Between-population Differences Research Articles

Bromus tectorum seed germination: between-population and between-year variation

Cheatgrass (Bromus tectorum L., Poaceae), an introduced winter annual, has invaded a variety of habitats in western North America. This study examines variation in cheatgrass germination response and after-ripening patterns that are related to differences in habitat and to yearly differences in weather conditions during seed maturation. Seeds collected from five contrasting populations in 1992 and 1993 were subjected to controlled dry storage and then incubated across a range of temperatures. Recently harvested seeds were dormant and germinated slowly, while fully after-ripened seeds were nondormant and germinated rapidly. The optimal incubation temperature for mean germination time shifted from 5:15 to 20:30 °C as a result of after-ripening. Between-population differences in germination response appear to be related to the potential risk of precocious summer germination. The results from this 2-year study suggest that the more extreme yet predictable environments select for seed germination and after-ripening patterns that are genetically fixed, while populations from more favorable environments tended to show more between-year variations, suggesting more phenotypic plasticity. Germination percentage showed greater between-year variation than mean germination time. Between-year differences could not be explained simply by differences in maximum temperature or total precipitation during maturation. Adaptive germination responses in cheatgrass populations from contrasting habitats may have both genetic and environmental components, thus explaining why this species can become established in such a variety of habitats. Keywords: after-ripening, invading species, dormancy, mean germination time, cheatgrass, downy brome.

Haemostatic factors and lipoprotein (a) in three geographical areas in Finland: the Finrisk Haemostasis Study.

An increasing volume of evidence suggests that haemostatic factors play a role in the risk of coronary heart disease. It is not known, however, whether between-population differences in haemostatic factors correspond with the differences in mortality related to coronary heart disease. We examined this question in Finland, where, in North Karelia (in the eastern part of the country), the mortality from coronary heart disease is 1.5-1.7 times higher than that in southwestern areas. A random sample of 3000 people aged 45-64 years was drawn from the population registers of North Karelia, of the area surrounding Turku and Loimaa in southwestern Finland and of the Helsinki area in southern Finland. Of the 3000 people approached, 79.6% took part in the study. differences in coronary heart disease mortality and morbidity. Factor-VII coagulant activity was significantly higher in North Karelia than in the other areas (P = 0.0008). The fibrinogen level was also higher in North Karelia, although the difference was significant only among non-smokers (P = 0.02). Levels of factor-VII antigen, plasminogen and lipoprotein (a) did not differ between the areas. Within North Karelia, the levels of both factor-VII coagulant activity, and factor-VII antigen were higher in rural areas than in urban areas. Levels of factor-VII coagulant activity, factor-VII antigen and plasminogen were higher in women than in men and increased with age in women but not in men. The fibrinogen level increased with age in both sexes. These baseline findings of the Finrisk Haemostasis Study demonstrate that the geographical differences in levels of factor-VII coagulant activity and fibrinogen in Finland are consistent with the population

Review and analysis of variation between spirometric values reported in 29 studies of healthy African adults.

Within- and between-population variation in spirometric measurements has been addressed in a systematic review of spirometric measurements from 29 studies published between 1965 and 1990 involving 9,690 men and 2,638 women of sub-Saharan African ancestry; FVC and FEV1 were age- and height-standardized at BTPS. Between- population differences were related to geographic region and sample source (workforce versus community). The effects of altitude, variation in sample mean height, and year of study publication were also significant variables in multivariate models explaining between-population differences. Altitude was the most important variable with an effect of 263 ml/1,000 m (95% confidence interval [CI] 120-410) on FVC in men. In women, variation in sample mean height was also important, with taller populations having larger values for FVC (64 ml/cm). In men, secular trends were evident, with date of study associated with negative trends among men in the U.S.A. (-35.3 ml/year), and positive trends (14.7 ml/year) in other regions. These differences in trend could not be explained. Population selection factors, altitude, date of study, and other biological sources of variation need to be taken into account in evaluating between- and within-population comparisons of spirometric measurements.

Reduced levels of DNA polymorphism and fixed between-population differences in the centromeric region of Drosophila ananassae.

