Том 85, № 4 (2024)

Using the example of multiple species groups and species complexes, it is empirically shown that the resolving power of a set of 10–20 nuclear loci is insufficient for the study of their genetic differentiation. For the adequate analysis of phylogenetic relationships (including reticulation events) and assessment of divergence levels within such groups of closely related species, it is necessary to multiply the number of nuclear loci and transit to high-throughput next-generation deep sequencing. However, the question of the genomic coverage required for the purposes of such study remains open. In other words, exactly how many genes in a set are needed to measure the genetic distance resolving the relationships between branches on the phylogenetic tree reconstruction of a complex of closely related species? We chose protein-coding sequences as a standard set of markers. Distances for 160–180 genes with a combined length of 270 000–300 000 bp were used to estimate the divergence levels of closely related mammalian species. In most cases, the interspecific distances are within the 0.15–0.75% range (median of 0.33%). The range of distances between semi-species is 0.12–0.28% (median of 0.14%). Intraspecific distances are always lower than 0.11%. Rodents show higher values of interspecific distances, 0.25–2.3% (median of 0.72%); distances between half-species range from 0.1 to 0.35%. To determine the number of nuclear loci and their combined length sufficient for the calculation of a genetic distance, we use simulations based on a model that included the following parameters: the average rate of gene evolution, its dispersion, and the level of polymorphism in the modern and ancestral populations. We performed a preliminary analysis of the distribution of loci evolution rates among mammalian taxa based on the data on ~50 thousand nuclear markers. It is shown that a relative error of 10–15%, comparable to the same value for mitochondrial distances between close species based on individual genes (approximately 1000 bp in length), is achieved using approximately 100 loci of 300 bp in length. Based on these data, we propose the following working hypothesis: the threshold of interspecific/intraspecific genetic distance calculated on the basis of the exons most frequently used in mammalian molecular phylogenetics is approximately 0.15%. This hypothesis assumes a species rank for the forms in statu nascendi. It should be noted that not all “good” species have significant genetic distances, since in some cases reproductive barriers form faster than substitutions accumulate in the genome.

The influence of the neurochronaxic theory of phonation of the French physiologist Raoul Husson (1901–1967) on the development of research on voice formation in the Soviet Union, mainly in the 1950–1970s, is discussed. Husson contrasted the neurochronaxic theory with the traditional myoelastic theory of voice formation. The myoelastic theory considers the vocal folds as a self-oscillatory system. Vibrations are caused by the energy of the air flow. According to Husson’s concept, vibrations of the vocal cords do not depend on subglottic pressure. The frequency of vibration of the vocal cords corresponds to the frequency of impulses arriving along the recurrent nerve. To explain the high frequency of vibration of the vocal cords, Husson used Wever’s “Volley Principle”. According to this principle, the activity of each subsequent nerve fiber occurs during the refractory phase of the previous fiber. The responses of all nerve fibers are summed up into a common high-frequency oscillation. In 1950–1970s, Soviet physiologists took an active part in testing the new concept proposed by Husson. They came to the conclusion that both mechanisms, myoelastic and neurochronaxic, are involved in the functioning of the vocal apparatus. But the recurrent nerve does not directly control the vibrations of the vocal cords, but indirectly. Žhinkin called this control system the “code principle,” when a command is sent to the vocal cords to change their physical characteristics, changing the properties of the self-oscillating system.

Data on the breeding success of hybrids, collected during direct field observations, are principally important for understanding nature of the species isolating factors and future fate of the hybridogeneous populations. In the zone of secondary contact between Eurasian magpie Pica pica and Oriental magpie Pica serica, emerging right now, limited hybridization occurs, what has been shown in our reported data on nuclear single nucleotide polymorphisms (SNP). In the present work, we have analyzed composition of 119 nesting pairs and content of 89 nests in the hybridogeneous population of P. pica leucoptera × P. serica jankowskii in Eastern Mongolia, then in the recent contact zone in Eastern Transbaikalia (South Siberia) and the relatively pure populations of P. p. leucoptera in Central Transbaikalia and P. s. jankowskii in Northeast China. In the hybridogeneous population of Mongolia, significantly increased portion of nonviable clutches with all dead eggs was recorded, as well as a portion of partly dead clutches, compared with the data on the pure population of Central Transbaikalia. The egg mortality was found to be much less dramatic in the population of the Eastern Transbaikalia, where hybridization is less pronounced than in Mongolia. Several possible mechanisms of genetic incompatibilities breaking the reproductive barriers are discussed. The future fate of this magpie contact zone is considered, taking in account selection against hybridization which was revealed in this study. Among possible scenarios, reinforcement of prezygotic isolation may occur, i. e., in the species-specific calls. It is possible that a kind of mosaic hybrid zone with some features of tension zone will appear. Monitoring of the unique situation with the emerging zone of contact and hybridization of two young magpie species is needed, as a necessary addition to genomic studies.