Horned gena, an atavistic sex-linked dominant mutation in Tribolium confusum

Horned gena (Hg), a sex-linked dominant mutation with semilethal effects in the imago stage, was found in Tribolium confusion. The Hg mutant is characterized by a pair of horns of variable size and shape that arises from the genoclypeal suture in mildly expressed beetles or a more pronounced horn-like structure resulting from a folding of the genal shelf near the compound eyes. In these beetles there is considerable stress on the exoskeleton of the head so that the cranium is fragmented between the eyes, leaving large, irregularly shaped areas of the head unprotected by cranial exoskeleton. These beetles die presumably because of bacterial infection or because they cannot retain moisture within their bodies. This mutation differs from the mutation V-Grube found in another tenebrionid, Tenebrio molitor. Taxonomic, genetic, and cytological evidence is presented suggesting that Hg is a gene of ancient origin, having existed at least since the genera of Tenebrionidae were being evolved.