Gene Flow in Natural Populations of DROSOPHILA MELANOGASTER with Special Reference to Lethal Allelism Rates and Protein Variation

A simultaneous survey of 14 protein loci, together with frequencies and within- and between-population allelism rates of lethal chromosomes, was carried out in five (four Japanese and one Korean) natural populations and one cage population of Drosophila melanogaster. It was found that lethal allelism rates decrease rapidly as geographic distance between two populations increases, while variation at protein loci shows a remarkable similarity over all populations examined. These findings suggest that there are very high levels of gene flow in these natural populations and that selection at protein loci which can maintain substantial geographic variation, if present, is overshadowed by gene flow. There is no indication that invasion of D. melanogaster to the Far East occurred so recently that the frequencies of lethal chromosomes are still in nonequilibrium.     

Variation in the Settling Velocity of Suspended Particulate Matter in Shallow Lakes,with Special Implications for Mass Balance Modelling

Measurements of sedimentation were combined with water samples to calculate settling velocity of suspended particulate matter (SPM) in lakes. The study sites were open water stations and enclosures in Lake Erken (Sweden) and Lake Balaton (Hungary). Settling velocities were found to vary considerably both inside and outside the enclosures. Within sites, the differences between 25th and 75th percentiles of measured settling velocities of SPM were two‐ or three‐fold. Median settling velocities of SPM ranged from around 0.5 m/d in the enclosures of Lake Erken to more than 8 m/d in the open water of Lake Balaton. Special relevance was attributed to flocculation, which is known to be affected by, e.g., SPM concentration and turbulence. Even though not directly measured, the less turbulent environment inside the enclosures was suggested to explain the low settling velocity compared to the open water environment. Settling velocity apparently correlated with water current speed (r² = 0.66; n = 12). Stepwise multiple linear regressions were used to relate the variability in settling velocity of SPM to the variability of possible controlling factors in a number of data subsets. In most cases, one variable describing the total amount of settling material (e.g., SPM) and one variable reflecting the composition of settling material (e.g., total phosphorus) were chosen. The use of suspended solids concentration to predict settling velocity in mass balance models was discussed. It was found that the mean slope between SPM and v_SPM was close to 0.1 (m⁴d^–1 g^–1). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Provenance Variation in

Variation in seedling growth and form between provenances of Podocarpus totara from 42 sites throughout New Zealand was investigated. Seedlings were grown for three years under uniform nursery conditions. There were significant differences between provenances in height growth in the first three years after sowing. Early growth was highly correlated with germination rate after sowing. In the third year, growth followed a different pattern and was negatively correlated with provenance latitude, i.e., provenances from southern latitudes grew more slowly than those from further north. This suggests that genetic factors correlated with mean summer temperature of the locality of seed source were beginning to predominate. Stem form and branch length also varied between provenances, but foliage colour and leaf size did not. Neither stem form nor branch length were related to any provenance site variable. Since provenance variation is appreciable, it is recommended that P. totara plantings for ecological purposes should be of seedlings raised from locally collected seed. However, for growing P. totara in plantations to produce special-purpose high value timber, considerable scope exists for an in-depth breeding study that will eventually lead to producing planting stock with both superior height growth and good tree form.     

Clonal Variation in the Sprouting Pattern of the Tubers in Eleocharis kuroguwai, a Cyperaceous Weed, with Special Reference to its Perennation Strategy

Abstract Clonal variation in the sprouting pattern of tubers in Eleocharis kuroguwai Ohwi was studied, using 39 clones collected within a longitudinally narrow belt from Wakasa Bay to the Kii Peninsula of Japan and one of "Ohkuroguwai", a cultivated form.
The sprouting pattern of tubers and the relationship between sprouting time and other tuber characteristics varied noticeably among clones. Based on the polygonal graphs of × (mean), (standard deviation), g₁ (skewness) and á (kurtosis) of the sprouting time, the sprouting pattern of 40 clones could be divided into the following three groups. Group A: and α were small, but g₁ and a' were generally great; almost all tubers sprouted early and simultaneously. Group B: and α were greater, but g₁ and a' were smaller than Group A; the majority of tubers sprouted quickly, but the rest of the tubers sprouted gradually. Group C: and α were very large, g₁ was small, but a' showed a comparatively large negative value; all tubers sprouted gradually over a long period.
Groups A and B were represented by the irrigation pond group from the Banshu Plain and by the Ohshima Island group in the paddy fields of the southern extremity of the Kii Peninsula. Clones from the paddy field group and from the plain group, both referable to typical rstrategists, exhibited various sprouting patterns of tubers.     

