21 research outputs found

    Vague modeste efficace pronom

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

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    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

    African queens find mates when males are rare

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    This is the final version. Available from Wiley via the DOI in this record. DATA AVAILABILITY STATEMENT: Sex ratio, spermatophore numbers and Rcode: Figshare doi:10.6084/ m9.figshare.21947729.In butterflies and moths, male-killing endosymbionts are transmitted from infected females via their eggs, and the male progeny then perish. This means that successful transmission of the parasite relies on the successful mating of the host. Paradoxically, at the population level, parasite transmission also reduces the number of adult males present in the final population for infected females to mate with. Here we investigate if successful female mating when males are rare is indeed a likely rate-limiting step in the transmission of male-killing Spiroplasma in the African Monarch, Danaus chrysippus. In Lepidoptera, successful pairings are hallmarked by the transfer of a sperm-containing spermatophore from the male to the female during copulation. Conveniently, this spermatophore remains detectable within the female upon dissection, and thus, spermatophore counts can be used to assess the frequency of successful mating in the field. We used such spermatophore counts to examine if altered sex ratios in the D. chrysippus do indeed affect female mating success. We examined two different field sites in East Africa where males were often rare. Surprisingly, mated females carried an average of 1.5 spermatophores each, regardless of male frequency, and importantly, only 10-20% remained unmated. This suggests that infected females will still be able to mate in the face of either Spiroplasma-mediated male killing and/or fluctuations in adult sex ratio over the wet-dry season cycle. These observations may begin to explain how the male-killing mollicute can still be successfully transmitted in a population where males are rare.National Geographic SocietyRoyal Societ
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