Úspěch na Zoologických dnech v Ostravě

Abstract: Early embryos of many turtles may or even must enter diapause, a state of arrested development that occurs in response to or in anticipation of adverse environmental conditions. However, the harsh physical environment and the risk of predation are not the only dangers to dormant eggs, which also have to survive surrounded by numerous bacteria and fungi. Little is known about the active protection of diapausing eggs against such threats. In the diapausing eggs of the leopard tortoise (Stigmochelys pardalis) of the family Testudinidae, we discovered previously undocumented extraembryonic blood structure. The structure develops at the beginning of the dormant period while the embryo stays in the gastrula stage, persists for several weeks or even months during the whole diapause, and regresses as the embryo continues to develop after the diapause termination. Surprisingly, the blood structure develops at a very early embryonic stage, long before other known hemopoietic tissues such as blood islands differentiate. The adaptive function of the structure in embryonic immunity is not only supported by the timing of its development, but primarily by the presence of numerous granulocytes and other cells with significant immune function, including red blood cells. We revealed the same blood structure in diapausing eggs in several other testudinids; the phylogenetic distribution suggests that it evolved no later than the Eocene. This newly uncovered structure highlights the significant role and evolutionary potential of extraembryonic tissues in vertebrates and reinforms concepts on early blood development.