Showing papers on "Fluctuating asymmetry published in 2002"

Fluctuating asymmetry as an indicator of fitness: can we bridge the gap between studies?

Abstract: There is growing evidence from both experimental and non-experimental studies that fluctuating asymmetry does not consistently index stress or fitness. The widely held ‐ yet poorly substantiated ‐ belief that fluctuating asymmetry can act as a universal measure of developmental stability and predictor of stressmediated changes in fitness, therefore staggers. Yet attempts to understand why the reported relationships between fluctuating asymmetry, stress and fitness are so heterogeneous ‐ i.e. whether the associations are truly weak or non-existent or whether they become confounded during different stages of the analytical pathways ‐ remain surprisingly scarce. Hence, we attempt to disentangle these causes, by reviewing the various statistical and conceptual factors that are suspected to confound potential relationships between fluctuating asymmetry, stress and fitness. Two main categories of factors are discerned: those associated with the estimation of developmental stability through fluctuating asymmetry, and those associated with the effects of genotype and environment on developmental stability. Next, we describe a series of statistical tools that have recently been developed to help reduce this noise. We argue that the current lack of a theoretical framework that predicts if and when relationships with developmental stability can be expected, urges for further theoretical and empirical research, such as on the genetic architecture of developmental stability in stressed populations. If the underlying developmental mechanisms are better understood, statistical patterns of asymmetry variation may become a biologically meaningful tool.

Fluctuating Asymmetry as an Early Warning System in the Critically Endangered Taita Thrush

Abstract: Environmental and genetic factors increasingly stress natural populations, and conservationists need simple tools to measure the effect of these stresses before populations become irreversibly affected The inability of an organism to withstand random perturbations during its development—so-called developmen- tal instability—has been proposed as a potential early indicator of stress To act as a true early warning sys- tem, however, stress-mediated changes in developmental instability should be manifest in the phenotype be- fore major changes occur in more direct components of fitness We tested this hypothesis by estimating the survival probabilities of 260 Taita Thrushes ( Turdus helleri ) inhabiting three differentially disturbed forest fragments ( little, moderately, and highly deteriorated) and relating these to individual estimates of tarsus asymmetry (a measure of developmental instability), two other putative indices of expected fitness (size and body condition), and a coefficient of inbreeding Tarsus symmetry, but not survival, was lower in the moder- ately disturbed population than in the least disturbed one, whereas both symmetry and survival were lower in the most disturbed population Thus, higher levels of habitat disturbance were reflected by increased popu- lation levels of asymmetry before a decrease in survival became apparent In contrast, none of the other vari- ables showed a significant response to habitat disturbance At the individual level, asymmetric thrushes showed lower probabilities of survival than more symmetric ones, and the magnitude of the relationship in- creased with habitat disturbance Birds in better condition (ie, higher residual body mass) survived better, irrespective of the quality of the habitat The key finding that stress-mediated increase in fluctuating asymme- try may precede decrease in survival suggests that single-trait asymmetry can serve as an early warning sys- tem in conservation

An epistatic genetic basis for fluctuating asymmetry of mandible size in mice.

Abstract: The genetic basis of fluctuating asymmetry (FA), or nondirectional variation in the subtle differences between left and right sides of bilateral characters, continues to be of considerable theoretical interest. FA generally has been thought to arise from random noise during development and therefore to have a largely or entirely environmental origin. Whereas additive genetic variation for FA generally has been small and often insignificant, a number of investigators have hypothesized that interactions between loci, or epistasis, significantly influence FA. We tested this hypothesis by conducting a whole-genome scan to detect any epistasis in FA of centroid size in the mandibles of more than 400 mice from an F2 intercross population formed from crossing the Large (LG/J) and Small (SM/J) inbred strains. Genotypic deviations were imputed at each site 2 cM apart on all 19 autosomes, and these and centroid size asymmetry values were used in canonical correlation analyses for each of the 171 possible pairs of 19 autosomes to identify the most probable sites for epistasis. Epistasis for centroid size asymmetry was abundant, occurring far more often than was expected by chance alone (there were 30 separate instances of epistasis at the 0.001 significance level, when only two were expected by chance alone). The contributions of epistasis from 30 pairwise combinations of loci tended to suppress the additive and dominance genetic variance, but greatly increased the epistatic genetic variance for FA in centroid size given the intermediate allele frequencies of an F2 intercross population.

