Phenotypic diversity of alien species under different mechanisms of introduction into the Vychegda river basin

This paper presents a description of the morphological diversity of populations of white-eye bream and Chinese sleeper, which are alien to the Vychegda River basin. Their introduction occurred as a result of different mechanisms of invasion - self-settlement and acclimatization. It is shown that the white-eye bream has widely spread along the main channel of the Vychegda River, up to the upper stream. The acclimatized Chinese sleeper inhabits several fire ponds of dacha communities in the middle stream of the Vychegda River. Comparison of morphological descriptions of the white-eye bream sample with its nominative form allowed establishing a wider range of variability in the number of rays in the anal fin and rakers on the first gill arch. For the Chinese sleeper, there are also a greater number of rays in the pectoral and dorsal fins. These changes can be regarded as the result of the adaptation of the studied populations of alien species to inhabit the conditions of the acquired part of the range. Using the Zhivotovsky µ indicator, a similar level of intrapopulation morphological diversity of Chinese sleeper and white-eye bream samples was revealed. This may indicate the similarity of ongoing processes when a species moves into a new territory. However, the frequency of asymmetric manifestation per trait in the Chinese sleeper sample turned out to be high (4 points) and corresponded to the level of significant deviation from the norm. Based on the work done, a hypothesis was put forward that a population formed from a small number of individuals in a small reservoir area is more influenced by environmental factors during the period of early ontogenesis compared with species independently settle along riverbeds. It is assumed that the "founder" and "bottle neck" effects are the basis of this process.