Showing papers on "Fluctuating asymmetry published in 2003"

Developmental instability as a research tool: using patterns of fluctuating asymmetry to infer the developmental origins of morphological integration.

Abstract: This paper takes the study of fluctuating asymmetry (FA) beyond its conventional use as a measure of developmental instability, and turns it into a new research tool for evolutionary developmental biology. Covariation between morphological traits can have two developmental origins: direct developmental interactions, for instance between traits that derive from a common developmental precursor or interact by induction, and parallel variation in separate pathways that are subject to the same environmental or genetic variation. Analysis of covariances in signed FA can be used to distinguish between these two origins of trait covariation. For signed FA in two traits to be correlated, the developmental perturbations causing asymmetry must be transmitted between the developing traits, which requires a direct developmental link between them. Therefore, the analysis of covariation in signed FA can be

Fluctuating asymmetry in a secondary sexual trait: no associations with individual fitness, environmental stress or inbreeding, and no heritability

Abstract: It has been suggested that fluctuating asymmetry (FA) in secondary sexual traits may be a useful indicator of either individual quality or environmental stress. We tested this concept using a series of analyses of FA in male antler size in a wild red deer (Cervus elaphus) population, using four measures of size repeated across successive years on the same individuals. We found no consistent evidence of correlations between traits in levels of FA, nor of any associations between known environmental or developmental conditions. None of the four measures of FA showed a significant heritability (average h2 = 0.041), nor was there any evidence of inbreeding depression. For three of the four traits, fluctuating asymmetry did not predict either annual or lifetime breeding success. However there were significant associations between breeding success and FA in antler length. Given the series of null results in our other tests, it seems likely that this was a direct mechanistic effect rather than because measures of FA were indicative of individual quality or condition.

Fluctuating Asymmetry, Animal Behavior, and Evolution

Abstract: Publisher Summary The chapter introduces fluctuating asymmetry and shows why it is relevant to behavioral ecologists. It illustrates where the knowledge about fluctuating asymmetry is lacking in important areas, and to offer suggestions that will help behavioral ecologists fill those gaps. The chapter reviews relationships between asymmetry and fitness. These relationships appear to be taxon and trait specific. The specificity of such relationships probably arises from the weak correlation of fluctuating asymmetry with developmental instability. The chapter discusses common methodological problems of studying fluctuating asymmetry. A hypothesis is presented that fluctuating asymmetry may have significant genetic redundancy and could be viewed as a neutral character. Many behavioral ecologists have quantified fluctuating asymmetry in secondary sexual characters and investigated whether such asymmetry plays a role in sexual selection processes. The chapter concludes that a link is established between behavioral studies of fluctuating asymmetry and broader evolutionary questions, and it is suggested that researchers adopt a more integrated approach that brings together a proximate understanding of the impact of asymmetry with more long-term studies of the origins of asymmetry and evolutionary consequences of selection against fluctuating asymmetry.

The Ontogeny of Fluctuating Asymmetry

Abstract: 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.

Relationship between fluctuating asymmetry and fitness within and between stressed and unstressed populations of the wolf spider Pirata piraticus.

Abstract: Although developmental instability, measured as fluctuating asymmetry (FA), is expected to be positively related to stress and negatively to fitness, empirical evidence is often lacking or contradictory when patterns are compared at the population level. We demonstrate that two important properties of stressed populations may mask such relationships: (i) a stronger relationship between FA and fitness, resulting in stronger selection against low quality (i.e. developmental unstable) individuals and (ii) the evolution of adaptive responses to environmental stress. In an earlier study, we found female wolf spiders Pirata piraticus from metal exposed populations to be characterized by both reduced clutch masses and increased egg sizes, the latter indicating an adaptive response to stress. By studying the relationship between these two fitness related traits and levels of FA at individual level, we here show a significant negative correlation between FA and clutch mass in metal stressed populations but not in unstressed reference populations. As a result, levels of population FA may be biased downward under stressful conditions because of the selective removal of developmentally unstable (low quality) individuals. We further show that females that produced larger eggs in stressed populations exhibited lower individual FA levels. Such interaction between individual FA and fitness with stress may confound the effect of metal stress on FA, resulting in an absence of relationships between FA, fitness and stress at the population level.

