Mechanisms of Diversification during Changes in Habitat in the Three-Spine Stickleback (Gasterosteus aculeatus) Are Fundamentally Different from the Mechanisms of Speciation within the Genus Gasterosteus

In evolutionary biology, the dominant idea is that the mechanisms of intraspecific evolution and speciation are the same, and intraspecific forms are, in essence, emerging species. The extensive literature on the three-spined stickleback, a model species for evolutionists, allows us to verify whether this is so, and the analysis shows that although this fish, when living in fresh water, give a variety of forms that are morphologically very different from marine ones, postzygotic reproductive isolation between representatives of different forms does not usually occur. No such form of isolation has been found between populations from different parts of the range of the species. The adaptation strategy of the three-spined stickleback includes long-distance migrations that facilitate the inhabiting of newly emerging favorable habitats and the exchange of genes between populations, the acceleration of selection, and a decrease in the probability of recombination of alleles of genes necessary for adaptation. This strategy does not facilitate speciation in representatives of the genus Gasterosteus, so it occurs extremely rarely and due to the fusion of chromosomes (similar chromosomal rearrangements within the species G. aculeatus have not been noted). Thus, at least in this case, the mechanisms of speciation (saltation mechanisms) are completely different from the mechanisms of generation of forms within the species.