A selfish gene chastened: Tribolium castaneum Medea M4 is silenced by a complementary gene

Maternal-effect dominant embryonic arrest (Medea) of Tribolium castaneum are autosomal factors that act maternally to cause the death of any progeny that do not inherit them. This selfish behavior is thought to result from a maternally expressed poison and zygotically expressed antidote. Medea factors and the hybrid incompatibility factor, H, have a negative interaction consistent with complementary genes of the Dobzhansky-Muller model for post-zygotic isolation. This negative interaction may result from H suppression of Medea zygotic antidote, leaving zygotes incompletely protected from maternal poison. I report here a test of the hypothesis that H also suppresses the Medea maternal poison. Viable F1 females were generated from a cross of Medea M4 strain males to H strain females. These females, heterozygous for both M4 and H, failed to express M4 maternal lethal activity when crossed to their male sibs. Transmission of non-M4 homologues from these females was confirmed using a dominant transgenic enhanced green fluorescent protein eye color marker, tightly linked in cis to M4. M4 beetles, lacking H, were selected from the F2 population. Female descendants of these clearly expressed M4 maternal lethal activity, indicating restoration of this activity after H was segregated away. I conclude that H, or a factor tightly linked to H, suppresses Medea M4 maternal poison.