[The role of chemoreception in forming of Daphnia longispina sustainable population (the simulation experiments)]

Individual-based mathematical models may be considered a promising tool for studying the patterns of aquatic animals population development under conditions of exposure to various environmental factors including those ones that are difficult to measure directly. To test the hypotheses on the role of chemoreception in vital activity of aquatic invertebrates, we used the previously designed individual-based simulation model of a mass pelagic species, Daphnia longispina, population. The model describes a population as an ordered list of individuals with specific set of traits. For each individual, its energetic traits are calculated, also the probabilities of outcomes from different life situations are assigned or calculated. Included in the model are responses of adult individuals to two types of chemical signals: 1) diurnal vertical migrations from surface to hypolimnion when detecting fish cairomones; 2) active search for mature females by adult males via pheromones, effects of which grow stronger with water temperature raising. By comparison with previous versions of the model, introduction of these responses allowed to reproduce seasonal dynamics of the model population most closely to real dynamics of the prototype population. Consecutive, and then joint switching off of the ability to detect chemical signals made it possible to obtain a quantitative estimate of their role in population dynamics optimization and to determine limiting levels of predators, both vertebrate and invertebrate, pressure on organisms lacking the ability to use chemotaxis. In particular, it was found out that, in the model population, the size of water flea spring generation is determined by the amount of overwintered dormant eggs which increases as a result of active search for mature females due to chemoreception. The size of summer-autumn generation is practically independent of initial numbers and is determined by living conditions during the season, first of all by the factor of consumption by predators. Chemoreception helps adult water fleas in avoiding to be eaten, which turns out to be effective in maintaining high abundance even at considerable pressure by predatory fishes. When a water flea population is deprived of the ability to response to chemical signals (for example, when there is no hypolimnion or shelters among vegetation), predation press increasing above some threshold, which depends on duration of embryonic development, leads to population instability and its decreasing in numbers till the total extinction. The model allowed to obtain a quantitative estimate of the role of chemoreception in forming of water flea population dynamics. In the present version of the model, annual production of the population is shown to raise 1.5 times due to chemoreception. In the absence of chemoreception, water flea population fails to use environmental resources in full measure and come up to production rates observed in nature.