Temperature shock during development fails to increase the fluctuating asymmetry of a sexual trait in stalk-eyed flies.

The fluctuating asymmetry (FA) of bilateral traits is claimed to be a general indicator of environmental stress. Exaggerated sexual ornaments are thought to show elevated levels of FA and a greater response to stress than other traits. Previous work with stalk-eyed flies (Cyrtodiopsis dalmanni) has shown that the FA of the sexual trait (male eye stalks), wing length and wing width were unaffected by a continually applied food stress. Here we tested whether a transient stress (24-h heat shock at 31 degrees C during development) affected the FA of these traits. A second experiment tested the combined stresses of transient heat shock at 31 degrees C with continuous exposure to desiccation. In each experiment, temperature shock reduced the trait size, confirming that the treatments were stressful. However, stress had no effect on the FA of individual traits or the FA summed across all traits. Exposure to the combined stresses significantly elevated mortality and reduced trait size compared to the single-stress regime. However, FA did not differ significantly between flies from the two experiments. We found no evidence that FA in sexual and non-sexual traits reflects transient stress during the development of C. dalmanni.     

Rhodnius prolixus and Rhodnius robustus–like (Hemiptera, Reduviidae) wing asymmetry under controlled conditions of population density and feeding frequency

Habitat change in Rhodnius spp may represent an environmental challenge for the development of the species, particularly when feeding frequency and population density vary in nature. To estimate the effect of these variables in stability on development, the degree of directional asymmetry (DA) and fluctuating asymmetry (FA) in the wing size and shape of R. prolixus and R. robustus–like were measured under laboratory controlled conditions. DA and FA in wing size and shape were significant in both species, but their variation patterns showed both inter-specific and sexual dimorphic differences in FA of wing size and shape induced by nutrition stress. These results suggest different abilities of the genotypes and sexes of two sylvatic and domestic genotypes of Rhodnius to buffer these stress conditions. However, both species showed non-significant differences in the levels of FA between treatments that simulated sylvan vs domestic conditions, indicating that the developmental noise did not explain the variation in wing size and shape found in previous studies. Thus, this result confirm that the variation in wing size and shape in response to treatments constitute a plastic response of these genotypes to population density and feeding frequency.     

Thermal evolution of pre-adult life history traits, geometric size and shape, and developmental stability in Drosophila subobscura

Replicated lines of Drosophila subobscura originating from a large outbred stock collected at the estimated Chilean epicentre (Puerto Montt) of the original New World invasion were allowed to evolve under controlled conditions of larval crowding for 3.5 years at three temperature levels (13, 18 and 22 degrees C). Several pre-adult life history traits (development time, survival and competitive ability), adult life history related traits (wing size, wing shape and wing-aspect ratio), and wing size and shape asymmetries were measured at the three temperatures. Cold-adapted (13 degrees C) populations evolved longer development times and showed lower survival at the highest developmental temperature. No divergence for wing size was detected following adaptation to temperature extremes (13 and 22 degrees C), in agreement with earlier observations, but wing shape changes were obvious as a result of both thermal adaptation and development at different temperatures. However, the evolutionary trends observed for the wing-aspect ratio were inconsistent with an adaptive hypothesis. There was some indication that wing shape asymmetry has evolutionarily increased in warm-adapted populations, which suggests that there is additive genetic variation for fluctuating asymmetry and that it can evolve under rapid environmental changes caused by thermal stress. Overall, our results cast strong doubts on the hypothesis that body size itself is the target of selection, and suggest that pre-adult life history traits are more closely related to thermal adaptation.     