Locomotor capacity and dominance in male lizards Lacerta monticola: a trade-off between survival and reproductive success?

Abstract: Trade-offs between reproduction and survival are important determinants of life-history characteristics of lizards. Organisms cannot increase the allocation of limited resources to reproduction without diverting a proportional amount of energy from another trait. Locomotor performance is an ecologically relevant trait that potentially influences survival by affecting the ability to escape from predators. Most studies have used female lizards as subjects because pregnancy is known to reduce their locomotor abilities, whereas little is known on costs of reproduction in males. In this study we suggest that in males of the lizard Lacerta monticola reproductive investment in morphological traits that confer dominance (i.e. head size) might lead to a low probability of survival by decreasing investment in other traits that affect locomotor performance (i.e. limb symmetry). We staged laboratory agonistic encounters between males and measured their morphology and burst speed on a race track to examine possible relationships between morphology, social dominance and locomotor capacity. Our results indicate that social dominance was positively related to relative head height, and that escape speed was negatively related to levels of fluctuating asymmetry in femur length, but also negatively related to relative head height. Males with greater relative head height also had more asymmetrical femurs, thus dominant males suffered a decrease in locomotor performance. Males with higher heads tend to dominate male–male interactions and hence may gain access to reproductive females, thus increasing their current reproduction success. However, this might occur at the expense of future survivorship mediated by a decrease in escape speed. Therefore, in male L. monticola there might be a trade-off between current reproductive success and survival. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002; 77, 201–209.

Blood concentration of organochlorine pollutants and wing feather asymmetry in Glaucous Gulls

Abstract: Summary1. Non-directional asymmetries (fluctuating asymmetry, FA) from bilateral symmetryin morphological traits have been used as an indicator of environmental stress and maybecome an important diagnostic tool in environmental sciences, such as ecotoxicology. 2. In this study the relationship was examined between wing feather asymmetry, meas-ured as the difference between the length of the third primary on the left and right wing,and blood concentration of selected persistent organochlorines (OCs) in Arctic breed-ing Glaucous Gulls ( Larus hyperboreus , Gunnerus). 3. There was a positive relationship between primary asymmetry and blood concen-trations of two PCB (polychlorinated biphenyl) congeners ( P < 0·05), oxychlordane( P < 0·05), DDE ( p ′ p ′ -dichlorodiphenyldichloroethylene) (P < 0·05), and especiallyHCB (hexachlorbenzene) ( P < 0·001). At HCB levels above 30 ng g − 1 (wet mass) therewas a 60% probability that the birds had asymmetric wing feathers. 4. This study indicated that the present levels of organochlorines in the EuropeanArctic are stressors for Glaucous Gulls, and that asymmetry measurements of wingfeathers may be used as an indicator of both exposure and effects of such contaminants.FA may also be a promising measurement for monitoring the early effects of organo-chlorine pollution on bird populations.

Fluctuating asymmetry—indicator of what?

Abstract: In a population the optimal phenotype is promoted by buffering mechanisms that keep inter- and intra-individual variation low. A link exists between canalization, that controls phenotypic variation, and developmental stability, mostly measured as fluctuating asymmetry of bilateral traits (FA). Both types of variation are associated with the functional importance of a trait, and both are increased by stress of various kinds. But there are also several instances of non-congruence. The concept of developmental stability has been found elusive, and low FA is not the unambiguous measure of well being and good genes that has been claimed. It can be concluded that developmental stability is partly governed by specific, as yet unknown, molecular processes.

Dermatoglyphics, handedness, sex, and sexual orientation.