Female preference for symmetry in computer-animated three-spined sticklebacks, Gasterosteus aculeatus

Abstract: Fluctuating asymmetries are subtle random deviations from perfect symmetry in bilateral traits caused by the inability of individuals to buffer their development against the disruptive effects of genetic and environmental stresses The degree of asymmetry of secondary sexual characters is supposed to convey information about a male's phenotypic and/or genetic quality, and females may thus be expected to use bilateral symmetry as a cue in mate choice We independently and simultaneously manipulated the length and the relative symmetry of the pelvic spines of computer-animated three-spined sticklebacks, Gasterosteus aculeatus In all mate choice tests involving two male models differing in spine symmetry, females preferred the symmetric model, irrespective of spine length, though only significantly so when both male models had short spines Females did not significantly discriminate between male models differing in spine length alone The preference for symmetry was stronger the higher the females' physical condition Our study demonstrates that female sticklebacks master the perceptual abilities required to discriminate between potential mates basing exclusively on small length differences between paired structures, and provides experimental evidence that spine symmetry is subject to sexual selection through female choice in this species

Asymmetry in structural defenses: insights into selective predation in the wild.

Abstract: Assessment of geographical patterns in fluctuating asymmetry (small, random differences between sides of bilateral characters) among populations shows promise as a tool to resolve the relative biomechanical importance of traits, in addition to being a possible indicator of habitat quality. We used 115 endemic freshwater populations of threespine stickleback (Gasterosteus aculeatus) from Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada, to explore the degree of concordance between geographical variation of asymmetry in a predator defense structure (bony lateral plates) and geographical variation in several indirect measures of predation regime as well as several abiotic habitat variables. We found a geographical cline in the population frequency of lateral plate asymmetries, with reduced asymmetry in the southern clear-water regions of the archipelago characterized by long reaction distances and greater chance of capture by predators, and elevated asymmetry in the northern stained-water regions with poor visibility and low chances of capture. Lateral plate asymmetry was strongly correlated with expression of several defensive armor traits, including total plate numbers among populations, mean cross-sectional diameter of stickleback with the dorsal and pelvic spines erect, and mean degree of overlap between the plates and spine supports. There were no significant correlations between frequency of asymmetric fish and any of our abiotic habitat variables. Stickleback with structural plate asymmetries had fewer trout-induced scars than symmetric fish in the significant majority of populations, and there was a decrease in structural plate asymmetry with age in stained-water habitats, suggesting that trout predators may be selectively removing asymmetric fish in some lakes. This study provides evidence that geographical variation in developmental stability of threespine stickleback, as seen in the frequencies of asymmetry, reflects differences among populations in the importance of structural defenses to fitness rather than differences in habitat quality, and that asymmetry may be a target of selection by predators in wild populations.

A female melanin ornament signals offspring fluctuating asymmetry in the barn owl.

Abstract: Sexual selection theory predicts that males advertise quality by displaying extravagant ornaments. By contrast, whether phenotypic variation in females has a signalling function remains an open question. Here, to our knowledge, we provide the first evidence that a female plumage trait can signal fluctuating asymmetry in the offspring. We experimentally demonstrate in wild barn owls (Tyto alba) that the extent to which females display black spots on their plumage does not only signal offspring parasite resistance as shown in a previous study but also developmental homeostasis in the offspring. A greater number of spotted females produced offspring that had more symmetrical feathers during the period of growth. Males, that pair non-randomly with respect to female plumage spottiness therefore appear to gain substantial benefits by mating with heavily spotted females. Genetic variation in plumage spottiness is nevertheless maintained as the covariation between offspring body mass and mother plumage spottiness varies annually depending on environmental conditions.

Sexual selection on morphological and physiological traits and fluctuating asymmetry in the yellow dung fly.

Abstract: Previous univariate studies of the yellow dung fly (Scathophaga stercoraria) have demonstrated strong sexual selection, in terms of mating success, on male size (estimated as hind tibia length). To identify specific target(s) of selection on body size and possible conflicting selection pressures on particular body parts, two multivariate field studies of sexual selection were conducted. In one study using point samples from three populations, we assessed several morphological traits, including genital traits and measures of fluctuating asymmetry (FA) of all paired traits. There was sexual selection for large male size in general, confirming previous, univariate studies. With the possible exception of thorax width, which was selected in the opposite direction, no main target of selection was identified, as most morphological traits were highly correlated. There was no detectable sexual selection on the male external genital structures assessed. In a second study using multiple samples from one population, we included physiological measures of energy reserves (lipids, glucose and glycogen) known to affect mating success, in addition to trait size and FA of wings and legs. Inclusion of physiological traits is rare in phenomenological studies of selection. This study again confirmed the mating advantage of large males, and additionally showed independent positive influences of lipid and glucose but not glycogen levels. FA in paired traits generally did not affect male mating success, but was negatively correlated with energy reserves. Our study suggests that inclusion of physiological measures and genital traits in phenomenological studies of selection would be fruitful in other species.

