Geographical variation in asymmetry in Gasterosteus aculeatus

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

Fitness, developmental instability, and the ontogeny of fluctuating asymmetry in Daphnia magna

Fluctuating asymmetry (FA) is the most commonly used measure of developmental instability. The relation between FA and individual fitness remains controversial, partly due to limited knowledge on the mechanisms behind variation in FA. To address this, we investigated the associations between FA, growth and reproduction as well as the ontogeny of FA in a clonal population of Daphnia magna . FA was not correlated with growth and reproduction, either at the between- or the within-individual level, in a high ( N  = 48 individuals) or in a low ( N  = 52 individuals) food-quantity regime. There were therefore no indications of functional effects of FA or of phenotypic trade-offs between developmental stability, growth and reproduction. Individual asymmetries varied randomly in sign and magnitude between subsequent molts ( N  = 19 individuals, 9–11 instars), but the levels of FA were generally lowest at intermediate ages. No feedback between right and left sides was detected. This suggests that FA only reflects the most recent growth history, that developmental instability may increase in old age, and that FA depends on processes operating on each side of the body independently. The results also suggest that FA differences within and among individual Daphnia are largely random, with limited biological significance.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 179–192.     

Macro-alga population shows low but significant heterogeneity in developmental instability with no detectable association with individual fitness

We studied among-individual variation in developmental instability (DI) and fitness-related parameters in 80 individual plants of Fucus vesiculosus (Phaeophyta). To minimize differential environmental effects, plants were sampled from one environmentally homogenous population. DI was measured as fluctuating asymmetry (FA) of four bilaterally symmetric traits (branch length, receptacle length and width, and bladder width) for an average total of 30 structures per individual. FA levels varied significantly among individual plants, consistent with a coefficient of variation of 0.12 for organism-wide DI or 0.13–0.21 for trait-specific DI. These values are lower than estimates for other organisms, suggesting that the genetic heterogeneity in DI was low. The data provide some evidence for organism-wide DI, but simulations show that organism-wide and trait-specific variation cannot be conclusively separated. Growth rate of branch tips was determined experimentally, demonstrating significant variation among individuals. FA was not significantly correlated with growth rate or with morphological variables associated with fecundity, age, size, and health. At the same time, the signs of all the correlation coefficients were consistent with the expectation of a negative relationship between DI and fitness. The simulations indicated that the correlation between FA and the underlying DI was comparatively strong (high hypothetical repeatability), implying that the lack of significant associations between FA and fitness variables reflected a weak relationship between DI and these fitness parameters. This weak relationship may be related to the low amount of DI variation in the study population.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 277–286.     

Stable isotope niche differentiation in sticklebacks with symmetric and asymmetric pectoral fins

Fluctuating asymmetry (FA) is often, but controversially, viewed as an indicator of fitness and a target of selection. In the brook stickleback, Culaea inconstans (Kirtland), FA of the pectoral fins, which are the main source of propulsion, is inversely correlated with fecundity. We examined the hypothesis that asymmetry of the pectoral fins could affect locomotion in such a way as to influence foraging and niche use in prereproductive brook stickleback. Nitrogen and carbon stable isotope analysis showed the diet of symmetric and asymmetric males diverged with increasing body size. Larger symmetric males fed at higher trophic levels and had a diet based on carbon emanating from a more pelagic source than their asymmetric counterparts. Such effects were not observed in females or smaller males. The number of chironomid larvae found in the gut was greater on average in asymmetric than symmetric fish. The results from this study strongly suggest FA of pectoral fins affects the foraging behaviour of C. inconstans and that stable isotope analyses of individual phenotypes provides a useful tool for assessing the ecological consequences of FA.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 617–623.     

Direct and correlated responses to selection for longevity in Drosophila buzzatii

The possible associations between longevity, early fecundity, and stress-resistance traits were explored using artificial selection on longevity in a laboratory population of Drosophila buzzatii . Three replicated lines were selected for increased lifespan (L lines) and compared with the respective unselected controls (C lines) after the 14th generation of selection. Mean longevity exhibited a significant response to selection. The baseline mortality tended to decrease in the L lines and a negative correlated response to longevity selection was found for early fecundity. Egg-to-adult developmental time increased in L lines. Longevity selection increased stress resistance for both high and low temperatures, as measured by heat knockdown resistance and chill-coma recovery. Starvation resistance also tended to be higher in L than in C lines. The results obtained are consistent with the hypothesis of trade-offs between longevity and early fecundity, and also suggest a trade-off association between adult longevity and developmental time. Correlated selection responses were generally consistent with correlations among the traits previously inferred from altitudinal clines for longevity and stress-resistance phenotypes.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 738–748.     

