A recent invasive population of the European starling sturnus vulgaris has lower genetic diversity and higher fluctuating asymmetry than primary invasive and native populations

Biological Invasions - Fluctuating asymmetries (FA) are small stress-induced random deviations from perfect symmetry that arise during the development of bilaterally symmetrical traits. One of the...     

The Developmental Instability—Sexual Selection Hypothesis: A General Evaluation and Case Study

Developmental instability results from small, random perturbations to developmental processes of individual traits. Phenotypic outcomes of developmental instability include fluctuating asymmetry (FA, subtle deviations from perfect bilateral symmetry) and phenodeviance (minor morphological abnormalities). A great deal of research over the past 18 years has focused on the role of developmental instability in sexual selection. A driving force behind this research has been the developmental instability-sexual selection hypothesis, which posits that symmetry and lack of phenodeviance in secondary sexual traits are assessed by mates and rivals because they provide a reliable cue of individual genetic quality. The present article tests this hypothesis by evaluating its five main predictions using published results: expressions of developmental instability in secondary sexual traits should be (1) negatively correlated with mating success; (2) directly assessed by mates and sexual rivals; (3) heritable; (4) condition-dependent; and (5) negatively correlated with ornament size. The first two predictions receive considerable, though not ubiquitous, support from a range of animal species. However, FA in secondary sexual traits is generally not significantly heritable, indicating that FA is unlikely to reveal genetic quality that can be transmitted to offspring. Similarly, there is little evidence to support the predictions that FA is condition dependent, and that it is negatively phenotypically or genetically correlated with sexual trait size. Based on an evaluation of the evidence overall, it is concluded that this hypothesis is unlikely to be viable; it appears unlikely that mate choice for symmetry evolves by “good genes” sexual selection. Hypotheses that do not require asymmetry and phenodeviance to reveal heritable genetic quality may explain observed links between FA/phenodeviance and mating success. Results of a case study of Drosophila bipectinata are summarized, which reinforce this general conclusion. It is suggested that nonadditive genetic variation arising from an interaction between trait-specific developmental genes and genetic background may drive sexual selection for reducing developmental instability in some cases. Levels of developmental instability variation in a population may need to surpass a critical threshold for sexual selection to operate, possibly explaining some of the pronounced heterogeneity in the effect of developmental instability on sexual selection reported in the literature.     

Are human preferences for facial symmetry focused on signals of developmental instability?

Humans find symmetrical faces more attractive than are asymmetricalfaces. Evolutionary psychologists claim that our preferencefor symmetry can be explained in the context of mate choicebecause symmetry is an honest indicator of the genetic qualityof potential mates. These arguments assume that asymmetry inhuman faces is fluctuating asymmetry (FA), because this formof asymmetry can be revealing of developmental instability.However, no study has yet examined the characteristics of facialasymmetry. Here we provide the first detailed study of the patternsof asymmetry in human faces. We measured asymmetry in 35 facialtraits. Although some traits had distributions characteristicof FA, many had distributions that characterize directionalasymmetry (DA); on average, both men and women had right hemi-facedominance. For DA traits we used deviations from the mean asymmetryas a measure of developmental instability. Our measures of asymmetryaccounted for a moderate proportion of the variance in perceivedsymmetry. Importantly, only FAs and random deviations from DAcontributed to people's perception of symmetry. DA was not importantin symmetry judgments. Faces rated as symmetrical were alsorated as attractive. Random deviations from DA were weakly relatedto women's attractiveness judgments of men's faces. DAs didnot influence attractiveness judgments. Our data suggest thatpeople focus on aspects of facial asymmetry that may be revealingof developmental instability. Further studies that isolate FAfrom other forms of asymmetry are required to accurately assessthe influence of developmental instability on the quality ofindividuals and its potential role in mate preferences.     