We have estimated DNA sequence variation within and between two populations of Drosophila ananassae, using six-cutter restriction site variation at vermilion (v) and furrowed (fw). These two gene regions are located close to the centromere on the left and right X chromosome arms, respectively. In the fw region, no DNA polymorphism was detected within each population. In the v region, average heterozygosity per nucleotide was very low in both populations (pi = 0.0005 in the Burma population, and 0.0009 in the India population). These estimates are significantly lower than those from loci in more distal gene regions. The distribution of DNA polymorphisms between both populations was also striking. At fw, three fixed differences between the Burma and India populations were detected (two restriction site differences and one insertion/deletion of approximately 2 kb). At v, each DNA polymorphism in high frequency in the total sample was nearly fixed in one or the other population, although none of them reached complete fixation. The observed pattern of reduced variation within populations and fixed differences between populations appears to correlate with recombination rate. We conclude that recent hitchhiking associated with directional selection is the best explanation for this pattern. The data indicate that different selective sweeps have occurred in the two populations. The possible role of genetic hitchhiking in rapid population differentiation in gene regions of restricted recombination is discussed.

Components of recruitment in populations of the acorn barnacle Semibalanus balanoides (Linnaeus)

Recruitment in marine species with pelagic larvae is sensitive to variation in larval supply, settlement rates, and early settler mortality, but the relative contribution of these processes to variation in recruitment is rarely known. We examined these components of recruitment success in two populations of the acorn barnacle Semibalanus balanoides (Linneaus). Water column larval supplies differed by four-fold between populations. In the high larval supply population, benthic settlement sites were rapidly saturated with settlers. As a consequence of the saturation of settlement sites, daily settlement to remaining free space was intessified to 15 times higher than in the population with lower larval abundances. In sharp contrast to this augmentation of settlement rates, however, the saturation of settlement sites reduced differences between sites in the cumulative recruitment of calcified juveniles. Within-population patterns in settlement were also conspicucous but of lower magnitude than between-population differences. Settlement decreased with increasing tidal height but increased both with wave exposure and proximity to conspecifics. This local variation in settlement diminished over time at the high-settlement site as available settlement space was preempted. Larvae settle less selectively once preferred locations are saturated with settlers. Our results demonstrate that population differences in larval supply can lead to dramatic differences in recruitment within as well as among populations. Further elucidation of recruitment variation in marine species with planktonic larvae will require paying more attention to processes that dictate larval supply rates.

Changes in chronic respiratory symptoms in two populations of adults studied longitudinally over 13 years

Data from two longitudinal studies conducted in Cracow, Poland, and Tucson, Arizona, USA, were used to evaluate the differences in period prevalence, incidence and remission rates of respiratory symptoms between two populations, as well as to assess the between-cities similarities in the relationships of the symptoms to age and smoking habit. The analysis was based on data from 3,082 adult Cracow residents, interviewed twice 13 yrs apart, and from 1,452 Tucson adults, with mean period between initial and final survey of 12.2 yrs. Log-linear models were used to consider possible interactions of the symptoms, age, smoking, gender and city. The relationship of the symptoms to smoking was similar in both cities, after adjustment for age and gender, with at least doubled incidence rates of most symptoms in continuous smokers compared to lifetime nonsmokers. The between-population differences in the symptoms were related to age, indicating onset of bronchitic symptoms occurring earlier in life in Cracow, and of asthmatic symptoms in Tucson. These differences were due to factors other than tobacco smoking e.g. various types of ambient air pollution.

Population and sex differences in arm circumference and skinfold thicknesses among Indo-Pakistani children living in the East Midlands of Britain

Arm circumference, triceps and subscapular skinfold thicknesses of 2224 Indo-Pakistani children aged 3-10.9 years living in Nottingham and Leicestershire were measured. The children were classified into populations according to country of origin, and religion, prior to analysis. Significant between-population differences were shown for all three variables, the effect being stronger in males than in females. Sex differences in arm circumference and triceps skinfold thickness were greater than those found in the British reference populations, whilst the patterns of fat distribution differed from the British standards for all the Indo-Pakistani populations, male and female.

