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The butterfly Danaus chrysippus is infected by a male-killing Spiroplasma bacterium
F M Jiggins1, G D Hurst, C D Jiggins
1Department of Genetics, University of Cambridge, UK. fmj1001@mole.bio.cam ac.uk
Abstract:
Many insects carry maternally inherited bacteria which kill male offspring. Such bacteria will spread if male death benefits the female siblings who transmit the bacterium, and they are therefore expected in insects with antagonistic sibling interactions. We report that the butterfly Danaus chrysippus is host to a maternally inherited male-killing bacterium. Using diagnostic PCR and rDNA sequence, the bacterium was identified as a Spiroplasma closely related to 2 ladybird beetle male-killers and the tick symbiont Spiroplasma ixodetis. The male-killer was found to have a geographically restricted distribution, with up to 40% of females being infected in East Africa, but no detectable infection in small samples from other populations. Danaus chrysippus is a surprising host for a male-killer as its eggs are laid singly. This suggests that the ecological conditions permitting male-killers to invade may be more widespread than previously realized.
Insights
A male-killing bacterium, Spiroplasma, was discovered in the butterfly Danaus chrysippus. This finding suggests that the conditions for such bacteria to spread may be more common than previously thought.
Area of Science:
- Entomology
- Microbiology
- Evolutionary Biology
Background:
- Maternally inherited bacteria can kill male insect offspring.
- These bacteria spread when male death benefits female siblings, often seen in species with antagonistic sibling interactions.
Purpose of the Study:
- To identify and characterize a male-killing bacterium in the butterfly Danaus chrysippus.
- To investigate the distribution and implications of this symbiosis.
Main Methods:
- Diagnostic PCR and rDNA sequencing were used to identify the bacterium.
- Field surveys were conducted to assess the bacterium's geographical distribution.
Main Results:
- A Spiroplasma bacterium, closely related to known male-killers, was identified in Danaus chrysippus.
- The male-killer bacterium exhibited a geographically restricted distribution, with infection rates up to 40% in East African populations.
- No detectable infection was found in other sampled populations.
Conclusions:
- Danaus chrysippus is a novel host for a maternally inherited male-killing bacterium.
- The presence of this bacterium in a species that lays eggs singly challenges previous assumptions about the ecological requirements for male-killer invasion.
- This suggests that the ecological conditions enabling male-killer bacteria to spread might be more widespread than previously understood.