城市胁迫生境下二球悬铃木叶片的发育稳定度及其环境指示功能

对采自上海市区14个样点的二球悬铃木叶片发育稳定度、叶片气孔密度和气孔长径进行研究。结果表明,在3个采样时期,根据叶片宽度确定的非稳态不对称指数(FA1)和根据叶片侧脉长度确定的偏向性不对称指数(RDA1)在不同环境胁迫程度(UESL)下均表现出显著的差异,但进一步分析表明,各样点FA1与环境胁迫程度UESL之间呈显著的非线性回归关系,而RDA1与环境胁迫程度之间却未显示类似关系。此外,FA1与叶片气孔密度和气孔长径之间的显著相关关系表明,它们可共同作为指示小尺度上环境胁迫的有效指标,而RDA1是叶片的一种正常发育状态参数,并不适于反映环境胁迫状态。     

Effect of three types of ecological stress on the variability of morphological traits in Drosophila melanogaster

The effect of temperature, nutrition, and density stresses on phenotypic and genetic variation in morphological traits (thorax length, wing length, number of sternopleural and abdominal bristles, and number of arista branches) was examined in Drosophila melanogaster. In addition, the effect of stress on developmental stability measured as fluctuation asymmetry of bilateral traits was analyzed. All of the stresses were shown to increase phenotypic variation and fluctuating asymmetry of bilateral traits. Genetic variation of morphometric traits estimated using the isofemale line technique was higher under stressful than under normal conditions. Biotic and abiotic stresses were similar in their effect on phenotypic and genetic variation. The effect of stress on variability of morphometric traits was generally higher than on that of meristic traits. Possible causes of the increase of genetic variation under stress are discussed.     

Stability of Development and Variability in Morphological Traits in a Natural Population of Drosophila melanogaster: Seasonal Dynamics in 1999

Seasonal dynamics of developmental stability and variability of morphological traits was examined in a natural population of Drosophila melanogaster in order to compare these two parameters as indicators of temperature stress. Morphometric (thorax length and wing length) and meristic (number of sternopelural and orbital bristles) were studied. Variability was measured as the coefficient of variation. Stability of development was estimated as fluctuating asymmetry (FA) of bilateral traits. Thorax length and wing length did not exhibit consistent seasonal trends whereas wing loading significantly decreased. Significant seasonal changes in FA were not detected in any trait examined. Two traits showed reduced variation in autumn. The use of FA as an indicator of ecological stresses in insects is discussed on the basis of these results and the literature evidence.     

Stability in development and variability in morphological signs in a natural population of Drosophila melanogaster: seasonal dynamics in 1999

Seasonal dynamics of developmental stability and variability of morphological traits was examined in a natural population of Drosophila melanogaster in order to compare these two parameters as indicators of temperature stress. Morphometric (thorax length and wing length) and meristic (number of sternopelural and orbital bristles) were studied. Variability was measured as the coefficient of variation. Stability of development was estimated as fluctuating asymmetry (FA) of bilateral traits. Thorax length and wing length did not exhibit consistent seasonal trends whereas wing loading significantly decreased. Significant seasonal changes in FA were not detected in any trait examined. Two traits showed reduced variation in autumn. The use of FA as an indicator of ecological stresses in insects is discussed on the basis of these results and the literature evidence.     

Effects of parental radiation exposure on developmental instability in grasshoppers

Mutagenic and epigenetic effects of environmental stressors and their transgenerational consequences are of interest to evolutionary biologists because they can amplify natural genetic variation. We studied the effect of parental exposure to radioactive contamination on offspring development in lesser marsh grasshopper Chorthippus albomarginatus. We used a geometric morphometric approach to measure fluctuating asymmetry (FA), wing shape and wing size. We measured time to sexual maturity to check whether parental exposure to radiation influenced offspring developmental trajectory and tested effects of radiation on hatching success and parental fecundity. Wings were larger in early maturing individuals born to parents from high radiation sites compared to early maturing individuals from low radiation sites. As time to sexual maturity increased, wing size decreased but more sharply in individuals from high radiation sites. Radiation exposure did not significantly affect FA or shape in wings nor did it significantly affect hatching success and fecundity. Overall, parental radiation exposure can adversely affect offspring development and fitness depending on developmental trajectories although the cause of this effect remains unclear. We suggest more direct measures of fitness and the inclusion of replication in future studies to help further our understanding of the relationship between developmental instability, fitness and environmental stress.     