Comparative energetics of a northern and southern population of Drosophila melanogaster

1. 1. Weight-adjusted metabolic rates of laboratory-reared, female descendents of Drosophila melanogaster collected from northern New York and northern Florida were compared at 18,21, and 25°C. 2. 2. New York flies had significantly higher rates of metabolism at incubation temperatures of 21 and 25°C but not at 18°C. 3. 3. A nested analysis of variance showed that at 2PC, 29% of the total variance in metabolic rate was due to between-population differences and 27% was due to line differences within populations. 4. 4. The metabolic rate characteristics of both groups of flies are consistent with their patterns of fecundity and seasonal abundance.

Epidemiology and public health aspects of non-insulin-dependent diabetes mellitus.

NIDDM is the predominant form of diabetes mellitus in all populations, almost exclusively so in some. Its prevalence varies enormously, with particularly high rates in populations whose lifestyle has drastically changed since World War II. Epidemiologic data from the developed countries of Europe and North America are not adequate to determine whether their incidence rates have also increased. Genetic factors are clearly implicated in the etiology of NIDDM, but their location and mode of expression remain to be determined. The two variables most strongly related to the incidence of NIDDM are age and degree of obesity, although there is emerging evidence of an independent association with fat distribution. Whether the nature of the habitual diet and the degree of physical activity influence the incidence of NIDDM remains uncertain and should be further researched. Cardiovascular disease is strongly associated with NIDDM in most populations, but there are between-population differences in the degree of association and the relative excess in the two sexes. There is increasing evidence, in particular for coronary heart disease, that increased risk precedes the onset of hyperglycemia; the implication of this is that NIDDM and atherosclerosis share common antecedents. The specific complications of NIDDM--eye and renal disease--are important causes of morbidity and mortality and for those populations, often relatively poor, in which NIDDM is already or is becoming very common will pose substantial problems in provision of health care.

Ecological factors in skin color variation among Papua New Guineans.

An EEL reflectance spectrophotometer was used to measure the skin color of the inner upper arm and the forearm of 913 Karkar Islanders (Madang District) and 684 Lufa villagers (Eastern Highlands District). The samples were subdivided to study sex, age, and population variation against a background of ecological observations, including sunlight exposure, clothing, and erythemally effective wavelengths of ultraviolet light (Robertson, unpublished Ph.D. thesis, 1974). Population differences in sex and age variation in upper arm skin color may largely be attributable to the effects of culturally associated clothing differences. Not only do the Lufa villagers wear substantially less clothing than the Karkars, but also their arms are exposed more frequently to ultraviolet light during heavy manual work in unshaded gardens. For the melanin content of the forearm skin there are similar patterns of age variation in both populations; however, the populations differ in mean percentage of reflectance throughout most of the age span. These between-population differences are interpreted as a consequence of greater average daily exposure to sunlight and the higher intensity of ultraviolet light in the highland environment. On the forearm the percentage of reflectance at 685 nm decreases more rapidly with age in the prepubertal and adult age groups, a result attributed to endocrine changes superimposed on cumulative changes in the melanin pigmentary mechanism.

INTRA- AND INTERPOPULATION VARIATION IN THE THERMAL CHARACTERISTICS OF PREADULT DEVELOPMENT OF TWO LATITUDINALLY DIVERSE POPULATIONS OF TOXORHYNCHITES RUTILUS SEPTENTRIONALIS (DIPTERA: CULICIDAE)

AbstractLinear regression analysis was used to estimate the developmental threshold, t0, and thermal constant, K, for all preadult stages of two laboratory colonies of the mosquito Toxorhynchites rutilus septentrionalis (Dyar and Knab). The colonies originated from Newark, Delaware and Lake Charles, Louisiana. The physiological and ecological significance of the within- and the between-population differences in the slopes of the regressions,t0's and K's, are discussed.

