ИСТИНА

Investigations of the influence of eggs and tadpoles density on the mortality and developmental rate are based on the calculation of the number of individuals in the certain water volume. Usually an attention is not paid to the distribution of individuals in this volume. It may be correct for actively moving tadpoles, but the embryonic stages are passive, and not only volume of water, but also an allocation of individuals in this volume is important for these stages. It is known, that in the natural reservoirs the mortality in the different parts of Rana temporaria egg aggregation is unequal. By the moment of hatchling, at the edges of egg aggregation the mortality is about of 9%, while in the central and bottom parts of aggregation mortality can reach 80%. Unlike a frog, the spawn of Bufo bufo looks like a long cord to 5 meters. These cords twine around the underwater objects, or lie on the bottom. The egg aggregations of Bufo bufo are formed by the stacking of cords and by the reeling of one cord over another one. As a result, one part of egg laying has a structure of the dense tangle generated by the reeling of cords, and an other part lies on the bottom or stretches between stalks of water plants. It was discovered that under experimental conditions the mortality of eggs situated in the stretched cords is lower, than in the unstretched ones, eggs developmental rate is highest in the stretched cords. The mortality and developmental rate depend also on the packing of egg cord: in the convoluted cord egg mortality is higher and developmental rate is lower, than in the straightened one.