Bat genitalia: allometry, variation and good genes

Male genitalia are typically highly variable across species, for which sexual selection is thought to be responsible. Sexually selected traits characteristically show positive allometry and high phenotypic variation, although genitalia seem to be typified by negative allometry due to stabilizing selection. Additionally, while sexual selection appears to be the primary force responsible for genital evolution, the precise mechanism is unclear, but good-genes selection could be involved. If so, male genital variation should correlate with some male quality measure(s). We investigated the allometry of male Nyctalus noctula genitalia and investigated associations between genital size and three phenotypic measures of male quality (body size, relative body mass, and fluctuating asymmetry (FA)). We found that the penis exhibited positive allometry and high phenotypic variation, and was positively associated with male body size and relative body mass, but not with FA. This pattern is more typical of sexually selected display traits, contrasting with general patterns of genital allometry. The baculum was negatively allometric and was not associated with any quality measure. Our results suggest that the N. noctula penis is under directional sexual selection and is a reliable indicator of male phenotypic quality.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 497–507.     

Inbreeding effects on pair fecundity and population persistence

Despite strong empirical evidence of the harmful effects of inbreeding on fecundity, spontaneous recessive deleterious mutations are generally considered as acting on survival only in evolutionary models and population viability analyses. In this study, we modelled a species with separate sexes to assess the effect of selection on fecundity in small populations on the risk of extinction. We showed that the impact of inbreeding on short-term fitness changes and that population dynamics are strongly influenced by phenotypic interactions among males and females during reproduction. In particular, population persistence was found to be highly sensitive to the level at which selection acts (i.e. individual vs. pair) and to asymmetry among sexes (in terms of mutation rates and mutational effects).  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 86 , 467–476.     

Procrustean analysis of fluctuating asymmetry in the bulb mite Rhizoglyphus robini Claparede (Astigmata: Acaridae)

We studied fluctuating asymmetry (FA) in two generations of the bulb mite Rhizoglyphus robini . We used Procrustes analyses, which allow the comparison of dimensionless shapes of body sides. We found little (<4%) directional asymmetry in either sex. Of the two morphs occurring in this species, fighters, which possess a thickened third pair of legs, exhibited higher FA than did scramblers, the morph with unmodified legs; this may reflect the costliness of the fighter developmental pathway. There was a negative relationship between FA and female fecundity, but the regression slope of mid-offspring on mid-parent FA was not significantly greater than zero. We propose that heritability estimates can be biased downwards if highly asymmetric individuals produce fewer viable offspring. However, we found no significant association between parental FA and the proportion of viable embryos in their broods. Furthermore, we hypothesized that parental FA might indicate the presence of largely recessive mutations deleterious to developmental homeostasis that would cause increased embryo mortality under inbreeding. However, we found no significant association between FA of parents that were mated to their full sibs and the proportion of viable embryos in their inbred progeny.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 499–505.     

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

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.     

Temperature dependence of fitness components in geographical populations of Drosophila melanogaster: changing the association between size and fitness

Contrary to the conventional wisdom 'bigger is better', evolution at high temperature invariably leads to small individuals in Drosophila melanogaster . Natural selection is known to be responsible, meaning that genotypes that are small because of adaptation to high temperature must have some temperature dependent fitness advantage. In this study we consider both preadult and adult fitness components, and show that large adults from a cold adapted population significantly outperform small adults from a warm adapted population only when tested at low temperature and low larval density. In all other conditions 'bigger is not necessarily better', meaning that environmental influences are capable of altering the association between size and fitness. Yet, 'smaller wasn't better either' under any condition, when considering the overall measure of fitness. Examination of individual fitness components revealed population by temperature interaction in preadult survival; this interaction is potentially capable of explaining the temperature specific advantage of small adult body size. At high temperature, the warm adapted population exhibits superior preadult survival while producing small adults. Geographical variation in adult body size seems to be the result of selection on larval growth and competitive strategies, resulting in alterations in the association between fitness components.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 717–725.     

Individual differences in developmental precision and fluctuating asymmetry: a model and its implications

In many studies, fluctuating asymmetry (FA) has been used as a measure of individual differences in developmental imprecision. A model of how variation in developmental imprecision is associated with variation in asymmetry is described and applied to important issues about FA. If individual differences in developmental imprecision exist, asymmetry due to developmental error should be leptokurtically distributed. Moreover, the greater the magnitude of individual differences, the greater the leptokurtosis. Asymmetry purportedly due to developmental error in a variety of species is indeed leptokurtically distributed. The level of leptokurtosis suggests that the CV in individual differences in underlying developmental imprecision is generally 20–25, consistent with it being a fitness trait. In addition, data suggest that: (1) the individual differences that underlie the developmental imprecision of different traits are largely shared across traits and not trait-specific; (2) the heritability of these individual differences may average between 35 and 55%, despite small heritabilities of individual trait FAs; and (3) correlations between FA and fitness traits or components suggest high correlations between underlying variation in developmental precision and fitness in many species. Theoretical implications are discussed.     