Abstract: Both handedness and dermatoglyphic asymmetry reflect early, prenatal influences and both have been reported to be associated with male sexual orientation; handedness has been related to female sexual orientation as well. Neurohormonal and developmental perturbation are two competing hypothesis that attempt to explain these connections. We attempted to replicate these associations and to extend dermatoglyphic asymmetry findings to women. Dermatoglyphic directional asymmetry and fluctuating asymmetry were unrelated to sexual orientation. Homosexual women, but not homosexual men, had highly significant increases in non-right-handedness compared with same-sex heterosexual controls. Although this pattern of results does not allow resolution of the two competing models, it does lend additional support to a biological basis of sexual orientation.

Temperature and genotypic effects on life history and fluctuating asymmetry in a field strain of Culex pipiens.

Abstract: Fluctuating asymmetry (FA) has been proposed as a tool to measure levels of stress experienced by populations of organisms during development. To be of value as a bio-marker to highlight conditions at particular sites, it is important that variation in FA is due to environmental (eg pollution) variation and not genetic variation among populations and families, in other words heritability for FA should be very close to zero. A full-sib design was set up in which families of Culex pipiens mosquitoes collected from the field were reared at three different developmental temperatures. The effects of temperature and family on developmental rate, egg to adult survival and four wing morphological measures were assessed. There was both a temperature and a family effect on development rate and survival. Temperature affected all four wing traits, but an influence of family was only evident in two of the wing traits. Two separate measures of FA for each of the wing traits were obtained. The mean estimates of FA were mainly around 1% of the value of the character measured. There was evidence of an increase in FA with increase in temperature stress. Heritability was estimated for the wing traits and wing trait FA's using restricted estimation maximum likelihood. The estimates of heritability for the wing traits were small and, individually, did not differ significantly from zero. There was also no evidence of heritable genetic variation for any of the wing trait FA's. The results are discussed in relation to other studies where FA heritabilities have been estimated and in relation to the use of FA as an indicator of environmental stress.

Fluctuating asymmetry and the human brain.

Abstract: Adaptive development requires the organism to resist genetic and environmental stresses that disrupt the genetic plan for growth, a buffering capacity termed developmental stability. Developmental instability is revealed by fluctuating asymmetry (FA), which has been demonstrated in many species to reflect phenotypic and genetic quality. We report (1) that a measure of developmental instability based on body FA predicts deviation from typical brain asymmetry, (2) that a combined measure of atypical brain asymmetry and body FA correlated negatively with the area of the corpus callosum, especially the portion connecting the left and right planum temporale, and (3) that this combined measure also predicted atypical asymmetry of the size of the somatosensory representation of the two hands, as determined from magnetic source imaging.

Why do some traits show higher fluctuating asymmetry than others? A test of hypotheses with tail feathers of birds.

Abstract: Certain characters are more susceptible to increased fluctuating asymmetry (FA) than others. This trait-specific susceptibility has normally been attributed to different degrees of developmental stability, which could be caused by different modes of selection, functionality, or the stress experienced during the development process. Recently, it has also been suggested that the expression of FA not only depends on developmental stability, but also on the cost of growth of the trait, defined as the amount of structural components necessary to form a unit of length of a given character. In accordance with this argument, a trait with more structural components per unit of length should show lower asymmetry than a simpler one. To test this hypothesis, we examine the structure (number of barbs, barb length, and rachis width) and asymmetry of the longest tail feathers in 26 bird species. Regression analyses using phylogenetically independent contrasts show that FA is negatively correlated with the number of barbs and feather rachis width in males (including species with elongated tails subjected to sexual selection), and with rachis width in females, whose tails supposedly evolve by natural selection. Moreover, the negative correlation between FA and rachis width persisted when taking only the males of non-dimorphic species. These results confirm the hypothesis, suggesting that a trait's susceptibility to express developmental instability by fluctuating asymmetry depends on its structural composition.