Leaf developmental stability of Platanus acerifolia under urban environmental stress and its implication as an environmental indicator

The developmental stability indices,leaf width based fluctuating asymmetry (FA1),and lateral vein length based directional asymmetry (RDA1) of Platanus acerifolia were studied.All the leaves were sampled from 14 sites that were categorized based on different urban environmental stress levels (UESL) in Shanghai metropolitan,China.Besides,foliar stomatal density and stomatal length were also studied as the subsidiary indices to test the availability of developmental stability indices as the indicator under a stressful environment.Results showed seasonal variation of FA1 and RDA1 existed among the 14 sites,but the data showed significant negative correlation between FA1 and UESL (FA1=0.029-0.000 9UESL+0.000 3UESL2,r=0.766 5,P=0.001 4).However,a similar trend was not found between RDA1 and UESL.Furthermore,the significant correlation among FA1 and leaf stomatal length and stomatal density implied they could be used as indicators of urban stress levels on a small scale.It seemed that RDA1 was possibly a normal parameter during leaf development but it was unavailable for use as an indicator of urban stresses.     

Effect of a permanent magnetic field on wing size parameters in Drosophila melanogaster.

The width and length variability of both D. melanogaster wings were measured in samples of flies after two and six generations under a permanent magnetic field of 35 mT. While in earlier generations under exposure sexes differ in the size response, later they both show a decrease in the wing size under the magnetic field exposure if compared to the control. The bilateral asymmetry in wings as a potential indicator of developmental instability does not increase significantly under exposure. The ecological and adaptive implications of the change of the magnetic intensity as an environmental factor generating stress in populations is discussed.     

Does fluctuating asymmetry of wing traits capture relative environmental stress in a lepidopteran?

1. Fluctuating asymmetry (FA) is hypothesized to be a useful predictor of population canalization, especially for organisms at risk from environmental change.
2. Identification of traits that meet statistical criteria as FA measures remains a challenge.
3. Here, a laboratory experiment subjected immature butterflies (Vanessa cardui) to diet and temperature conditions of varying stress levels. Variation in dietary macronutrient ratio (protein: carbohydrate) and rearing temperature (optimal: 25°C; elevated: 32°C) was introduced as stressors. Temperature and nutrition are key variables influencing ectotherm growth and fitness and so are likely to be important stressors that influence FA.
4. Individuals subjected to stressful conditions were predicted to show elevated FA of three wing size traits, as well as increased mortality and decreased adult body size.
5. Trait FA did not vary across treatments. Instead, treatment levels impacted viability: The combined incidence of pupal death and expression of significant wing malformations increased in treatment levels designated as stressful. Variation in adult dry mass also reflected predicted stress levels. Results suggest that individuals predicted to display increased FA either died or displayed gross developmental aberrations.
6. This experiment illustrates important constraints on the investigation of FA, including selection of appropriate traits and identification of appropriate levels of stressors to avoid elevated mortality. The latter concern brings into question the utility of FA as an indicator of stress in vulnerable, natural populations, where stress levels cannot be controlled, and mortality and fitness effects are often not quantifiable.

     

How Useful is Fluctuating Asymmetry in Conservation Biology: Asymmetry in Rare and Abundant Coenonympha Butterflies

It has been suggested that minor, fluctuating differences in size of bilateral traits could validly indicate individual differences in developmental stability. One plausible reason for instability to occur could be lowered population size, which has been suggested to increase fluctuating asymmetry due to inbreeding, for example. We measured seven wing asymmetries of three Coenonympha butterfly species in central Sweden. One species is abundant (nobreak C. pamphilus), one rather common (C. arcania), and one rare (C. hero). We expected that if fluctuating asymmetry is a reliable indicator of population quality and thus a useful tool for conservation purposes, the most abundant species should show lowest asymmetry and the most endangered, the highest. Contrary to our expectations, the highest wing asymmetry was found in the relatively common species C. arcania and the most abundant and rare species did not show significant differences in levels of wing asymmetry. Our results obtained from three Coenonympha species hence suggest that the use of fluctuating asymmetry as an indicator of population conservation status may be misleading. Possible increase in asymmetry of small and/or isolated populations of butterflies may be masked by local differences in environmental conditions that could have high impact on bilateral development as well.     

