Hybrid queen butterflies from the cross Danaus chrysippus (L.) × D. gilippus (Cramer):confirmation of species status for the parents and further support for Haldane's Rule |
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Authors: | DAVID A S SMITH IAN J GORDON GUGS LUSHAI DAVE GOULSON JOHN A ALLEN † and NORMAN MACLEAN |
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Institution: | Natural History Museum, Eton College, Windsor, Berkshire SL4 6EW, UK;Kipepeo Project, National Museums of Kenya, Box 58, Gede, Coast Province, Kenya;Agriculture and Agri-food Canada, Eastern Cereal and Oilseed Research (ECORC), Ottawa, Ontario K1A OC6, Canada;Ecology and Biodiversity Division, School of Biological Sciences, University of Southampton SO16 7PX, UK |
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Abstract: | A cross between queen butterflies of the Palaeotropical species Danaus chrysippus and the Neotropical D. gilippus was achieved with difficulty in both directions. Only one progeny ( N = 70) was reared comprising sterile males and inviable females in a precisely 1 : 1 ratio. Both prezygotic and postzygotic barriers to gene flow are strong. The result supports Haldane's Rule, to which we propose a minor amendment. The F1 hybrids were intermediate for background colour between the brown (genotype BB ) of gilippus and orange (genotype bb ) of chrysippus . Most F1 pattern characters were also intermediate. In polymorphic chrysippus populations, because Bb heterozygotes are brown, or nearly so, we suggest the B allele may have evolved towards dominance in sympatry. Hybrid males show positive heterosis for body size. The close similarity of male genitalia between the allopatric, genetically distant species chrysippus and gilippus , compared to their divergence between gilippus and its largely sympatric sister species eresimus , suggest that reinforcement of sexual isolation or reproductive character displacement have evolved in sympatry. © 2002 The Linnean Societyof London, Biological Journal of the Linnean Society , 2002, 76 , 535–544. |
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Keywords: | evolution of dominance heterosis prezygotic barriers postzygotic barriers reinforcement reproductive character displacement sexual isolation |
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