Fluctuating asymmetries and reproductive success in the peacock blenny

Abstract: In an investigation of the relationship between reproductive success and fluctuating asymmetry (FA) in the peacock blenny Salaria pavo, FA was measured in four bilaterally paired characters in successful and unsuccessful males during the breeding season. Reproductive success among successful males was assessed by calculating the number of eggs the males were defending. Absolute FA values relative to trait size were high for all characters and it is suggested that this could be a consequence of sub-optimal environmental conditions. Two of the traits presented higher absolute FA values suggesting a lower canalization during ontogeny. No difference in FA between successful and unsuccessful males was found and no relationship between FA and number of eggs among the successful males occurred for any of the measured traits. A composite index of FA, that should better reflect overall developmental competence, was also unrelated to reproductive success. These results indicate that FA is not associated with reproductive success among males of S. pavo. Successful males were larger than unsuccessful males and a strong positive correlation was detected between the body length of the parental males and the number of eggs they had in the nest, even when controlling for the internal nest area. Body size may give males a reproductive advantage by being preferred by females and by having an advantage in male-male competition for nests of higher quality.

Exploration of the utility of fluctuating asymmetry as an indicator of river condition using larvae of the caddisfly Hydropsyche morosa (Trichoptera: Hydropsychidae)

Abstract: Organisms are subject to three types of morphological asymmetry: Directional Asymmetry, Antiasymmetry and Fluctuating Asymmetry, but only the latter (FA) is related to the environmental stress acting upon individuals during their development. Larvae of Hydropsyche morosa from five rivers in Ontario, Canada, each exhibiting different degrees of human impact, were examined for FA. Specimens were obtained from collections in the Royal Ontario Museum dating back to 1951, and from fresh collections to 1999. Twelve morphological characters were assessed on both the left and right sides of 297 larvae, and eight of them demonstrated FA. There was a tendency to increase the levels of FA over time. Levels of nitrogen, conductivity and chloride in the river water, used as an index of pollution, were significantly and positively correlated with increasing incidence of FA in four of the characters, the remainder were independent of pollution.

Developmental instability and sexual selection in stag beetles from Chernobyl and a control area

Abstract: Radioactivity may have both phenotypic and genetic effects through its disruption of physiological processes and mutations. I studied the size and asymmetry of secondary sexual and ordinary morphological characters of stag beetles (Lucanus cervus) in two areas in the Ukraine: near Chernobyl, where levels of radiation are high, and in a control area with low background radiation. Developmental instability of morphological characters was estimated from the degree of fluctuating asymmetry using the restricted maximum likelihood parameter estimation (REML) method to partition measurement error from asymmetry. The degree of asymmetry estimated from unsigned differences in size of right and left secondary sexual character was similar to estimates based on the REML method. Beetles from the contaminated area had a significantly elevated level of fluctuating asymmetry in the secondary sexual character compared with animals from the control area. Male stag beetles found with a female had significantly lower asymmetry than males found alone. While mated males did not differ in asymmetry between areas, unmated males from Chernobyl were much more asymmetric than unmated males from the control area. These findings provide evidence for radiation disrupting developmental homeostasis, and thereby affecting the mating status of free-living beetles.

Antisymmetry in male fiddler crabs and the decision to feed or breed

Abstract: Summary 1 In male Sand Fiddler Crabs, Uca pugilator, a major cheliped (with claw), used in intersexual displays and intrasexual contests, develops opposite a minor cheliped used for feeding. Cheliped size demonstrates antisymmetry because greater development is equally likely on the right or left side. 2 The side with the major cheliped (major side) also has longer walking legs which may facilitate use of the claw. In contrast, eye stalk asymmetry is equally due to antisymmetry and fluctuating asymmetry. Fluctuating asymmetry is a subtle, non-adaptive departure from the population-level trajectory relating growth on major and minor sides. 3 In a South Carolina (USA) marsh, cheliped and leg antisymmetries are greater and eye stalk asymmetry is less among males able to defer feeding in favour of breeding. However, the composition of up-slope breeding and down-slope feeding subpopulations changes across the lunar cycle. 4 The number of mates sequestered in breeding burrows is positively correlated with cheliped and leg antisymmetry and negatively correlated with eye stalk asymmetry. Male fitness is a function of the product of time spent breeding and the number of mates per unit time while breeding. Both fitness components are predicted by relative cheliped antisymmetry and eye stalk fluctuating asymmetry, which are themselves significantly negatively correlated.

