Sine oculis 3/optix (six3) controls eye size but not adult dorsal head shape in beetles. (a) Gene structure of six3 orthologues from Tribolium castaneum (Tc-six3), Onthophagus taurus (Ot-six3), and O. sagittarius (Os-six3). Thick colour bars represent exons (dark blue for the coding region, light blue for the untranslated region (UTR), thin green bars highlight the homeodomain region and thin black bars show the fragments used for dsRNA interference. (b,c) Sham control (left) and six3 RNAi (right) phenotypes in Tribolium castaneum (b) and O. sagittarius (c); arrowheads point at eyes; outlines shows measured eye area. (d) Sham control (left) and six3 RNAi (right) dorsal head phenotypes in Tribolium castaneum (top), O. taurus (second and third row from top), and O. sagittarius (bottom two rows); arrowheads point at eyes.