Instability Stabilized: Mechanisms of Evolutionary Stasis and Genetic Diversity Accumulation in Fishes and Lampreys from Environments with Unstable Abiotic Factors

As studies have shown, individuals from well morphologically distinct groups often represent the same species and may even belong to one population in fishes and lampreys from environments with unstable abiotic factors (Arctic, mountain, and desert regions). Phenotypic plasticity ensures broad variation ranges of morphological traits in unstable conditions, which require rapid transitions from one morphogenetic variant to another. The choice of a morphogenetic pathway can be influenced by the level of individual heterozygosity, changes in the copy numbers of certain DNA sequences, heteroplasmy, and the presence of several allelic variants in the genes that strongly affect the phenotype. A cyclic character is often observed for evolutionary processes driven by these mechanisms, and speciation usually does not take place in unstable environmental conditions. However, mobilization reserve accumulate in a species with a broad reaction norm, and particular morphogenetic pathways may be genetically fixed when its population finds its way into stable environmental conditions, facilitating fast allopatric speciation.