High levels of genetic change in rodents of Chernobyl.
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Retraction Notice↗
Biomedical subjects
R K Chesser
Publications and source records attributed to R K Chesser.
High levels of genetic change in rodents of Chernobyl.
Base-pair substitution rates for the mitochondrial cytochrome beta gene of free-living, native populations of voles collected next to reactor 4 at Chernobyl, Ukraine, were estimated by two independent methods to be in excess of 10(-4) nucleotides per site per generation. These estimates are hundreds of times greater than those typically found in mitochondria of vertebrates, suggesting that the environment resulting from this nuclear power plant disaster is having a measurable genetic impact on the organisms of that region. Despite these DNA changes, vole populations thrive and reproduce in the radioactive regions around the Chernobyl reactor.
Animals↗
Effective sizes and dynamics of uniparentally and diparentally inherited genes.
Models to determine the temporal dynamics and spatial heterogeneity for maternally and paternally inherited genes were derived for populations that may or may not exhibit spatial subdivision. Results were compared to those for diparentally inherited genes. The models permit definition of parameters for mean and variance of litter sizes, breeding group (subpopulation) sizes, and numbers of female mates per male, dispersal rates, and multiple paternity. Exact solutions for asymptotic effective size and spatial divergence (FLS) for maternal and paternal genes are derived. It is shown that solutions for effective size and FLS are transformations of the same quadratic equation. When compared to values for diparentally inherited genes, it is shown that effective sizes for maternal genes may be considerably higher when female dispersal is low as in many mammalian taxa. Likewise, effective sizes for paternal genes may be higher than for diparentally inherited traits when male dispersal is relatively low, as in many species of birds. The traditional assumption that the effective size for maternal genes is approximately equal to the number of females is seldom realized. Spatial heterogeneity and temporal dynamics of genes are inextricably linked as is shown by the interdependency of effective size and spatial heterogeneity.
Animals↗
Sources of error associated with sample collection and preparation of nucleated blood cells for flow cytometric analysis.
Analysis of cellular DNA content by flow cytometry has been used to detect genetic changes associated with exposure to environmental contaminants. In lower vertebrates, nucleated red blood cells can be collected for analysis without harm to the animal. Because erythrocytes sampled from an individual should have identical amounts of DNA, the coefficient of variation (CV) around the G0/G1 peak should be small. Increases in CV can indicate genetic aberrations, but may also be caused by sample handling and preparation or problems with instrumentation. To increase confidence in associating increases in CV with external causes, artifactual changes in CV due to sample treatment and instrument parameters should be identified and minimized. We assessed the effects of various sampling and handling protocols on the CV of nucleated blood cells collected from largemouth bass (Micropterus salmoides). We also compared the distribution of cells among the G0/G1, S, and G2/M phases of the cell cycle to see whether these were affected by sampling or treatment protocols. Groups of 7 fish were bled on 7 consecutive days, and blood from each fish was analyzed by flow cytometry when freshly collected, and after freezing for 1 hour or 10 days. The same fish were bled again over a consecutive 7-day period, and the experiment was repeated. CV and cell cycle distribution were not affected by our freezing protocol. Repeat sampling from the same individual did not affect CV, but altered the distribution of cells in the cell cycle, suggesting increased hemopoiesis in response to blood sampling.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Effective population sizes with multiple paternity.
While the concept of effective population size is of obvious applicability to many questions in population genetics and conservation biology, its utility has suffered due to a lack of agreement among its various formulations. Often, mathematical formulations for effective sizes apply restrictive assumptions that limit their applicability. Herein, expressions for effective sizes of populations that account for mating tactics, biases in sex ratios, and differential dispersal rates (among other parameters) are developed. Of primary interest is the influence of multiple paternity on the maintenance of genetic variation in a population. In addition to the standard inbreeding and variance effective sizes, intragroup (coancestral) and intergroup effective sizes also are developed. Expressions for effective sizes are developed for the beginning of nonrandom gene exchanges (initial effective sizes), the transition of gene correlations (instantaneous effective sizes), and the steady-state (asymptotic effective size). Results indicate that systems of mating that incorporate more than one male mate per female increase all effective sizes above those expected from polygyny and monogamy. Instantaneous and asymptotic sizes can be expressed relative to the fixation indices. The parameters presented herein can be utilized in models of effective sizes for the study of evolutionary biology and conservation genetics.
Algorithms↗
Effective sizes for subdivided populations.
Many derivations of effective population sizes have been suggested in the literature; however, few account for the breeding structure and none can readily be expanded to subdivided populations. Breeding structures influence gene correlations through their effects on the number of breeding individuals of each sex, the mean number of progeny per female, and the variance in the number of progeny produced by males and females. Additionally, hierarchical structuring in a population is determined by the number of breeding groups and the migration rates of males and females among such groups. This study derives analytical solutions for effective sizes that can be applied to subdivided populations. Parameters that encapsulate breeding structure and subdivision are utilized to derive the traditional inbreeding and variance effective sizes. Also, it is shown that effective sizes can be determined for any hierarchical level of population structure for which gene correlations can accrue. Derivations of effective sizes for the accumulation of gene correlations within breeding groups (coancestral effective size) and among breeding groups (intergroup effective size) are given. The results converge to traditional, single population measures when similar assumptions are applied. In particular, inbreeding and intergroup effective sizes are shown to be special cases of the coancestral effective size, and intergroup and variance effective sizes will be equal if the population census remains constant. Instantaneous solutions for effective sizes, at any time after gene correlation begins to accrue, are given in terms of traditional F statistics or transition equations. All effective sizes are shown to converge upon a common asymptotic value when breeding tactics and migration rates are constant. The asymptotic effective size can be expressed in terms of the fixation indices and the number of breeding groups; however, the rate of approach to the asymptote is dependent upon dispersal rates. For accurate assessment of effective sizes, initial, instantaneous or asymptotic, the expressions must be applied at the lowest levels at which migration among breeding groups is nonrandom. Thus, the expressions may be applicable to lineages within socially structured populations, fragmented populations (if random exchange of genes prevails within each population), or combinations of intra- and interpopulation discontinuities of gene flow. Failure to recognize internal structures of populations may lead to considerable overestimates of inbreeding effective size, while usually underestimating variance effective size.
