Introduction-
Sacculina carcini is a parasite that carries on a symbiotic relationship
with crabs [1]. This particular genus practices a form of parasitic castration
whereby hindering the reproductive ability of its host [2]. According to our
text, “Certain parasites appear to make an amazingly boneheaded move: they
castrate their hosts (as do many trematodes in mollusks and crustaceans in
other crustaceans) or they end up killing the host (most parasitoid insects
[3].” Unlike the parasites referred to by Combes, the parasite S. carcini only partially castrates their hosts enough to control
their sexual reproduction. It should also be noted, since crabs are found in a
variety of marine habitats, that the parasite is vastly allocated in terms of
global distribution. In regard to the ecological impact, the parasite prevents
the crabs from reproducing eggs other than that of the parasite. This may in
turn lead to the steady destruction of crab populations in certain parts of
marine habitats [4].
Symbiont Description-
Until S. carcini finds a crab to infect, it looks like a small slug
floating in the water [1]. The female parasite finds a break in the crab’s
protective outer covering, usually in the crab’s joint, and injects itself into
the crab [1]. The parasite will grow root-like structures inside the crab that
hinder the crab from reproducing anymore, and will continue its life gathering
nutrients for the eggs of the parasite [4].
Host Description-
The definitive host or the host where the parasite reaches
sexual maturity is the crab. The parasite, S.
carcini, has no intermediate hosts and thus has no acting vector
hosts [5]. The parasite only shares a relationship with one host, the crab, so
it is considered a holoxenous parasite. The host specificity of S. carcini helps it keep selective pressures on simply one host, and
there is then no need to adapt to different kinds of hosts [3].
Life Cycle-
The overall life cycle of S. carcini
is rather simple. First, a free-swimming
barnacle larva of the parasite finds a crab to inject its inner worm-like body
[2]. Next, the parasite makes root-like tentacles to obtain nutrients from the
host crab. Finally, after achieving the desired amount of nutrients, the
parasite is able to make its eggs, and the host crab will care for the
parasitic eggs as it were its very own fertilized eggs [2].
Ecology-
Initially, the consequences of
this interaction in nature do not seem terribly severe. However, the prevalence
of S. carcini is widespread since their
hosts, crabs, are found in most all marine habitats. Most of the crab
population is found in the marine habitats of China, Japan, and the United
States. Another fair amount of crabs can also be found in the Atlantic Ocean
around the United Kingdom [5]. Nearly half of certain crab populations are
infected with this parasite [2]. This continued infection could result in the
steady decrease of the crab population as a whole.
An example of regular parasite distribution-
References-
[2] Piper, Ross. Extraordinary
Animals: An Encyclopedia of Curious and Unusual Animals. Westport, CT: Greenwood, 2007.
[3] Combes, Claude. Parasitism: The Ecology and Evolution
of Intimate Interactions; Translated by Isaure De Buron and Vincent A. Connors;
with a New Foreword by Daniel Simberloff.
Chicago: University of Chicago, 2001.
[5] Zimmer, Carl. Parasite Rex: Inside the Bizarre World
of Nature's Most Dangerous Creatures.
London: Arrow, 2003.