Correlated development, organism‐wide asymmetry and patterns of asymmetry in two moth species

Understanding the mechanisms that determine the development of a bilaterally symmetrical trait is crucial to the interpretation of patterns of fluctuating asymmetry (FA). Experimental and theoretical studies have indicated that feedback mechanisms both within and between developing traits, may participate in the developmental control of asymmetry. This study provides evidence that naturally occurring patterns of FA are affected by interactions between different traits. We found positive between‐trait correlations in signed FA values for tibia lengths on different legs, but not between wing and tibia FA in two moth species. Further research should investigate if trait functionality is related to this presumed correlated development. An extension of the Rashevsky–Turing model of morphogenesis further showed that correlations between the signed FA values can be generated by feedback mechanisms that regulate growth patterns between traits. We argue that such feedback mechanisms can be expected to be widespread and show that between‐trait correlations in the unsigned FA then become confounded with correlations in the signed FA. In addition, correlated development appeared to invalidate the use of the hypothetical repeatability to translate correlations between the unsigned FA values into correlations in the presumed underlying developmental instability. In conclusion, the presence of an organism‐wide asymmetry, which are most frequently found in morphologically integrated traits, may be even less common than previously thought. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of the mixture of avermectin and imidacloprid on mortality and developmental stability of Copera annulata (Odonata: Zygoptera) larvae

The present study explored the effects of mixture of avermectin and imidacloprid on the level of fluctuating asymmetry (FA) and mortality of Copera annulata larvae. The results showed that the mortality of larval damselflies treated with different concentrations of insecticide did not differ significantly. However, we found that the levels of FA of two traits were significantly different with different treatments but the others did not show any differences. Explicitly, FA of two traits increased with increasing pesticide concentration. There was a significantly negative relationship between first femur length and the absolute difference between its right and left sides. There was no relationship with respect to the absolute difference between the right and left sides of all traits and their body size. FA was not associated with mortality. Our results emphasized that insecticide had potential effects on bilaterally symmetrical traits of damselfly larvae, although they were no longer treated with insecticide during the last rearing.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 44–50.     

Behavioural and physiological correlates of personality in greylag geese (Anser anser)

Personality means suites of correlated behavioural traits, also referred to as “behavioural syndromes” or “personality dimensions”. Across animal taxa similar combinations of traits seem to prevail, which may have proximate foundation in common neuroendocrine mechanisms. Hitherto, these have been rarely studied in intact social settings. We investigated personalities of greylag goose males from a free-roaming flock that shows complex social relationships. In connection with our longitudinal study on the consistency of behavioural and physiological responses to multiple challenges, we asked whether and how single, personality-related behavioural traits correlate with each other to form personality dimension(s). We tested whether these dimensions were related to physiological characteristics that previously showed limited plasticity (heart rate (HR), baseline and stress-induced excreted immuno-reactive corticosterone (BM), and testosterone metabolites levels) and, furthermore, to age, body measures, and dominance rank. Principal-components analysis based on behavioural variables revealed two factors: 51.1% of variability was explained by “aggressiveness” and a further 19.1% by “sociability”. “Aggressiveness” comprised correlated measures of aggression, subordinance, boldness, vigilance, and proximity to the mate. This “aggressiveness” positively correlated with stress-induced BM levels, the HR increase during aggressive interactions, and with dominance rank, which may suggest proximate and functional contingencies of this personality dimension.     

Geographical variation in asymmetry in Gasterosteus aculeatus

We tested whether fluctuating asymmetry (FA) in undisturbed populations is associated with several natural environmental factors and whether FA is negatively correlated with fitness in the wild. We compared the FA of multiple bony structural defences among 87 endemic populations of threespine stickleback ( Gasterosteus aculeatus L.) inhabiting pristine freshwater habitats on the islands of Haida Gwaii, British Columbia, Canada. Multi-trait FA for adults and juvenile fish varied extensively among populations, but only in adults did it correlate with geography and two habitat characteristics (pH and water colour). Mean FA among individual traits varied concordantly among populations but was not correlated within individuals. While asymmetrical fish showed slightly higher levels of parasitism as predicted, selection differentials based on age class comparisons suggested that asymmetrical fish had the same or marginally higher survival than symmetrical fish. Selection differentials of FA varied significantly among traits and may reflect variability in their functional importance and in the strength of selection on their developmental stability. The data imply that FA/fitness associations are heterogeneous and character-specific.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 9–22.     

