Speciation in Allopatric Species of the Hamster Subfamily Cricetinae (Rodentia, Cricetidae)

Abstract—According to the Dobzhansky–Muller model (Dobzhansky, 1937; Muller, 1942), in the absence of gene flow, conspecific populations can become reproductively isolated, and postzygotic isolation should increase proportionally to the square of divergence time. On the example of four pairs of allopatric species of the subfamily Cricetinae, which is characterized by different levels of divergence, the extent of the formation of reproductive barriers was established by behavioral and physiological methods. The potential prezygotic isolation was assessed by the results of behavioral experiments where female olfactory stimuli were exposed to males. A crossbreeding analysis was performed to detect postzygotic isolation. The divergence time was determined by molecular genetic methods. It was shown that complete reproductive isolation formed in a pair of allopatric species of the genus Phodopus (P. roborovskii and P. sungorus) approximately for 5 million years. The sterility of F1 males and conspecific preferences with slight differences in chromosome morphology formed in hamsters (P. sungorus and P. campbelli) in course of 0.8–1.0 million years. In the pair of species belonging to the genus Allocricetulus, which diverged only 0.3–0.4 million years ago, postzygotic isolation mechanisms and conspecific preferences for a number of traits have already partially formed on the background of differences in the structure and number of chromosomes, although in laboratory conditions it is possible to obtain fertile hybrids (F1 and F2). In the species (chromosomal forms) of the superspecies Cricetullus barabensis sensu lato, which diverged later than the pair of species of the genus Allocricetulus (0.16–0.2 million years ago), the reproductive barriers are less pronounced. Thus, the example of the closely related species of Cricetinae shows that reproductive barriers can develop in allopatry and are more pronounced in species that remain isolated for a longer time. Prezygotic barriers in allopatry can develop as rapidly as postzygotic ones, which makes the mechanism of “reinforcement,” proposed by F.G. Dobzhansky, not so relevant (in case of secondary contact zones).