PARTHENOGENESIS AND GEOGRAPHIC-VARIATION OF SEX-RATIO IN 2 SPECIES OF LEIOBUNUM (ARACHNIDA, OPILIONES)

Analysis of sex ratios in various populations and laboratory rearing of virgin females from some populations revealed occurrence of thelytoky in two Japanese harvestmen, Leiobunum manubriatum Karsch and L. globosum Suzuki. Circumstantial evidence suggests that thelytoky in these species is automictic and facultative. The ratios of males in each population tends to decrease with the increase of latitude and altitude in L. manubriatum. The presence of a similar trend is also suggested in L. globosum. Ecological and evolutionary implications of this geographic trend of thelytoky are discussed. No evidence which favors the models based on the "Red Queen" hypothesis or frequency-dependent selection was obtained. Alternatively, significance of low vagility in the evolution and maintenance of parthenogenesis is suggested.