Stress-Induced Mutagenesis in Bacteria

ABSTRACT

Bacteria spend their lives buffeted by changing environmental conditions. To adapt to and survive these stresses, bacteria have global response systems that result in sweeping changes in gene expression and cellular metabolism. These responses are controlled by master regulators, which include: alternative sigma factors, such as RpoS and RpoH; small molecule effectors, such as ppGpp; gene repressors such as LexA; and, inorganic molecules, such as polyphosphate. The response pathways extensively overlap and are induced to various extents by the same environmental stresses. These stresses include nutritional deprivation, DNA damage, temperature shift, and exposure to antibiotics. All of these global stress responses include functions that can increase genetic variability. In particular, up-regulation and activation of error-prone DNA polymerases, down-regulation of error-correcting enzymes, and movement of mobile genetic elements are common features of several stress responses. The result is that under a variety of stressful conditions, bacteria are induced for genetic change. This transient mutator state may be important for adaptive evolution.     

Stress-induced mutagenesis in bacteria

Bacteria spend their lives buffeted by changing environmental conditions. To adapt to and survive these stresses, bacteria have global response systems that result in sweeping changes in gene expression and cellular metabolism. These responses are controlled by master regulators, which include: alternative sigma factors, such as RpoS and RpoH; small molecule effectors, such as ppGpp; gene repressors such as LexA; and, inorganic molecules, such as polyphosphate. The response pathways extensively overlap and are induced to various extents by the same environmental stresses. These stresses include nutritional deprivation, DNA damage, temperature shift, and exposure to antibiotics. All of these global stress responses include functions that can increase genetic variability. In particular, up-regulation and activation of error-prone DNA polymerases, down-regulation of error-correcting enzymes, and movement of mobile genetic elements are common features of several stress responses. The result is that under a variety of stressful conditions, bacteria are induced for genetic change. This transient mutator state may be important for adaptive evolution.     

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

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.     

Dental arch asymmetry in an isolated Adriatic community

Developmental stability reflects the ability of a genotype to develop in the same way under varying environmental conditions. Deviations from developmental stability, arising from disruptive effects of environmental and genetic stresses, can be measured in terms of fluctuating asymmetry, a particularly sensitive indicator of the ability to cope with these stresses during ontogeny. In an inbred Adriatic island population, we expected dental arch fluctuating asymmetry 1) to be higher than in an outbred sample from the same island, and 2) within this population, to increase with the level of inbreeding. Due to environmental stress, we also expected to find higher fluctuating asymmetry in the outbred island population than in an urban reference group from the same country. The material consisted of 506 dental casts of 253 children from 1) the island of Hvar, and 2) Zagreb, Croatia. Three-dimensional coordinates of 26 landmarks spanning the arches were digitized. The analysis partitioned the asymmetry of arch forms into components for directional and fluctuating bilateral asymmetry, using the appropriate Procrustes method (geometric morphometrics). The results corroborated the hypotheses. Fluctuating asymmetry was found to be higher on the island than in Zagreb in all groups and in both jaws, and increased significantly with endogamy level in the lower jaw. There was no significant directional asymmetry in the Zagreb sample and likewise none in the upper jaws of the outbred island group, but significant directional asymmetry in both jaws of the inbred population and also in the lower jaws of the outbred island group. These results suggest an environmental as well as a genetic influence on dental arch asymmetry. Although the lower jaws expressed these two stresses almost additively, the upper jaws appeared to be better buffered. The role of directional asymmetry as a potential indicator of craniofacial developmental instability clearly merits further attention.     

Parasites increase fluctuating asymmetry of maleDrosophila nigrospiracula: Implications for sexual selection

Fluctuating asymmetry (minor deviations from perfect bilateral symmetry) is manifested by individuals less able to buffer environmental stress during development. I utilized a system of two naturally-occurring parasites ofDrosophila nigrospiracula to test whether parasitic infection during host development yields elevated degrees of fluctuating asymmetry in two morphological traits of males. This hypothesis has important implications for sexual selection, as it may explain why asymmetric males are often found to be sexually disadvantaged. In my system, nematodes infect larvae and therefore are more likely to disrupt development than mites which only parasitize adult flies. As predicted, nematode-infected maleD. nigrospiracula had a higher degree of bristle asymmetry than did mite-infested and control (carrying neither parasite) males. There was also a significant relation between nematode number and degree of asymmetry. There was a significant negative relation between nematode load and size of adult males, implicating a causal link between nutritional stress during host development and fluctuating asymmetry. Patterns of wing length asymmetry were inconsistent with those of bristle asymmetry. Nematode-infected males did not differ in wing length asymmetry relative to mite-infested and control males, nor was there a significant relation between nematode number and wing asymmetry. This inconsistency in expression of asymmetry may reflect different intensities of selection operating on each morphological trait.     

