Analysis Of Fluctuating Asymmetry Research Articles

Use of otolith microchemical and morphological analyses for stock discrimination of Sarpa salpa on two Tunisian islands, Djerba and Kerkennah

Abstract Otolith morphological and microchemical analyses are relatively new scientific research methods used in fish stock evaluation and management. However, in Tunisia, only morphological methods have been used. The objective of this study was the Sarpa salpa stock discrimination of Djerba and Kerkennah by the otoliths morphological and microchemical analysis, while carrying out a fluctuating asymmetry analysis and a stock comparison of males and females for each population. The results revealed significant differences between the Djerba and Kerkennah populations, significant differences between the stocks of males and females in each population, and a highly significant fluctuating asymmetry for both populations. The results of the otolith morphological analysis were similar to those of the microchemical analysis. This result proves that both morphological and microchemical analyses are powerful tools for fish stock discrimination.

Fluctuating asymmetry and environmental stress in a reptile under different levels of anthropogenic disturbance

In the Monte region of Argentina, the local population is causing severe habitat degradation by extracting native vegetation and domestic animal grazing. To assess whether disturbed environments have higher levels of asymmetry than control environments, we examined morphological variation and fluctuating asymmetry in the cephalic region of the longtail whiptail lizard Aurivela longicauda (Teiidae) using a Procrustes analysis with geometric morphometry. This is the first study of asymmetry using geometric morphometry in a lizard from Argentina. While there was no difference in the size of the cephalic region between the two environments, there were differences in shape between the right and left side of the lizard's head (object symmetry), the differences being greater at disturbed sites (fluctuating asymmetry), suggesting that anthropogenic activities may act as stressors driving alterations in the fitness (reproduction) of reptile populations. Fluctuating asymmetry analysis is an excellent conservation biology and environmental monitoring tool for measuring stress in different organisms.

Superfrogs in the city: 150year impact of urbanization and agriculture on the European Common Frog.

Despite growing pressure on biodiversity deriving from increasing anthropogenic disturbances, some species successfully persist in altered ecosystems. However, these species' characteristics and thresholds, as well as the environmental frame behind that process are usually unknown. We collected data on body size, fluctuating asymmetry (FA), as well as nitrogen stable isotopes (δ15 N) from museum specimens of the European Common Frog, Rana temporaria, all originating from the Berlin-Brandenburg area, Germany, in order to test: (a) if specimens have changed over the last 150years (1868-2018); and (b) if changes could be attributed to increasing urbanization and agricultural intensity. We detected that after the Second World War, frogs were larger than in pre-war Berlin. In rural Brandenburg, we observed no such size change. FA analysis revealed a similar tendency with lower levels in Berlin after the war and higher levels in Brandenburg. Enrichment of δ15 N decreased over time in both regions but was generally higher and less variable in sites with agricultural land use. Frogs thus seem to encounter favorable habitat conditions after pollution in postwar Berlin improved, but no such tendencies were observable in the predominantly agricultural landscape of Brandenburg. Urbanization, characterized by the proportion of built-up area, was not the main associated factor for the observed trait changes. However, we detected a relationship with the amount of urban greenspace. Our study exemplifies that increasing urbanization must not necessarily worsen conditions for species living in urban habitats. The Berlin example demonstrates that public parks and other urban greenspaces have the potential to serve as suitable refuges for some species. These findings underline the urgency of establishing, maintaining, and connecting such habitats, and generally consider their importance for future urban planning.

