Aerobic capacities in the skeletal muscles of Weddell seals: key to longer dive durations?
2002
SUMMARY In contrast to terrestrial animals that function under hypoxic conditions
but display the typical exercise response of increasing ventilation and
cardiac output, marine mammals exercise under a different form of hypoxic
stress. They function for the duration of a dive under progressive asphyxia,
which is the combination of increasing hypoxia, hypercapnia and acidosis. Our
previous studies on short-duration, shallow divers found marked adaptations in
their skeletal muscles, which culminated in enhanced aerobic capacities that
are similar to those of atheltic terrestrial mammals. The purpose of the
present study was to assess the aerobic capacity of skeletal muscles from
long-duration divers. Swimming and non-swimming muscles were collected from
adult Weddell seals, Leptonychotes weddelli , and processed for
morphometric analysis, enzymology, myoglobin concentrations and fiber-type
distribution. The results showed that the skeletal muscles of Weddell seals do
not have enhanced aerobic capacities compared with those of terrestrial
mammals but are adapted to maintain low levels of an aerobic lipid-based
metabolism, especially under the hypoxic conditions associated with diving.
The lower aerobic capacity of Weddell seal muscle as compared with that of
shorter-duration divers appears to reflect their energy-conserving modes of
locomotion, which enable longer and deeper dives.
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