Intraspecific hybridization, developmental stability and fitness in Drosophila mercatorum

Abstract: One of the possible effects of intraspecific hybridization is outbreeding depression, due to a breakdown of coadapted gene complexes, which can lead to reduced fitness and decreased developmental stability in hybrids. Alternatively, increased fitness and increased developmental stability in hybrids (hybrid vigour) may be a result of hybridization, probably due to increased heterozygosity. Developmental stability is assumed to be correlated with fitness and is commonly measured as fluctuating asymmetry or phenotypic variance. Drosophila mercatorum is capable of reproducing sexually, but also parthenogenetically in the laboratory. When selecting for parthenogenesis, the flies become homozygous in one generation; strong selection, therefore, is acting on the genome of these flies for coadaptation among genes. Intraspecific hybridization is therefore expected to have an impact when coadaptation is disrupted. Intraspecific hybridization between a parthenogenetic and a sexually reproducing strain of Drosophila mercatorum resulted in significant changes in fecundity as well as fluctuating asymmetry and phenotypic variance for the number of sternopleural bristles and in the length of two wing traits over three generations after hybridization. We found a 'hybrid vigour effect' in Fl females with an increase in fecundity relative to their parental populations. The F2 and F3 females showed increased fluctuating asymmetry in several traits and reduced fecundity compared with the Fl females, probably due to a breakdown in coadapted gene complexes. The males followed the same pattern of fluctuating asymmetry for bristles but there was no increase in wing fluctuating asymmetry in the F2 and F3 generations. Trait differences in phenotypic variance were found between wings and bristles. We found an increase in phenotypic variance in the Fl generation for both sexes and all traits, which could be due to increased genetic variance after hybridization. The phenotypic variance increased further in generations F2 and F3 for bristle number. For the wings, phenotypic variance generally decreased in generations F2 and F3 when compared with Fl, which we attribute to canalization and selection on the wings.

Fluctuating asymmetry, fecundity and development time in Drosophila: Is there an association under optimal and stress conditions?

Abstract: A number of studies have reported a significant negative association between fluctuating asymmetry (FA) of bilateral morphological traits and individual fitness traits, but almost all of these are unreplicated and based on small sample sizes using single trait estimates of FA. We therefore tested if there was a relationship between the FA of five bilateral traits and fecundity and development time in Drosophila in a multiple replicated experimental design. Stressed treatments were included to increase the variability of traits and to test whether associations among traits were affected by changes in the environment. Significant positive relationships were found between the size of wing characters and mean fecundity for the 5-day period and this relationship tended to be stronger in the stress treatments. No association was found between FA and mean fecundity for any of the traits measured. Similarly, a significant positive relationship was detected between wing trait size and development time but no association was detected between trait FA and development time. There were no differences between mean fecundity or development time of extreme asymmetry phenotypes compared with modal phenotypes. These results are discussed with reference to suggestions in the literature that FA can be used to estimate individual fitness.

Inbreeding and developmental stability in three-spined sticklebacks ( Gasterosteus aculeatus L.)

Abstract: Fluctuating asymmetry, small non-directional departures from perfect symmetry in bilateral traits, results from the inability of individuals to buffer development against genetic and environmental perturbations. Fluctuating asymmetry is a widely used measure of developmental stability, and developmental stability has been hypothesised to be inversely related to heterozygosity. We compared male three-spined sticklebacks (Gasterosteus aculeatus L.) that had been inbred for one generation to outbred control males with respect to the asymmetry of a set of bilateral morphometric traits. Inbred fish developed significantly more asymmetric pectoral fins than their outbred counterparts, whereas neither the magnitude of asymmetry for pelvic spines nor for gill covers significantly responded to the treatment. Our results conform to a pattern of heterogeneity amongst traits in their tendency to develop asymmetrically in response to stress.