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

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

Asymmetry in the common wall lizard Podarcis muralis under different levels of urbanization: The effect of trait and FA index selection

The use of fluctuating asymmetry (FA) as a measure of developmental instability and its relationship to stress and fitness is highly controversial. We examined whether the selection of different FA indices and traits influences the results of FA analysis. We chose four meristic traits and three FA indices (two single-trait and two multiple-trait indices) to assess FA levels in the common wall lizard (Podarcis muralis) from three different habitat types (urban, suburban and natural). Urbanization has already been linked to developmental instability in P. muralis. We therefore expected to detect different FA levels among the habitats. However, we also wanted to see whether we obtained the same patterns using different indices and traits. Our results showed that different traits can yield different FA patterns between habitats. The only statistically significant difference between habitats was detected for the FA2 index in femoral pores. The highest level of FA was detected in the urban population, while the lowest level was in the natural population. It is clear that caution must be exerted when deciding on which traits and indices are to be used for FA analysis. [Projects of the Serbian Ministry of Education, Science and Technological Development, Grant no. OI173043, Grant no. III43001]

Herbivory causes increases in leaf spinescence and fluctuating asymmetry as a mechanism of delayed induced resistance in a tropical savanna tree

Background and aims – Leaf spinescence is thought to be a defense against herbivory and may increase in years following high herbivory pressure (DIR – delayed induced resistance). Besides DIR, herbivory also causes plant stress, which can be assessed using fluctuating asymmetry analysis (FA – random departures from leaf bilateral symmetry). In this two-year field study we first investigated the relationships between herbivory, FA and spinescence in Solanum lycocarpum trees during an outbreak of moth caterpillars in 2010; then in 2011 we examined whether plants with intense herbivory the previous year presented changes in FA (herbivory induced stress) and spinescence. Key results – In 2010, leaves damaged by moths were significantly more asymmetrical than undamaged leaves. In addition, moths preferentially fed on leaves with fewer and shorter spines. In 2011, plants severely attacked by moths the year before showed significant increases in FA (28%), spine abundance (21%) and spine length (84%), compared to less damaged plants. Conclusions – Our data suggest a delayed response of S. lycocarpum to herbivory, in that plants subjected to high leaf damage the previous year maximized their display of anti-herbivore mechanisms, in this case, leaf spinescence. This is one of the few studies to show that FA increased as a response to herbivore attack. We conclude that FA can be used as an indicator of plant stress following leaf damage.

Asimetría fluctuante en Apis mellifera (Hymenoptera: Apidae) como bioindicador de ambientes antropogénicos

The successful distribution of A. mellifera is due to their ability to adjust to seasonal variations, considerable control over their internal physical environment and exploration of different resources. However, their populations have experienced different forms and levels of environmental pressure. This research aimed to verify the phenotypic plasticity in both size and shape of wings in A. mellifera using fluctuating asymmetry, based on geometric morphometrics from apiaries located in sites with high and low levels of anthropization. We sampled 16 locations throughout all five geographic regions of Brazil. At each site, samples were collected from 20 beehives installed in apiaries: 10 installed near high anthropogenic environments (Cassilandia - MS, Fortaleza - CE, Maringá - PR, Aquidauana - MS, Rolim de Moura - RO, Riachuelo - SE, Ubiratã - PR and Piracicaba - SP), and 10 in sites with low levels of human disturbance (Cassilândia - MS, Itapiúna CE, União da Vitória - PR, Aquidauana - MS, Rolim de Moura - RO, Pacatuba - SE, Erval Seco - RS, Rio Claro - SP). A sample of 10 individuals was taken in each hive, totaling 200 per location, for a total of 1,600 individuals. We used fluctuating asymmetry (FA) in size and shape of the forewing through geometric morphometrics. The FA analysis was conducted in order to check bilateral differences. The indexes of size and shape were submitted to analysis of variance (ANOVA), where the characters evaluated were used as factors to verify the size and shape differences. The results indicated an asymmetry on the shape of the wing (P < 0.001) but no asymmetry was observed on wing size. Considering FA as an environmental response and high and low impacted areas as a fixed factor, we observed significant differences (P < 0.05). The results for the wing shape in A. mellifera demonstrated that this feature undergoes more variation during ontogeny compared to the variation in size. We concluded that bee samples collected from colonies with higher levels of human disturbance had higher wing-shape asymmetry; the variation of fluctuating asymmetry in the wing shape of honeybees can be used as an indicator of the degree of environmental anthropization.

