Crossing between Seven Strains of the Rotifer Brachionus plicatilis

Abstract

Cross-mating experiments were carried out using seven S- and L-type strains of the rotifer Brachionus plicatilis O. F. Muller, to determine the probability of sexual recombination. Rotifer rearing conditions were controlled to eliminate any effects of external factors. Of 39 crossing and selfing trials, fertilization was observed only among S-type and L-type strains. All crosses between S- and L-type strains failed. Percent fertilization obtained by cross-mating between strains of the same type was significantly lower than that of selfing. A negative correlation was found between the genetic distance of mated pairs and percent fertilization. The results suggest that whether the strains can be crossed successfully depends on the differences in their genetic constitution. Isozyme analysis on rotifers from resting eggs produced in the cross-matings indicated that classical sexual recombination occurred in S- or L-type rotifers. S- and L-type rotifers exhibit differences not only in morphological and physiological characteristics but also in genetic constitution and karyotypes. In addition, the current study has demonstrated reproductive isolation between the two types. From these facts, S- and L-type rotifers should be classified as different species. © 1993, The Japanese Society of Fisheries Science. All rights reserved.