ISSN 1995-4255, Contemporary Problems of Ecology, 2012, Vol. 5, No. 4, pp. 450–458. © Pleiades Publishing, Ltd., 2012. Original Russian Text © A.P. Tolomeev, O.P. Dubovskaya, N.N. Sushchik, O.N. Makhutova, G.S. Kalacheva, 2012, published in Sibirskii Ekologicheskii Zhurnal, 2012, No. 4, pp. 607–618. 450 INTRODUCTION A study of the relationship of the growth parame- ters of organisms with environmental factors plays a key role in modern population ecology. The main parameters of the biological cycle of the organism development (life history) include the rate of somatic and generative growth, the life span, and the duration of development needed to reach sexual maturity, the initial weight (size) of newborn and mature individu- als, the size of eggs and laying, and the probability of survival. These parameters form a link between the physiology of an individual and the demography at the population level [1]. Currently, studies on the individ- ual development of organisms are of great demand in the field of ecological modeling. Recently, individual- based approach to modeling the development of the population has been intensively developed by many domestic and foreign authors [2–4]. This new approach allows one to take the description of the interconnection of living organisms with environmen- tal factors to a higher level. Moreover, a wider spec- trum of individual parameters can be used in models compared to the traditional approach based on simple systems of differential equations. In the field of mod- eling the water ecosystem, the growth of zooplankton is usually described as a function of the amount of food available (or any limiting substance) according to the Mono equation [5]. However, some recent investiga- tions of zooplankton feeding revealed more a compli- cated functional correlation between the food content and the population growth. This is related to some sea- sonal changes that constantly occur, not only in the amount, but also the quality of food. Moreover, as a consequence of synergistic effects, the quality of food cannot be described using the principle of simple lim- itation by a certain substance in food [6]. On the other hand, the description of growth using just one coeffi- cient, i.e., the specific rate, yields no opportunity to separate important components, such as somatic and generative population production; however, the flexi- bility of the distribution of resources between the accumulation of structural biomass, reserve nutrients, and generative mass is the main mechanism of adapta- tion to the trophic situation [7]. The food-quality parameters can be combined in three major groups as follows: (1) the content of bio- genic elements such as P and N and its stoichiometric ratio to the content of carbon (C : N : P or C : P and C : N); (2) both the content and the composition of essential polyunsaturated fatty acids (mainly eicosap- entaenoic and docosahexaenoic acids); and (3) the content of other important components, such as ste- rols, amino acids, and vitamins [8–10]. A problem of food quality and its role in the development of an organism, as well as its effect on certain growth param- eters, i.e., somatic or generative growth, is the subject of continued discussion. Some authors propose that the discussion of mineral or biochemical limitation is basically pointless, since all parameters in the above- discussed groups are tightly correlated [11, 12]. Never- theless, other authors prove that phosphorus and poly- unsaturated fatty acids (PUFAs) are independent and Differentiated Influence of Quality of Seston (Content of C, N, P, and Polyunsaturated Fatty Acids) on Rate of Somatic and Generative Growth of Daphnia A. P. Tolomeev a , O. P. Dubovskaya a, b , N. N. Sushchik a, b , O. N. Makhutova a , and G. S. Kalacheva a a Institute of Biophysics, Siberian Branch, Russian Academy of Sciences, Akademgorodok, Krasnoyarsk, 660036 Russia b Siberian Federal University, pr. Svobodnyi 79, Krasnoyarsk, 660041 Russia e-mail: tolomeev@ibp.ru Abstract—The data set obtained in 19 experiments aimed at studying the growth of Daphnia of the longispina group on natural seston of the Bugach water reservoir (Krasnoyarsk) was used to analyze the relationship between the parameters of somatic and generative growth of the studied animals and the amount and quality of food. Depending on the quality of the seston, two models of the development of Daphnia were proposed. It was demonstrated that, despite the existing positive correlation between somatic and generative growth, a noticeable fraction of the variations of the specific rate of generative production is determined by external fac- tors of the environment, such as the relative content of N and α-linolenic acid (N : C and ALA : C) in seston. Keywords: Daphnia, food quality, somatic growth, generative growth, fatty acids, C : N : P DOI: 10.1134/S1995425512040130