Saccular otoliths (sagittae) have long been shown to be species-specific and exhibit inland geospatial intra- and interpopulation morphological differences with variations in environmental conditions. Here, we analysed inland and outland geospatial variations in sagittae shape, length (Lo), width (Wo), perimeter (Po), and area (Ao), and fluctuating asymmetry (FA) in Chelon auratus males and females collected from Ghar El Melh (Tunisia) and Etoile Bay (Mauritania) stations to assess whether sagittae shape and morphometry differ between these two niches having different environmental conditions. At the intrapopulation level, a significant otolith shape asymmetry was observed between left and right and left–left and right–right otoliths among males and females of the Ghar El Melh (Tunisia) population and a significant symmetry among those of the Etoile Bay (Mauritania) population. At the interpopulation level, a significant asymmetry was found between left and right otoliths' shape among males and females of the two populations. Besides, a discriminant function analysis of otoliths' contour shape separated left and right otoliths among males and females at the intra- and interpopulation levels and also separated those of the two populations. Moreover, differential significant asymmetry in Lo, Wo, Po, and Ao between left and right otoliths was observed among males and females at the intra- and interpopulation levels. Therefore, the geospatial variations in environmental conditions between the two ecological niches effectively induced differences in otolith morphology. These significant asymmetries were discussed in terms of FA caused by environmental stress conditions resulting from variations in abiotic factors between the two ecological niches.

Variations in sagittal otolith shape and morphometry, including length (Lo), width (Wo), area (Ao), and perimeter (Po), were investigated in two populations of Chelon ramada collected from the Boughrara and El Bibane lagoons located in southeastern Tunisia. The objective was to assess the geographic variation in the sagittal otoliths' shape and morphometry and the effect of potential fluctuating asymmetry (FA) in morphometry on the stock structure of C. ramada in the two lagoons to inform on appropriate management procedures. At the interpopulation level, analysis of sagittal otolith shape showed a statistically significant difference (P = 0.0001), i.e. there was a bilateral asymmetry, in the shape of left and right otoliths between individuals of the two populations. In addition, significant FA was found only in Lo between the left and right otoliths. At the intrapopulation level, a significant shape difference (P < 0.0001), particularly asymmetry, was observed in both left and right otoliths between males and females, indicating sexual dimorphism in shape within the Boughrara lagoon. However, significant shape similarity, i.e. symmetry, was observed in the left and right otoliths among individuals of the El Bibane lagoon. Moreover, a significant FA was detected in Lo between the left and right otoliths only among males, as well as between males and females of the Boughrara lagoon. However, a significant FA between the left and right otoliths was found only in Wo among males and in all morphometric dimensions among females and Wo between males and females of the El Bibane lagoon. Discriminant function analysis of the otolith contour shape confirmed the presence of two separate C. ramada stocks, one corresponding to the Boughrara lagoon and the other representing the El Bibane lagoon, which should be managed separately. The possible cause of morphological variation in the sagittal otoliths' shape and morphometry due to FA between individuals of the two populations was discussed in relation to the biotic and abiotic factors.

Developmental instability, of which fluctuating asymmetry is the most commonly used and recommended measure, has recently been claimed to be an objective, integrated and retrospective indicator of animal welfare. The theoretical and empirical grounds for these claims are reviewed. In theory, carefully selected composite indices of fluctuating asymmetry are valid indicators of animal welfare in the sense that they reflect the ability of the developmental processes of an animal, with a given genetic constitution, to cope with environmental stressors. Relevant scientific experiments are scant and are mainly restricted to poultry, but they are on the increase and they largely support the application of developmental instability for assessing animal welfare. A scheme for monitoring farm animal welfare based purely on measures of developmental instability would have important advantages, but cannot be recommended yet. It cannot be ruled out that certain factors are clearly relevant to the welfare status of an animal but do not notably/proportionally affect its morphogenesis. Moreover, such a monitoring scheme would not be appropriate for applications with an emphasis on problem analysis/management.

