Reproductive Criteria of Multicellularity and Original Modes of Reproduction

Abstract

The reproductive criteria of multicellularity are proposed for the first time. Terminologically the multicellularity is advised to subdivide into three variants: 1) protonemal – the most primitive, known in multicellular prokaryotes, in majority groups of multicellular algae and in gametophytes of some embryophyte plants; 2) siphonoseptal, distributed amongst multicellular fungi, some groups of green and yellow-green algae; 3) embryogenic, the most complicated, characteristic of all animals (Metazoa), sporophytes and some gametophytes of embryophyte plants, charophyte algae (Charophyceae s.s.), oogamous genera of green and brown algae, some genera of red algae. In addition to well-known subdivision of the reproduction into sexual and asexual variants, it is advised to consider monocitic (appearance of the new organism from one cell in course of sexual or asexual reproduction) and polycitic (fragmentation, longitudinal/transverse division, budding, basing on numerous cells of maternal organisms), because both these modes have different evolutional and ontogenetic origin. It is demonstrated that the internal fertilization was the original feature of reproduction in animals (Metazoa), land plants (Embryophyta), most groups of multicellular oogamous algae, in oogamous and pseudoogamous fungi. Correspondingly, in course of the sexual reproduction, viviparous development was the ancestral for animals, whereas the germination of the zygote on (or inside) maternal organism was the ancestral for Embryophyta and most oogamous algae.