Spatial phenotypic structure of Red squirrel (Sciurus vulgaris) populations in the Altai-Sayan part of the area

The study of the intraspecific structure allows a deeper understanding of the evolution of living organisms and the features of the formation of biodiversity. Knowledge of the population structure of the hunting object is necessary to make a prediction of the abundance and to extrapolate the results of the abundance counts and to determine the species resources. The possibility of establishing the boundaries of populations by phenotypic traits in the red squirrel has not yet been studied. The aim of the research was to study the possibility of using the occurrence of animals with different tail colors as a marker for identifying spatial population groups of the species in Southern Siberia. The study area covered the southwestern extremity of the West Siberian lowland and a significant part of the Altai-Sayan mountain country (Kuznetsk Alatau, Altai, East and West Sayans). At 44 sites located in different environmental conditions, 6153 squirrel skins, shot by hunters in 1979, 1980 and 1995, were selected. The places of material collection are indicated by numbers (See Fig. 1). The following morphs were identified by hair color: black tail, black-brown tail, brown tail and red tail. The color was determined visually by the general background from the dorsal side of the tail; later, samples were checked according to the RAL Classic catalog. The phenotypic composition of squirrels at 43 sites is presented in Table 1. By the method of cluster analysis, the samples were compared with each other, the distance between them in a multidimensional space was determined, and then they were grouped by the similarity index. The calculations were performed in the StatSoft STATISTICA 13.3. The analysis was used to find groups of objects (clusters) that are similar in phenotypic composition. Based on the results of these calculations, a dendrogram was obtained illustrating the closeness of the samples to each other (See Fig. 2). To establish the dependence of the phenotypic composition of the population on forest conditions, the nature of woody vegetation was studied according to the materials of the Forestry Regulation of the forestry of the administrative region where the material was collected. The correlation between the studied traits was studied according to the above program. By the method of cluster analysis according to the similarity index of squirrel populations by phenotypic composition, 11 clusters were identified in the studied area (See Table 1). Clusters have a specific phenotypic composition. The samples included in one cluster statistically reliably belong to one population. Each cluster in the phenotypic composition is statistically significantly different from the others. On the geographic map, by delineating the places where the material was collected in the same aggregate, the boundaries between the clusters were determined (See Fig. 3). The resulting formations had a narrow elongated shape. In some cases, their length reached 780 km, and the width ranged from 20 to 100 km. According to the phenotypic composition, the selected clusters can be considered as populations, but in form they do not fit into the prevailing idea of the population. The method of correlation analysis established the preference for melanists (black tail) of Siberian spruce (Picea obovata Ledeb.) and Siberian cedar pine (Pínus sibírica Du Tour.) with dark bark, and for chromists (brown tail and red tail) pine ordinary ((Pínus sylvéstris L.)) with red bark. The black-brown tail are more common in Siberian fir (Abies Sibirica Ledeb.) forests, whose stands have a dark bark and needles that acquire a red color when damaged (See Table 2). Consequently, the phenotypic composition of the group is formed not only by the genotype, but also by the ability of the animals to select stands that provide them with mimicry. It has been established that in southern Siberia the occurrence of squirrel of different morphs is variable in space. On the southern macro slope of the Western Sayan Mountains, melanists dominate, where black tails account for more than 70% of animals (See Fig. 4). Melanists prevail in cedar forests. With the advance to the north-west, their specific gravity in the samples decreases. On the border with the West Siberian Lowland, chromists (brown and red tail) dominate. Their share in the population is estimated at about 70% (See Fig. 5). Chromists clearly prefer pine stands with red bark. The black- brown tail predominate in fir forests. Fir plantations occupy a niche between pine and cedar forests. In the black taiga with fir forests, the proportion of the black-tail is about 40% (See Fig. 6). The established close relationship between the structure of forest stands and the phenotypic composition of the population reveals yet another mechanism for the adaptation of the species to the environment and partially reveals the nature of the formation of boundaries between clusters. Natural barriers for squirrels, such as the steppes of Khakasia, the mountains of the East Sayan and the Kuznetsk Alatau and the full-flowing Yenisei River, do not affect the location of the boundaries of the selected clusters (See Table 3). Cluster configurations do not copy the boundaries of landscapes and forest vegetation. Although the population structure of the species could not be clearly established, the technique allowed us to determine the contours of the subspecies. The boundaries of 3 subspecies described earlier (West Siberian; Yenisei, Altai) were specified, a new subspecies of the common squirrel (Sciurus vulgaris tuvinicus) was described (See Table 4). Thus, the analysis of the occurrence of different phenotypes according to the color of the tail allows to reveal the mechanisms of adaptation of the species to the environment and to study the intraspecific structure of the red squirrel, which, of course, is of theoretical and practical interest. The paper contains 4 Tables, 6 Figures and 25 References. The Author declares no conflict of interest. No animal was caught for the purposes of this study. Animals were hunted by legal hunters using humane methods of catching.

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