Metabolic characteristics of the gray seal (Halichoerus grypus Fabricius, 1791) in early postnatal development

Abstract

Two breeding colonies of the gray seal ( Halichoerus grypus Fabricius, 1791) are situated in the Murman coastal area, one (western) on the Ainov Islands and the other one (eastern) on the Seven Islands Archipelago [1]. The interest to these colonies is determined by their location in the vicinity of the northeastern boundary of the modern range of the gray seal, where the adaptive potential of this species is most pronounced. The first studies of the biochemical status of the gray seal from the Murman colonies were performed by the Murmansk Marine Biological Institute, Kola Research Center, Russian Academy of Sciences, in 1991. Studies performed later are fragmentary. However, these studies are of great importance for elucidating the general and particular mechanisms of adaptation of marine animals, which determine the distribution and possibility of their habitation under various environmental conditions. In addition, such studies make it possible to predict the fate of a given population if the environmental conditions change [2]. The early stages of animal development are of particular importance, because the structural and functional systems of the organism are formed at this time. In view of above, the goal of this study was to investigate the metabolism of gray seal pups in the period from birth to the beginning of independent feeding. Data for this study were collected during an expedition to the Ainov Islands at the end of 2006. The animals were divided into three groups depending on their developmental stage, which in early postnatal period is determined by the feeding type: the newborns ( n = 6), the pups actively feeding on breast milk ( n = 12), and the pups that finished milk feeding ( n = 8). To obtain an integrated notion on the development of metabolic and immunological adaptations in relation to the feeding type, we also used our earlier data ( n = 6) on the blood composition of gray seal pups that survived starvation after the end of milk feeding (this stage is characteristic of pinnipeds, in contrast to terrestrial mammals) and started autonomous feeding on fish. Blood samples were taken from the extradural vein [3]. Blood plasma was tested for the main parameters of protein, lipid, carbohydrate, and mineral metabolism using the conventional laboratory techniques [4]. The results of this study are summarized in the table. The biochemical composition of blood of newborns reflects the adaptations related to birth, when the flow of nutrients with mother’s blood is stopped. A characteristic feature of this period is an extremely low concentration of glucose, the key energy substrate. At the end of milk feeding, when the fat contained in breast milk is used as the major source of energy, the concentration of glucose decreases more than three times. The level of glucose in the blood of seals begins to increase at an age of 1.5‐2 months [5] and significantly (more than eight times) increases when seals begin to feed autonomously, apparently due to the onset of gluconeogenesis. The characteristic features of the chemical composition of blood plasma of newborn animals are also a low urea concentration, a high activity of γ -glutamyltransferase, and a low activity of alkaline phosphatase. In the majority of marine mammals, whose diet is rich in protein and fat, the concentration of urea in blood plasma is normally higher than in terrestrial mammals [6]. Such data were reported for the harp [7, 8], harbour [9], and ringed [10] seals. In newborn gray seals, this parameter amounts to only 3.55 ± 0.94 mM, which is several time smaller than in 1.5- to 2-month-old pups. Such a low content of urea in blood of newborns is characteristic of all mammals and reflects, as mentioned above, the adaptations of animals associated with birth. Urea appears in blood at high concentrations during intensive degradation of proteins. The metabolic strategy of young animals consists in the prevalence of