Ephemera have the misfortune of experiencing the shortest breeding season in the world of insects, but as if that were not enough, 10% of males of the species Baetis bicaudatus suffer the torments caused by a small worm nematode ( Gasteromermis ) which radically modifies the behavior of male ephemera, rendering them sterile and obliging them to adopt a typically feminine behavior.
Outdoors, the infected males look exactly like females: the parasite, during the development of its host, modifies its morphological characteristics, so that it can not be distinguished from the complementary genus. But internally, infected males do not produce eggs and do not have the internal organs of females.
In addition to this, Gasteromermis also modifies the behavior of infected males. While uninfected males will form breeding swarms and never return to the water that gave birth to them, parasitized males, like their half, return to water by adopting the behavior of females laying their eggs. The larvae of nematodes perforate the ephemeral abdomen and sink into the water where they can parasitize new hosts. Well, anyway, the poor males would not have lived very long , but still.
And the case is not unique: localized on two small islands of Japan ( Tanegashima Island and Okinawa Island ), the larvae destined to become males of the Eurema mandarina species can be infected by the queens of the sex change, the bacteria of the genus Wolbachia .
These bacteria possess powerful mechanisms of regulation of the genus or the reproduction in their hosts:
In the species of Armadillidium vulgare , they transform males into females, not only in appearance and behavior, but also in functionality! Trans males in spite of themselves can be fertilized and give birth to offspring.
In the ephemeral species Eurema mandarina , they induce parthogenesis by forcing the females to reproduce without the intervention of a male, giving birth only to cloned and infected females (males not spreading Wolbachia , which is transmitted by the cytoplasm).
In other cases, like ladybugs, Wolbachia will simply kill male larvae, increasing the chances of survival and thus the number of females.
Finally, Wolbachia strains may involuntarily cooperate to control the host population by preventing infected males from infecting females infected with another strain (cytoplasmic incompatibility).