Application of fluctuating asymmetry indexes of silver birch leaves for diagnostics of plant communities under technogenic pollution

The prospects for applying the fluctuating asymmetry (FA) of silver birch (Betula pendula Roth) leaves for diagnosis of plant community conditions in technogenically polluted environments are considered with an example of the effect of heavy metals and chronic ionizing radiation. An increase in the minimum sample size to 150–180 leaves and measurements of morphometric traits with an improved accuracy of 0.06–0.07 mm made it possible to overcome the influence of sample size on FA parameters. The excess content of nickel (18.5 times with respect to the background level), lead (16.0 times), manganese (5.8 times), and copper (3.0 times) in birch leaves was accompanied by the increase in multivariate FA index by 20.0%. The chronic exposure to ionizing radiation (at absorbed dose rate on the soil surface of 4.74 µGy/h) elevated the multi-variate FA index of leaves by 29.8% and the content of chlorophylls a and b in leaves by 50.3 and 82.9%, respectively. It was found that the most informative morphometric trait for analysis of birch leaf FA is the distance between the bases of the first and second lateral veins; its FA index rose to 40.4% under the influence of heavy metals and to 53.6% under exposure to chronic ionizing radiation. Thus, FA can be regarded as a sensitive biomarker for detecting early negative responses of forest ecosystems to technogenic pollution.

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

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

Regeneration interferes with fluctuating asymmetry analysis in odonate larvae

Regeneration interferes with fluctuating asymmetry analysis in odonate larvae

The ecological context of bilateral symmetry of organ and organisms

A particular phenotype is generated through numerous networks of interactions from within the cell to the whole ecosystem. The level of the environmental noise and the ability of a given genotype to render different phenotypes under different environmental conditions, called phenotypic plasticity, determine survival or death at individual and/or population level. It is important to highlight that non-lethal environmental changes are important for generating genetic variability and promoting biological adaptations. However, when the level of environmental noise starts to be stressed, the developmental stability (DS) of the organism can be perturbed. The DS has been analysed through the symmetry deviations in organs or organisms with bilateral structure. The symmetry deviations occur due to inability to contain disorders from environmental or endogenous conditions during its development. This deviation is called fluctuating asymmetry (FA) when is a non-directional deviation in the symmetry of a bilateral structure normally distributed in a population. Low FA has been associated with greater DS. The analysis of FA has often been used to measure the effects of environmental perturbations. In this review, I discuss the concept of plant stress and phenotypic plasticity connecting both to the generation of an asymmetry phenotype, highlighting the usefulness of FA as an indicator of the level of stress which the organism is subjected to. Further, although this review explores mainly the connection between FA and stress in plants, the ecological context of symmetry in animals and plant-insect interaction is also discussed. Finally, I provided some methodologies used to detect symmetry variations in organs or organisms with bilateral structure.

Skulls Symmetry of “White Rasquera” Goat

Three common categories of bilateral asymmetry have been described: directional asymmetry, antisymmetry, and FA (fluctuating asymmetry). FA is the most subtle of the three types of asymmetry, and differs from the patterns of the others in that paired structures tend to be symmetric in size. The analysis of FA allows to estimate the influence of stress factors on animal development and enables evaluation of resistance to stress. The aim of this work was to estimate the symmetry of skulls of a contemporary pure goat breed, as there is currently no study of FA as an estimate of individual quality for domestic goats. For this purpose, 11 landmarks were digitized in two dimensions from the crania of 24 adult goats (12 males and 12 females) belonging to the White Rasquera breed. The skulls showed nearly perfect bilateral symmetry. The low detected values of FA in skulls revealed a weak influence of developmental stress on this goat contemporary population and its strong ability to compensate stress.

