Release:2016, Vol. 2. №4
About the authors:Alexander G. Selyukov, Dr. Sci. (Biol.), Professor, Department of Zoology and Evolution Ecology of Animals, University of Tyumen; email@example.com
The article aims to study the primordial germ cells morphology and processes of the sex cells fund formation in different forms of Coregonus lavaretus: the marine Baltic whitefish and two Ladoga whitefishes — Volkhov and Lake forms in the embryogenesis. The analysis of the qualitative and quantitative characteristics of primary sex cells was carried out on the developing embryos, beginning from the age about 50 day before the hatching.
The results show that embryos have relatively early sex cells determination. There are some differences noted on the cytomorphological characteristics of primary gonocytes between the Ladoga whitefishes and the Baltic whitefish. Thus, in the first case the decrease of sex cells sizes during embryonic growth was observed. In the Baltic whitefish, on the contrary, the sex cells sizes during embryogenesis increased, and nuclear-cytoplasmic relation was reduced correspondingly.
The paper shows that in all the whitefishes an intensive increase of the number of gonocytes to the 2.5 months after fertilization was observed. The total calculation of primordial germ cells showed the large range of their quantity in the investigated embryos of whitefishes. That, presumably, can be connected with the different rate of the detachment of sex cells both in different forms and separate individuals.
The syncytial complexes of germ cells and their fragmentation to separate gonocytes that are characteristic for the whitefish embryos, have, obviously, an essential influence on the number of sex cells. It is also assumed that the variations in the number of sex cells can result from the direction of the future gonad sexualization, which is shown in other fish. In this case it is possible to consider that in the Baltic whitefish with small number of sex cells (10-25), as in Ladoga whitefishes embryos with low gonocytes number (10-20), the sex differentiation does not happen. Individuals that have the number of sex cells below these numbers will be differentiated into the males, above — possibly into the females.