Parasitic castration is the strategy, by a

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

, 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 mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...

s and

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

s but also

secondary sexual characteristic Secondary sex characteristics are features that appear during puberty in humans, and at sexual maturity in other animals. These characteristics are particularly evident in the sexual dimorphism, sexually dimorphic phenotypic traits that distinguis ...

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 ( el, γίγας, ''gígas'', "giant", plural γίγαντες, ''gígantes''), also known as giantism, is a condition characterized by excessive growth and height significantly above average. In humans, this condition is caused by ove ...

. 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 In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have s ...

barnacles 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 Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...

s. The parasitic castration strategy is used by some larval

trematode Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host ...

parasites of

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

s and some isopod and barnacle parasites of

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s. For example, 18 species of trematodes parasitically castrate the California horn snail, ''

Cerithidea californica ''Cerithideopsis californica'', common name the California hornsnail

''. 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 processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...

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 natural capability to pr ...

fertility Fertility is the capability to produce offspring through reproduction following the onset of sexual maturity. The fertility rate is the average number of children born by a female during her lifetime and is quantified demographically. Fertili ...

, or

parasitoids In evolutionary ecology, a parasitoid is an organism that lives in close association with its host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionary strategies within parasi ...

that may consume reproductive organs first.

Taxonomic range

References

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