Morph frequencies, sex ratios and infections in Danaus chrysippus populations in Rwanda

The African Queen butterfly (Danaus chrysippus) is noted for its colour pattern polymorphism despite its aposematic and chemically defended lifestyle and for its infection with a male-killing endosymbiont (Spiroplasma). The polymorphism is largely restricted to east and central Africa where three different colour forms meet and interbreed in a large contact or hybrid zone. The primary objective of this study is to present recent data on the polymorphism, sex ratio and the incidence of male killing in D. chrysippus populations in Rwanda. We also report previously unpublished data from a random sample collected in 1914 in Bujumbura in Burundi and on the differential effects of weather on males and females in Ghana from 1972 to 1974. We sampled butterflies using butterfly nets and either marked, recorded and released them or kept specimens for subsequent examination. We used PCR/microscopy on the preserved specimens to detect Spiroplasma and the presence of a protozoan parasite (Ophryocystis). Our findings suggest that Rwanda lies close to the western edge of the joint distribution of both Spiroplasma and the polymorphism. Further biogeographical studies are recommended to test the hypothesis that male killing is restricted to the contact zone in which polymorphism is commonly observed.