A New Type of Hybrid Sterility in Drosophila paulistorum

Abstract

IT has been shown¹ that Drosophila paulistorum is a group of at least six sub-species or incipient species, and that, at our time-level, reproductive isolation is in the process of formation between these incipient species. Crosses between three (Centro-American, Amazonian., Andean-South Brazilian) of the six sub-species result in the production of fertile female and sterile male hybrids. The male sterility² has been found to depend on the genotype of the male's mother. Any female which carries any mixture of the chromosomes of different sub-species deposits eggs giving rise to sterile male zygotes and to fertile female ones. The male sterility is independent of the genotype of the male parent and the genotype of the sons themselves. What happens is evidently that the presence of a foreign chromosome in the female so alters the structure of her eggs, presumably by some modification of the egg cytoplasm, that male individuals developing from these eggs are sterile, and this regardless of the chromosome complement which they come to possess after fertilization. Furthermore, any one foreign chromosome (the species has three pairs of chromosomes) suffices to induce this male sterility³.