Inbreeding, developmental stability, and canalization in the sand cricket gryllus firmus

Abstract: Inbreeding, the mating of close relatives, is known to have deleterious effects on fitness traits in organisms. Developmental stability (DS) and canalization may represent two processes that allow an organism to maintain a stable development that will produce the fittest phenotype. Inbreeding is thus expected to affect either DS or cana- lization. We tested if inbreeding affects DS and canalization using an inbreeding experiment on the cricket Gryllus firmus . We compared mean length, fluctuating asymmetry (as an index of DS), and morphological variation (as an index of canalization) of four limb traits between seven highly inbred lines, their F 1 crosses, and outbred lines originated from the same stock population and maintained in the same environmental conditions. We show evidence for moderate inbreeding depression on the four measures of leg length. The nonsystematic difference in fluctuating asymmetry indices between breed types indicates that inbreeding or heterozygosity did not affect DS, or that fluctuating asymmetry is not a reliable index of DS. In contrast, inbreeding appears to affect canalization, as shown by the significantly higher variation in inbred lines compared to other lines. Identical low variation values in the crossbred and outbred lines indicate that heterozygosity could affect canalization. High variation in morphological variation and fluctuating asymmetry within crossbred or inbred lines, however, suggest the effect of recessive deleterious alleles on both canalization and DS. Although the strong correlation in morphological variation among traits suggests that identical genetic mechanisms govern canalization for all the limb traits, the absence of significant correlation in fluctuating asymmetry among traits causes us to reject this hypothesis for DS. For most of the traits, morphological variation and fluctuating asymmetry were not significantly correlated, which support the hypothesis that canalization and DS consist in two distinct mechanisms.

Directional and fluctuating asymmetry in finger and a-b ridge counts in psychosis: a case-control study.

Abstract: Several studies have reported alterations in finger and a-b ridge counts, and their derived measures of asymmetry, in schizophrenia compared to controls. Because ridges are fully formed by the end of the second trimester, they may provide clues to disturbed early development. The aim of this study was to assess these measures in a sample of patients with psychosis and normal controls. Individuals with psychosis (n = 240), and normal controls (n = 228) were drawn from a catchment-area case-control study. Differences in finger and a-b ridge count and Fluctuating Asymmetry were assessed in three group comparisons (non-affective psychosis versus controls; affective psychosis versus controls; non-affective psychosis versus affective psychosis). The analyses were performed separately for males and females. There were no significant group differences for finger nor a-b ridge counts. While there were no group difference for Directional Asymmetry, for Fluctuating Asymmetry measures men with non-affective psychosis had significantly higher fluctuating asymmetry of the index finger ridge count (a) when compared to controls (FA-correlation score, p = 0.02), and (b) when compared to affective psychosis (adjusted FA-difference score, p = 0.04). Overall, measures of finger and a-b ridge counts, and their derived measures of directional and fluctuating asymmetry were not prominent features of psychosis in this sample. While directional asymmetry in cerebral morphology is reduced in schizophrenia, this is not reflected in dermatoglyphic variables.

Embryological origins of developmental stability: size, shape and fluctuating asymmetry in prenatal random bred mice.

Abstract: Ontogenetic patterns of fluctuating asymmetry (FA) can be used to test models for the mechanisms underlying stability during embryonic development (developmental stability). In this study, we ask whether developmental processes initially show high levels of instability that are subsequently dampened through active compensatory mechanisms or passive properties of developmental systems or whether the effects of instability accumulate during embryonic development causing random drift away from an earlier stable state. Previous work on this question has dealt with postnatal skeletal growth and thus been unable to effectively distinguish developmental instability from the effects of mechanically mediated variation in bone modeling and remodeling. Here, we report that FA variances of limb skeletal elements in CD1 mice decrease with gestational age from day 14 to birth (day 20.5). Thus, in mouse limbs, skeletal development is characterized by a high level of developmental instability initially that is reduced during subsequent prenatal development. These results are consistent with the existence of active mechanisms that compensate for the effects of minor perturbations or deviations during development. However, they are also consistent with Soule's model of allomeric variation in which the variance of structures is reduced as the number of independent developmental events that produce them increases. This study illustrates that predictions based on morphometric analyses can yield insights into general properties of developmental systems in cases where specific developmental mechanisms are not yet known.

