Patterns Of Fluctuating Asymmetry Research Articles

Fluctuating Asymmetry and Stress in Macaca fuscata: Does Captivity Affect Morphology?

Fluctuating Asymmetry (FA) in morphology is used as a proxy for developmental instability in response to stress factors. FA has important implications for understanding the impact of differential environments and stressors on the skeletal phenotype. Here, we explore FA in the mandibular morphology of wild and captive Macaca fuscata to detect differences induced by the captive environment. We use two different approaches in Geometric Morphometrics to characterise the degree and patterns of FA and Directional Asymmetry (DA) based on 3D mandibular landmarks. Our results show that the wild and captive groups exhibit morphological dissimilarities in the symmetric component of shape while no significant degree of asymmetry (fluctuating or directional) was detected. Based on our results and on previous literature on the subject, we suggest that (I) captivity is likely to affect the mandibular morphology of M. fuscata; (II) FA may not be a suitable indicator to detect stress in the conditions analysed; and that (III) the mandible may not be the ideal region to study asymmetry because of its functional nature.

Wing asymmetry of a butterfly community: is altitude a source of stress?

We present a novel analysis of fluctuating asymmetry (FA) for butterfly wings at the community-level, along an altitudinal gradient. FA is an important biomonitoring tool that detects deviations of perfect symmetry in bilateral characters, assuming that genetic and/or environmental factors can be a source of stress. This study evaluated the effects of increased altitude on the symmetry of butterfly wings, testing the hypothesis that FA should increase with increased elevation in a tropical mountain. Butterflies were sampled along an altitudinal gradient of 800 to 1.400 m and forewings were detached, scanned and evaluated for symmetry. Length, width and area of the right and left forewings were measured as surrogates for FA and then combined into an index taking into account the variability of wing sizes of the whole butterfly community. We observed true patterns of FA in the length, width and area of the wings, and wing FA area increased with increased altitude. This study pioneered the analysis of FA for a community of butterflies and FA was efficient to detect developmental instability indicated by imperfections in butterfly wings.

Patterns of fluctuating asymmetry in the limbs of anurans.

It has been hypothesized that fluctuating asymmetry (FA) may provide an indication of the functional importance of structures within an organism, with structures that more strongly impact fitness being more symmetric. Based on this idea, we predicted that for tetrapods in which the forelimbs and hindlimbs play an unequal role in locomotion, the less functionally important limb set should display higher levels of FA. We conducted a multispecies test of this hypothesis in anurans (frogs and toads), whose saltatory locomotor mode is powered by the hindlimbs. We also tested whether FA in the forelimbs, which play a more important role during landing, differed between families that differ in the degree of forelimb use in locomotion (Bufonidae vs. Ranidae). We calculated FA from the lengths of humeri and femora measured from disarticulated skeletal specimens of four anuran taxa (Bufonidae: Anaxyrus americanus, Rhinella marina; Ranidae: Lithobates catesbeianus, Lithobates clamitans). Our findings were consistent with the hypothesis that natural selection for increased locomotor performance may influence patterns of FA seen in vertebrate limbs, with all species displaying lower mean FA in the hindlimbs. More subtle functional roles between the forelimbs of bufonids and ranids, however, did not elicit different levels of FA.

Mouse Skull Mean Shape and Shape Robustness Rely on Different Genetic Architectures and Different Loci.

The genetic architecture of skull shape has been extensively studied in mice and the results suggest a highly polygenic and additive basis. In contrast few studies have explored the genetic basis of the skull variability. Canalization and developmental stability are the two components of phenotypic robustness. They have been proposed to be emergent properties of the genetic networks underlying the development of the trait itself, but this hypothesis has been rarely tested empirically. Here we use outbred mice to investigate the genetic architecture of canalization of the skull shape by implementing a genome-wide marginal epistatic test on 3D geometric morphometric data. The same data set had been used previously to explore the genetic architecture of the skull mean shape and its developmental stability. Here, we address two questions: (1) Are changes in mean shape and changes in shape variance associated with the same genomic regions? and (2) Do canalization and developmental stability rely on the same loci and genetic architecture and do they involve the same patterns of shape variation? We found that unlike skull mean shape, among-individual shape variance and fluctuating asymmetry (FA) show a total lack of additive effects. They are both associated with complex networks of epistatic interactions involving many genes (protein-coding and regulatory elements). Remarkably, none of the genomic loci affecting mean shape contribute these networks despite their enrichment for genes involved in craniofacial variation and diseases. We also found that the patterns of shape FA and individual variation are largely similar and rely on similar multilocus epistatic genetic networks, suggesting that the processes channeling variation within and among individuals are largely common. However, the loci involved in these two networks are completely different. This in turn underlines the difference in the origin of the variation at these two levels, and points at buffering processes that may be specific to each level.

