Sexually mediated shedding of Myxobolus fallax spores during spermiation of Litoria fallax (anura).

Myxobolus fallax (Myxosporea) infects the testes of the dwarf green tree frog Litoria fallax without apparently affecting the host's health, behavior, or testicular sperm numbers or quality. We investigated the shedding M. fallax spores and the relationship between M. fallax infection and fertility in L. fallax. During natural spawning, comparisons were made between the prevalence and intensity of M. fallax infection, spore shedding, and fertilization rates. During the hormonal induction of spermiation, comparisons were made between the prevalence and intensity of M. fallax infection, and the number of sperm and spores shed. During natural spawning, the prevalence or intensity of infection or spore shedding did not affect fertility. Spermiation and spore shedding was induced in 10 males by the administration of human chorionic gonadotrophin, with 10 controls. Histology showed that all 10 males were infected by M. fallax. The controls shed no sperm or spores. Nine infected males shed sperm 3 h post-administration (PA), and 3 of these also shed spores. Only the 3 males that shed sperm and spores at 3 h PA also shed sperm at 6 h PA, at which time they also shed spores. In total, the 3 males that shed spores gave higher sperm numbers than the 6 males that did not shed spores. Overall, these results show that the shedding of M. fallax spores is sexually mediated through reproductive hormones without affecting fertility.