Female health,attractiveness, and desirability for relationships: Role of breast asymmetry and waist-to-hip ratio

Fluctuating asymmetry (FA) of ordinarily bilaterally symmetrical traits in humans has been proposed to indicate developmental anomaly. Recent research has shown that individuals with minimal FA are judged to be attractive, and preferred as sexual partners (Thornhill and Gangestad 1993). Waist-to-hip ratios (WHR) have been also shown to reflect health and reproductive capability of woman and those with low WHRs are judged more attractive and healthy (Singh 1993a,b). The present study examines the relative roles of WHR and FA in female breasts in judgments of female attractiveness, health, and desirability for short-term and long-term relationships. Male college students were asked to judge attractiveness of female figures that differed in WHR (high and low) and breast symmetry (none, low, or high). In the first test, paired comparison method was used in which each figure was paired one at a time with all other figures. In the second test, subjects examined all figures simultaneously, estimated their age, and rated each figure for attractiveness, feminine looks, health, overall degree of body symmetry, and willingness to engage in short- and long-term relationship. Results from both tests show that figures with low WHRs were judged to be more attractive than figures with high WHRs, regardless of their degree of breast asymmetry. The figure with low WHR and symmetrical breasts was judged to be most attractive and youngest of all other figures. It appears that men use both WHR and breast asymmetry in judging attractiveness and being willing to develop romantic relationships. It is proposed that WHR and breast asymmetry may signal different aspects of overall female mate quality.     

The association of three indicators of developmental instability with mating success in humans

Developmental instability (DI) has been proposed to relate negatively to aspects of evolutionary fitness, like mating success. One suggested indicator is fluctuating asymmetry (FA), random deviations from perfect symmetry in bilateral bodily traits. A meta-analytically robust negative association between FA and number of lifetime sexual partners has been previously shown in men and women. We examined the relationship between bodily FA across twelve traits and indicators of quantitative mating success in 284 individuals (141 males, age 19–30 years). Two further indicators of DI, minor physical anomalies (MPAs) and asymmetry in palmar atd angles, were also assessed. For men, no significant associations were detected, whereas for women, unexpected positive relationships of FA with the number of lifetime sexual partners and one-night stands emerged. Thus, in a large sample and using a more highly aggregated FA index, our study fails to replicate previous findings, though equivalence testing also did not support deviation from previous meta-analytic estimates, especially for men. No associations were found for MPAs and FA in atd angles in either sex.     

Effects of maternal body morphology, morning sickness, gestational diabetes and hypertension on fluctuating asymmetry in young women

The magnitude of fluctuating asymmetry (FA)—an indicator of genetic and phenotypic quality—can be affected by genetic perturbations, environmental stressors, and maternal effect (maternal age, diseases, dietary deficiency). Maternal effect on human FA has been typically investigated in newborns or very young children. There are no studies investigating whether maternal effect can disrupt developmental mechanisms responsible for the secondary sexual traits that are manifested at adulthood under the influence of steroid hormones. We investigated the effect of maternal degree of obesity, gestational diabetes and hypertension, and morning sickness on the magnitude of FA in nonsexual traits as well as asymmetric thigh circumference—a sexually differentiated trait—in adult daughters. Results revealed that gestational diabetes and hypertension and maternal obesity are positively associated with FA in nonsexual traits. FA in nonsexual traits was not associated with morning sickness; however, the FA in the sexual trait (thigh circumference) was positively related to third-trimester morning sickness. Fluctuating asymmetries of nonsexual traits and thigh circumference were significantly correlated. This preliminary study demonstrates a maternal effect on adult daughters' developmental instability as measured by sexual and nonsexual traits.     