Impact of sewage pollution on two species of sea urchins in the Mediterranean Sea (Cortiou, France): Radial asymmetry as a bioindicator of stress

BackgroundThe surroundings of the Cortiou sewage are among the most polluted environments of the French Mediterranean Sea (Marseilles, France). So far, no studies have precisely quantified the impact of pollution on the development of organisms in this area. MethodsWe used a fluctuating asymmetry (FA) measure of developmental instability (DI) to assess environmental stress in two species of radially symmetric sea urchins (Arbacia lixula and Paracentrotus lividus). For six sampling sites (Cortiou, Riou, Maire, East Maire, Mejean, and Niolon), levels of FA were calculated from continuous and discrete skeletal measures of ambulacral length, number of pore pairs and primary tubercles. ResultsFor both species, the most polluted sampling site, Cortiou, displayed the highest level of FA, while the Maire and East Maire sampling sites displayed the lowest levels. A. lixula revealed systematic differences in FA among sampling sites for all characters and P. lividus showed differences in FA for the number of primary tubercles. ConclusionsStatistical analyses of FA show a concordance between the spatial patterns of FA among sampling sites and the spatial distribution of sewage discharge pollutants in the Cortiou area. High developmental stress in these sampling sites is associated with exposure to high concentrations of heavy metals and many harmful organic substances contained in wastewater. FA estimated from structures with complex symmetry appears to be a fast and reliable tool to detect subtle differences in FA. Its use in biomonitoring programs for inferring anthropogenic and natural environmental stress is suggested.

Amniotic fluid deficiency and congenital abnormalities both influence fluctuating asymmetry in developing limbs of human deceased fetuses.

Fluctuating asymmetry (FA), as an indirect measure of developmental instability (DI), has been intensively studied for associations with stress and fitness. Patterns, however, appear heterogeneous and the underlying causes remain largely unknown. One aspect that has received relatively little attention in the literature is the consequence of direct mechanical effects on asymmetries. The crucial prerequisite for FA to reflect DI is that environmental conditions on both sides should be identical. This condition may be violated during early human development if amniotic fluid volume is deficient, as the resulting mechanical pressures may increase asymmetries. Indeed, we showed that limb bones of deceased human fetuses exhibited increased asymmetry, when there was not sufficient amniotic fluid (and, thus, space) in the uterine cavity. As amniotic fluid deficiency is known to cause substantial asymmetries and abnormal limb development, these subtle asymmetries are probably at least in part caused by the mechanical pressures. On the other hand, deficiencies in amniotic fluid volume are known to be associated with other congenital abnormalities that may disturb DI. More specifically, urogenital abnormalities can directly affect/reduce amniotic fluid volume. We disentangled the direct mechanical effects on FA from the indirect effects of urogenital abnormalities, the latter presumably representing DI. We discovered that both factors contributed significantly to the increase in FA. However, the direct mechanical effect of uterine pressure, albeit statistically significant, appeared less important than the effects of urogenital abnormalities, with an effect size only two-third as large. We, thus, conclude that correcting for the relevant direct factors allowed for a representative test of the association between DI and stress, and confirmed that fetuses form a suitable model system to increase our understanding in patterns of FA and symmetry development.

Fluctuating asymmetry and herbivory in two ontogenetical stages of Chamaecrista semaphora in restored and natural environments

Reintroduced environments represent stressful conditions to plants that can be observed in different ways. We evaluated the relationships between fluctuating asymmetry (FA), herbivory, and plant ontogeny of Chamaecrista semaphora (Fabaceae) under natural and restored habitat conditions. The patterns of leaf FA and herbivory by folivorous insects (chewing) on saplings and mature plants in each habitat were determined. No relationship was found between FA and herbivory on the two ontogenetic stages in both environments, suggesting that FA did not represent an indicator of stress. The frequency and amount of leaf area removed by folivores were higher in saplings compared to adult plants under the natural habitat, while the opposite trend was observed on restored habitat for adult plants. The restored habitat did not represent an environmental stress condition to C. semaphora, indicating that this endemic plant may represent a good candidate to restoration programs in harsh environments. However, we observed great differences in leaf FA and herbivory among individuals within habitats. Knowledge on plant quality, competition, physiology, and interactions with natural enemies are highly needed to support long lasting programmes on restoration of harsh environments.

