Morphology of sweat glands in the skin of Saimaa (Pusa hispida saimensis) and Baltic ringed (Pusa hispida botnica) seals

The endangered Saimaa ringed seal (Pusa hispida saimensis) is an endemic freshwater subspecies inhabiting Lake Saimaa in Finland. The Baltic ringed seal (Pusa hispida botnica) inhabits the brackish Baltic Sea, which is almost entirely landlocked. Recent research shows that Saimaa and Baltic ringed seals may be genetically even further apart from each other than from other ringed seal subspecies. We documented histologically the integument microstructure of Saimaa and Baltic ringed seals to determine whether the geographic and genetic isolation was manifested as variation in the integument microstructure of these subspecies adapted to icy aquatic environments. The skin structures of these subspecies were similar to those of other phocids. The association of the sweat glands with hair follicles in both subspecies suggested that they were small apocrine sweat glands described previously in terrestrial or aquatic mammals. None of the apocrine glands had large lumina, and some of the ducts were relatively straight and short. Further studies analysing the mode of secretion, for example, apocrine versus eccrine, in the sweat glands are necessary to confirm the types of sweat glands in seals.