FLUCTUATING ASYMMETRY IN A SALIX HYBRID SYSTEM: THE IMPORTANCE OF GENETIC VERSUS ENVIRONMENTAL CAUSES

To examine the effects of hybridization and environmental stress on developmental instability, we examined fluctuating asymmetry (FA), the variance in random deviations from perfect symmetry in bilaterally symmetrical traits, for leaf symmetry in a Salix hybrid system. An abiotic environmental stress (water stress), an interspecific biotic stress (pathogen attack), and an intraspecific biotic stress (competition) were examined to determine which factors increase developmental instability. None of these three environmental stressors significantly increased FA. However, genetic stress through hybridization was detected; hybrid plants showed significantly higher levels of FA than parental species. In contrast to hybridization providing greater developmental stability through heterozygosity, these results suggest that complex, nonadditive interactions provided developmental stability and that developmental instability increased when coadapted gene complexes were disrupted through hybridization. In addition, plant biomass was significantly, negatively correlated with FA, suggesting that those individuals that were more able to buffer themselves against the disruptive effects of environmental stress may have a selective advantage over those that are less able to buffer themselves against these disruptive effects.     

Genetic and environmental influence on the asymmetry of dermatoglyphic traits

Fluctuating asymmetry (FA) is defined as random deviations from bilateral symmetry of the body. Thus, its magnitude is often used to evaluate developmental homeostasis. In this study we evaluate the following hypotheses: 1) FA of dermatoglyphic traits has a significant genetic component; 2) prenatal maternal environment (PME) has a significant effect on the FA of dermatoglyphic traits in developmentally healthy individuals; and 3) genetic or environmental factors affect FA on organismal or systemic levels. Therefore, their effect is better seen in composite scores of FA rather than in FA indices for single traits. We analyzed 15 dermatoglyphic traits from 140 pairs of monozygous twins, 120 pairs of dizygous twins, and 106 pairs of mothers and daughters. All individuals were developmentally healthy. The influence of genetic and environmental factors on FA was evaluated by analysis of variance and regression analysis. For a majority of the traits in our study, FA showed significant but weak heritabilities, with values falling within the 0.20-0.35 range. None of the traits taken separately demonstrated the effect of PME on FA to be significantly greater than zero. The composite score of FA tended to have greater heritability values than individual traits. One of them, obtained in principal components analysis, showed a significant PME effect, supporting the hypothesis that FA is a systemic property.     

The sound of symmetry: Voice as a marker of developmental instability

Low fluctuating asymmetry (FA, a measure of deviation from bilateral symmetry) appears to be a phenotypic marker of reproductive viability and health. In the present study, we investigated whether ratings of voice attractiveness were correlated with variations in FA. Several bilateral traits were measured to calculate a FA index and independent raters who did not know and never saw the subjects assessed the attractiveness of recordings of each subject's voice. Voices of subjects with greater bilateral symmetry were rated as more attractive by members of both sexes than those with asymmetrical traits.     

Intraspecific competition influences the symmetry and intensity of aggression in the Argentine ant

Cooperative social groups rely on the ability to distinguishmembers from nonmembers. Accordingly, social insects have evolveda variety of systems that allow discrimination of nest matesfrom non–nest mates. In this study, we show that experiencecan modify patterns of intraspecific aggression in Argentineants (Linepithema humile). In laboratory experiments, we foundthat aggression between colonies was often asymmetrical, butin all five cases, this asymmetry shifted to symmetrical aggressionafter contact with a hostile colony. Moreover, in the field,aggression between workers collected from colony borders wassymmetrical, whereas polarized aggression occurred between workerscollected 500 m away from colony borders. Coinciding with thisshift in aggression symmetry, we also observed an increase inboth the overall level of aggression and the frequency of aggressionin both the field and laboratory bioassays. We found littleevidence for colony-level competitive asymmetries stemming frompolarities in aggression at the worker level, either in thelaboratory or in the field. These results illustrate that recognitionsystems in Argentine ants are surprisingly dynamic and provideexperimental evidence for how recognition can be adjusted inresponse to specific circumstances—in this case the presenceof intraspecific competitors.     

