THE MOLECULAR THROUGH ECOLOGICAL GENETICS OF ABNORMAL-ABDOMEN IN DROSOPHILA-MERCATORUM .5. FEMALE PHENOTYPIC-EXPRESSION ON NATURAL GENETIC BACKGROUNDS AND IN NATURAL ENVIRONMENTS

The abnormal abdomen (aa) syndrome in Drosophila mercatorum depends on the presence of R1 inserts in a third or more of the X-linked 28S rDN A genes and the absence of selective under replication of inserted rep eats in polytene tissues that is controlled by an X-linked locus (ur) half a map unit from the rDNA complex. This syndrome affects both life history and morphology in the laboratory. Because abnormal morphologi es are rarely encountered in nature, the purpose of this study is to s ee if the female life history traits are still affected under more nat ural genetic backgrounds and environmental conditions. Two outbred sto cks were extracted from the natural population living near Kamuela, Ha waii: KaaX that has only X chromosomes with ur(aa) alleles, and K+X th at has only ur+ alleles. These two stocks have nonoverlapping distribu tions of insert proportions, indicating strong disequilibrium between the ur locus and the rDNA complex. The KaaX stock had almost no morpho logical penetrance of ur(aa), indicating that genetic background is im portant. KaaX expressed longer female egg-to-adult developmental times , increased early adult female fecundity, and decreased female adult l ongevity compared with K+X. By bagging natural rots of the cactus Opun tia megacantha near Kamuela, Hawaii, it was shown that egg-to-adult de velopmental time is slowed down by 0.92 days in females bearing ur(aa) alleles in nature, with no detectable slowdown in ur(aa) males. The b agged rot data also indicate that females bearing ur(aa) alleles have a strong fecundity advantage in nature under some ecological condition s but not others.