Geographic Variation in Camouflage Specialization by a Decorator Crab
Author(s)
Stachowicz, John J.
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Abstract
In North Carolina, the decorator crab Libinia dubia camouflages
almost exclusively with the chemically noxious alga Dictyota
menstrualis. By placing this alga on its carapace, the crab behaviorally
sequesters the defensive chemicals of the plant and gains protection
from omnivorous consumers. However, Dictyota is absent north of
North Carolina, whereas Libinia occurs as far north as New England.
Crabs from three northern locations where Dictyota is absent (Rhode
Island, Connecticut, and New Jersey) camouflaged to match their
environment, rather than selectively accumulating any one species.
When D. menstrualis was offered to crabs from northern sites, they
did not distinguish between it and other seaweeds for camouflage,
whereas crabs from Alabama and two locations in North Carolina
used D. menstrualis almost exclusively. In addition, in winter and
spring, when Dictyota was seasonally absent in North Carolina, Libinia
selectively camouflaged with the sun sponge Hymeniacidon heliophila,
which was chemically unpalatable to local fishes. Thus,
southern crabs were consistent specialists on chemically defended
species for camouflage, while northern crabs were more generalized.
The geographic shift in crab behavior away from specialization coincides
with a reported decrease in both total predation pressure and
the frequency of omnivorous consumers. These shifts in the nature
and intensity of predation pressure may favor different camouflage
strategies (generalist vs. specialist), contributing to the observed geographic
differences in camouflage behavior.
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Date
2000-07
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Article