The Main Patterns of Transformation in Organs of Reproductive System During the Evolution of Vertebrates

Abstract

The article presents an analysis of the main directions of transformations of the organs of the reproductive system during the evolution of vertebrates at various levels of the hierarchical organization of vertebrates - cellular, tissue, organ, organism, population. During the evolution of vertebrates, gonadal oligomerization occurred, a decrease in the number of hermaphrodite species, a decrease in the relative mass of gonads in the body, and a transition from isogamy to heterogamy (oogamy) was observed. In vertebrates, 4 types of structural and functional organization of male gonads have been formed: follicular type, follicular-cystic type, tubular-cystic type, tubular type. In representatives of different classes of vertebrates, the transformation of the ovaries proceeded in different directions. Large, grape-shaped ovaries have evolved in fish, amphibians, reptiles, birds, and cloacal mammals. These ovaries, just before the breeding season, can occupy almost the entire abdominal cavity. The ovaries of placental mammals are small in size, their shape is most often oval, the surface is smooth. One  of  the  directions  of  the  evolutionary  transformation  of  the  gonads  was  the  compartmentalization  of  the structures of the male and female gonads, while there was a structural and topographic division into the actual gonads and the genital tract, which were formed on the basis of the structures of the primary kidney. Higher vertebrates have well-developed accessory sex glands. In the gonads, there was a clear topographical distinction between endocrine and germinal structures. Against the background of an increase in the number of species with internal  fertilization,  against  the  background  of  the  formation  of  a  complexly  organized vagina  and  uterus  in female mammals, the formation and complication of the copulatory organs of males occurred.