Growth and developmental instability.

Abstract: Developmental stability reflects the ability of an individual to develop a regular phenotype under given environmental and genetic conditions. Measures of developmental instability include the degree of fluctuating asymmetry and the frequency of phenodeviants. Endocrine, neural and circulatory mechanisms that control similar development of morphological characters on the two sides of the body are also involved in controlling overall development. Cross-validation studies have shown that measures of developmental instability are positively correlated with other measures of welfare such as tonic immobility in poultry. Asymmetric animals grow less rapidly than symmetric individuals. Eleven studies have investigated the relationship between growth rate and developmental instability, and the observed effect size (Pearson correlation coefficient adjusted for sample size) is −0.15. Studies of chickens have shown that asymmetry increases as a response to selection for increased growth rate. As conditions for rearing deteriorate by higher density, fluctuating asymmetry increases and growth rate decreases, both within and among farms. Fluctuating asymmetry can be considered a measure of animal welfare since larger values reflect worse environmental conditions as experienced by the individual animal itself. Since growth rate and fluctuating asymmetry are negatively correlated, we can infer that improvement of rearing conditions leading to reduced asymmetry will both benefit the producer (in terms of increased growth), but also the animals in terms of better conditions for rearing.

Fluctuating asymmetry and nutritional condition of Baltic cod (Gadus morhua) larvae

Abstract: The level of fluctuating asymmetry (FA), defined as random deviations from perfect bilateral symmetry, is assumed to reflect the developmental instability (DI) of an organism. Because environmental and genetic stress may increase DI, FA has been used to assess the level of stress experienced by, for example, fish. In this study, left–right asymmetry of lapillar otoliths was related to nutritional condition as estimated from RNA/DNA ratios, in order to investigate the utility of FA to detect feeding-related stress in Baltic cod, Gadus morhua L., larvae. Cod larvae in intermediate and good nutritional condition showed similar values of FA, and these were more symmetric than for larvae in poor condition. As increased levels of FA were restricted to larvae in a condition comparable to that of larvae experiencing at least 3 days of starvation in laboratory experiments, it is suggested that FA is an insensitive indicator of short-term feeding success of larval cod. However, FA can be used to reveal severely starved larva populations and probably also populations that have been subjected to prolonged sub-optimal feeding conditions.

Developmental instability: measures of resistance and resilience using pumpkin (Cucurbita pepo L.)

Abstract: Fluctuating asymmetry measures random deviations from bilateral symmetry, and thus estimates developmental instability, the loss of ability by an organism to regulate its development. There have been few rigorous tests of this proposition. Regulation of bilateral symmetry must involve either feedback between the sides or independent regulation toward a symmetric set point. Either kind of regulation should decrease asymmetry over time, but only right–left feedback produces compensatory growth across sides, seen as antipersistent growth following perturbation. Here, we describe the developmental trajectories of perturbed and unperturbed leaves of pumpkin, Cucurbita pepo L., grown at three densities. Covering one side of a leaf with aluminium foil for 24 h perturbed leaf growth. Reduced growth on the perturbed side caused leaves to become more asymmetrical than unperturbed controls. After the treatment the size-corrected asymmetry decreased over time. In addition, rescaled range analysis showed that asymmetry was antipersistent rather than random, i.e. fluctuation in one direction was likely to be followed by fluctuations in the opposite direction. Development involves right–left feedback. This feedback reduced size-corrected asymmetry over time most strongly in the lowest density treatment suggesting that developmental instability results from a lack of resilience rather than resistance. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78, 27–41.

