Showing papers on "Fluctuating asymmetry published in 1990"

Fluctuating asymmetry: an epigenetic measure of stress

Abstract: (1) Fluctuating asymmetry (FA) is a useful trait for monitoring stress in the laboratory and in natural environments. (2) Both genomic and environmental changes can increase FA which represents a deterioration in developmental homeostasis apparent in adult morphology. Genetic perturbations include intense directional selection and certain specific genes. Environmental perturbations include temperature extremes in particular, protein deprivation, audiogenic stress, and exposure to pollutants. (3) There is a negative association between FA and heterozygosity in a range of taxa especially fish, a result consistent with FA being a measure of fitness. (4) Scattered reports on non-experimental populations are consistent with experiments under controlled laboratory conditions. FA tends to increase as habitats become ecologically marginal; this includes exposure to environmental toxicants. (5) In our own species, FA of an increasing range of traits has been related to both environmental and genomic stress. (6) Domestication increases FA of the strength of homologous long bones of vertebrate species due to a relaxation of natural selection. (7) FA levels are paralleled by the incidence of skeletal abnormalities in stressful environments. (8) Increased FA is a reflection of poorer developmental homeostasis at the molecular, chromosomal and epigenetic levels.

Lack of response to family selection for directional asymmetry in Drosophila melanogaster: left and right are not distinguished in development.

Abstract: Family selection for directional asymmetry in the expression of the Drosophila melanogaster mutant scute had no result. Fluctuating asymmetry did not show a selection differential correlated with directional asymmetry. The unfolding of bilateral symmetry in embryogenesis can be used to explain the lack of genetic variation for directional asymmetry. Directional asymmetry provides a well-understood example of a developmental constraint in evolution. It is proposed that as no evidence is available for an independent left-right gradient in the embryo, quantitative traits can only be expressed variably along an existing gradient of positional information or a morphogen.

Fluctuating asymmetry and allozymic heterozygosity among natural populations of pocket gophers (Thomomys bottae)

Abstract: Fluctuating asymmetry, or random deviations from bilateral symmetry, has been widely used as a measure of developmental stability. The relationship between fluctuating asymmetry (FA) and allozymic heterozygosity was evaluated using 18 natural populations of pocket gophers (Thomomys bottae). Heterozygosity in local populations of pocket gophers ranges over more than an order of magnitude (1.5—18.4%), making this burrowing rodent particularly apt for such studies. Two measures of FA in mensural skull characters were examined: absolute deviations between left and right sides and the variance of signed differences. After log transformations, levels of FA among individuals and populations were not related to size. Repeated-measures analyses of variance showed that FA was significant relative to measurement error, both across populations and within them. Asymmetries of different characters were uncorrelated, despite positive significant correlations among the characters themselves. FA levels varied only slightly among populations of gophers, and this variation was not significant for most characters. FA levels of populations were not correlated with allozymic heterozygosity, and analyses of variance in FA employing heterozygosity were not significant. Heterozygosity levels in these rodents appear more strongly related to aspects of population history (especially effective size and gene flow) than to developmental stability. Because so many genomic and environmental factors can affect morphological variation, caution is needed in interpreting correlations between genetic and phenetic variation.

Morphological asymmetry and interspecific hybridization: A case study using hylid frogs

Abstract: The limited studies addressing developmental stability of interspecific hybrids suggest a positive association between the level of fluctuating asymmetry and 1) the degree of divergence between parental species, and 2) the recency of the contact zone. To evaluate these associations, we examined asymmetry in a recentlyestablished hybrid population of treefrogs (Hyla cinerea and H. gratiosa) that show marked structural gene divergence. Fluctuating asymmetry (FA), directional asymmetry, and antisymmetry were assessed for eight paired osteometric traits in allozymically-defined parental and hybrid categories. FA levels varied considerably among traits. Nonetheless, for any given trait, the hybrid categories did not demonstrate elevated levels of FA compared to the parental categories, or compared to frogs from a non-hybridizing parental population. The only trait that differed statistically among categories (pterygoid length) involved a significantly lower FA value for the Fl hybrids. Thus, observed FA values do not support expectations that the hybrid categories should experience decreased developmental stability.

Fluctuating asymmetry and testing isolation of Montana grizzly bear populations

Abstract: Fluctuating asymmetry of adult skulls was used to test the genetic isolation of the Yellowstone grizzly bear population from its nearest neighbor. An overall summary statistic was used in addition to 16 other parameters. Tests found the males ofthe Yellowstone population to be more variable than those ofthe North Continental Divide Ecosystem. Evidence for precipitation effects is also included. This test tends to support the existing management hypothesis that the Yellowstone population is isolated. Int. Conf. Bear Res. and Manage. 8:421-424 Although mammals are bilaterally symmetrical, dif? ferences in growth occur between the 2 sides ofthe body. Some of this asymmetry is normal or directional. A second type of asymmetry is non-functional and is called fluctuating asymmetry. This developmental "noise" has been observed to be greater in inbred populations (Soule 1967, Leamy 1984, Wayne et al. 1986) than in popula? tions with normal genetic diversity. It is also considered to be an indicator of environmental stress (Leamy 1984) and represents pressure put upon developmental homeostatic mechanisms by genetic limitations in interaction with the environment. Thus it can be hypothesized that high levels of fluctuating asymmetry may indicate ge? netic limitations on the ability to accommodate environ? mental variation. This would then indicate a manage? ment need to supplement or expand the population. Grizzly bear (Ursus arctos horribilis) skulls were collected from both the Yellowstone and Northern Con? tinental Divide ecosystems since 1967 and are held in the collections of the Montana Fish, Wildlife and Parks Department. This collection is a unique resource and data from its analysis may have a direct bearing upon the threatened Montana grizzly bear populations. Although the Yellowstone grizzly bear population is regarded as an isolated population, bears have been recently observed in the mountain ranges connecting to the Northern Conti? nental area (Picton 1986). Therefore, this project was undertaken to provide information concerning the extent ofthe genetic isolation ofthe Yellowstone population by using fluctuating asymmetry.

Asymmetry and intraindividual diversity in digital dermatoglyphics of Bulgarians

Abstract: A random sample of 2,130 apparently healthy Bulgarians, 1,065 of each sex, was investigated to obtain a detailed picture of finger dermatoglyphic asymmetry and intraindividual diversity in the population examined. Both sexes showed an almost equal pattern of asymmetry and diversity. Relative pattern asymmetry, taking into account the pattern type frequencies, tends to be higher in males, being especially pronounced on fingers which show a low asymmetry in other aspects. Like other populations so far examined, Bulgarians display higher rates in males than in females concerning the total, ulnar, and radial ridge-counts, their asymmetries, and intraindividual diversities. However, the more analysis of the ridge-count asymmetry is worked out in detail, the more it becomes evident that both sexes are asymmetrical not so much to a different degree as in a different manner. As a whole, the ambidirectional, directional, fluctuating, and relative asymmetries are practically consistent in both sexes. Important sex differences are revealed in the structure of the directional and fluctuating asymmetries concerning contrasts between their radial and ulnar levels. The sex differences in directional asymmetry are discussed in the light of possible effects of the sex chromosomes upon the mediolateral developmental gradients. Expressed modulation of the fluctuating asymmetry by finger is interpreted as evidence for considerable differences between separate finger pairs in their sensitivity to stressful factors. Presented results are relevant to anthropology and population genetics and could have implications in medical genetics and teratology, serving as normative data in pathological conditions.