ASEXUAL AND SEXUAL REPRODUCTION IN THE ROTIFER BRACHIONUS-PLICATILIS CULTURED AT DIFFERENT SALINITIES

Two strains of the rotifer Brachionus plicatilis (L-type) differing in the levels of mictic female and male production, were grown in batch cultures with the alga Nannochloropsis gaditana as food, at two low (2.5 and 10 parts per thousand), and two high (40 and 50 parts per thousand) salinities. While both the low (strain S-1) and the high (strain S-3) sexual reproducing strains developed similar growth cycles at 2.5 and 10%., the population growth response at 40 and 50 parts per thousand showed that; 1) in strain S-1, mixis can be suppressed in conditions that still allow asexual reproduction, and 2) in strain S-3 mictic female and male production are possible at nearly zero asexual population growth rates. In strain S-3, a double log linear relationship between the densities of males and females was found. These results show that mixis can occur over a wide ranges of female population density, and support the hypothesis that sexual reproduction is a strain dependent component of the general reproductive response.