Genome-wide deficiency mapping of the regions responsible for temporal canalization of the developmental processes of Drosophila melanogaster

Developmental processes of organisms are programmed to proceed in a finely regulated manner and finish within a certain period of time depending on the ambient environmental conditions. Therefore, variation in the developmental period under controlled genetic and environmental conditions indicates innate instability of the developmental process. In this study, we aimed to determine whether a molecular machinery exists that regulates the canalization of the developmental period and, if so, to test whether the same mechanism also stabilizes a morphological trait. To search for regions that influence the instability of the developmental period, we conducted genome-wide deficiency mapping with 441 isogenic deficiency strains covering 65.5% of the Drosophila melanogaster genome. We found that 11 independent deficiencies significantly increased the instability of the developmental period and 5 of these also significantly increased the fluctuating asymmetry of wing shape although there was no significant correlation between the instabilities of developmental period and wing shape in general. These results suggest that canalization processes of the developmental period and morphological traits are at least partially independent. Our findings emphasize the potential importance of temporal variation in development as an indicator of developmental stability and canalization and provide a novel perspective for understanding the regulation of phenotypic variability.     

Effects of asymmetry on the strength of the chelonian shell: A comparison of three species

A major focus of the field of organismal biology is to understand how morphology impacts performance. Although the functional implications of certain aspects of shape have been widely examined, the functional implications of a related parameter, symmetry, remain mostly unknown. We used finite‐element models to examine the effects of turtle shell asymmetry on shell strength across three morphologically distinct emydid species. The goals of this study were to: 1) test the hypothesis that increased asymmetry (independent of differences in shape) is associated with increased stress levels for a given load, and thus with weaker shells, 2) ascertain how asymmetry and the position of load application interact to influence shell strength, and 3) determine how interspecific differences in shape influence the effect of asymmetry. We found that increased asymmetry does produce higher stresses for both midline and non‐midline loads. Non‐midline loads produce slightly larger and more variable stresses. Species‐specific shell shape can mitigate the effects of asymmetry; stronger shapes are potentially more resistant to the negative effects of asymmetry. Our findings indicate that changes in asymmetry associated with relatively small changes in shape can have as much of an effect on stress incurred by the shell as the changes in shape themselves. J. Morphol. 274:901–908, 2013. © 2013 Wiley Periodicals, Inc.     

Multidimensional analysis of Drosophila wing variation in Evolution Canyon

Environmental stress has been suggested to be a major evolutionary force, both through inducing strong selection and because of its direct impact on developmental buffering processes that alter the evolvability of organisms. In particular, temperature has attracted much attention because of its importance as an ecological feature and the relative ease with which it can be experimentally manipulated in the lab. Evolution Canyon, Lower Nahal Oren, Israel, is a well studied natural site where ecological parameters are suspected to drive evolutionary differentiation. In this study, using Drosophila melanogaster isofemale lines derived from wild flies collected on both slopes of the canyon, we investigated the effect of developmental temperature upon the different components of phenotypic variation of a complex trait: the wing. Combining geometric and traditional morphometrics, we find only limited evidence for a differentiation among slopes. Investigating simultaneously phenotypic plasticity, genetic variation among isofemale lines, variation among individuals and fluctuating asymmetry, we could not identify a consistent effect of the stressful conditions encountered on the south facing slope. The prevailing structuring effect is that of the experimentally manipulated temperature which clearly influences wing mean size and shape. Variability, in contrast, is not consistently affected by temperature. Finally, we investigated the specific relationship between individual variation and fluctuating asymmetry. Using metric multi-dimensional scaling we show that the related patterns of wing shape variation are not identical, supporting the view that the underlying developmental processes are to a certain extent different.