[The genotypy structure of a natural Daphnia population based on the phenotypic response on change in the amount of food].

Natural populations of Daphnia are genetically heterogeneous with regard to phenotypic response to modification in the food quantity (a set of metric quantitative traits). In the majority of the traits, three genetically determined response types to the environmental factor studied have been detected: arithmetic means decrease (R1), increase (R2) or remain constant (St) as a result of a decrease in the food quantity. This phenotypic response was shown to occur in the whole set of the metric traits studied, irrespective of physiological specialization. The problems of assessment of genetic population structure based on phenotypic response of the individuals reflected in quantitative traits are discussed.

[Population structure of Drosophila on quantitative measure traits and its seasonal changes]. / Populiatsionnaia struktura drozofily po kolichestvennym mernym priznakam i ee sezonnoe izmeneniie.

In the Drosophila population the individuals of medium, small and large size prevail in spring, summer and autumn correspondingly. Such differences are genetically determined. Small individuals are characterized by the highest modification variability while the large individuals--by the lowest one. Genotypic heterogeneity of the population was also found in the body size of individuals, which is the highest in summer and the lowest in autumn. Dynamics of the individual sizes and of genetic heterogeneity is determined by radical seasonal changes in genotypic composition of the population. Such reconstruction influences the substantial part of gene pool, which defines the dimension of individuals. One of the possible reasons of this process is an integral selective action of the population density and temperature. It provides the regulation of variations in numbers and adaptation to the seasonal changes in life conditions.

[Phenotypic and genotypic structure of a natural Drosophila population for meristic morphologic characters and its seasonal changes]. / Fenotipicheskaia i genotipicheskaia struktura prirodnoi populiatsii drozofily po schetnym morfologicheskim priznakam i ee sezonnoe izmenenie.

A natural population of Drosophila was genetically heterogeneous in the number of sternopleural bristles and the number of arista branches. In the summer, these characters had a low mean value and high coefficient of variation: in autumn, this relationship was reversed; in late spring, the values of the mean and coefficient of variation were intermediate. The dynamics of the character mean was determined by changes in phenotypic and genotypic composition of the population, which was examined during different seasons of the year. On average, the number of sternopleural bristles was higher, and the number of arista branches was lower in females than in males. The number of sternopleural bristles exhibited a higher phenotypic and genotypic variation than the number of arista branches.

[Seasonal changes in the resistance of a Drosophila population to low temperatures and their association with fertility]. / Sezonnoe izmenenie ustoichivosti populiatsii drozofily k nizkoi temperature i ee sviaz' s plodovitost'iu.

Significant genetic variation in resistance to cold was detected in samples collected from a natural Drosophila population in spring, summer, and autumn. In the summer sample, phenotypic variation was determined by genetic factors; in the summer and autumn samples, exclusively by environmental factors. Flies collected in spring had the highest longevity at low temperatures. In summer, their longevity at low temperatures was drastically reduced but it was shown to increase in autumn. Cold-resistant flies had high fertility in spring and low fertility in autumn. The seasonal differences in resistance to cold were genetically determined and are probably caused by natural selection.

[Phenotypic and genotypic structure of a natural Drosophila population with respect to the reaction of individuals to an increase in population density and its seasonal change]. / Fenotipicheskaia i genotipicheskaia struktura prirodnoi populiatsii drozofily po reaktsii osobei na uvelichenie plotnosti i ee sezonnoe izmenenie.

In spring and summer, the natural population of Drosophila studied exhibited a high level of phenotypic and genotypic heterogeneity with regard to change of individual fertility with an increase of density of adult flies. From spring to autumn, the level of genotypic variation decreased. In autumn, all phenotypic variation resulted from environmental factors. In spring, individuals sensitive to overcrowding, adapted to low density, and highly fertile in low-density conditions prevailed in the population. In summer and autumn, the population was mostly composed of individuals with opposite characteristics. On the basis of the obtained results, a conclusion on operation of cyclic density-dependent selection in the population examined was made. Selection's functional role in control of seasonal population size dynamics is discussed.