Life Cycle Modifications, Neoteny, Retardation, Heterochrony (Using the Example of Amphibians)

Amphibians are animals with a complex biphasic life cycle, which can threaten the possibility of successful reproduction of their populations. Evolutionary variants of life cycle transformation, towards simplification or reduction of duration, can proceed by acceleration (the predominant strategy in northern amphibian populations) or by retardation and wintering in the larval stage, which is more typical for southern species in the northern part of their ranges. In other cases, retardation and progenesis lead to the emergence of variants of facultative neoteny. Evolutionary fixation of the latter leads to shortening of ontogeny by forming obligate neoteny. In tropical amphibians, a transition to direct development is possible, when a radical loss of a number of developmental stages with their provisional adaptations is impossible without replacing the cenogenetic functions of these larval organs. In a moderate continental climate, as well as in urbanization conditions, heterochrony in the formation of individual organs or systems is more often observed, based on ecological mechanisms. The same heterochronic processes precede the emergence of new life cycle variants with their special morphological appearance.