The pathology of embryo death caused by the male-killing Spiroplasma bacterium in Drosophila nebulosa

Background: Inherited bacteria that kill male offspring, male-killers, are known to be common in insects, but little is understood about the mechanisms used by male-killing bacteria to kill males. In this paper we describe the tempo and changes that occur during male-killing by Spiroplasma bacteria in the host Drosophila nebulosa. Results: Spiroplasma infected D. nebulosa males were developmentally retarded from 6 - 8 h into embryonic development at 25 degrees C, and arrested at between stages 12 and 13 of embryogenesis ( 10 - 12 h). Dying males were characterized by a failure to form segments, and ultimately disintegration of the normal oval embryonic shape. Prior to death, dying males exhibited widespread apoptosis, as testified by TUNEL staining. Conclusion: The Spiroplasma kills male Drosophila in a narrow developmental period, shortly after the formation of the host dosage compensation complex that is required for male-killing. Male death is preceded by widespread apoptosis, but it is uncertain if this is primary or secondary apoptosis.