Fluctuating and directional asymmetry in young human males: Effect of heavy working condition and socioeconomic status

Many adverse environmental and genetic factors can affect stability of development during human growth. Although the level of fluctuating asymmetry (FA) may be influenced by environmental and genetic stress encountered during this period, directional asymmetry (DA) is largely attributable to differential mechanical loading during bone growth, for example, handedness. I assessed the effects of heavy working conditions and socioeconomic conditions on asymmetry levels in three groups of young human males: 1) individuals employed in the heavy industry sector (n = 104, mean age = 18.48 +/- 0.61 years), 2) individuals who had the same socioeconomic status as the laborers (n = 102, mean age = 18.39 +/- 0.58 years) but were not laborers, and 3) nonlaborers from the higher socioeconomic levels of society (n = 103, mean age = 18.43 +/- 0.67). For all subjects, hand length, hand width, elbow width, wrist width, knee width, ankle width, foot length, foot width, ear length, and ear width were measured. All measurements of the upper extremities in the labor group appeared to exhibit DA; in the other two groups only hand measurements exhibited DA. According to analysis of FA, subjects living in poor conditions exhibited more FA than their nonlaborer peers living in better conditions. In addition, biomechanical pressures due to heavy working conditions of the labor group appeared to cause increased DA in the upper extremities: DA increased with an increase in the number of years working.

Disentangling fluctuating asymmetry from otolith shape

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 399:261-272 (2010) - DOI: https://doi.org/10.3354/meps08347 Disentangling fluctuating asymmetry from otolith shape M. Palmer*, M. Linde, B. Morales-Nin IMEDEA (CSIC-UIB), Instituto Mediterráneo de Estudios Avanzados, Miquel Marquès 21, 07190 Esporles (Mallorca), Spain *Email: palmer@imedea.uib-csic.es ABSTRACT: Fluctuating asymmetry (FA), defined as random deviations from ideal, perfect symmetry, has been hypothesized to be negatively associated with fitness and positively associated with stress. Fish otoliths deserve special attention in regard to this topic because their FA is relatively easy to measure, unlike the fitness of wild fish themselves. In addition, otoliths are convenient for estimating FA, because they are systematically extracted for aging purposes, and otolith collections might allow the use of FA as a bioindicator of change at different spatio-temporal scales. Here we demonstrate 2 key methodological tools: the use of shape instead of previously used univariate (metric or meristic) traits, and the use of a statistical protocol capable of disentangling true FA from other types of asymmetry (namely, directional asymmetry and antisymmetry) and from measurement error. In the case of the razor fish Xyrichthys novacula; fluctuation asymmetry of the otolith shape of 180 individuals from 5 populations accounted for 23.2% total shape variability (5 fold larger than the measurement error). Moreover, FA clearly differed between populations. In contrast, FA measured using a univariate trait (radius at the sulcus) did not detect between-population differences. Moreover, in a simulation experiment, we demonstrate that FA measured using shape is able to reveal a true pattern, while FA measured using a univariate trait extracted from the same data is unable to do so. Therefore, the analysis of FA using shape paired with an adequate statistical model may increase our knowledge of the potential links between otolith FA and fitness or stress. KEY WORDS: Fluctuating asymmetry · Shape · Geometric morphometrics · Two-factor mixed effects model · Procrustes ANOVA · Directional asymmetry Full text in pdf format PreviousNextCite this article as: Palmer M, Linde M, Morales-Nin B (2010) Disentangling fluctuating asymmetry from otolith shape. Mar Ecol Prog Ser 399:261-272. https://doi.org/10.3354/meps08347 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 399. Online publication date: January 28, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Fluctuating asymmetry in Ichthyophonus-sp. infected newts, Notophthalmus viridescens, from Vermont

Measures of fluctuating asymmetry (FA) have been used to assess the significance of stress in amphibian populations. When animals with bilateral body plans are challenged by environmental stressors, departures from bilateral symmetry can emerge during development. The tendency for FA to develop has been linked to greater susceptibility to pathogens in many organisms. In our study, newts (Notophthalmus viridescens) infected with Ichthyophonus-sp. exhibited greater size-corrected FA of the hind limbs than uninfected animals from the same population. Among infected animals, however, the intensity of infection and the extent of hind limb asymmetry were not correlated, suggesting that asymmetry did not arise following infection, but rather that newts having greater FA may have been more susceptible to infection as a result of the same stresses that produced the increase in FA. There was no relationship between dorsal spot pattern FA and infection status or hind limb FA. We suggest that spot pattern may be less canalized than hind limb development. Newts are widely distributed and important components of freshwater communities in eastern North America and, thus, any change in their vitality may affect the composition of those communities. Analyses of hind limb FA may be a useful and non-invasive tool for identifying potentially vulnerable amphibian

Fluctuating asymmetry in the otoliths of larval Atlantic menhaden Brevoortia tyrannus (Latrobe) – a condition indicator?

