Parasitic castration is the strategy, by a parasite, of blocking reproduction by its host, completely or in part. For example, Hemioniscus balani

Hemioniscus balani

Hemioniscus balani is a species of isopod crustacean that is a widespread parasitic castrator of barnacles in the north Atlantic Ocean. Its range extends from Norway to the Atlantic coast of France, and as far west as Massachusetts.-Life history:H...

, a parasitic castrator of hermaphroditic barnacle

Barnacle

A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...

s, feeds on ovarian fluid, so that its host loses female reproductive ability but still can function as a male. This would be a case of direct parasitic castration (feeding on host gonad

Gonad

The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...

s). Indirect strategies are also seen such as diverting host energy from gonad development or secreting castrating hormone

Hormone

A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

s.

The parasitic castration strategy is used by some larval trematode parasites of snail

Snail

Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...

s and some isopod

Isopoda

Isopods are an order of peracarid crustaceans, including familiar animals such as woodlice and pill bugs. The name Isopoda derives from the Greek roots and...

 and barnacle

Barnacle

A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...

 parasites of crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s. For example, 18 species of trematodes are known to parasitically castrate the California horn snail, Cerithidea californica

Cerithidea californica

Cerithidea californica, common name the California hornsnail or the California horn snail, is a species of sea snail, a marine gastropod mollusk in the family Potamididae.-Distribution:...

.

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 gonad

Gonad

The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...

s and gamete

Gamete

A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...

s 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.

The evolutionary pressure of parasitic castrators on a potential host population is in the direction of resistance to being infected rather than on post-infection recovery. Once fertility has been lost or reduced, the host gains much less evolutionary advantage by surviving the parasite than it would have by avoiding it.

Once the host's reproductive ability is lost, any future changes in host behavior cannot benefit the host's reproductive fitness but may benefit the parasite's. Several cases have been described where infection with a parasitic castrator causes the host to change its behavior in ways that benefit the parasite.

Parasitic castrators and parasitoids

The parasitoid

Parasitoid

A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...

 strategy, which results in the death of the host, has many similarities to the parasitic castration strategy, which results in the reproductive death of the host. For example, both parasitoids and parasitic castrators tend to be similar to their host in size, whereas most non-castrating parasites are many orders of magnitude smaller than the host. In both strategies, an infected host is much less hospitable to new parasites than an uninfected one.

Examples of parasitic castrators

Parasite	Host	Remarks
Protist Protist Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...  Sporozoa Mackinnonia tubificis	Annelid Annelid The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...  Oligochaete Tubifex tubifex	Destroys gonad
Protist Protist Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...  Haplosporidia Urosporidium charletti	Cestoda Cestoda This article describes the flatworm. For the medical condition, see Tapeworm infection.Cestoda is the name given to a class of parasitic flatworms, commonly called tapeworms, of the phylum Platyhelminthes. Its members live in the digestive tract of vertebrates as adults, and often in the bodies...  Catenotaenia dendritica	"Hypercastrator" (a hyperparasite Hyperparasite A hyperparasite is a parasite whose host is a parasite. This form of parasitism is especially common among entomophagous parasites....  that castrates the parasite it parasitizes)
Platyhelminthes Trematoda Trematoda Trematoda is a class within the phylum Platyhelminthes that contains two groups of parasitic flatworms, commonly referred to as "flukes".-Taxonomy and biodiversity:...  Bucephalus mytili Bucephalus mytili Bucephalus mytili is a parasitic flatworm of the class Trematoda. It is a parasite of fish and a parasitic castrator of the mussel Mytilus edulis, where it destroys the mussel's gonads and causes the mussel to grow much larger than normal....	Mollusca Mollusca The Mollusca , common name molluscs or mollusksSpelled mollusks in the USA, see reasons given in Rosenberg's ; for the spelling mollusc see the reasons given by , is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest...  Bivalvia Bivalvia Bivalvia is a taxonomic class of marine and freshwater molluscs. This class includes clams, oysters, mussels, scallops, and many other families of molluscs that have two hinged shells...	Destroys gonad, host grows larger
Platyhelminthes Cestoda Cestoda This article describes the flatworm. For the medical condition, see Tapeworm infection.Cestoda is the name given to a class of parasitic flatworms, commonly called tapeworms, of the phylum Platyhelminthes. Its members live in the digestive tract of vertebrates as adults, and often in the bodies...	Pisces Pisces Pisces may refer to:*Pisces , a constellation*Pisces , an astrological sign*Fish , as an obsolete taxonomic term*OZ-09MMS Pisces, a fictional mecha in the Gundam Wing anime...  Cyprinidae	Destroys gonad, behavioral changes
Arthropoda Isopoda Isopoda Isopods are an order of peracarid crustaceans, including familiar animals such as woodlice and pill bugs. The name Isopoda derives from the Greek roots and...  Hemioniscus balani Hemioniscus balani Hemioniscus balani is a species of isopod crustacean that is a widespread parasitic castrator of barnacles in the north Atlantic Ocean. Its range extends from Norway to the Atlantic coast of France, and as far west as Massachusetts.-Life history:H...	Arthropoda Cirripedia barnacles	Drains ovarian fluid of hermaphrodite, but spares male function
Arthropoda Cirripedia Sacculina Sacculina Sacculina is a genus of barnacles that is a parasitic castrator of crabs. The adults bear no resemblance to the barnacles that cover ships and piers; they are recognised as barnacles because their larval forms are like other members of the barnacle class Cirripedia...	Arthropoda Decapoda Decapoda The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...  crabs	Destroys gonad, behavioral changes
Arthropoda Strepsiptera Strepsiptera The Strepsiptera are an order of insects with ten families making up about 600 species...	Arthropoda Hymenoptera Hymenoptera Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...  or Hemiptera Hemiptera Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...	Males feminized, females produce no eggs but instead disperse eggs of parasite