The aposematic savanna butterfly Danaus chtysippw seems to be an exception to the rule that Batesian models and Miillerian mimics are not polymorphic. Throughout Asia and in much of Africa the species is in fact monomorphic and polytypic, as expected. It is, however, polymorphic for 3 4 colour genes over a large area of central and eastern Africa, where deviant sex ratios and non-Mendelian segregations also occur. AU-female broods are widespread and frequent, often outnumbering bisexual progenies and giving rise to heavily female-biased populations. Full and partial sex linkage, which is not controlled from the X or Y chromosomes, and male-biased broods also occur. Genetical analysis for the BC-autosome carrying colour genes suggests there are two, probably mitochondrial, cytotypes (microbe-induced early male death syndrome is considered unlikely) and an autosomal, incompatibility (I) gene, two alleles of which are male-specific killers. F2 and backcross matings by females heterozygous at the I-locus give progenies which are either thelygenic, all males dying at or soon after hatching, or bisexual but showing full or partial sex linkage. Male death is attributed to nuclearcytoplasmic incompatibility (NCI). Females achieve reversion from a thelygenic to a bisexual line by mating with males of compatible (maternal) cytotype. A second NCI system causes

No abstract

No abstract

Samples of'the polymorphic buttcrfly Dunnus c.hys$qus arc analysed from six well separated sitrs in East Africa. Morph-ratio clines are described for four diallelic genes A, B, C: and I., each o f which influences the visual phenotype. Each of the four clines has a diircrcnt orientation, consistent with an hypothesis that the polymorphisrri originated from hybridization between a ii~irnbcr ofpolytypic denies which have at various times undergone range expansion. Allopatric suhsprciation in isolated Pleistocene rcfugia is postulated. Thc phenotype of each geographical race is shared with one of the moiphs within the hybrid zonr; other sympatrically miiintained polymorphic forms arc normally confined to the hybrid zoiic. Wright's isolation-by-distance model best explains the prcsent disrribu~iori o f p i c frequencies. Morph-ratios difler significantly bctwecn the sexes and are sornctiinrs associated with hctcroxygote excess; garnctic and genotypic disequilihria are general throughout the region and suggest the clines are maintained by strong natural selection. Seasonal cycling of phenotype frequency is believrd to result from extrnsive misgrgratory rriovenients rat her than natural selection. Female-biased sex-ratio, which is also seasonal, and Haldaric rule cffects, result from hybrid breakdown when genetically distinct drmcs meet and interhreed. Oscillating sex-ratios and frequency ofcolour genes are functionally (:orrespondciice to: I>r 1). A. S. Smith. 0024-4082/97/05005 I + 28 $25 00/O/zj0(10073 51 0 1997 The Linnean Sotircy of 1,mdon 52 L). A. S. SMI'I'H B'TAL.linked by negative feedback. The polymorphism owcs its origin t o allnpatric evolution but is now mairitaincd sympatrically. 0 l9!17 ' I ' h 1.innean So< irly 1~i'I.i~ndnn ADI)I'FIONAL KEY WOl

No abstract