Is phenotypic canalization involved in the decline of the endemic Aquilegia thalictrifolia? Rethinking relationships between fluctuating asymmetry and species conservation status

Fluctuating asymmetry (FA), the deviation from the normal symmetrical condition of a morphological trait having specific morphological symmetry, increases in response to environmental and genetic stress, is related to phenotypic plasticity and is considered a tool for monitoring a species conservation status. However, FA–stress relations are dependent on measured traits or species‐specific characteristics such as mating system and habitat. This study investigates the relationships between FA, genetic diversity, population size, density and individual fitness traits (plant height, fruit and seed set), in the endemic Aquilegia thalictrifolia, a mixed breeder that is declining, but maintaining high levels of heterozygosity. Leaf and flower FA and other traits were investigated in 10 populations of A. thalictrifolia, the whole species range. As a result, we found similar patterns of FA in leaves and flowers between populations, indicating a homogenous level of stress between populations that differed for other traits. FA and the other traits were not related, including heterozygosity. Heterozygosity was not related to individual fitness traits with the exception of plant height. In accordance with other studies, we found that the role of FA as a tool for assessing the conservation status of a species or population should be reconsidered. However, we conclude that a low level of FA should not automatically be considered an indicator of good conservation status or low level of stress, because in species that evolved in highly stable environments it may indicate a scarce ability to plastically respond to environmental changes, as a consequence of environmental and genetic canalization. Further investigation of this point is needed.     

Sexual selection for symmetrical male medflies (Diptera: Tephritidae) confirmed in the field

The role of fluctuating asymmetry as an indicator of fitness to females in mate choice remains controversial. Previous studies indicated that male medflies with symmetrical supra-fronto-orbital (SFO) bristles achieve relatively high mating success under laboratory conditions. Here we present data from field cage studies of wild collected medflies in Guatemala and Crete, which reveal the same association between fluctuating asymmetry in SFO bristle length and mating success as that seen in the laboratory. The experiments in Crete included males that were missing one or both of their bristles. A comparison of mating success between the three groups indicated that the mere presence of bristles did not exert a major influence. Analysis of attempted courtships suggests that the association between male mating success and FA in bristle length appears to be generated as a result of females being more likely to enter into courtships with symmetrical males, rather than through a rejection of asymmetrical males during or after it. This raises the possibility that the primary stimulus that makes a symmetrical male attractive is acting at too great a distance to depend on symmetry itself. Alternatives might include superior pheromone emissions or the occupation of a prime location within the lek.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81 , 347–355.     

Fluctuating Asymmetry and Environmental Stress: Understanding the Role of Trait History

While fluctuating asymmetry (FA; small, random deviations from perfect symmetry in bilaterally symmetrical traits) is widely regarded as a proxy for environmental and genetic stress effects, empirical associations between FA and stress are often weak or heterogeneous among traits. A conceptually important source of heterogeneity in relationships with FA is variation in the selection history of the trait(s) under study, i.e. traits that experienced a (recent) history of directional change are predicted to be developmentally less stable, potentially through the loss of canalizing modifiers. Here we applied X-ray photography on museum specimens and live captures to test to what extent the magnitude of FA and FA-stress relationships covary with directional shifts in traits related to the flight apparatus of four East-African rainforest birds that underwent recent shifts in habitat quality and landscape connectivity. Both the magnitude and direction of phenotypic change varied among species, with some traits increasing in size while others decreased or maintained their original size. In three of the four species, traits that underwent larger directional changes were less strongly buffered against random perturbations during their development, and traits that increased in size over time developed more asymmetrically than those that decreased. As we believe that spurious relationships due to biased comparisons of historic (museum specimens) and current (field captures) samples can be ruled out, these results support the largely untested hypothesis that directional shifts may increase the sensitivity of developing traits to random perturbations of environmental or genetic origin.     

