Infection by the Microsporidian Octosporea effeminans sp. n., and Its Sex Determining Influence in the Amphipod Gammarus duebeni

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Abstract
Life cycle, taxonomy, host specificity, and host-parasite relationships of a new microsporidian species, O. effeminans, living in the crustacean Gammarus duebeni, are described. This species has been found in the cells of ovarian tissue (oocytes, follicle cells, and connective ovarian tissue). It does not occur in males, although the testicular tissue is suitable for its development, as shown in inter-sexes, in which hermaphroditic gonads may be developed. In these individuals, in addition to the ovarian tissue, large mucus-producing cells surrounding the testicular tubes, and the cytoplasm of spermato-cytes and spermatids can be infected. The microsporidian is transmitted transovarially and has a sex determining influence on the offspring of infected females, as all infected eggs develop into females only and occasionally into intersexes. The infection is mild and causes no pathogenic effects on the tissues and cells of the host. The host-parasite relationship is well balanced as the infection does not influence any vital functions of the amphipod. On the other hand, it is supposed that the parasite may exert an adverse effect on the sex ratio of populations living in closed habitats; by gradually increasing parasitism the percentage of females may grow to such a level that the population will suffer from a lack of males for fertilizing the eggs. Some geneal aspects of this hereditary infection[long dash]previously known as a case of plasmatic inheritance[long dash]are considered. Possible mechanisms of the influence of the microsporidians on the differentiation of sex are outlined. A suppression of the development of the androgenic gland, stimulating sex differentiation to males by producing a sex hormone, is assumed to be responsible for this aberrant sex ratio.