Fluctuating asymmetry in bank vole populations (Rodentia, Arvicolinae) reflects stress caused by landscape fragmentation in the Mont-Saint-Michel Bay

Abstract: In intensively farmed, reclaimed areas (polders) of Mont-St-Michel Bay, France, bank voles (Clethrionomys glareolus) live in fragmented hedgerows, where populations are small and dispersal rates and genetic diversity are low. These small populations are likely to have been exposed to potential environmental and/or genetic stress. The sensitivity of development to stress can be measured by fluctuating asymmetry (FA). FA was calculated for three samples from a disturbed area and one sample from an adjacent, more connected and undisturbed landscape. Size FA was estimated from 16 measurements of the skull and teeth whilst shape asymmetry was estimated from the skull alone. Bank voles in fragmented hedgerows of the disturbed area had a higher degree of FA than bank voles from the more extensive and more connected hedges of the undisturbed area. These results were confirmed by the study of shape asymmetry, body mass and centroid size of the skull. There were no differences in FA between the three disturbed area samples. We conclude that FA does not reveal differences in the development of bank voles living in isolation under different local conditions in the various parts of the disturbed area. However, FA may allow differentiation between populations from greatly contrasting landscapes. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 37–44.

The use of fluctuating asymmetry and phenotypic variability as indicators of developmental instability: a test of a new method employing clonal organisms and high temperature stress

Abstract: Developmental instability, as estimated by two measures - fluctuating asymmetry and phenotypic variability - was examined using sternopleural bristle number and two wing traits in a clonal strain of Drosophila mercatorum. Eggs were exposed to short-term (30 min) heat stress in water baths at different temperatures (35-40°C in 0.5°C steps) or to a control temperature regime at 25°C. Fluctuating asymmetry and phenotypic variability in sternopleural bristle number were not affected to a significant extent by heat stress, whereas the fluctuating asymmetry and phenotypic variability of both wing measures were significantly higher in adults developed from heat-stressed eggs than in adults developed from eggs kept at 25°C. For both wing measures, there was a tendency for the highest fluctuating asymmetry and phenotypic variability to be observed at temperatures of 37-39°C, suggesting that individuals who experienced the greatest developmental instability at very high temperatures (39.5-40°C) did not survive the heat stress. For the two wing measures, the fluctuating asymmetry and phenotypic variability were significantly correlated, but this was not the case for sternopleural bristle number. Based on a new method, we quantified the effect that environmental variability had on fluctuating asymmetry and phenotypic variability, but found no correlation with the temperatures at which the eggs were stressed. This shows the unpredictability or the impossibility of controlling environmental variability, even in laboratory experiments. We suggest that the method introduced here may in part explain why non-reproducible results have been obtained in developmental instability studies.

Fluctuating asymmetry and other parameters of morphological variation of eelpout Zoarces viviparus (Zoarcidae, Teleostei) from different parts of its distributional range

Abstract: Five populations of eelpout Zoarces viviparus from the White Sea, the Baltic (Gulf of Gdansk and Gulf of Finland) and the North Sea (Wadden Sea and Hafrsfjord) were studied. Using 17 bilateral meristic characters (number of holes in cranial bones) we assessed the following parameters: (i) fluctuating asymmetry (minor deviations from perfect bilateral symmetry), (ii) the factorial component of total phenotypic variance, which is a measure of within-population heterogeneity and (iii) mean values of each character. Morphological similarity among samples was only weakly correlated with geographical distances between sample locations. The magnitude of fluctuating asymmetry was higher in the samples from the White Sea and Hafrsfjord than in samples from the Wadden Sea and the Baltic Sea. The sample from the Gulf of Gdansk was characterized by the lowest fluctuating asymmetry and the highest factorial variation. We propose that among the most important factors determining fluctuating asymmetry in eelpout populat...

Translational asymmetry as a sensitive indicator of cadmium stress in plants: a laboratory test with wild‐type and mutant Arabidopsis thaliana

Abstract: • Translational and bilateral asymmetry have been proposed as sensitive measures of stress in plants, but few studies have addressed the asymmetry-stress association for individuals grown under strictly defined conditions. Here, we assess the impact of cadmium (Cd) stress on various asymmetry measures in a wild-type and mutant strain of Arabidopsis thaliana. • Fitness measures (fresh weight, pod count and shoot length) and developmental stability (DS) measures (bilateral asymmetry and translational asymmetry (TA)) were compared between plants grown under different cadmium concentrations. • Cadmium stress sharply increased TA in both strains but had inconsistent effects on bilateral asymmetry. The TA effects were detected at a Cd concentration when effects on growth and reproduction were not yet evident. • Translational asymmetry, but not bilateral asymmetry, may therefore act as a sensitive indicator of cadmium stress and could be used to assess soil contamination in transplanted A. thaliana.