Saccular otolith shape and size were analysed for the first time in 120 adult individuals of D. vulgaris collected from two localities, the Bizerte and Ghar El Melh lagoons (north-east Tunisia). The objectives were (1) to examine the specific inter- and intra-individual variation in the otolith shape using elliptical Fourier analysis combined with measures of length (LO), width (WO) and area (AO); (2) to use the otolith shape and size analysis as a phenotypic-based approach to discriminate the stock structure of this species in the two localities to investigate whether they represent two separate stocks to inform on appropriate management procedures; and (3) to test for biases resulting from potential fluctuating asymmetry (FA) in the otolith size on the discrimination of stock structure. Discriminant function analysis performed with the normalized elliptical Fourier descriptors coefficients showed statistically significant differences (P < 0.0001) in the otolith contour shape, i.e. asymmetry, either between the left and right sides or between the same sides (left-left and right-right) within and among individuals of the two localities. Besides, a significant asymmetry (P < 0.05) was found in WO and AO among individuals within the Bizerte locality and in WO only within the Ghar El Melh locality. Moreover, significant FA was observed in the otolith size parameters among individuals of the two localities. This significant asymmetry detected in the otolith shape, as well as in the size due to FA, within and among individuals of D. vulgaris collected from the Bizerte and Ghar El Melh localities confirms that the two stocks could be discriminated from each other and should be managed separately. This asymmetry is discussed in light of the instability of development caused either by environmental stress associated with the variation in water temperature, salinity, depth, feeding conditions and pollutants that have led to abnormalities in the development of individuals or by the presence of poor living conditions for the larvae resulting from unfavourable environments.

During human evolutionary history, there were “trade-offs” between expending time and energy on child-rearing and mating, so both men and women evolved conditional mating strategies guided by cues signaling the circumstances. Many short-term matings might be successful for some men; others might try to find and keep a single mate, investing their effort in rearing her offspring. Recent evidence suggests that men with features signaling genetic benefits to offspring should be preferred by women as short-term mates, but there are trade-offs between a mate's genetic fitness and his willingness to help in child-rearing. It is these circumstances and the cues that signal them that underlie the variation in short- and long-term mating strategies between and within the sexes.

Eye flukes are common infections of freshwater fish and their occurrence as metacercarial stages may occur non-randomly resulting in an asymmetrical distribution within the host eyes. However, from previous studies the presentation of bias by these trematodes lacks consistency suggesting that congenital asymmetrical effects are unlikely to be the cause and exogenous factors, such as environmental stress, may be more influential. The present study, undertaken over a 4-year period, investigates the impact of an extreme heatwave and drought on the annual bilateral asymmetry and occurrence of two eye fluke species (Diplostomum sp. in the lens and Tylodelphys sp. in the vitreous humour) from perch (Perca fluviatilis) and roach (Rutilus rutilus). The onset of the extreme climatic event resulted in a significant negative effect on the occurrence of the eye flukes. Bilateral asymmetry, which was present within both trematode species and hosts, appeared to be highly variable between eye fluke and fish species and also year of study. However, during the pre-drought period both host species demonstrated significant asymmetry for Tylodelphys sp. but not for Diplostomum sp. while during the drought this bias was reversed. The potential role of fluctuating asymmetry of fish hosts in structuring the bilateral asymmetry of eye flukes is discussed.

The role that physical attractiveness and fluctuating asymmetry (FA), a measure of developmental instability, play in self-perception and peer associations were explored in a well-studied cohort of Jamaican children using a novel research paradigm where subjects were already known to each other for extensive periods of time. The results showed that how attractive a child was perceived by others was significantly positively correlated with self-ratings of attractiveness. Contrary to findings from WEIRD (Western, Educated, Industrialized, Rich, Democratic) samples, the study found a reversal in the sex differences in self-perceived attractiveness and self-esteem, where Jamaican females rate themselves more attractive and report higher self-esteem than do males. Attractiveness also predicts overall popularity, as measured by desirability as a friend and the percentage of peers who choose an individual as a friend. Attractive individuals of both sexes were chosen more often as ‘friends’. A significant correlation was also found between an individual’s FA and the average FA of those chosen as friends. However, the effect was primarily due to preferences by males for female friends possessing similar levels of FA, which could be an effective strategy in reducing future mating effort.

Polistes paper wasps can be used to monitor trace metal contaminants, but the effects of pollution on the health of these insects are still unknown. We evaluated, in a south-eastern area of Spain, whether workers of Polistes dominula collected at urban and rural sites differ in health of midgut tissue and in fluctuating asymmetry, an estimate of developmental noise. We found that wasps collected at the urban sites had abundant lead (Pb)-containing spherites, which were less visible in wasps from the rural sites. Evident ultrastructural alterations in the epithelium of the midgut of the wasps collected at the urban sites included broken and disorganized microvilli, a high amount and density of heterochromatin in the nucleus of epithelial cells, cytoplasmic vacuolization and mitochondrial disruptions. Altogether, these findings suggest a negative effect on the transmembrane transport and a less efficient transcription. On the contrary, a healthy epithelium was observed in wasps from the rural sites. These differences may be preliminarily linked with levels of lead pollution, given that wasps from urban sites had double the Pb concentrations of wasps from rural sites. Level of fluctuating asymmetry was unrelated to wasp origin, thus suggesting no link between developmental noise and Pb-driven pollution.

