Effect of food concentration on the production and viability of resting eggs of the rotiferBrachionus: implications for the timing of sexual reproduction

Abstract

Summary1. Life‐table experiments withBrachionus calyciflorustest several hypotheses related to the idea that sexual reproduction in monogonont rotifers should occur when food resources are favourable.2. The food concentration necessary for a fertilised mictic female to produce one phenotypically normal resting egg was higher than that for an amictic female to produce one daughter. At the lowest concentration ofCryptomonas erosa(1.25 × 103 cells mL−1), the lifetime fecundity of these two types of females was 0.9 and 1.4, respectively.3. The lifetime fecundity of both fertilised mictic females and amictic females increased with food concentration to 3.4 resting eggs and 15.2 daughters female−1, respectively. The approach to maximal fecundity with increasing food concentration was more rapid for fertilised mictic females, such that their lifetime fecundity relative to that of amictic females gradually decreased from 0.64 (at 1.25 × 103 C. erosa mL−1) to 0.22 (at 2.5 × 104 C. erosa mL−1).4. The probability of a fertilised mictic female producing one or more abnormal resting eggs during her lifetime was high (approximately 75%). The mean proportion of abnormal eggs produced per female varied among the different food‐concentration treatments (26–38%) but was not higher at the low food concentrations.5. The proportion of normal resting eggs that hatched was high (51–71%); those produced at low food concentrations were no less likely to hatch than those produced at high food concentrations. No abnormal resting eggs hatched.6. The probability of a fertilised mictic female producing an abnormal resting egg increased rapidly with her age at all food concentrations. The probability of a normal resting egg hatching declined with maternal age at the low food concentration in one of two experiments.7. The results support the idea that induction of mictic females should occur when food resources are good. Coincidence of sexual reproduction with low food availability risks low production of resting eggs for several reasons. Population size may be small, with a low probability of encounters between young mictic females and males, and fertilised mictic females may be unable to mature and produce resting eggs.