Quantitative-genetic analysis of wing form and bilateral asymmetry in isochromosomal lines of Drosophila subobscura using Procrustes methods.

Abstract: Fluctuating asymmetry (FA) is often used as a measure of underlying developmental instability (DI), motivated by the idea that morphological variance is maladaptive. Whether or not DI has evolutionary potential is a highly disputed topic, marred by methodological problems and fuzzy prejudices. We report here some results from an ongoing study of the effects of karyotype, homozygosity and temperature on wing form and bilateral asymmetry using isochromosomal lines ofDrosophila subobscura. Our approach uses the recently developed methodologies in geometric morphometrics to analyse shape configurations of landmarks within the standard statistical framework employed in studies of bilateral asymmetries, and we have extended these methods to partition the individual variation and the variation in asymmetries into genetic and environmental causal components. The analyses revealed temperaturedependent expression of genetic variation for wing size and wing shape, directional asymmetry (DA) of wing size, increased asymmetries at suboptimal temperature, and a transition from FA to DA in males as a result of increase in the rearing temperature. No genetic variation was generally detected for FA in our samples, but these are preliminary results because no crosses between lines were carried out and, therefore, the contribution of dominance was not taken into account. In addition, only a subset of the standing genetic variation was represented in the experiments.

Geography of fluctuating asymmetry in the greenfinch, Carduelis chloris

Abstract: Levels of fluctuating asymmetry (FA) in 12 bilateral skeletal traits were estimated from 12 populations of greenfinches (Carduelis chloris) collected along a north-south gradient across Europe. Average FA of measured traits was positively correlated with latitude indicating that the younger and genetically less diverse northern European populations are developmentally less stable than the older and genetically more diverse southern populations. Levels of FA differed significantly between different traits being lowest for functionally important traits (limb and wing bones) and highest for functionally less important traits such as foramina (apertures through bones)- a pattern that was highly concordant across different populations. Males tended to exhibit higher levels of FA than females, a finding consistent with the suggestions that males are more prone to developmental perturbations than females. Age differences in levels of FA were relatively clear, but inconsistent across traits with different degree of functionality. Individual heterozygosity - as enumerated from variation in allozyme loci - was unrelated to individual FA. No evidence for existence of individual asymmetry parameter (IAP) was found although traits related to locomotion indicated some degree of integration, which was expressed by correlations in the signed asymmetry. Nevertheless, an individual's overall asymmetry was poorly predicted by asymmetry of individual characters. Evidence for existence of population asymmetry parameter (PAP) was clear since all traits exhibited a similar degree of association with latitude. That the latitudinal cline of increasing FA towards north coincided with decreasing levels of genetic variability across the cline could be indicative of break down of developmental stability in the recently established and genetically impoverished populations. To what extent a reduced heterozygosity, the break up of co-adapted gene complexes and/or environmental differences contributed to this process cannot be distinguished from our data.

Quantitative variation of four morphological traits in Drosophila melanogaster under larval crowding.

Abstract: Effects of three different larval densities (low, intermediate and high) on phenotypic and genetic variation of four morphological traits (thorax and wing length, sternopleural and abdominal bristle number) were studied in Drosophila melanogaster using the isofemale line technique. Phenotypic variation was found to increase at high larval density in all traits examined. Environmental variance for three traits (exception was sternopleural bristle number) and fluctuating asymmetry for both bilateral traits were also increased under high density conditions. For estimates of genetic variability (among isofemale lines variance, heritability and evolvability), no statistically significant differences among density regimes were detected. However, the trends in changes of these estimates across densities indicated a possibility for enhanced genetic variation under larval crowding for all traits except abdominal bristle number. For the latter trait, genetic variation seemed not to be dependent on density regime. Generally, two metric traits (thorax and wing length) were more affected by larval crowding than two meristic ones (sternopleural and abdominal bristle number). The Results are in complete agreement with those previously obtained for D. melanogaster using extreme temperatures as stress-factors.