Population variation in Plantago major from southern Ontario

The morphological variation and growth and flowering responses in 15 populations of Plantago major collected from different climatic regions and habitat types in southern Ontario were examined. Both within- and between-population differences were assessed using canonical variates analyses. These were carried out on data obtained from field-collected specimens, and from plants grown from seed for a 2-year period in a standard garden trial. Four groupings of the 15 population samples were recognized in the field data. These included the two lawn populations, 8 and 15; population 14, collected from a cultivated field; population 9, originating from a nonmown wasteground site; and the remaining populations collected from a range of trampled roadside – waste ground sites. Analyses of the garden trial data indicated similar groupings. Population 14 remained a distinct group containing individuals characterized by long narrow leaves, a semiprostrate growth form, earlier flowering, greater reproductive effort, reduced rosette production, a larger number of seeds per capsule, and smaller seeds. These individuals would appear to correspond to ssp. pleiosperma. The remaining population samples were characterized by a smaller number of seeds per capsule, larger seeds, a smaller reproductive effort, and later flowering and they would appear to be referable to ssp. major. The two lawn populations, 8 and 15, contained the largest number of prostrate individuals, which were smaller in size and produced less biomass than individuals in the remaining populations. The latter group consisted of large erect plants which produced considerable floral and vegetative growth. There was no evidence for clinal patterns of variation in flowering behaviour and growth features in relation to the climatic gradients in southern Ontario among the 15 populations of P. major.

Geographical variation in populations of Chenopodium album resistant and susceptible to atrazine. I. Between- and within-population variation in growth and response to atrazine

Between- and within-population variation in growth characteristics, isoenzyme patterns, and response to atrazine were studied in individuals from four atrazine-resistant (R) and four susceptible (S) populations of Chenopodium album L. collected from sites of contrasting climate in southern Ontario. In both the R and S types, population differences in growth characteristics were correlated with geographical location and climatic differences. The more northerly R and S populations had a greater rate of development, earlier maturation, lower biomass at maturity, and greater reproductive effort compared, respectively, with the more southerly R and S populations.Estimates of within-population variation were obtained statistically for a number of growth characters and from the electrophoretic patterns of five enzyme systems (PGM, PGI, GOT, MPI, and LAP). These indicated marked homogeneity in the four R populations as compared with the more variable S populations. Populations from the two disjunct areas of resistance were different for two of the enzymes studied and would appear to represent two different genotypes. This would suggest that mutation for resistance in populations of C. album has occurred independently in the two areas. Coupled with the evidence for differential growth characteristics of these two genotypes in response to climate, we would suggest that resistance has developed in individuals already established in each of the two separate areas, rather than spreading from a single recent introduction of the R type in Ontario.As expected, distinct differences between the R and S types were obtained in response to postemergence treatments with atrazine. The four R populations either showed no effect or exhibited increased growth. S populations all showed marked decreases in growth and production of biomass. Significant between-population differences in growth features were apparent for both types in the control and were maintained in the presence of atrazine. Although small differences in relative susceptibility were obtained for the susceptible populations, statistically significant population by treatment interactions were not evident.

Ecotypic differentiation in guineagrass ( Panicum maximum Jacq.)

Six Brazilian populations of guineagrass ( Panicum maximum Jacq.) were studied in order to evaluate their quantitative and allozyme variation and to correlate their ecotypic differences with average monthly temperature and rainfall at the collection sites. All six populations came originally from old pastures in the northern and western regions of the State of Sao Paulo, Brazil. Highly significant between-population differences were found for a majority of the morphological and floral characters scored in greenhouse experiments as well as for two allozyme systems (esterase and alcohol dehydrogenase). A discriminant analysis performed on the quantitative characters yielded a cluster diagram showing marked population differences. Principal component analysis, based on the mean annual and monthly temperatures and total rainfall as independent variables, indicated that temperatures in September and January accounted for almost all the observed quantitative variability. The likely occurrence of distinct guineagrass ecotypes in Brazil as well as the roles of sexuality in the evolution of interpopulation variation and in adaptation to different environmental conditions are briefly discussed.

A multivariate approach to variation in microfilariae: examination of species Wuchereria lewisi and Demes of the species W. bancrofti

Morphological differences between W. lewisi and demes of W. bancrofti result primarily from differences in the size of the individual microfilaria. A canonical analysis shows complete separation of the species. Because of the poor correlations between the characters, shape differences are not consistent and are not revealed by this analysis. Shape differences may be postulated on the basis of the ratios of the means. However, these ratios tend to be highly variable within populations because of poor correlations between the characters, and there will be considerable overlap of the ratios between the two species. An assumption of high correlations (and hence consistent ratios) between characters results in two canonical variates which may be interpreted as reflecting shape differences. The relatively low correlations between the measurements tend to give a result similar to that by a principal components approach on the population means. Correlations within populations are generally low and therefore have little influence in determining between-population differences. Under these circumstances principal components and the more efficient canonical variates give similar results. The different assumptions implicit in the two approaches are discussed.

