Friday, August 27, 2010
One of the most spectacular migrations on Earth is that of the
Christmas Island red crab (Gecarcoidea
natalis). Acknowledged as one of the wonders of the natural
world, every year millions of the crabs simultaneously embark on a
five-kilometre breeding migration. Now, scientists have discovered
the key to their remarkable athletic feat.
A three-year project conducted by a team led by the late Professor
Steve Morris from the University of Bristol's School of Biological
Sciences in collaboration with Professor Simon Webster from Bangor
University, has discovered that hormonal changes play a significant
role in enabling the crabs to make their journey.
Lucy Turner, a researcher at the University of Bristol, said:
"During the wet season on the island, in November or December, and
prompted by the arrival of the monsoon rains, millions of the crabs
undertake an arduous breeding migration from their home on the high
rainforest plateau to the ocean to reproduce. This is a journey of
several kilometres - a long way when you are a relatively small
land crab (less than 20cm long).
"Scientists have long been puzzled by what mechanisms enable the
necessary changes to take place in the crabs' physiology to allow
this journey to take place, and how they make such a dramatic
switch from hypoactivity to hyperactivity."
The results of this project have proven that it is a Crustacean
Hyperglycaemic Hormone (CHH) that enables the crabs to make the
most efficient use of their stored energy in the muscles (glycogen)
and its conversion to glucose to fuel the migration.
Professor Webster, an endocrinologist at Bangor University, added:
"Their migration is extremely energetically demanding, since the
crabs must walk several kilometres over a few days. During the
non-migratory period, the crabs are relatively inactive and stay in
their burrows on the floor of the rain forest, only emerging for a
brief period at dawn, to feed. The behaviour change reflects a
fundamental change in the metabolic status of the animal.
"Surprisingly, we found that hyperglycaemic hormone levels were
lower in actively migrating crabs than those that were inactive
during the dry season. However, studying the crabs running and
walking after giving them glucose resolved the puzzle. During the
dry season, forced activity resulted in a tremendous release of
hormone, within two minutes, irrespective of whether glucose had
been administered. However, in the wet season, the glucose
completely prevented the release of the exercise-dependent hormone,
showing that they were controlled by a negative feedback
loop.
"Glucose levels were clearly regulating hormone release at this
time. This made sense since it ensures that during migration,
glucose is only released from glycogen stores when glucose levels
are low, using the crabs' precious reserves of glycogen, to ensure
that they can complete the migration."
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Thanks to University of Bristol for this
article.