title: Opsin transcripts of predatory diving beetles: a comparison of surface and subterranean photic niches.
abstract: The regressive evolution of eyes has long intrigued biologists yet the genetic underpinnings remain opaque. A system of discrete aquifers in arid Australia provides a powerful comparative means to explore trait regression at the genomic level. Multiple surface ancestors from two tribes of diving beetles (Dytiscidae) repeatedly invaded these calcrete aquifers and convergently evolved eye-less phenotypes. We use this system to assess transcription of opsin photoreceptor genes among the transcriptomes of two surface and three subterranean dytiscid species and test whether these genes have evolved under neutral predictions. Transcripts for UV, long-wavelength and ciliary-type opsins were identified from the surface beetle transcriptomes. Two subterranean beetles showed parallel loss of all opsin transcription, as expected under 'neutral' regressive evolution. The third species Limbodessus palmulaoides retained transcription of a long-wavelength opsin (lwop) orthologue, albeit in an aphotic environment. Tests of selection on lwop indicated no significant differences between transcripts derived from surface and subterranean habitats, with strong evidence for purifying selection acting on L. palmulaoides lwop. Retention of sequence integrity and the lack of evidence for neutral evolution raise the question of whether we have identified a novel pleiotropic role for lwop, or an incipient phase of pseudogene development.
authors.affiliation: Australian Centre for Evolutionary Biology and Biodiversity and School of Biological Sciences , University of Adelaide , South Australia 5005, Australia.
authors.forename: Simon M
authors.identifier: 0000-0002-8812-6753
authors.initials: SM
authors.lastname: Tierney
authors.affiliation: Australian Centre for Evolutionary Biology and Biodiversity and School of Biological Sciences , University of Adelaide , South Australia 5005, Australia ; Evolutionary Biology Unit , South Australian Museum, North Terrace , Adelaide, South Australia 5000, Australia.
authors.forename: Steven J B
authors.initials: SJ
authors.lastname: Cooper
authors.affiliation: Evolutionary Biology Unit , South Australian Museum, North Terrace , Adelaide, South Australia 5000, Australia.
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Saint
authors.affiliation: Australian Centre for Evolutionary Biology and Biodiversity and School of Biological Sciences , University of Adelaide , South Australia 5005, Australia ; Evolutionary Biology Unit , South Australian Museum, North Terrace , Adelaide, South Australia 5000, Australia.
authors.forename: Terry
authors.initials: T
authors.lastname: Bertozzi
authors.affiliation: Australian Centre for Evolutionary Biology and Biodiversity and School of Biological Sciences , University of Adelaide , South Australia 5005, Australia.
authors.forename: Josephine
authors.initials: J
authors.lastname: Hyde
authors.affiliation: Australian Centre for Evolutionary Biology and Biodiversity and School of Biological Sciences , University of Adelaide , South Australia 5005, Australia ; Terrestrial Zoology , Western Australian Museum, Locked Bag 49, Welshpool DC , Western Australia 6986, Australia ; School of Animal Biology , University of Western Australia , Nedlands, Western Australia 6907, Australia.
authors.forename: William F
authors.initials: WF
authors.lastname: Humphreys
authors.affiliation: Australian Centre for Evolutionary Biology and Biodiversity and School of Biological Sciences , University of Adelaide , South Australia 5005, Australia.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Austin
keywords: Bidessini; Hydroporini; opsin; pleiotropy; pseudogene; regressive evolution