Rotational stimulation-related changes of the motor asymmetry in the goldfish

We studied changes in the motor asymmetry of the goldfish induced by single-session long-lasting vestibular stimulations (clockwise and counter clockwise rotations around the rostro-caudal body axis) and repetitive everyday short sessions of such stimulation (training); the latter mode led to the development of adaptation (resistance to fatigue). Rotational stimulation of different durations and directions elicited effects of different patterns and intensities. Such stimulation enhanced or, vice versa, smoothed the motor asymmetry in “dextral” and “ sinistral” fishes, up to full symmetry or even a change of the preferred turning direction. Adaptation to unilateral rotational stimulation allows an experimenter to selectively and gradually induce the resistivity of the left-or right-ward asymmetry to fatigue effects. Earlier, we found that the motor asymmetry in the goldfish, which is determined by the functional asymmetry of the brain, correlates with the morphological asymmetry of Mauthner neurons localized in the medulla in a mirror manner and playing a crucial role in the control of turnings in the course of locomotion (swimming). Experimental rotational stimulation-induced gradual modification of the motor asymmetry in the goldfish can serve as a physiological model for more detailed studies of the structural base of the functional brain asymmetry and some mechanisms of adaptation on the level of single neurons. Neirofiziologiya/Neurophysiology, Vol. 37, Nos. 5/6, pp. 432–442, September–December, 2005.     

Effect of Ascaris infection on the nutritional status and I.Q. of children

It was estimated that about 1.3 billion persons all over the world were infected with Ascaris Lumbricoides (A.L.), Especially children in tropical and subtropical countries. AIM To investigate the effects of A.L. infection on the nutritional status and the intellectual level in a sample of Egyptian primary school children from rural Giza province. SUBJECTS AND METHODS A sample of 637 children (329 boys and 308 girls) aged 6–12 years, have been subjected to some anthropometric measurements including body weight, body height, arm circumference, head circumference and triceps skinfold thickness. In addition, the I.Q. was determined using “Draw-a-man” test. Blood hemoglobin concentration was also determined using a spectrophotometric method. All the children were then subjected to stools and urine examinations, and peri-anal swab. Only 242 children were included for further study, of whom 45 boys and 38 girls were found infected with A.L. solely, and 81 boys and 78 girls of about the same age free of parasitic infections were taken as control. RESULTS Children infected with A.L. has significantly lower body weight, height, and arm circumference but insignificantly lower skinfold thickness and head circumference as comparedto the control group. Infected children had significantly lower hemoglobin concentration and I.Q. than the controls. CONCLUSIONS Selected anthropometric measurements, biochemical and intellectual tests from a useful complementary battery for reliable and informative investigation of the effects of parasitic infection on child nutrition and health. A.L. was found to have a significant effect on the physical and intellectual status of the rural Egyptian children of age 6–12 years.     

Fluctuating asymmetry and psychometric intelligence.

Little is known about the genetic nature of human psychometric intelligence (IQ), but it is widely assumed that IQ''s heritability is at loci for intelligence per se. We present evidence consistent with a hypothesis that interindividual IQ differences are partly due to heritable vulnerabilities to environmental sources of developmental stress, an indirect genetic mechanism for the heritability of IQ. Using fluctuating asymmetry (FA) of the body (the asymmetry resulting from errors in the development of normally symmetrical bilateral traits under stressful conditions), we estimated the relative developmental instability of 112 undergraduates and administered to them Cattell''s culture fair intelligence test (CFIT). A subsequent replication on 128 students was performed. In both samples, FA correlated negatively and significantly with CFIT scores. We propose two non-mutually exclusive physiological explanations for this correlation. First, external body FA may correlate negatively with the developmental integrity of the brain. Second, individual energy budget allocations and/or low metabolic efficiency in high-FA individuals may lower IQ scores. We review the data on IQ in light of our findings and conclude that improving developmental quality may increase average IQ in future generations.