Variation in Drosophila acetylcholinesterase

We examined the Canton-S strain of Drosophila melanogaster for electrophoretic variation of the enzyme acetylcholinesterase. The pattern of bands obtained (stained with acetylthiocholine) depended on age, sex, and tissue (i.e., head vs. body part and hemolymph). However, through mixing experiments, it was concluded that most of these apparent differences were due to modification of the enzyme by unknown substances located in the fly's body. The electrophoretic pattern of head acetylcholinesterase was altered so that it became characteristic of the body which was present during extraction. For example, when heads of D. melanogaster were homogenized in an extract from D. lebanonensis bodies, the characteristic AChse bands of melanogaster were absent and instead the bands of lebanonensis were found. it was found that extraction of adult heads in 0.1 M potassium phosphate buffer alone or with a 2-min exposure to 1 mg/ml trypsin at 20 C gave the most reproducible results, independent of age and sex. Using these conditions, 25 strains of D. melanogaster and 30 strains of D. pseudoobscura were examined without finding any reproducible electrophoretic variant of acetylcholinesterase. In addition, 53 strains from 39 other Drosophila species produced a total of only six electrophoretic forms of the head enzyme. Additional electromorphs were found when whole flies were used, but these were not studied in detail because of the possibility that they could be due to postextraction modification.This study was supported by the National Research Council of Canada, Grant No. A0629 and A0235.     

Variation in human fertility

Data on family size distribution and inheritance are presented. Variance in sibship size is in general greater than mean sibship size. The inherited component in the variation appears in general to be small, though not in a Scottish sample examined in more detail. Changes in family size distribution for social (or other) reasons are considered, together with some of their effects on the change in gene frequency in small populations.     

Variation in juvenile dependence

Notable in cross-cultural comparisons is the variable span of time between when children become economically self-sufficient and when they initiate their own reproductive careers. That variation is of interest because it shapes the age range of children reliant on others for support and the age range of children available to help out, which in turn affects the competing demands on parents to support multiple dependents of different ages. The age at positive net production is used as a proxy to estimate the close of juvenile economic dependence among a group of Maya subsistence agriculturalists. Maya children produce more than they consume by their early to mid teens but remain in their natal households for a number of years before leaving home and beginning families of their own. The Maya results contrast markedly with those from several groups of hunter-gatherers and horticulturalists for whom we have similar data. Even in the Maya case, where children are self-sufficient at a relatively young age, parents are unable to support their children without help from others. The production surplus of older children appears to help underwrite the cost of large Maya families and subsidize their parents’ continued reproduction.     

Variation in epigenetic inheritance

Changing patterns of DNA methylation may underlie differential gene expression in development. Additional sources of variation in allelic methylation may be introduced by parental differences as well as by gamete of origin.     

Human Biology and Ecology: Variation in Nature and the Nature of Variation

Human biology seeks to understand human variation and the biological, environmental, social, and historical influences on that variation. Views of the nature of both variation and environment have changed during the past 100 years. Typological approaches to nature and human diversity shifted to an evolutionary perspective during the first half of the 20th century. In the second half, widespread human biological variation was documented and interpreted in terms of adaptation to the environment. Environmental physiology and reproductive ecology continue to document environmental influences on human biological functioning, but with (1) an expanded concept of environment that acknowledges more fully the interactions among its physical, biotic, and social aspects and (2) an expanded theoretical basis, drawing on evolutionary ecology and life history theory, acknowledging tradeoffs and changing constraints and opportunities over the lifetime. Human biology gains from greater interaction with other fields, such as political ecology, but also contributes to them. [Keywords: biological anthropology, human ecology, adaptation, environmental physiology, reproductive ecology]