Evidencing the cost of sexual reproduction in the rotifer Brachionus plicatilis

Sex poses an immediate cost for monogonont rotifers, which combine exclusively asexual reproduction with periods of co-occurrence between asexual and sexual reproduction in their life cycle. Because sex is linked to dormancy, sexual daughters do not contribute to the current growth of a clonal genotype, as they only produce males or diapausing eggs. Therefore, the expectation under the all-else equal assumption (i.e., sexual and asexual females having equivalent life-history traits) is that female genotypes investing more in sexual daughters during the planktonic growing season will have slower rates of clonal growth. Here, we tested if these genotypes compensate for this greater investment in sex with higher fecundity and/or survival. We studied 45 genotypes (clones) of Brachionus plicatilis established from diapausing eggs isolated from sediments of ten brackish ponds in Spain. Using a life-table experiment, we estimated the investment in sexual reproduction of these genotypes and several life-history traits (lifespan, lifetime reproductive success, generation time and intrinsic growth rate). Results showed that there was a lack of correlation between sex-investment and any other life-history trait. Neither fecundity nor survival compensated the investment in sexual reproduction, so we conclude that the all-else-equal assumption holds and sex is costly in B. plicatilis.