Effect of salinity during resting egg formation and hatching on descendent reproduction in the rotifer Brachionus rotundiformis Tschugunoff

Abstract

This study investigated the effect of salinity experienced during resting egg formation and hatching on the descendents' reproduction and on resting egg hatching in the monogonont rotifer Brachioraus rotundiformis Tschugunoff. The study was divided into two parts. First, the resting eggs formed at 17 psu were incubated at four salinities (8, 11, 22 and 33 psu) and then the hatchlings were cultured at the same salinities as during incubation. Second, the resting eggs formed at the four salinities were incubated at the same salinities as during their formation, and the hatchlings were cultured at 33 psu. The resting eggs formed at a salinity of 17 psu and incubated at four different salinities showed a higher hatching percentage at lower salinities (8 and 11 psu). When resting eggs were incubated at the same salinities as at formation (8, 11, 22 and 33 psu), the eggs showed no significant differences in a total hatching rate among treatments (83.3-86.7%). There was no significant difference in population growth when hatchlings did not experience a change in salinity. However, the population growth of hatchlings at 8 psu was comparatively arrested and at 33 psu caused by the acute increase in salinity. With regard to sexual reproduction, rotifers showed different patterns that were associated with the salinity experienced during resting egg hatching. This study shows that the salinity experienced during resting egg formation is the optimal one for egg hatching. Moreover, the salinity experienced during resting egg hatching strongly affects the descendents' sexual reproduction more than the salinity experienced during egg formation.