Genetic variation among marine Brachionus strains and function of mate recognition pheromone (MRP)

Abstract

Recent studies on morphology and genetics of marine rotifer populations have demonstrated the existence of considerable variation. Differences in the glycoprotein structure of a mate recognition pheromone (MRP) probably have a primary role in maintaining species boundaries among Brachionus species. This study examined factors involved in mating to clarify their relation with genetic variability. Three experiments were performed using 3 Brachionus plicatilis strains (Russia, Germany and Tokyo) and 4 B. rotundiformis strains (Hamana, Fiji, Thai and Spain).

Selfing and cross mating of 7 rotifer strains was conducted in the first experiment. Russian males mated with B. plicatilis females in the following increasing order, based on mating attempts: German, Tokyo and Russia. There was little mating attempts with females of B. rotundiformis strains.

In a second set of experiments, the binding of an antibody (anti-MRP) derived from the MRP of Russian strain was tested. A fluorescent label was attached to anti-MRP and the antibody reacted with the MRP on females of seven strains. The fluorescence intensity, indicating the degree of antibody binding, was measured with epifluorescence microscopy and image analysis. The binding intensity of the anti-MRP to the MRP was in the following increasing order: Hamana, Fiji, Spain, German, Tokyo, Thai and Russia.

It was expected that when the anti-MRP binds to the MRP of a female, the male’s recognition of the female would be inhibited. In the third experiment, male mating with females exposed to the anti-MRP was compared with unexposed females. Russia Tokyo, Thai and Spain females exposed to anti-MRP, elicited fewer male mating attempts than unexposed females. Mating frequency and anti-MRP binding significantly correlated with genetic distance obtained from isozyme analysis.