Parasitic castration


Parasitic castration is the strategy, by a parasite, of blocking reproduction by its host, completely or in part, to its own benefit. This is one of six major strategies within parasitism.
For example, Hemioniscus balani, a parasitic castrator of hermaphroditic barnacles, feeds on ovarian fluid, so that its host loses female reproductive ability but still can function as a male. This is a case of direct parasitic castration. Indirect strategies are also seen such as diverting host energy from gonad development or secreting castrating hormones.
The parasitic castration strategy is used by some larval trematode parasites of snails and some isopod and barnacle parasites of crustaceans. For example, 18 species of trematodes are known to parasitically castrate the California horn snail, Cerithidea californica.

Evolutionary considerations

A parasite that ends the reproductive life of its host theoretically liberates a significant fraction of the host's resources, which can now be used to benefit the parasite. Lafferty points out that the fraction of intact host energy spent on reproduction includes not just gonads and gametes but also secondary sexual characteristics, mate-seeking behavior, competition, and care for offspring. Poulin suggests that prolonged host life may also result from parasitic castration, benefiting the parasite.

Parasitic castrators and parasitoids

The parasitic castration strategy, which results in the reproductive death of the host, can be compared with the parasitoid strategy, which results in the host's death. Both parasitoids and parasitic castrators tend to be similar to their host in size, whereas most non-castrating parasites are orders of magnitude smaller than the host. In both strategies, an infected host is much less hospitable to new parasites than an uninfected one.

Taxonomic range