Ontogenetic changes in tracheal structure facilitate deep dives and cold water foraging in adult leatherback sea turtles
2009
SUMMARY Adult leatherbacks are large animals (300–500 kg), overlapping in
size with marine pinniped and cetacean species. Unlike marine mammals, they
start their aquatic life as 40–50 g hatchlings, so undergo a 10,000-fold
increase in body mass during independent existence. Hatchlings are limited to
the tropics and near-surface water. Adults, obligate predators on gelatinous
plankton, encounter cold water at depth (<1280 m) or high latitude and are
gigantotherms that maintain elevated core body temperatures in cold water.
This study shows that there are great ontogenetic changes in tracheal
structure related to diving and exposure to cold. Hatchling leatherbacks have
a conventional reptilian tracheal structure with circular cartilaginous rings
interspersed with extensive connective tissue. The adult trachea is an almost
continuous ellipsoidal cartilaginous tube composed of interlocking plates, and
will collapse easily in the upper part of the water column during dives, thus
avoiding pressure-related structural and physiological problems. It is lined
with an extensive, dense erectile vascular plexus that will warm and humidify
cold inspired air and possibly retain heat on expiration. A sub-luminal
lymphatic plexus is also present. Mammals and birds have independently evolved
nasal turbinates to fulfil such a respiratory thermocontrol function; for
them, turbinates are regarded as diagnostic of endothermy. This is the first
demonstration of a turbinate equivalent in a living reptile.
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