Despite the fact that symmetry is common in nature, it is rarely perfect. Because there is a wide range of phenotypes which differs from the average one, the asymmetry should increase along with deviation. Therefore, the aim of this study was to assess the level of asymmetry in normal individuals as well as in phenodeviants categorized as minor or major based on abnormalities in forewing venation in honey bees. Shape fluctuating asymmetry (FA) was lower in normal individuals and minor phenodeviants compared with major phenodeviants, whereas the former two categories were comparable in drones. In workers and queens, there were not significant differences in FA shape between categories. FA size was significantly lower in normal individuals compared with major phenodeviant drones and higher compared with minor phenodeviant workers. In queens, there were no significant differences between categories. The correlation between FA shape and FA size was significantly positive in drones, and insignificant in workers and queens. Moreover, a considerable level of directional asymmetry was found as the right wing was constantly bigger than the left one. Surprisingly, normal individuals were significantly smaller than minor phenodeviants in queens and drones, and they were comparable with major phenodeviants in all castes. The correlation between wing size and wing asymmetry was negative, indicating that smaller individuals were more asymmetrical. The high proportion of phenodeviants in drones compared with workers and queens confirmed their large variability. Thus, the results of the present study showed that minor phenodeviants were not always intermediate as might have been expected.

Musca domestica L. (Diptera: Muscidae) is a vector of a range variety of pathogens infecting humans and animals. During a year, housefly experiences serial population bottlenecks resulted in reduction of genetic diversity. Population structure has also been subjected to different selection regimes created by insect control programs and pest management. Both environmental and genetic disturbances can affect developmental stability, which is often reflected in morphological traits as asymmetry. Since developmental stability is of great adaptive importance, the aim of this study was to examine fluctuating asymmetry (FA), as a measure of developmental instability, in both wild populations and laboratory colonies of M. domestica. The amount and pattern of wing shape FA was compared among samples within each of two groups (laboratory and wild) and between groups. Firstly, the amount of FA does not differ significantly among samples within the group and neither does it differ between groups. Regarding the mean shape of FA, contrary to non-significant difference within the wild population group and among some colonies, the significant difference between groups was found. These results suggest that the laboratory colonies and wild samples differ in buffering mechanisms to perturbations during development. Hence, inbreeding and stochastic processes, mechanisms dominating in the laboratory-bred samples contributed to significant changes in FA of wing shape. Secondly, general patterns of left–right displacements of landmarks across both studied sample groups are consistent. Observed consistent direction of FA implies high degrees of wing integration. Thus, our findings shed light on developmental buffering processes important for population persistence in the environmental change and genetic stress influence on M. domestica.

Otolith shape analyses were conducted on three different species of Mullidae (Mullus barbatus barbatus, M. b. ponticus and M. surmuletus). The otolith shape was described by 19 harmonics from elliptic Fourier descriptors. In a first step, their comparison through canonical discriminant analyses (CDA) was run for all fish with right otoliths, left otoliths and both otoliths pooled. The latter possibility had a higher discriminating power and allowed much more visually explicit results. This implied that the two otoliths were not similar as often claimed, and had each their specific information. In a second step, the CDA demonstrated strong spatial discrimination of local populations from various areas within the Mediterranean basin, i.e. NW Mediterranean, Aegean Sea and Black Sea, and between sites within each area. The percentage of well classified individuals of M. barbatus in predefined groups varied between 78 to 100% depending on sites, and even reached 100% for each site for M. surmuletus. These spatial patterns were most likely linked to differences in environmental conditions between areas and sites, such as effects of strong river runoffs and differences in depths and/or habitat types. In a third step, CDA also evidenced ontogenetic discriminations of mullet populations that could be linked (i) to influence of diet of fish of various sizes and (ii) to changes in physiological conditions according to the stage of development of the fish.

