The butterfly Danaus chrysippus (L.) in East Africa: polymorphism and morph-ratio clines within a complex, extensive and dynamic hybrid zone

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<DS:-allop;itry hcterozygotr excess linkagr disequilibrium migration -mimicry ~ Pleistocene ~ polytypism sex-ratio -wbspeciation. CONTENTS

A classification of Danaus butterflies (Lepidoptera: Nymphalidae) based upon data from morphology and DNA

“…The subspecies of D. chrysippus are better known biologically, especially in Africa, than those of any other Danaus species (Smith et al ., 1997, 1998; Lushai et al ., 2003a). We treat the African subspecies of D. chrysippus s.l.…”

Mitochondrial DNA Clocks and the Phylogeny of Danaus Butterflies

“…According to independent analyses, then, D. chrysippus is not a phylogenetic species as defined by Cracraft (1983). And yet, this finding is paradoxical because its subspecies dorippus, chrysippus and alcippus hybridise extensively in East Africa (Smith et al, 1998;Lushai et al, 2003a, b) to produce offspring fertile in both sexes: thus, D. chrysippus has generally been regarded as a biological species (Mayr, 1942) that is both polymorphic and polytypic (Smith et al, 1997). Because the dorippus result, in particular, challenges taxonomic orthodoxy, the COI genes of dorippus and other representative taxa were sequenced twice using different primers (Table 1); in every case the original sequences were confirmed.…”

Rapid Evolution in the Nebria Gregaria Group (Coleoptera: Carabidae) and the Paleogeography of the Queen Charlotte Islands

“…In the South American and African tropics, the periodic fluctuations in global temperature that have characterized the late Pleistocene have promoted speciation through the creation of ecological refugia-isolating populations in fragmented forest and grassland ecosystems (Haffer 1977;Colinvaux 1998;Danin 1999) or on mountains and highlands 7 Corresponding author. during periods of global warming (Fjeldsa and Lovett 1997;Roy 1997;Smith et al 1997). The physical refugia generated by the ice sheets along the coast of northern North America may have played a similar role in promoting speciation by maintaining populations in isolation from each other for periods of several tens of thousands of years.…”