title: Evolutionary loss of cone photoreception in balaenid whales reveals circuit stability in the mammalian retina.
abstract: The classical understanding of mammalian vision is that it occurs through "duplex" retinae containing both rod and cone photoreceptors, the signals from which are processed through rod- and/or cone-specific signaling pathways. The recent discovery of rod monochromacy in some cetacean lineages provides a novel opportunity to investigate the effects of an evolutionary loss of cone photoreception on retinal organization. Sequence analysis of right whale (Eubalaena glacialis; family Balaenidae) cDNA derived from long-wavelength sensitive (LWS) cone opsin mRNA identified several mutations in the opsin coding sequence, suggesting the loss of cone cell function, but maintenance of non-photosensitive, cone opsin mRNA-expressing cells in the retina. Subsequently, we investigated the retina of the closely related bowhead whale (Balaena mysticetus; family Balaenidae) to determine how the loss of cone-mediated photoreception affects light signaling pathways in the retina. Anti-opsin immunofluorescence demonstrated the total loss of cone opsin expression in B. mysticetus, whereas light microscopy, transmission electron microscopy, and bipolar cell (protein kinase C-α [PKC-α] and recoverin) immunofluorescence revealed the maintenance of cone soma, putative cone pedicles, and both rod and cone bipolar cell types. These findings represent the first immunological and anatomical evidence of a naturally occurring rod-monochromatic mammalian retina, and suggest that despite the loss of cone-mediated photoreception, the associated cone signaling structures (i.e., cone synapses and cone bipolar cells) may be maintained for multichannel rod-based signaling in balaenid whales. J. Comp. Neurol. 524:2873-2885, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Biological Sciences, Florida Institute of Technology, Melbourne, Florida, 32901.
authors.forename: Lorian E
authors.initials: LE
authors.lastname: Schweikert
authors.affiliation: Department of Biological Sciences, The University of Tampa, Tampa, Florida, 33606.
authors.forename: Jeffry I
authors.initials: JI
authors.lastname: Fasick
authors.affiliation: Department of Biological Sciences, Florida Institute of Technology, Melbourne, Florida, 32901.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Grace
mesh_terms: D000818:Animals; D002417:Cattle; D019143:Evolution, Molecular; D009415:Nerve Net / Q000737:chemistry / Q000502:physiology*; D012160:Retina / Q000737:chemistry / Q000502:physiology*; D017949:Retinal Cone Photoreceptor Cells / Q000737:chemistry / Q000502:physiology*; D013045:Species Specificity; D013552:Swine; D014907:Whales / Q000502:physiology*
keywords: AB_141780; AB_143165; AB_177457; AB_2253622; AB_304300; RRIDs: AB_2156055; opsin mutation; retinal organization; rod monochromacy; rod signaling; whale