Can Crab Claws Be Used For Thermoregulation

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Can Crab Claws Be Used For Thermoregulation? Jason
Bishop (Advisor Mary Crowe crowe_at_coastal.edu) De
partment of Biology Coastal Carolina University
Introduction Fiddler crabs (Uca pugilator)
like all ectotherms behaviorally and
physiologically thermoregulate. The ability to
thermoregulate influences many processes, like
metabolism, digestion and enzyme activities.
Previous studies show that male fiddler crabs use
their enlarged cheliped to attract mates and
defend territories. Given that this cheliped can
comprise up to 48 of the crabs mass and 40 of
the crabs surface area, we were interested in
determining if this claw could also have a
thermoregulatory role. If this were true male
fiddler crabs with larger chelipeds may be able
to regulate their Tb more effectively than crabs
with smaller ones. Size and shape have been
shown to influence thermoregulatory abilities in
other species.
Could a claw be used in thermoregulation? To
determine if the large cheliped of U. pugilator
is used for thermoregulation, ice was used to
lower the claw temperature while observing the
change in Tb (n20). During testing crabs were
restrained on a metal rod using plastic tie
downs. The posterior leg furthest from the major
cheliped was removed and a thermocouple was
inserted into the body cavity of the crab. The
crab was allowed to stabilize for 10-min. The
major cheliped was then immersed in an ice bath
for 20 minutes. The ice was then removed and we
continued monitoring Tb for an additional 10-min.
A separate control groups whose claw was not
submerged in ice was also tested (n10).
Discussion Our results show that the thermal
conditions experienced by the claw is capable of
influencing Tb. We realize that fiddler crabs in
the field are likely to have their body and claw
experience the same Te . However, our study was
an important first step to documenting that the
enlarged cheliped may in fact serve another
function, thermoregulation. Field studies have
documented that male crabs Tb fluctuate less
severely than that of females. This may be a
result of the enlarged cheliped modulating heat
exchange. This study did not examine the mode of
heat transfer from the claw to the body. Heat
may simply be transferred by conduction or there
could be physiological mechanisms involved.
Comparing this data to the thermal attributes of
a model or freshly dead crabs could help to
determine if there are any physiological
mechanisms at work.
Determining Body Temperature (Tb) To determine
the best location to measure Tb several
thermocouples were attached to various locations
on eight ghost crabs (Ocypode quadrata). One
thermocouple was attached on the surface of the
back, one in the claw, and one in the body.
Temperatures were recorded for 30-min or until a
thermocouple ceased to function. The average
difference in temperature between the body and
claw was found to be 0.2124 oC. We decided
future experiments would only use the internal
body position for temperature determination
because in the field it would be less quickly
affected by wind, solar radiation than an
external sensor.
Special thanks to Amanda Windsor for valuable
input and help building thermocouples. Thanks to
the Brodie and Helmuth labs at USC for
stimulating discussion and ideas.
Relevant literature Crane, 1975 Fiddler crabs
of the world, Ocypodidae genus Uca. Princeton,
N.J. Helmuth 1998 Ecol. Monogr. 68, 29-52
Pope 1998. Behav. Ecol. Sociobiol. 47,
432-437. ,Porter et al 1973. Oecologia 13, 1-54