David W. Crumpacker

Density, Dispersion, and Population Structure in Drosophila Pseudoobscura

Wild D. pseudoobscura flies were captured, marked, and released in relatively low numbers at nine separate, centrally located sites in each of two Colorado, U.S.A., locations in midsummer 1970. The flies were marked by spraying with micronized dusts which fluoresce in characteristic colors under ultraviolet light. The dusts are harmless, they mark the flies well, and they are not transferred from one fly to another. The trapping design extending out from the central release points contained additional traps on eight evenly spaced radii. Data on the number of captured, unmarked flies and recaptured, marked flies in the central and outlying traps provided maximum likelihood estimates of adult density and dispersion. These data were adjusted for the presence of a sibling species, D. lowei, by means of an accurate morphological technique which permits classification of the two kinds of males. Preliminary analyses indicated that dispersal estimates made during an evening activity period 1 day after release of marked flies pertain mostly to dispersion during the intervening morning activity period, when no traps were exposed. It was necessary to base estimates of both density and dispersion on trapping days following days when only a few or no traps had been exposed in the habitat. The minimum attractive radius of a trap was approximately 46 m. The estimates of density at both locations were similar, averaging 0.38 flies/100 m2. An independent and much simpler estimate of density, based on the number of flies captured at the center trap, gave inconsistent results. This was attributed to accidental interference with normal fly activity. The mean distance (d) of marked flies from the release points after 1 day (presumably after one morning activity period) was 176 and 202 m at the two locations. The mean—squared distance (d2°) was 97 and 146, respectively, in units of 400 m2. The estimates for the first location are more reliable because those data were more homogeneous and extensive. The patterns of the observed dispersion agreed well with Brownian motion expectations on the basis of comparing first— and second—order moments of distance dispersed. This permitted the construction of graphs which depict the spread of released flies with an increasing number of activity periods. An activity parameter °, the standard deviation of dispersed flies along one direction in a two—dimensional environment, was estimated from @ under the assumption of Brownian motion (°b.m.) and without this assumption (°D.F.). These estimates refer only to the observed dispersion. At the first location the values were 141 and 139 m, respectively; at the second they were 162 and 171. Closer inspection of the observed dispersal patterns, accompanied by further analyses of the data, revealed a departure from Brownian motion and probably serious underestimates of the true dispersal rates. A certain proportion of flies dispersed rapidly to points outside the experimental area during the morning activity period following an evening release. Using an estimate of 95.3% daily survival of marked flies, 2—day dispersal data suggested that more than half the flies had moved beyond the experimental area in two morning activity periods. The earlier experiments on density and dispersion of D. pseudoobscura, conducted by Dobzhansky and Wright in California, were re—analyzed by the present methods. Midsummer density of wild flies in Colorado was one—seventeenth that on Mt. San Jacinto in southern California, and three—fifths that at Mather in the Sierra Nevada of central California. Comparison of °d.f. estimates indicated that the wild Colorado flies dispersed at a rate approximately 50% greater than the laboratory flies released in California, even though the latter probably had more opportunity for dispersion. This difference may result partly from an adaptive strategy for greater dispersion of flies in low density habitats, and partly from a fundamentally different behavior of wild and laboratory flies. The large values of °d.f. (which are underestimates due to dispersion beyond the experimental areas) in both Colorado and California suggest that natural populations of D. pseudoobscura are not broken up into a number of very small breeding units within which allelic variation could be stored by genetic drift. Wrights panmictic circle concept yielded estimates of effective population size (Ne) between 1,000 and 10,000 in both Colorado and California. According to existing theory, these values are not large enough to maintain the allelic diversity known to exist for certain enzyme loci. The need for more sophisticated experiments to determine which components of dispersion are most closely associated with distribution of emergence sites of parents and offspring is discussed.

Predicted Effects of Climatic Change on Distribution of Ecologically Important Native Tree and Shrub Species in Florida

A previously developed plant species-climatic envelope model was evaluated further and used to predict effects of hypothesized climatic change on the potential distribution of 124 native woody plant species in Florida, U.S.A. Twelve scenarios were investigated. These included mean annual temperature increases of 1 °C or 2 °C, achieved either by equal 1 °C or 2 °C increases on a monthly basis throughout the year, or by disproportionately larger seasonal increases in winter and smaller ones in summer. The various temperature increases were then combined with each of several precipitation changes, ranging from +10% to –20%, to produce the final set of scenarios. More detailed analysis involving six of the scenarios and a subset of 28 representative, ecologically important species suggested that (1) large decreases in the Florida range of many temperate species would result if 1 °C warming occurs predominantly in winter or with a 20% decrease in annual precipitation, or (2) if 2 °C warming occurs, with or without decrease in annual precipitation, and regardless of whether there is a uniform monthly warming pattern or one that is higher in winter than in summer. Available information concerning other factors that might also affect climatic-change responses suggests that these large predicted impacts on temperate Florida species may be underestimates. Subtropical Florida species will tend to move north and inland with warming but extensive human assistance may be needed, if they are to realize their newly expanded, potential natural ranges.

