Neo sex chromosomes, colour polymorphism and male-killing in the African queen butterfly, Danaus chrysippus (L.)

David A.S. Smith*, Walther Traut, Simon H. Martin, Piera Ireri, Kennedy S. Omufwoko, Richard Ffrench-Constant, Ian J. Gordon

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

Abstract

Danaus chrysippus (L.), one of the world’s commonest butterflies, has an extensive range throughout the Old-World tropics. In Africa it is divided into four geographical subspecies which overlap and hybridise freely in the East African Rift: Here alone a male-killing (MK) endosymbiont, Spiroplasma ixodetis, has invaded, causing female-biased populations to predominate. In ssp. chrysippus, inside the Rift only, an autosome carrying a colour locus has fused with the W chromosome to create a neo-W chromosome. A total of 40-100% of Rift females are neo-W and carry Spiroplasma, thus transmitting a linked, matrilineal neo-W, MK complex. As neo-W females have no sons, half the mother’s genes are lost in each generation. Paradoxically, although neo-W females have no close male relatives and are thereby forced to outbreed, MK restricts gene flow between subspecies and may thus promote speciation. The neo-W chromosome originated in the Nairobi region around 2.2 k years ago and subsequently spread throughout the Rift contact zone in some 26 k generations, possibly assisted by not having any competing brothers. Our work on the neo-W chromosome, the spread of Spiroplasma and possible speciation is ongoing.

Original languageEnglish
Article number291
JournalInsects
Volume10
Issue number9
DOIs
Publication statusPublished - 9 Sep 2019

Keywords

  • Colour polymorphism
  • Danaus chrysippus
  • Defence
  • Male-killing
  • Mimicry
  • Neo sex chromosomes
  • Resource competition
  • Speciation
  • ‘magic trait’

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