Leaf fluctuating asymmetry (FA) is considered an important indicator of environmentally induced stress in plants, but the relationship between herbivory and FA levels is not clear. In this study we compared leaf size and shape, leaf area consumed by herbivorous insects, and FA levels between individuals of Heliocarpus pallidus (Tiliaceae) from two adjacent and contrasting habitat types (deciduous and riparian) in the Chamela–Cuixmala tropical dry-forest biosphere reserve. Ten individuals of H. pallidus were collected in each habitat type. Leaf shape was assessed using geometric morphometric techniques. Results indicated statistically significant differences in leaf shape between individuals from the two habitat types. In individuals from the riparian habitat leaf area (mean = 42.3 ± 1.2 cm2), herbivory levels (mean = 25.5% ± 1.8%) and FA levels (mean = 0.38 ± 0.04 cm) were significantly higher than in individuals from the deciduous habitat (17.2 ± 3.5 cm2; 9.6% ± 1.0% and 0.18 ± 0.04 cm, respectively). Within habitats, significant correlations were found between total leaf area and percentage leaf area removed by insects (R2 = 0.92 in riparian habitats, R2 = 0.9 in deciduous habitats), and between percentage leaf area removed and FA (R2 = 0.70 in riparian habitats, R2 = 0.79 in deciduous habitats). As has been suggested for other plant species, it is possible that the more favourable conditions in the riparian habitat enhance leaf growth, resulting in higher FA. Also, individuals in this habitat might be characterized by lower chemical defence and/or higher nutritional quality, which would explain the higher herbivory levels.

The effects of sublethal concentrations of the insect growth regulators (IGRs) diflubenzuron and methoprene on some fitness components of an Aedes aegypti (L.) population in south-eastern Brazil were investigated. The fourth instar larvae of the mosquito were exposed to 20 ppb methoprene and 3 ppb diflubenzuron, and adult survivors were evaluated for fitness parameters, including body size and biomass, fecundity, fertility, longevity and symmetry. The sublethal concentrations had negative effects on longevity, but biomass, fecundity and fertility were not affected by either IGR. In separate experiments, A. aegypti individuals' surviving concentrations of 2, 3 and 3.5 ppb diflubenzuron and 5, 10 and 20 ppb methoprene were used for morphological analyses (size and symmetry). Diflubenzuron had negative effects on the mosquito's body symmetry. The observed decreases in longevity and symmetry may have negative impacts on the population dynamics of A. aegypti.

The effects of avermectin exposure on natural populations of the yellow dung fly, Scathophaga stercoraria Linnaeus, were investigated at the field scale on farms in south-west Scotland. Pastures forming the focus of the study were grazed with either untreated cattle or cattle receiving standard, manufacturer-recommended treatment regimes of an avermectin product. Flies were sampled between April and July in 2002 and 2003 using dung-baited pitfall traps. Abundance and wing asymmetry in S. stercoraria populations were examined in relation to a range of environmental and management variables (including avermectin exposure, pasture management intensity, weather and season). Data used for abundance analyses were collected in fields where treated cattle had been dosed with either doramectin or ivermectin, while the data for the asymmetry analyses were from a subset of fields where treated cattle had been dosed with doramectin only. While abundance of S. stercoraria varied significantly between years and with season, there was no difference in their abundance between fields grazed by avermectin-treated or untreated cattle. Asymmetry was significantly higher in fly populations in fields grazed by doramectin-treated cattle, suggesting that exposure to doramectin during development could have imposed some degree of environmental stress. While these results suggest that exposure to doramectin residues in dung on grazed pastures may have sublethal effects on the insects developing in that dung, there was no evident avermectin effect on the abundance of adult S. stercoraria occurring in the pastures.

Transgenerational maternal effects on performance (rm) after host transfer were evaluated in the generalist aphid Myzus persicae s.s., and in its subspecies specialized on tobacco, M. persicae nicotianae Blackman. We tested whether the performance of these taxa, when reared separately on optimal and suboptimal hosts (as sources of different maternal background) and then transferred to optimal hosts, experienced variations along four successive generations. Additionally, to compare the tolerance of both taxa to stress following host transfers, developmental instability (fluctuating asymmetry and body abnormalities) along the four generations was assessed. Taxon, rearing host, and generation affected the performance after host transfer. In the generalist, there was a significant improvement of rm along generations when transferred from suboptimal to optimal host and a significant decrease when transferred from optimal to optimal host; in the specialist, no increase or decrease occurred in any host transfer treatment. Transfer from suboptimal to optimal hosts caused higher losses of remaining replicates along generations than transfers from optimal to optimal hosts, and the specialist showed higher losses than the generalist. The only significant effect detected in comparisons involving fluctuating asymmetry values was that of taxon on length of siphunculi. Frequency of body abnormalities was not affected by treatments. Collectively, these results show a transgenerational weakening of maternal effects in the generalist but not in the specialist aphid, and suggest that rearing the latter in a suboptimal host causes not easily reversible changes that further give rise to constraints in performance.