Integrating developmental stability analysis and current amphibian monitoring techniques: an experimental evaluation with the salamander ambystoma maculatum

Abstract: Many amphibian populations have declined and others are at risk. Developmental stability analysis (DSA) has been proposed as an “early warning system” because it may detect environmental or genetic stress before they lead to population declines. Deviations from perfect symmetry (fluctuating asymmetry or FA) may indicate stress. We experimentally evaluated the efficacy of DSA to detect sublethal acid stress in the salamander Ambystoma maculatum. Our results indicate that traditional fitness correlates, such as size at metamorphosis, were affected by pH stress and revealed pond-specific responses to pH treatments. Fluctuating asymmetry was not correlated with pH stress, suggesting that pH stress did not disrupt aspects of the developmental program that enforce symmetry. Furthermore, FA was altered through preservation, changed through time, and differed in fore and hind limbs. Conclusions about developmental stability depended on whether traits were analyzed separately or with a composite index. Finally, we...

Asymmetry, testis and sperm size in Yellow Dung Flies

Abstract: Summary 1 Fluctuating asymmetry (FA), small random deviations from perfect bilateral symmetry, is a widely used measure of developmental stability, and has been linked to fitness measures including male primary reproductive traits such as sperm quality However, there have been relatively few investigations of potential associations between these male traits and FA, and hence the current balance of evidence is equivocal 2 There is also evidence that levels of FA vary across populations with, for example, organisms inhabiting marginal populations often displaying increased FA Moreover, environmental variation may select for different levels of developmental buffering across populations that are only revealed in ‘common garden’ experiments 3 Investigations of potential associations between male leg FA and testis and sperm size in Yellow Dung Flies are reported here In addition, levels of FA in a mainland and two island populations were compared when flies were reared under common conditions 4 No associations were found between any measure of FA and sperm size (or variation) or testis size Additionally, no evidence was found that FA varied across the three populations when flies were reared under identical controlled conditions

Ontogeny of Asymmetry and Compensational Growth in Elm Ulmus glabra Leaves under Different Environmental Conditions

Abstract: Levels of fluctuating asymmetry (random variation in size among sides) may be partly determined by compensational growth, and the efficiency of such compensation may be affected by stress. Here we provide the first test of this hypothesis by studying the effect of saline stress on the ontogeny of size and symmetry of leaf width in broad‐leaved elms Ulmus glabra. Leaves that developed on saline‐treated trees became more asymmetric with time but not significantly smaller than leaves on control trees. This saline effect resulted from an increase in the variance in ontogenetic trajectories. Serial autocorrelation in asymmetry between subsequent days was significantly more negative (i.e., indicating stronger compensational growth) in control than in saline‐treated trees. Leaves from saline‐treated trees took longer to develop than leaves on control trees. These findings indicate that ontogeny is disrupted by saline treatment, preventing or reducing compensational growth to constrain leaf asymmetry within the s...

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

Abstract: 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.

Morphological variability and developmental instability in subpopulations of the Eurasian badger (Meles meles) in Denmark

Abstract: Aim Local populations from different geographical regions may differ in the selection regimes to which they are exposed. Differences in environmental factors and population density may affect the relative importance of different selective forces (e.g. natural vs. sexual selection). We suggest a direction of investigation concerned with the developmental instability of morphological traits. The goal is to disclose putative small-scale geographical differences in the evolutionary forces, which may be hard to detect. Location Craniometrical investigations were carried out on ninety-eight skulls and teeth of the Eurasian badger (Meles meles) collected during the period 1995–97 from three different populations in Denmark. One of these thrives at low population density, whereas the two others are characterized by high local density. Methods The skulls were investigated for developmental instability (DI) using fluctuating asymmetry (FA) as its estimator. FA was measured on canines, molars, premolar teeth and other skull and mandible traits. For the statistical analyses, we applied nonparametric permutation tests. Results Evidence was found suggesting differentiation among populations in mean degree of FA, and the FA values measured on canines were higher in the high-density populations. FA of the canines was significantly higher in males than females, in contrast to FA of the other traits. Evidence of a negative relationship between canine size and their FA was found, whereas no significant correlations were found between the molar and premolar teeth measures and their FA. Main conclusions Our results suggest that canines could be under directional selection stemming from intrasexual competition, which may be stronger in high-density zones. The other teeth investigated seem to be under a stabilizing regime hence their FA is mainly affected by environmental stresses. The negative relationship between canine size and FA found in males suggests the capacity of badgers to respond in an evolutionary way to environmental changes, despite the low genetic variability previously found at the molecular level.