Fluctuating asymmetry in relation to indices of quality and fitness in the damselfly, Enallagmaebrium (Hagen)

Fluctuating asymmetry (FA) refers to random deviations from symmetry of otherwise bilaterally symmetric traits. Researchers have hypothesized that FA should be inversely related to individual quality or fitness. In this study, we tested for FA-quality and FA-fitness relations in the damselfly, Enallagmaebrium (Hagen). We used wet mass of an individual as a measure of its quality and longevity as a measure of its fitness. Contrary to predictions, we found no relation between FA and quality or fitness, even after we controlled for possible confounding factors, such as measurement error and inadequate sample size.     

Assemblage and population-level consequences of forest fragmentation on bilateral asymmetry in tropical montane birds

Habitat fragmentation has the potential to influence the development and thus the phenotype of organisms. The asymmetry of bilateral traits may be indicative of the extent to which developmental stability is compromised by the stressful conditions underlying fragmentation. Using an assemblage- and population-level approach, we explored asymmetry differences in tarsus and outermost tail feathers of birds inhabiting fragmented landscapes in the tropical Andes of Colombia. More than 2500 individuals of 185 species were mist-netted at nine forest sites representing continuous forest (> 1000 ha), medium- (70–110 ha), and small-sized (8–20 ha) fragments. Feathers showed true fluctuating asymmetry (FA), whereas tarsus presented a mixture of FA and directional asymmetry. Overall, asymmetry was lowest in continuous forest, and highest in small and medium fragments. These patterns remained unchanged when directionality and differences in species composition, abundance, and foraging tactics were considered. The population-level analyses showed a general trend of increased asymmetry variation in fragments, yet the responses were not always in the same direction. Increased asymmetry may represent an outcome of processes that contribute to the persistence of species in changing environments, and to the generation of phenotypic innovation, which suggests individual adjustments of development to deal with stress. This calls into question the deliberated application of FA as a biomonitoring tool for conservation.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 119–133.     

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

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

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

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

Repeatability of size and fluctuating asymmetry of antler characteristics in red deer (Cervus elaphus) during ontogeny

Fluctuating asymmetry (FA) has been suggested as a measure of the sensitivity of development to a wide array of genetic and environmental stresses. It has been also suggested that antlers in red deer could be important during social and rutting displays. We used antler measurements of 51 males that were measured over subsequent seasons, from 3–8 years of age, and analysed three antler traits: antler weight, length, and the number of antler tines (antler size). We calculated absolute and relative FA. All three size traits were highly significantly intercorrelated. By contrast to this, the FA of the three traits, did not show such relationships. With increasing age, antler size and FA also increased. When testing the repeatability of FA and antler size, there was a principal difference in the pattern between FA and antler size, with the latter being much more consistent than the former. This suggests that antler size, not FA, may be a good predictor of the bearer's quality in mate selection. This fits well with the good-genes hypothesis that the development of extravagant secondary sexual characters can be an honest advertisement of heritable male quality.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 215–226.     

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

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

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

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 normal distribution as appropriate model of developmental instability in Opuntia cacti flowers

Developmental instability (DI) as measured by fluctuating asymmetry (FA) has been proposed to reflect fitness and stress. Furthermore, the associated developmental buffering may reduce morphological variation, conceal the expression of genetic variation and as such play an important role in evolutionary biology. However, observed associations between FA and various forms of stress and quality appear very heterogeneous. Presently it is difficult to interpret the biological relevance of this heterogeneity because little is known about the link between FA and the underlying process of DI, casting doubt whether DI can be viewed as an individual property and how closely FA reflects the underlying process of DI. Therefore, studies that explicitly test the validity of assumptions of the proposed theoretical models and estimate between‐individual variations in DI are needed. We present data on Opuntia cacti floral traits confirming that the normal distribution can be viewed as an appropriate approximation of the distribution of DI and that the concept of hypothetical repeatability can provide useful insights into the interpretation of patterns in FA as a measure of DI. Furthermore, we detected significant between‐individual variation in DI. Measuring petals from several flowers within individual plants allowed making inference of individual DI.     

Asymmetry as a predictor of growth, fecundity and survival

Measures of developmental stability such as fluctuating asymmetry have been assumed to predict individual performance because asymmetry reflects an inability to cope with stressful situations, and because asymmetry hampers locomotion. However, the magnitude of this relationship between important fitness components (growth, fecundity, survival) and asymmetry has never been assessed. Based on a literature survey, estimates of the correlation between asymmetry and the three fitness components are presented. Pearson's correlation coefficients weighted for sample size between asymmetry and growth, fecundity, and survival, respectively, were –0.15, –0.35, and –0.25, respectively, with all three coefficients being highly significant. All three relationships were extremely robust given very large fail-safe numbers. The results were independent of whether studies or species were used as units of analysis. Hence asymmetry is a robust predictor of performance in fitness domains such as growth, fecundity, and survival, although only accounting for 2.1%, 12.3%, and 6.0% of the variance. This may be of importance for studies of sexual selection, but also for ecological and conservation biological studies, where the performance of individuals or groups of individuals are assessed.