Local Geographic Variation in Demographic Parameters and Body Size of Desmognathus fuscus (Amphibia: Plethodontidae)

Six Maryland populations of the dusky salamander Desnmognatlhus fuscus were analyzed for differences in several life history and related parameters: timing of reproductive season, age at sexual maturity, reproductive rate, sex ratio, age structure, survival rate, and body size. Life history features are essentially similar in the populations. Adult 9 9 lay eggs every year. Oviposition takes place during summer (June to early August). Larvae transform in late spring and early summer at about 9-12 mo of age. Males mature at 2 yr of age, 9 9 at 3 yr. Survival rates (determined from age structures and sex ratios) differ considerably among the populations. Between-population differences in survival are greater for 9 9 and older animals than for 9 9 and juveniles, respectively. Percentages of tail regeneration are in accord with these observations. Reproductive rate is greater in populations where adult survival is lower. Part, but not all, of these fecundity differences can be accounted for by positive size-fecundity relationships. Considerable interlocality variation in body size of trans- formed animals is evident. Body size and adult survival are negatively correlated, but no significant relationship between body size and juvenile survival exists. Populations in the same physiographic province are the most similar overall, but no general geographic trends are evident. Biotic interactions may account for some of the observed interpopulation varia- tion, but evidence is unavailable to demonstrate any evolutionary significance to this variation. This study suggests that a complete understanding of the magnitude and nature of broad geographic demographic trends in organisms may necessitate a consideration of local variation.

Copulatory behavior of old-field mice (Peromyscus polionotus) from different natural populations

In an effort to study a biologically important behavioral pattern in different naturally occurring populations of the same species, the copulatory behavior ofPeromyscus polionotus from South Carolina and from Santa Rosa Island, Florida, was compared with that ofP. polionotus from the Ocala National Forest, Florida. Twelve male and 16 female South Carolina mice received 71 tests, and five male and three female Santa Rosa mice received 18 tests. The basic pattern was identical across all three samples, being characterized by no lock, no intravaginal thrusting, multiple intromissions, and multiple ejaculations. Prolonged intromissions followed organized ejaculatory series. Quantitative differences among samples were found for several measures. Intromission Frequency appears particularly susceptible to local variation. Between-population differences in copulatory behavior appear to be of a quantitative rather than a qualitative nature.

Association of genetic polymorphisms with embryonic mortality in the chicken. II. The B blood-group system and the pure and crossbred progeny of two populations.

SUMMARYWe have studied the association of the ten possibleBblood-group genotypes with mortality during incubation in the 1966 generation of two relatively noninbred populations of Light Sussex chickens. These were related substrains 6D and 6F derived in the 1964 generation by equal division of strain 6, which we had previously studied in its 1962 generation. TheBblood-group genotypes of zygotes but not of dams were associated with marked mortality differences in 6F, while in 6D almost no differences were found. Comparisons of the findings in 6D and 6F with the results previously published for the ancestor strain 6, after adjustment for overall between-population differences, showed marked changes between 6 and 6F in the mortalities associated with the five most frequent genotypes. In four of these, the mortalities in 6D were about half way between those in 6 and 6F. Taken together, these results provide evidence that the selective pressures on theBlocus from differential embryonic mortality vary from generation to generation and even between populations differing apparently only slightly in environment and genetic composition.In progeny of crosses between females from 6D and 6F with males from 5D and 5F respectively, the latter being two related Rhode Island Red/New Hampshire substrains, embryonic mortality was much lower than in the pure matings within 6D and 6F, and only a few associations withBblood-group genotypes of zygotes were found.The results are discussed in relation to the general lack of association of polyallelic polymorphisms with aspects of fitness reported by other workers; and the importance is stressed of studying associations of genotypes rather than genes or serological factors.