Sexual conditions in a population of the Polychaete Ophryotrocha labronica La Greca & Bacci from Naples

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Abstract
The sexual conditions of a strain of Ophryotrocha labronica from Naples were studied. Unlike the hermaphroditic Leghorn strain, the Naples strain is gonochoristic. Isolation and group isolation experiments, similar to those previously carried out by other writers on O.puerilis, demonstrated sexual stability in both males and females. The mean percentage of males is 31.6 ± 1.1 in the progeny of individual females and 31.8 ± 0.77 in populations made up from many egg masses. The sex ratio was not affected when newly released larvae were isolated individually, nor by the presence of adult males or females in the rearing bowls during the period of growth. There was a significant negative correlation between the number of eggs in the egg masses and the percentage of males, but no correlation between the population density in the bowls and the sex ratio. It is suggested that sex determination occurs during the early period of development and that the sex is stable when larvae are released from the egg mass.