Mate Choice in Male Brachionus plicatilis Rotifers

Some proximate mechanisms that increase the probability of successful copulation are examined in Brachionus plicatilis Muller (Rotifera), a cyclical parthenogen. By means of behavioural tests, an analysis was performed as to whether male choice exists concerning female age. Second, male direct discrimination of sexual (mictic) and parthenogenetic (amictic) females, on the basis of male behaviour after encountering both kinds of females, was examined. 2. Results showed that the probability of male mating initiation decreases with the age of female, and that males copulate almost exclusively with females less than 24-h old. Preference for sexual females was also found in the probability of mating initiation, but no preference for copulating sexual females was found. 3. As only young, sexual females are fertilizable, these mechanisms would enhance the likelihood of a male copulating with a sexually receptive female, and thus male fitness. 4. A theoretical model shows that the surprisingly low degree of male preference for sexual females can be adaptively explained on the basis of relative frequency of young females and mictic females in the population when the sexual phase occurs.