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Blood viscosity in phocid seals: possible adaptations to diving
L L Wickham1, R Elsner, F C White
1Institute of Marine Science, University of Alaska, Fairbanks 99775.
Summary
Phocid seal red blood cells have higher oxygen-carrying capacity and lower blood viscosity than pigs. This unique blood composition is an adaptation for prolonged dives, facilitating circulatory redistribution.
Area of Science:
- Comparative physiology
- Marine mammal adaptation
- Hematology
Background:
- Phocid seals exhibit distinct red blood cell (RBC) characteristics, including elevated mean corpuscular volume (MCV) and mean corpuscular hemoglobin concentration (MCHC), compared to terrestrial mammals.
- Understanding how these RBC traits influence blood flow dynamics is crucial for comprehending physiological adaptations in marine mammals.
Purpose of the Study:
- To compare the blood viscosity (VIS) and RBC morphology of phocid seals (harbor and northern elephant seals) with domestic pigs.
- To investigate the relationship between RBC indices (MCV, MCHC, hematocrit) and blood viscosity in these species.
- To explore the functional significance of seal RBC characteristics in the context of diving physiology.
Main Methods:
- Blood samples from harbor seals, northern elephant seals, and domestic pigs were analyzed for RBC count, WBC count, total plasma proteins, hematocrit (HCT), MCV, and MCHC.
- Whole blood viscosity measurements were performed using a Wells-Brookfield cone-plate viscometer at 37°C across a range of shear rates (11.5–230.4 s⁻¹).
- Pig blood was reconstituted to match seal hematocrit levels for comparative viscosity analysis.
Main Results:
- Phocid seals displayed significantly higher HCT, MCV, and MCHC values compared to domestic pigs.
- Seal blood exhibited lower viscosity (28% less for harbor seals, 16% less for elephant seals) than pig blood at low shear rates, despite comparable HCT.
- Seal RBCs were larger, fewer in number, and carried more hemoglobin per unit volume, contributing to elevated oxygen storage capacity.
Conclusions:
- The unique RBC morphology of phocid seals, characterized by larger cells and higher MCHC, results in reduced blood viscosity and flow resistance.
- This adaptation, coupled with enhanced oxygen-carrying capacity, is likely crucial for efficient circulation and oxygen delivery during prolonged diving.
- The findings suggest a specialized adaptation of phocid seal blood rheology to support physiological demands during deep-sea foraging.