Fluctuating asymmetry (FA) was described for otolith length, width and area for two groups of larval and juvenile Atlantic menhaden Brevoortia tyrannus. The larvae and juveniles (age range: 20–120 days; standard length, LS, range: 14–35 mm) were separated into the two distinct groups a priori on the basis of their growth indices estimated from residuals of a LS‐at‐age model; slow growers had residuals &lt;8% of the average size at age and fast growers had residuals &gt;8%. Some indication supporting the fluctuating asymmetry methodology was found when unsigned normalized FA2 index was used for otolith area. That conclusion was not, however, supported by the other method used in this work, i.e. between‐group ANCOVA analysis of individual unsigned and not normalized FA1 indices plotted against trait size. These inconsistent results are most probably a consequence of error introduced during FA index normalization (accounting for trait size effect on absolute FA). Although it is concluded here that FA analysis of sagittal otoliths was not effective in describing differences in the natural variability of growth and condition of larval Atlantic menhaden, the possible species‐ and otolith type‐related differences should be considered in the future research on FA.

Fluctuating Asymmetry in Broiler Chickens: A Decision Protocol for Trait Selection in Seven Measuring Methods

Nonidentical development of bilateral traits due to disturbing genetic or developmental factors is called fluctuating asymmetry (FA) if such deviations are continuously distributed. Fluctuating asymmetry is believed to be a reliable indicator of the fitness and welfare of an animal. Despite an increasing body of research, the link between FA and animal performance or welfare is reported to be inconsistent, possibly, among other reasons, due to inaccurate measuring protocols or incorrect statistical analyses. This paper reviews problems of interpreting FA results in poultry and provides guidelines for the measurement and analysis of FA, applied to broilers. A wide range of morphological traits were measured by 7 different techniques (ranging from measurements on living broilers or intact carcasses to X-rays, bones, and digital images) and evaluated for their applicability to estimate FA. Following 4 selection criteria (significant FA, absence of directional asymmetry or antisymmetry, absence of between-trait correlation in signed FA values, and high signal-to-noise ratio), from 3 to 14 measurements per method were found suitable for estimating the degree of FA. The accuracy of FA estimates was positively related to the complexity and time investment of the measuring method. In addition, our study clearly shows the importance of securing adequate statistical power when designing FA studies. Repeatability analyses of FA estimates indicated the need for larger sample sizes, more repeated measurements, or both, than are commonly used in FA studies.

Fluctuating asymmetry as an animal welfare indicator — A review of methodology and validity

It has been suggested that fluctuating asymmetry (FA) reflects an animal's ability to cope with the sum of challenges during its growing period and, thus, is a potential welfare indicator. In this review we investigate the evidence of associations between FA and other welfare indicators measured at the level of the individual and of effects of welfare-relevant environmental conditions on FA in populations of captive birds and mammals including humans. As the question of validity cannot be treated independently from the quality of the available data, first a checklist for the proper measurement and analysis of FA is drafted and used to evaluate the methodological quality of the various studies. We recommend this checklist to be used as a standard for future FA studies. We found 17 relevant studies on associations between FA and other welfare indicators, and 36 studies on effects of welfare-relevant factors on FA. Frequent methodological shortcomings or insufficient methodological information allow for only cautious conclusions. The proportion of significant results supporting the link between higher FA and poorer welfare is only moderately high. Independent from statistical significance, almost all studies found the relationship between FA and welfare to be prevailingly in the expected direction. FA is a promising measure of animal welfare, despite a great number of open questions, e.g. relating to the ontogeny of FA or its sensitivity to various stressors. The considerable potential of FA as a welfare indicator makes it worthwhile to pursue more intensely validation studies as well as applied studies. These studies should pay particular attention to an appropriate methodological approach.

