal eyespots are reliable signals of male quality. High developmental stability is considered to result in low FA, and to be associated with high quality. Individuals of high quality are predicted to produce sexually selected traits that are large and symmetrical, at a relatively low cost. In this study, we manipulated eyespot development to uncouple eyespot size and FA in order to examine their independent roles in signalling to the female. Individual females in cages were given the choice between two or three males differing in eyespot traits. The results indicate that although size per se of the eyespots is used as a signal, FA and wing size are not. We discuss the use of FA in studies of sexual selection and aspects of sexual selection on dorsal eyespot size.

Low fluctuating asymmetry (FA) and short-term benefits in fertility?

Preference for partners with low fluctuating asymmetry (FA) may produce “good gene” benefits. However, Gangestad & Simpson's analysis does not exclude immediate benefits of fertility. Low FA is related to fertility in men and women. Short-term changes in FA are correlated with fertility in women. It is not known whether temporal fluctuations in the FA of men are related to short-term fertility status.

Adaptive flexibility, testosterone, and mating fitness: Are low FA individuals the pinnacle of evolution?

The expansion of human evolutionary theory into the domain of personal and environmental determinants of mating strategies is applauded. Questions are raised about the relation between fluctuating asymmetry (FA), testosterone, and body size and their effects on male behavior and outcomes. Low FA males' short-term mating pattern is considered in the context of an evolved tendency for closer and longer human relationships.