Genetics of wing size asymmetry in Drosophila buzzatii

Abstract: Contemporary approaches that use fluctuating asymmetry (FA) as a possible target for natural and sexual selection are based on the premise that FA is a quantifiable expression of developmental instability (DI) that is inherited. Previous work with Drosophila buzzatii found that male mating success was correlated positively to body size (wing length) and negatively to FA, but these relationships seem to be environmentally induced. Heritability of FA was low and not significantly different from zero, but statistical power was also estimated to be very low and, hence, no conclusive evidence could be obtained. A large half-sib mating design is used here to examine the relationships of different aspects of development for wing size. Consistently with previous findings, I found high heritabilities for wing length (WL) and wing width (WW), and positive correlations between both traits. Heritabilities of FA (FAWL, FAWW) were low (0.037) but significantly different from zero, and the genetic correlation between FAWL and FAWW was estimated as −1 because the absolute value for the genetic covariance was similar in magnitude or even larger than the estimated genetic variances of both traits. This suggests that these two traits should be considered to be the same character. The between-trait phenotypic correlation in FA, which reduces to the repeatability in this situation, was positive and statistically significant thus rendering an estimate of heritability for DI in D. buzzatii of . Nevertheless, the fact that left/right wing sizes were found to be determined by the same set of genes is difficult to reconcile with the presence of special genetic mechanisms that stabilize left/right development in this species. A qualitatively different pattern for asymmetry was observed when the nonlinear composite character wing area (WA ≈ WL × WW) was used, and . Although the results could be made compatible with the existence of a diallelic locus with antagonistic pleiotropic effects on FAWL and FAWW that combine multiplicatively to produce overdominance for FAWA, the available evidence is extremely weak at best. Finally, a test to the null hypothesis of a nongenetic basis of FA, particularly relevant to those situations when directional asymmetry may be heritable, is suggested.

Experimentally Manipulated Growth Rate in Threespine Sticklebacks: Assessing Trade Offs with Developmental Stability

Abstract: The evolution of ‘adaptive’ growth rate and its influence on how other life history traits evolve is a neglected topic in biology. Growth rate influences life history because size strongly influences age-specific survival and fecundity, and because growth rate defines the relationship between age and size. Improved predictions about the evolution of life history traits may be possible with a greater understanding of the factors that influence the evolution of growth rate. We experimentally tested the hypothesis that a trade off may exist between growth rate and developmental stability in freshwater threespine sticklebacks, Gasterosteus aculeatus. We compared the degree of developmental instability (measured as fluctuating asymmetry = FA) in four lateral plate and two fin traits of fish reared under a high vs. low growth regime in response to food ration and temperature. We found evidence that symmetry was reduced (FA increased) in fast growing compared to slow growing fish, suggesting that a trade off between developmental stability and growth is possible. FA plausibly reflected developmental instability because of significant associations between rank FA levels across traits in individuals. These results are preliminary because of the possible confounding effects of temperature and food ration on asymmetry, and because we do not know if this trade off has fitness or other life history consequences. Our results also do not support the hypothesis of honest signaling sometimes invoked in studies of sexual selection because greater symmetry was found under poorer rather than better resource levels.

Developmental Instability and Fitness in Periploca laevigata Experiencing Grazing Disturbance

Abstract: We investigated the sensitivity of developmental instability measurements (leaf fluctuating asymmetry, floral radial asymmetry, and shoot translational asymmetry) to a long‐standing natural stress (grazing) in a palatable tannin‐producing shrub (Periploca laevigata Aiton). We also assessed the relationship between these measures of developmental instability and fitness components (growth and floral production). Developmental instability, measured by translational asymmetry, was the most accurate estimator of a plant’s condition and, consequently, environmental stress. Plants with less translational asymmetry grew more and produced more flowers. Plants from the medium‐grazed population were developmentally more stable, as estimated by translational and floral asymmetry, than either more heavily or more lightly grazed populations. Leaf fluctuating asymmetry was positively correlated with tannin concentration. The pattern of internode growth also responded to grazing impact. Plants under medium to heavy graz...

