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

Recent studies on morphology and genetics of marinerotifer populations have demonstrated the existence ofconsiderable variation. Differences in theglycoprotein structure of a mate recognition pheromone(MRP) probably have a primary role in maintainingspecies boundaries among Brachionus species.This study examined factors involved in mating toclarify their relation with genetic variability. Threeexperiments were performed using 3 Brachionusplicatilis strains (Russia, Germany and Tokyo) and 4B. rotundiformis strains (Hamana, Fiji, Thai andSpain).Selfing and cross mating of 7 rotifer strains wasconducted in the first experiment. Russian malesmated with B. plicatilis females in thefollowing increasing order, based on mating attempts:German, Tokyo and Russia. There was little matingattempts with females of B. rotundiformisstrains. In a second set of experiments, the binding of anantibody (anti-MRP) derived from the MRP of Russianstrain was tested. A fluorescent label was attached toanti-MRP and the antibody reacted with the MRP onfemales of seven strains. The fluorescence intensity,indicating the degree of antibody binding, wasmeasured with epifluorescence microscopy and imageanalysis. The binding intensity of the anti-MRP to theMRP was in the following increasing order: Hamana,Fiji, Spain, German, Tokyo, Thai and Russia.It was expected that when the anti-MRP binds tothe MRP of a female, the males recognition of thefemale would be inhibited. In the third experiment,male mating with females exposed to the anti-MRP wascompared with unexposed females. Russia Tokyo, Thaiand Spain females exposed to anti-MRP, elicited fewermale mating attempts than unexposed females. Matingfrequency and anti-MRP binding significantlycorrelated with genetic distance obtained from isozymeanalysis.