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

<jats:title>Abstract </jats:title> <jats:sec> <jats:title>Background </jats:title> <jats:p>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 <jats:italic>Spiroplasma</jats:italic> bacteria in the host <jats:italic>Drosophila nebulosa</jats:italic>.</jats:p> </jats:sec> <jats:sec> <jats:title>Results </jats:title> <jats:p> <jats:italic>Spiroplasma</jats:italic> infected <jats:italic>D. nebulosa</jats:italic> males were developmentally retarded from 6–8 h into embryonic development at 25°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.</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusion </jats:title> <jats:p>The <jats:italic>Spiroplasma</jats:italic> kills male <jats:italic>Drosophila</jats:italic> 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.</jats:p> </jats:sec>