Integument in Antarctic seals: A comparative study and its relation to extreme environments

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.

Immunolabeling for filaggrin and acidic keratins in the granular layer of mammalian epidermis indicates that an acidic-basic interaction is involved in cornification

The soft epidermis of mammals derives from the accumulation of keratohyaline granules in the granular layer, before maturing into corneocytes. Main proteins accumulated in the granular layer are pro-filaggrin and filaggrin that determine keratin clumping and later moisturization of the stratum corneum that remains flexible. This soft epidermis allows the high sensitivity of mammalian skin. Presence and thickness of the stratum granulosum varies among different species of mammals and even between different body regions of the same animal, from discontinuous to multilayered. These variations are evident using antibodies for filaggrin, a large protein that share common epitopes among placentals. Here we have utilized filaggrin antibodies (8959 and 466) and an acidic keratin antibody (AK2) for labeling placental, marsupial and monotreme epidermis. AK2 labeling appears mainly to detect K24 keratin, and less likely other acidic keratins. Immunoreactivity for filaggrin is absent in platypus, discontinuous in Echidna and in the tested marsupials. In placentals, it is inconstantly or hardly detected in the thin epidermis of bat, rodents, and lagomorphs with a narrow, mono-stratified and/or discontinuous granular layer. In contrast, where the granular layer is continuous or even stratified, both filaggrin and AK2 antibodies decorate granular cells. The ultrastructural analysis using the AK2 antibody on human epidermis reveals that a weak labeling is associated with keratohyalin granules and filamentous keratins of transitional keratinocytes and corneocytes. This observation suggests that basophilic filaggrin interacts with acidic keratins like K24 and determines keratin condensation into corneocytes of the stratum corneum.

Conditions influencing the appearance of thermal windows and the distribution of surface temperature in hauled-out southern elephant seals

Pinnipeds (true seals, sea lions and walruses) inhabit two thermally different environments, air and water, so need to make continuous adjustments to maintain a balanced body temperature. The thermal isolation properties of thick blubber keep warmth within the body's core, ideal for mammals while in the water; however, when on land, this thick blubber makes it difficult to lose heat. Some pinnipeds use thermal windows, discrete patches where temperature changes on their body surface, as a mechanism to dissipate excessive heat. We identify the factors that correlate with the appearance of thermal windows and changes in body surface temperature on southern elephant seals, Mirounga leonina, while they are hauled out ashore. Infrared thermography was used to measure surface temperature of the seals. Temperature was lower on the torso than the flippers and head, suggesting that not all body sites have the same role in thermal balance. Air temperature was the main driver of variation in the surface temperature of the seals' flippers and head; seals cool their superficial tissues when the air temperature is below ~ 2°C. This minimizes heat loss by reducing the thermal gradient between their skin and the ambient air. Wind speed was the main predictor of whether thermal windows appear on a seals' body surface. When wind speed was minimal, thermal windows occurred more often, which may be associated with either hair and skin drying, or producing thermal conditions for hair and skin regrowth. The type of aggregation (huddled or alone) influenced the surface temperature of the fore flippers; however, we did not find statistical influence of the seal's sex, state of moult, or the substrate on which they were hauled out (kelp or sand). Understanding how animals maintain their thermal balance is important if we are to predict how they will respond to future climate change.

Thermoregulatory costs in molting Antarctic Weddell seals: impacts of physiological and environmental conditions: Themed Issue Article: Conservation of Southern Hemisphere Mammals in a Changing World

For polar marine mammals, the energetic cost of thermoregulation depends on ambient conditions in the highly variable surrounding environment. Heat conservation strategies used by pinnipeds to reduce total heat loss include small surface area to volume ratios, the ability to limit perfusion and thick subcutaneous blubber layers. There are limits to how cool the skin surface may remain without compromising function, especially during the annual pelage molt, when hair and skin are replaced. To determine if actively molting seals incur higher thermoregulatory costs, surface temperature (ST) and heat flux (HF) were measured in 93 adult female Weddell seals (Leptonychotes weddellii) both prior to and during the active molting period using direct sensors and infrared imaging. Linear mixed-effect models revealed that ST increased significantly with increased ambient temperature and decreased wind speed (contributing 44.6 and 41.7% of the attributed variance, respectively). Seal STs were not impacted by molt status, but were maintained at 11.2 ± 0.3°C warmer than the ambient temperature. Infrared imaging results averaged 15.1 ± 1.4°C warmer than direct ST measurements. In contrast, HF was significantly higher in seals in early molting stages compared to the pre-molt season ( P < 0.001) and molt status accounted for 66.5% of the variance in HF. Thermoregulatory costs calculated from estimated basal metabolic rate and measured HF were more than double for molting seals as compared to those in pre-molt. This suggests that perfusion is increased during molt to support follicle development, despite the increased energetic costs associated with higher HF rates. Because ST, HF and thermoregulatory costs are strongly influenced by ambient conditions, molt timing is likely under selective pressure to occur during the warmest period of the year. Shifts in environmental conditions that delay molt phenology or increase HF rates could negatively impact seal populations by further increasing thermoregulatory costs.

Adaptations to a semiaquatic lifestyle in the external ear of southern pinnipeds (Otariidae and Phocidae, Carnivora): Morphological evidences

Pinnipeds are semiaquatic carnivorans that spend most of their lives in water and use coastal terrestrial, or ice pack, environments to breed, molt and rest. Certain characteristics of the ear have been linked to ecological aspects. In our contribution we focus on the study of the macroscopic and microscopic morphology of the external ear (with the exception of the osseous outer ear canal) of six species of Southern pinnipeds. In order to recognize the different components of tissues, sections were stained following several routine protocols. In addition, double-staining and enzymatic clearing (Alcian blue-alizarin red) was performed to assess the arrangement of skeletal elements in the OEC. The basic structure of the pinna in the southern otariids studied match those previously analyzed for Northern Hemisphere species. The cartilage macro anatomy of the OEC of Mirounga leonina and Arctocephallus gazella is different from that of the Northern Hemisphere species, with only one plate of cartilage, but markedly different between them. The histology of the otariids OEC is homogeneous along the entire extension, but phocids has three different regions (distal, middle, and proximal). The cartilage histology of most phocids is also different from that of analyzed otariids, with an elastic cartilage that resembles a myxoid-like tissue, but is not present in M. leonina, were the tissue around the OEC is very rich in adipocytes. The southern elephant seal M. leonina OEC has a combination of features similar to both the rest of the phocids and to the otariids. An auditory organ that is functional both over and under water could be essential for social behavior in these species.