Induction by streptococcal L-forms of two reproductive isolating mechanisms in Drosophila paulistorum.

The six semispecies of the Drosophila paulistorum complex do not normally interbreed, but when hybrids are produced in the laboratory, the males are sterile. In earlier work, cytoplasmic components responsible for this sterility had been transferred by injection of streptococcal L-forms isolated from the Mesitas and Santa Marta flies. To extend these findings, and L-form from the Centro-American flies was injected into three semispecies. Transfer of L-form from one semispecies to another resulted in sterile male progeny. The L-form isolated from Mesitas was injected into all six semispecies. Results simulated "hybrid inviability," i.e., only the Mesitas semispecies produced the expected number of offspring, and the total number of progeny from the other five semispecies was considerably reduced. Despite the small numbers of males, reflecting induced inviability, there was evidence that the transfer of L-forms from one semispecies to another simultaneously caused sterility in male progeny.