Parasitic castration

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.

Infected hosts may have a different appearance, lacking said sex characteristics and sometimes even devoting more energy to growth, resulting in gigantism.

[4] Parasitic castration may be direct, as in Hemioniscus balani, a parasite of hermaphroditic barnacles which feeds on ovarian fluid, so that its host loses female reproductive ability but still can function as a male.

[3] For example, 18 species of trematodes parasitically castrate the California horn snail, Cerithidea californica.

[6] Certain other effects of a parasite on its host may appear similar to parasitic castration, such as the host's immune system diverting energy from reproduction in response to numerous parasites that singly would have no impact on fecundity or fertility, or parasitoids that may consume reproductive organs first.

Crab with egg sac of the parasitic barnacle Sacculina carcini . The parasite stops reproduction in its host, the crab, and stimulates the female crab to disperse parasite eggs with the same behavior that she would normally use for her own eggs. [ 1 ]