Parasitic castration is the strategy, by a

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

, of blocking reproduction by its host, completely or in part, to its own benefit. This is one of six major strategies within parasitism.

Evolutionary strategy

The parasitic castration strategy, which results in the reproductive death of the host, can be compared with the

parasitoid In evolutionary ecology, a parasitoid is an organism that lives in close association with its host (biology), host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionarily stable str ...

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. A

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. The fraction of intact host energy spent on reproduction includes not just

gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gon ...

s and

gamete A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as s ...

s but also

secondary sexual characteristic A secondary sex characteristic is a physical characteristic of an organism that is related to or derived from its sex, but not directly part of its reproductive system. In humans, these characteristics typically start to appear during puberty ...

s, mate-seeking behavior, competition, and care for offspring. Infected hosts may have a different appearance, lacking said sex characteristics and sometimes even devoting more energy to growth, resulting in

gigantism Gigantism (, ''gígas'', "wiktionary:giant, giant", plural γίγαντες, ''gígantes''), also known as giantism, is a condition characterized by excessive growth and height significantly above average height, average. In humans, this conditi ...

. The evolutionary parasitologist Robert Poulin suggests that parasitic castration may result in prolonged host life, benefiting the parasite. Parasitic castration may be direct, as in '' Hemioniscus balani'', a parasite of hermaphroditic

barnacle Barnacles are arthropods of the subclass (taxonomy), subclass Cirripedia in the subphylum Crustacean, Crustacea. They are related to crabs and lobsters, with similar Nauplius (larva), nauplius larvae. Barnacles are exclusively marine invertebra ...

s which feeds on ovarian fluid, so that its host loses female reproductive ability but still can function as a male. Parasitic castration may equally be indirect, as when a parasite diverts host energy from developing gonads or secretes castrating

hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...

s. The parasitic castration strategy is used by some larval

trematode Trematoda is a Class (biology), class of flatworms known as trematodes, and commonly as flukes. They are obligate parasite, obligate Endoparasites, internal parasites with a complex biological life cycle, life cycle requiring at least two Host ( ...

parasites of

snail A snail is a shelled gastropod. The name is most often applied to land snails, terrestrial molluscs, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gas ...

s and some

isopod Isopoda is an Order (biology), order of crustaceans. Members of this group are called isopods and include both Aquatic animal, aquatic species and Terrestrial animal, terrestrial species such as woodlice. All have rigid, segmented exoskeletons ...

and

parasites of

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s. For example, 18 species of trematodes parasitically castrate the California horn snail, '' Cerithidea californica''. Certain other effects of a parasite on its host may appear similar to parasitic castration, such as the host's

immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

diverting energy from reproduction in response to numerous parasites that singly would have no impact on

fecundity Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the capability to produc ...

fertility Fertility in colloquial terms refers the ability to have offspring. In demographic contexts, fertility refers to the actual production of offspring, rather than the physical capability to reproduce, which is termed fecundity. The fertility rate ...

, or parasitoids that may consume reproductive organs first.

Taxonomic range

References

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