A twin methodology for the study of genetic and environmental control of variation in human smoking behavior.

A method is presented for partitioning the variance associated with human smoking behavior into additive genetic, nonadditive genetic, prenatal environmental, postnatal familial environmental, and postnatal extrafamilial environmental components. Estimations can also be made of additive genetic and residual correlations between spouses and of the correlation between parental additive genetic effect and progeny nonadditive genetic and environmental effect. The variance estimates are free of the biases that might result from these correlations. The statistical genetic analysis is being applied to a large group of MZ and DZ twins, their spouses, and their adult children who live in southern Sweden. Blood samples from each subject will be used to identify their genetic constitution for a number of biochemical polymorphisms, some of which may be considered a priori to have possible relationships to smoking. Associations and genetic linkages between biochemical marker loci and quantitative behavioral traits will be sought. Traits of interest include a wide array of tobacco-use variables, motives for smoking, personality and cognitive variables, and other variables associated with drug use and health. Zygosity determinations based on biochemical polymorphisms have indicated MZ to DZ and DZ to MZ misclassification rates of 0% and 6.15%, respectively, when based solely on external morphology and questionnaire data. The nonpaternity ratio of the fathers with respect to their supposedly biological children is estimated to be 0.28%. Gene frequency estimates for 21 marker loci show that the sample of twins and their relatives is quite representative of the Swedish population at large. All loci were in Hardy-Weinberg-Castle equilibrium, with no evidence of assortative mating for biochemical traits. The MZ twins are significantly more concordant than the DZ twins with respect to whether they have ever had a smoking habit.

Fertility and offspring survival in mice selected for different sensitivities to alcohol

The LS (long-sleep) and SS (short-sleep) selected lines of mice exhibit relatively high and low sensitivity to alcohol, respectively, because of their previous history of selective breeding. The present study identifies other differences between the two lines. SS animals are almost twice as fertile as LS animals. Analysis of vaginal plug formation suggested that higher sexual activity of SS mice is an important component of their greater fertility. Forced maternal drinking of a 10% ethanol solution during gestation, and especially during lactation, caused a decrease in survival of LS but not of SS offspring. Increased cannibalism of pups by LS mothers was probably an important component of this decrease in progeny survival. Maternal consumption of liquid in both lines was decreased during gestation, and especially during lactation, when 10% ethanol was the only available liquid in each case. The physiological basis for decreased survival of LS progeny may involve either direct effects of alcohol on progeny or indirect effects caused by water, nutritional, or hormonal imbalance in LS mothers when they are exposed to alcohol stress. The relationship of fertility and progeny survival differences in the two lines to their differences in alcohol sensitivity produced by selective breeding is discussed.

Genetic differences in reproductive fitness and offspring viability in mice exposed to alcohol during gestation

The effect of prenatal exposure to alcohol was studied in two lines of mice selectively bred for different sensitivities to alcohol: the long-sleep (LS) and short-sleep (SS) lines. LS females took longer than SS females to be come pregnant. Fewer LS offspring survived, even when not treated with alcohol. Although LS females tended to consume smaller doses of alcohol, offspring of LS dams consuming alcohol during the second half of gestation survived considerably less than 50% of the time. No such effect was seen in the SS line. These results are in agreement with others, indicating a line difference in several aspects of alcohol sensitivity.

Stability of a factor-analytic description of smoking behavior

Three types of human smoking behavior, identified by factor analysis of questionnaire responses, were found to exhibit a stable structure in a series of different populations and environments. Type I smoking behavior is closely related to a personally perceived need for tobacco products. Types II and III are related to psychosocial-sensorimotor rewards and the intensification of pleasure, respectively. The typology is easily detectable and remarkably constant in the following populations: staff, employees, and patients of a teaching hospital in London, England; urbanites and suburbanites of mixed ages in a part of metropolitan Denver, Colorado, U.S.A.; college students in Fort Collins, Colorado, U.S.A., elderly urbanites and suburbanites in the metropolitan areas of (a) Stockholm, Sweden and (b) Göteborg, Sweden; and the adult children of the Swedish groups (a) and (b).