Analysis of the predetermining effect of a sex realizer by ovary transplantations in the monogenic flyChrysomya rufifacies

Abstract

In the heterozygousF'/f female-producing females of the strictly monogenic blowflyChrysomya rufifacies the gene product of the dominant or epistatic female sex realizerF' which causes sexpredetermination is thought to be synthesized either by cells of the germ line (oocytes, nurse cells or oogonia) or by somatic cells and then transferred into the oocytes. To determine the possible site of synthesis, reciprocal transplantations were made of prepupal ovaries between female-producing (thelygenic; t) and male-producing (arrhenogenic; a) females ofChrysomya rufifacies. In another series of experiments prepupal host females of the wild t-type and a-type were each provided with one additional ovary either from a0type (f/f) or a t-type (F'/f) prepupa (neither were distinguishable by their phenotypes). In all these experiments the donor females were marked by the recessive sex-linked mutation 'white' (w/w); white eyes, white Malpighian tubules). In a considerable number of cases the implanted ovaries were in contact with the host's own oviduct and grew normally, but the rate of hatched adults was somewhat reduced. Crosses between such host females andw/w males (f/f) produced female or male offspring with white eyes from the eggs of the implantedw/w ovary, as well as flies with wild-type eyes (+/w) which had developed in the host's own ovaries. In all cases so far examined, the genetically thelygenic (or arrhenogenic) host females with an additional ovary implanted from an arrhenogenic (thelygenic) donor, produced progeny of both sexes: sons (daughters) from the eggs of the donor's ovary and daugthers (sons) from the eggs of the host's own gonads.These results demonstrate that the ovaries of the t-females ofChrysomya rufifacies at least from the early prepupal stage, are autonomous for the product of theF' gene. Transplantations of the premordial germ cells (pole cells) are planned to find out whether the predeterminingF' gene product is synthesized before the prepupal stage, by somatic cells outside the ovary or by somatic (follicle) cells of the ovary itself.

Keywords: Chrysomya rufifacies (Diptera); Monogeny; Ovary transplantation; Predetermination (Maternal effect); Sex realizer.