Fluctuating asymmetry in fish otoliths and heterozygosity in stressful estuarine environments (West Africa)

Fluctuating asymmetry (FA) is assumed to reflect the developmental instability caused by environmental or genetic stress. Fish otoliths represent a very good tool for investigating the consequence of different effects on FA. Otolith FA analysis, coupled with genetic analysis, has been undertaken on two common West African estuarine species, Ethmalosa fimbriata (EFI) and Sarotherodon melanotheron (SME), in two neighbouring estuaries, in order to highlight the impact of salinity on developmental stability. The Gambia estuary has a normal functioning and the Saloum estuary is inverse (saltier waters in the upper river), reaching extremely high salinities (&gt;100 psu) and constituting severe environmental stress. Five sub-populations of EFI and six of SME were studied along a salinity gradient. The differences between right and left otoliths were estimated with image processing by measuring five dimensions (area, perimeter, diameter, rostrum and posterior radii). Analyses of genetic differentiation at three EPIC and one anonymous nuclear gene loci for EFI and six polymorphic enzymatic loci for SME were carried out to measure the level of heterozygosity. Absolute FA in all otolith traits examined was unaffected by gender but increased significantly with fish size. Size-corrected absolute FA did not show any significant difference among sites differing largely in salinity, although a higher asymmetry in otolith area was recorded in the saltiest site. These findings suggest that otolith asymmetry is a poor indicator of osmotic stress. The individual heterozygosity level did not seem to have an effect on otolith FA for either species, even though a slight correlation appeared with otolith area or perimeter. Otolith FA cannot be considered to be a useful indicator for estimating changes linked with environmental or genetic stress in these estuaries.

Trends in fluctuating asymmetry in East Greenland polar bears ( Ursus maritimus) from 1892 to 2002 in relation to organohalogen pollution

Fluctuating asymmetry (FA) was studied in skulls of 283 polar bears ( Ursus maritimus) sampled in East Greenland from 1892 to 2002. Fourteen metric bilateral traits in skull and lower jaw were measured and compared between polar bears born until 1960 ( n=94) and from 1961 ( n=189). The period 1892–1960 was chosen to represent a period prior to appearance of organohalogens (polychlorinatedbiphenyls [PCBs], dichlorodiphenyltrichloroethanes [DDTs], hexacyclohexanes [HCHs], chlordanes [CHLs], hexachlorobenzene [HCB], polybrominateddiphenylethers [PBDEs] and dieldrin) originating from long-range transport to East Greenland from southern latitudes. The period 1961–2002 represents the period when polar bears have been exposed to organohalogens. During this latter period, the level of organochlorines is believed to have increased from 1960 to the late 1980s followed by a likely decrease from 1990 to 2002. Within this later period, other compounds such as, e.g., polybrominated flame retardants are believed to have increased throughout the period. Two different analysis showed, that the degree of fluctuating asymmetry did not differ statistically between the two periods in ten of thirteen traits (one trait excluded due to high measurement error). In fact, when significant differences were found in four of the traits, the fluctuating asymmetry was lower in skulls sampled after 1960. The degree of fluctuating asymmetry was higher in adults than in subadults for 6 of the 14 traits, whereas a higher degree of fluctuating asymmetry was found for only one trait in one of the analyses for subadults relative to adults. Females had a higher degree of fluctuating asymmetry than males in one trait. A time trend analysis did find fluctuations over time for five traits but the relationship was weak as the trend appeared to occur by chance due to the high number of regressions analysed ( n=42). A correlation analysis of FA versus the sum concentrations of various classes of organohalogens in adipose tissue from a subsample of 94 recently collected polar bears (1999–2002) did not show a trend either. Hence, the present study could not document a relationship between skull asymmetry in polar bears and periods with different exposure to organohalogens. These findings are possibly influenced by nutritional status, genetic factors, a subeffect exposure of organohalogens or confounded by other environmental factors (e.g. temperature) within the two investigated periods.