Animals↗
Gene diversity and female philopatry.
The effect of female philopatry on the apportionment of gene diversity within a population is evaluated. Even with random mate selection, the apportionment of gene diversity within and among social lineages (groups of related females) is inherently different than in classically defined demic groups. Considerable excess heterozygosity occurs within lineages without substantial changes in total or population heterozygosity. The proportion of genetic variance among lineages within the population was dependent on the lineage size and the number of male breeders per lineage. The greatest genetic differentiation among lineages was evident when there was one polygynous male breeding within a lineage of philopatric females, a common breeding tactic in mammalian social systems. The fixation indices depicting the genetic structure of the population were found to attain constant values after the first few generations despite the continuous loss of gene diversity within the population by genetic drift. Additionally, the change of gene correlations within individuals relative to the change within the population attains a state of dynamic equilibrium, as do the changes of gene correlations within lineages relative to the total and within individuals relative to within lineages. Comparisons of coancestries and fixation indices for philopatric versus randomly dispersing females indicate that philopatry and polygyny have probably not evolved independently and that promotion of gene correlations among adults rather than offspring has been of primary importance.
Animals↗
Influence of gene flow and breeding tactics on gene diversity within populations.
Expressions describing the accumulation of gene correlations within and among lineages and individuals of a population are derived. The model permits different migration rates by males and females and accounts for various breeding tactics within lineages. The resultant equations enable calculation of the probabilistic quantities for the fixation indices, rates of loss of genetic variation, accumulation of inbreeding, and coefficients of relationship for the population at any generation. All fixation indices were found to attain asymptotic values rapidly despite the consistent loss of genetic variation and accumulation of inbreeding within the population. The time required to attain asymptotic values, however, was prolonged when gene flow among lineages was relatively low (less than 20%). The degree of genetic differentiation among breeding groups, inbreeding coefficients, and gene correlations within lineages were found to be primarily functions of breeding tactics within groups rather than gene flow among groups. Thus, the asymptotic value of S. Wright's island model is not appropriate for describing genetic differences among groups within populations. An alternative solution is provided that under limited conditions will reduce to the original island model. The evolution of polygynous breeding tactics appears to be more favorable for promoting intragroup gene correlations than modification of migration rates. Inbreeding and variance effective sizes are derived for populations that are structured by different migration and breeding tactics. Processes that reduce the inbreeding effective population size result in a concomitant increase in variance effective population size.
Animals↗
Differential rates of genic and chromosomal evolution in bats of the family Rhinolophidae.
Data for nondifferentially stained chromosomes from 10 species of Rhinolophus (Chiroptera: Rhinolophidae) suggest a conserved chromosomal evolution. G-banded chromosomes for three well differentiated species (Rhinolophus hipposideros, Rhinolophus blasii, and Rhinolophus acuminatus) corroborate a low level of gross chromosomal rearrangements. Additionally, a comparison between G-banded chromosomes of Rhinolophus (Rhinolophidae) and Hipposideros (Hipposideridae) suggests extreme conservatism in chromosomal arms between these two distantly related groups. On the other hand, we report extensive genic divergence as assayed by starch gel electrophoresis among these 10 species, and between Rhinolophus and two hipposiderid genera (Hipposideros and Aselliscus). The present chromosomal data are not sufficient for phylogenetic analysis. Phylogenies based on electrophoretic data are in many aspects discordant with those based on the classical morphological criteria. Different (and as yet not clearly understood) evolutionary forces affecting chromosomal, morphologic, and electrophoretic variation may be the reason for the apparent lack of concordance in these independent data sets.
Alleles↗
Genetic differentiation among cottontails from isolated playa basins.
Protein variation in 182 Sylvilagus floridanus from 19 playa basins in Castro Co., Texas was examined using starch-gel electrophoresis. Heterozygote deficiencies were noted for all populations. This heterozygote deficiency may be due to differential selection against heterozygous individuals over the winter months. Results of F-statistics indicated a significant degree of population differentiation at six loci. Nei's genetic distance between populations ranged from 0.20 to 0.388 and a significant association between genetic distance and linear geographic distance among playas was found. These results suggest that genetic exchange and long-distance dispersal may be hindered by expanses of unsuitable habitat.
Animals↗
Estimation of fixation indices and gene diversities.
Considering the multinomial sampling of genotypes, unbiased estimators of various gene diversity measures in subdivided populations are presented. Using these quantities, formulae for estimating Wright's fixation indices (FIS, FIT, and FST) from a finite sample are developed.
Acid Phosphatase↗
Effects of sex, age, habitat and body weight on kidney weight in white-tailed deer.
Kidney (Y) and body (X) weights in kilograms are highly correlated (r = 0.88) in white-tailed deer. As in other mammals, the relationship between the two variables is curvilinear with Y = -2.493 X0.746. Habitat did not affect the parameters of the realationship although certain sex-age and sex month categories did. However, use of kidney weight in standardizing body condition indices in deer of different sizes still seems warranted for white-tailed deer in the southeastern United States during the hunting season because of the relatively high predictability of the overall kidney-body weight relationship.
Age Factors↗
Effect of jet aircraft noise upon in vitro adrenocortical response to ACTH in feral Mus musculus.
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Adrenal Glands↗