Senescence can be defined as accelerating phenotypic deterioration with old age. For traits that grow throughout life, such as the horns of some ungulates, senescence may be expressed as a decrease in annual growth rates, or an increase in asymmetry, in the years preceding death. Age-specific yearly horn-growth segments of 378 male Alpine ibex Capra ibex L. that died from natural causes were analysed in the Gran Paradiso National Park (Italian Alps). Horn annuli displayed fluctuating asymmetry. The hypothesis that asymmetry and size of the annuli of the horns could predict annual survival probability was tested. It was found that between 5 and 11 years of age, male ibex that grew shorter annuli than the average for the population had a greater probability of mortality over the following years than those with greater rates of horn growth. Horn asymmetry and mortality rates were not significantly correlated. Annulus size, reflecting the onset of senescence, seemed to be a better indicator of individual quality than annulus asymmetry.

Japanese cupped oysters suffer summer mortality in many culture sites along the French Atlantic coast. To ascertain whether mortality might be associated with morphological features of the shells, we estimated fluctuating asymmetry (FA) of hatchery/nursery-produced oysters kept in culture bags in the intertidal. FA is defined as random variations from a perfect symmetry plane (bilateral or radial) in some morphological trait. FA increases with disruption of homeostasy during ontogeny and has both genetic and environmental determinants. We found significant differences in FA between dead and live oysters in two of our three study groups. Therefore, lack of developmental stability may be involved in the summer mortality syndrome of oysters. We also found indirect evidence that once acquired, FA patterns of shells are retained at least partially. Since FA likely appears early during ontogeny and is recorded in the shells, we hypothesise that it might be useful for forecasting the ability of spat to resist environmental stress.

Recent reviews of specific topics, such as the relationship between male attractiveness to females and fluctuating asymmetry or attractiveness and the expression of secondary sexual characters, suggest that publication bias might be a problem in ecology and evolution. In these cases, there is a significant negative correlation between the sample size of published studies and the magnitude or strength of the research findings (formally the ‘effect size’). If all studies that are conducted are equally likely to be published, irrespective of their findings, there should not be a directional relationship between effect size and sample size; only a decrease in the variance in effect size as sample size increases due to a reduction in sampling error. One interpretation of these reports of negative correlations is that studies with small sample sizes and weaker findings (smaller effect sizes) are less likely to be published. If the biological literature is systematically biased this could undermine the attempts of reviewers to summarise actual biology relationships by inflating estimates of average effect sizes. But how common is this problem? And does it really affect the general conclusions of literature reviews? Here, we examine data sets of effect sizes extracted from 40 peer-reviewed, published meta-analyses. We estimate how many studies are missing using the newly developed ‘trim and fill’ method. This method uses asymmetry in plots of effect size against sample size (‘funnel plots’) to detect ‘missing’ studies. For random-effect models of meta-analysis 38% (15/40) of data sets had a significant number of ‘missing’ studies. After correcting for potential publication bias, 21% (8/38) of weighted mean effects were no longer significantly greater than zero, and 15% (5/34) were no longer statistically robust when we used random-effects models in a weighted meta-analysis. The mean correlation between sample size and the magnitude of standardised effect size was also significantly negative (rs =−0·20, P<0·0001). Individual correlations were significantly negative (P<0·10) in 35% (14/40) of cases. Publication bias may therefore affect the main conclusions of at least 15–21% of meta-analyses. We suggest that future literature reviews assess the robustness of their main conclusions by correcting for potential publication bias using the ‘trim and fill’ method.

Nephila edulis is a spider with large body size variability in males and females. Genital characters show negative allometric values compared to somatic characters. In males, the embolus (the most important structure for sperm transfer) had a significantly lower coefficient of variation than body size. This suggests that male genitalia are under stabilizing selection favouring intermediate size. Female N. edulis showed a trend similar to males regarding allometric values in genitalia. In females, however, the variation coefficient in a specific genital character crucial for successful copulation did not differ from that of indicators for overall body size. This suggests that in Nephila the genitalia of the females experience less stabilizing selection than those of the males. In male and female genitalia, the mode of selection seems to cause developmental instability not in degrees of fluctuating asymmetry but in the degree of data scatter which indicates a lower coefficient of determination.

Ball rolling in dung beetles is an energy expensive activity associated with elevated thoracic temperatures. The ability of individuals to engage in such energetically costly behaviour may be dependent on their body condition. Bilateral asymmetries arising from the interaction between an individual's genes and its environment have been hypothesized to reflect an organism's quality. A number of studies have shown that individuals with elevated levels of asymmetry perform less well under stress. We tested this hypothesis by measuring correlates of dung ball rolling speed in males and females of Kheper nigroaeneus (Coleoptera: Scarabaeidae). We found that larger beetles produced larger dung balls and rolled them faster along an experimental track. However, there was no relationship between ball rolling speed and the asymmetry of fore and hind tibia. There was also no relationship between the asymmetry of the beetle or the number of mites that it carried, and the level of mite infestation did not influence ball rolling speed.