Insect Herbivores ofCoccoloba cereiferaDo Not Select Asymmetric Plants

Fluctuating asymmetry (FA) represents small, random variations from the symmetric bilateral pattern, and it is a frequently used measurement of plant and animal stresses. Some studies have shown a relationship between FA and herbivory, suggesting that FA might be a reliable indicator of plant quality and plant susceptibility to herbivore attack. In this study, we investigated the relationship between leaf FA of Coccoloba cereifera Schwacke (Polygonaceae) and the pattern of attack by the scale insect Abgrallaspis cyanophylly Signoret (Hemiptera: Diaspididae). Thirty individuals of C. cereifera were marked and followed during 2007 in southeastern Brazil, and all leaves of three shoots per plant were sampled, numbered, and categorized as young, mature, or senescent. We measured right and left widths of all leaves after digitizing the images to determine levels of FA for each leaf sampled per plant. Individuals of A. cyanophylli were counted using a stereoscope in the laboratory to determine infestation levels. Leaves of C. cereifera exhibited true patterns of FA, as shown by the normal distribution of asymmetry values. We observed high variation in attack rates by A. cyanophylly among C. cereifera individuals, with 43.3% of plants with no insects, whereas others exhibited up to 23,000 insects. No statistically significant relationship was observed between variation in FA and variation in A. cyanophylli among plants. These results suggest that FA cannot be used as an indicator of plant quality and susceptibility to herbivore attack but suggest that herbivores themselves might act as plant stressors.

PLASTICITY, CANALIZATION, AND DEVELOPMENTAL STABILITY OF THEDROSOPHILAWING: JOINT EFFECTS OF MUTATIONS AND DEVELOPMENTAL TEMPERATURE

The phenotypic effects of genetic and environmental manipulations have been rarely investigated simultaneously. In addition to phenotypic plasticity, their effect on the amount and directions of genetic and phenotypic variation is of particular evolutionary importance because these constitute the material for natural selection. Here, we used heterozygous insertional mutations of 16 genes involved in the formation of the Drosophila wing. The flies were raised at two developmental temperatures (18 degrees C and 28 degrees C). Landmark-based geometric morphometrics was used to analyze the variation of the wing size and shape at different hierarchical levels: among genotypes and temperatures; among individuals within group; and fluctuating asymmetry (FA). Our results show that (1) the phenotypic effects of the mutations depend on temperature; (2) reciprocally, most mutations affect wing plasticity; (3) both temperature and mutations modify the levels of FA and of among individuals variation within lines. Remarkably, the patterns of shape FA seem unaffected by temperature whereas those associated with individual variation are systematically altered. By modifying the direction of available phenotypic variation, temperature might thus directly affect the potential for further evolution. It suggests as well that the developmental processes responsible for developmental stability and environmental canalization might be partially distinct.

There is no heterotic effect upon developmental stability in the ventral side of the skull within the house mouse hybrid zone

Fluctuating asymmetry (FA) of a body is expected to be related to an organism's developmental instability. We studied patterns of FA in the ventral side of the skull along a transect across the central-European portion of the hybrid zone between two house mouse subspecies, Mus musculus musculus and Mus musculus domesticus. We found that FA was not significantly different between introgression classes relative to differences between localities within those classes and that the within-class differences were much larger than differences between individual-signed asymmetries within localities. However, if year was added to the same analysis as another factor, FA was not significantly different among localities within the same introgression class. When individual asymmetries were plotted against individual hybrid indices, hybrids appeared more asymmetric than individuals from outside of the zone. Thus contrary to previous studies, we did not find lower FA indicating heterotic effect in hybrids for the traits studied. It is suggested that the impact of hybridization on FA in the ventral side of the mouse skull is negligible or overwhelmed by other factors.

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.

On avian asymmetry: evidence of natural selection for symmetrical tails and wings in birds

Fluctuating asymmetry (FA), or minor deviations from perfect bilateral symmetry in otherwise symmetrical structures, may reflect exposure to environmental or genetic stresses during trait development. Consequently, several authors have recently suggested that FA in elaborate secondary sexual characters such as the long tails of some birds could play an important role in sexual selection, perhaps by being used as a reliable signal of phenotypic quality during mate choice. Here we examine an alternative possibility: that the extent of FA in long tails and wings of birds is constrained primarily by natural selection for aerodynamic efficiency. Predictions developed from aerodynamic theory were tested by using comparative data from 63 long-tailed species. Data on FA in wing lengths confirmed that aerodynamic requirements may underlie patterns of FA in lifting surfaces: species that spend much of their time flying and those that migrate had more symmetrical wings than other birds. There was also substantial variation in the extent of tail FA. As predicted, long-tailed species with aerodynamically functional forked tails had more symmetrical outer tail feathers than those with other long tail types in which feather symmetry has less impact on flight performance. However, in common with several other recent studies, our data failed to support the predictions of the sexual selection hypothesis. In sexually dimorphic species, there was no evidence that tail asymmetry was greater in the longer-tailed sex, nor was tail FA negatively correlated with tail length. Our results therefore suggest that patterns of FA in long tails and wings may often be better understood in a context of natural rather than sexual selection.