The diversity of ontogeny in animals with asexual reproduction and plasticity of early development

Diversity of blastogenesis and embryogenesis in animals with different reproductive strategy and different variants of the specification of germ lineage cells, defined in the literature as preformation, epigenesis, and somatic embryogenesis, is discussed. In the course of somatic embryogenesis (or, more precisely, blastogenesis), the oozooid that has developed from the egg is naturally cloning and forms numerous genetically and morphologically identical clonal individuals or modular units of a colony. This cloning results in amplification of the parent genotype; the subsequent sexual reproduction provides for genetic recombination, and the emergence of a huge number of larvae with dispersal function provides for reproductive success. In invertebrates that reproduce asexually, no isolation of the germ cell lineage takes place; the population of stem cells capable of realizing the complete developmental program, which includes gametogenesis and blastogenesis, is represented by a diaspora of cells dispersed in the organism and possessing evolutionarily conservative features of morphofunctional organization typical to cells of the germ lineage. The plasticity of early animal embryogenesis is revealed in experiments with embryonic cells cultivated in vitro. Asexual reproduction emerged repeatedly in the course of metazoan evolution; blastogenesis in animals of different taxa is more variable and less conservative than embryogenesis, but the integration of blastogenesis into the process of early embryogenesis undermines the conservatism of embryonic development.