Fluctuating Asymmetry, Sexual Selection, and Survivorship in Male Dark-Winged Damselflies

Abstract: We examined fluctuating asymmetry and morphology as they relate to reproductive success, territoriality, and relative survivorship in the dark-winged damselfly Calopteryx maculata. Fluctuating asymmetry was not correlated with any aspect of morphology in males, but it did predict mating status in males. Mating males showed significantly lower levels of forewing asymmetry than did non-mating males holding adjacent territories. While fluctuating asymmetry did not relate to survivorship or resource holding ability, body size did. Larger males were able to hold territories longer and lived longer than smaller individuals. We suggest that size is of greater importance in this species with regards to fitness and that fluctuating asymmetry may play a minor role by impacting short-term mating success.

Geographical variation in asymmetry in Gasterosteus aculeatus

Abstract: 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.

Effects of temperature and genetic stress on life history and fluctuating wing asymmetry in Culex pipiens mosquitoes

Abstract: Fluctuating asymmetry (FA) of bilaterally symmetrical organisms has been introduced as a promising indicator of environmental stress. Stress factors reported to contribute to developmental stability include inbreeding and the presence of resistance genes. In the current study we examined the effect of stress derived from high developmental temperatures, resistance genes and low genetic variation on life history variables and wing FA in Culex pipiens mosquitoes. Three strains were compared: two inbred laboratory strains sharing a similar genetic background but differing in that one strain contained organophosphate (OP) resistance genes, and a third strain that was an outbred OP resistant field strain recently collected from India. There were no strong and general trends that suggested that the OP resistant lab strain was less fit than the OP susceptible strain, although there were some specific among strain differences for some treatments. Fluctuating asymmetry (FA) of wing traits was higher in the laboratory strains than the field strain, suggesting that inbreeding may cause elevated FA in the study species. There was no evidence that the resistance genes were associated with increased wing FA. Wing FA increased with increasing developmental temperature in females, but the association was less strong in males. There was a significant difference between the sexes in this respect. The results are discussed with reference to the value of FA as a biomonitor of environmental stress.

Parasitic infection and developmental stability: fluctuating asymmetry in Gammarus pulex infected with two acanthocephalan species.

Abstract: Several studies have reported a negative association between developmental stability and parasitic infection. However, the host–parasite associations examined so far consist only of a limited number of parasite taxa, and developmental stability was appraised on definitive hosts. The present study examines the association between infection by 2 acanthocephalan parasites, Pomphorhynchus laevis and Polymorphus minutus, and the developmental stability of their common intermediate host Gammarus pulex. Developmental stability was estimated from the fluctuating asymmetry (FA) levels of 6 morphological traits. A positive association was found between FA and infection. Infected gammarids tended to be more asymmetrical than the noninfected ones for an index generated by combining FA scores from 2 characters out of the 6 studied, even though no significant relationships were found between FA levels and parasitic loads. The simultaneous presence of both acanthocephalan species in the same host seems to be associated ...

Flower and cotyledon asymmetry in Brassica cretica: genetic variation and relationships with fitness

Abstract: Plants of the partially self-incompatible perennial herb Brassica cretica, derived from controlled cross- and self-pollinations within each of seven populations, were raised under uniform conditions and scored for two measures of developmental stability, flower asymmetry (quantified as the difference in length and width between opposite petals) and cotyledon asymmetry (quantified as the difference in the area of the two lobes of each cotyledon). The primary goals were to assess the level of heritable variation in asymmetry, the effect of selfing on mean asymmetry, and the relationship between asymmetry and components of fitness. A paternal half-sibling analysis of data on flower asymmetry failed to detect significant levels of genetic variation at the within-population level, whereas the between-population component reached significance for all measures of asymmetry. Analysis of family-structured data from another crossing experiment revealed significant between-population variation in cotyledon asymmetry and a tendency for inbred progeny to produce more asymmetric cotyledons than outbred progeny. However, the response to inbreeding was weak and differed in magnitude between populations. Judging from the ranking of populations, we found no support for the hypothesis that the mean expression of developmental stability is controlled by genomewide characteristics such as the level of inbreeding. Correlations between measures of asymmetry and fitness were too low to be declared statistically or biologically significant. The present study provides little evidence that flower and cotyledon asymmetry serve as more appropriate predictors of genetic health than conventional (direct) measures of fitness.