title: Rhabdom evolution in butterflies: insights from the uniquely tiered and heterogeneous ommatidia of the Glacial Apollo butterfly, Parnassius glacialis.
abstract: The eye of the Glacial Apollo butterfly, Parnassius glacialis, a 'living fossil' species of the family Papilionidae, contains three types of spectrally heterogeneous ommatidia. Electron microscopy reveals that the Apollo rhabdom is tiered. The distal tier is composed exclusively of photoreceptors expressing opsins of ultraviolet or blue-absorbing visual pigments, and the proximal tier consists of photoreceptors expressing opsins of green or red-absorbing visual pigments. This organization is unique because the distal tier of other known butterflies contains two green-sensitive photoreceptors, which probably function in improving spatial and/or motion vision. Interspecific comparison suggests that the Apollo rhabdom retains an ancestral tiered pattern with some modification to enhance its colour vision towards the long-wavelength region of the spectrum.
authors.affiliation: Laboratory of Neuroethology, Sokendai (The Graduate University for Advanced Studies), Shonan Village, Hayama 2400193, Japan.
authors.forename: Atsuko
authors.initials: A
authors.lastname: Matsushita
authors.forename: Hiroko
authors.initials: H
authors.lastname: Awata
authors.forename: Motohiro
authors.initials: M
authors.lastname: Wakakuwa
authors.forename: Shin-ya
authors.initials: SY
authors.lastname: Takemura
authors.forename: Kentaro
authors.initials: K
authors.lastname: Arikawa
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002080:Butterflies / Q000033:anatomy & histology / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure*; D054910:Compound Eye, Arthropod / Q000033:anatomy & histology / Q000502:physiology / Q000648:ultrastructure*; D007564:Japan; D008297:Male; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D017956:Photoreceptor Cells, Invertebrate / Q000166:cytology / Q000502:physiology / Q000648:ultrastructure*; D013045:Species Specificity; D014466:Ultraviolet Rays