卷 103, 编号 6 (2024)

The determination of individual age and ontogenetic stage (juvenile, subadult, adult) of fossil vertebrates is important for the initial determination of taxonomic affiliation, as well as for further evolutionary and paleobiological interpretations. Determination of individual age and ontogenetic stage (= relative age) is carried out by various methods, including paleohistological analysis. The study of thin sections of tetrapod bones allows us to assume how many years the animal lived (skeletochronological method) and to determine the ontogenetic stage according to a set of age-related histological markers: change in the type of bone matrix and vascularization, change in the distance between growth marks, formation of the external fundamental system (EFS), formation of the inner (endosteal) and outer (periosteal) circumferential layers (OCL, ICL), occurrences of secondary remodeling – Haversian substitution and formation of trabeculae. Depending on the phylogenetic position and biological peculiarities of the study group of tetrapods, the set of age “histologic markers” may be different.

The increments on the surface of the incisors of young spotted ground squirrels are wide, of medium definition. They probably reflect intensive nutrition and growth of the body. Starting with the third month of life, growth slows down, the width of the growths is decreased, and they become narrower and more distinct. Deformations appear in the form of swellings of the incisor wall. The frequency of occurrence of the deformations in underyearlings reaches a peak in the second half of July. The same pattern is observed in adult ground squirrels. By this time, gophers reach their maximum body weight. The majority of adult ground squirrels kept in captivity also reach the maximum body weight in the first half of July, this indirectly indicating the relationship between the appearance of deformations and the achievement of maximum fatness. Under laboratory conditions, at a temperature not exceeding 22°C, overwintered males and dry females after reaching their maximum body weight, even in the presence of food, fall into a stupor resembling a state of hibernation. Their body temperature is only 1–1.5°C higher than the room temperature, the animals are lethargic, they do not open their eyes during manipulations, and the frequency of breaths is 4–6 per minute. These observations suggest that ground squirrels living in natural conditions also fall into a similar hibernation, since the proportion of overwintered males and females among the individuals caught in the middle of summer is decreased. The appearance of deformations at this time seems to be associated with a violation of the normal growth of the incisors during physiological changes in the body, these being caused by the onset of a transition from the active nutrition of plant food to endogenous consumption of fat reserves characteristic of the state of hibernation. The record of autumn-winter hibernation is characterized by very narrow increments or deformations, a change in the enamel boundary, as well as a change in the contour of the incisor surface. After spring awakening, growths are at first narrow and distinct, 150–160 µm each, subsequently increasing in width, which is probably due to a gradual transition from endogenous nutrition of the body with fat deposits during hibernation to intensive nutrition of green vegetation. Lactation of females usually does not affect daily gains.

Competition is known to render significant impacts both on population dynamics and community structure. As it has traditionally been believed, Dryophytes japonicus larvae inhibit Bombina orientalis larvae when cohabiting. The study is devoted to the study of the influence of these species on the development of each other in experimental conditions. The larvae were grown before metamorphosis in three variants: with single maintenance, together with conspecifics at different densities, as well as with the joint maintenance of individuals of the two species. When kept alone, B. orientalis larvae, in comparison with D. japonicus, are characterized by a higher survival rate (100% vs. 85%), a shorter duration of larval development and a longer body length of individuals during the period of metamorphosis. With an increase in the duration of larval development, the size of D. japonicus juveniles is increased. There are no differences in survival rate when growing larvae of each species at different densities. The duration of larval development varied significantly in different experimental groups. In both species, the duration of development correlated with the initial density per unit volume of water and per unit area of the bottom. With increasing density, the length and mass of the larvae are decreased. The bottom area renders a greater impact on the duration of larval development, as well as the length and body weight of B. orientalis juveniles than the volume of water. According to the results of regression analysis, with an increase in the initial planting density of B. orientalis by 100 specimens per square mof the bottom, the duration of larval development was increased by 4.7 days, the body length decreased by 0.83 mm, and the weight dropped by 0.06 g. The volume of water has a greater influence on the same indicators of larval development of D. japonicus. With an increase in the initial density by 1 specimen per water liter, the duration of larval development of D. japonicus was increased by 11.7 days, the body length decreased by 0.37 mm, and the weight dropped by 0.07 g. When the larvae of the two species were grown together with an increased proportion of one of them, a negative impact was observed neither on the survival nor the development, nor the growth of the other species. On the contrary, with an increased number of conspecifics in the container due to a decrease in the number of individuals of the other species, the development and growth of larvae of the former species was inhibited. Thus, in the laboratory conditions, no noticeable interspecific competition was observed between the larvae of B. orientalis and D. japonicus. The authors suggest that a successful coexistence of these two species is associated with pronounced intraspecific competition in each of them, this previously noted for other animal taxa.

Using SEM and morphometry, the fine structure of guard hairs and the elements of their medulla were compared in the Lena horse (Equus lenensis) and the domestic horse (E. caballus caballus) of five breeds. A number of features of hair fine structures have been identified, most clearly revealed when comparing horses of the northern (Mezen, Pechora, Yakut) and southern (Arabian, Akhal-Teke) groups of breeds. Seasonal changes in the structure of hair in horses of northern breeds (thickening of the hair medulla and an increase in the volume of its air cavities) indicate an increase in the heat-protecting properties of wool in winter, this being of adaptive significance. Both Pleistocene and recent domestic horses are shown to have developed convergent morphological adaptations of wool to low air temperatures.