title: The molecular origin and evolution of dim-light vision in mammals.
abstract: The nocturnal origin of mammals is a longstanding hypothesis that is considered instrumental for the evolution of endothermy, a potential key innovation in this successful clade. This hypothesis is primarily based on indirect anatomical inference from fossils. Here, we reconstruct the evolutionary history of rhodopsin--the vertebrate visual pigment mediating the first step in phototransduction at low-light levels--via codon-based model tests for selection, combined with gene resurrection methods that allow for the study of ancient proteins. Rhodopsin coding sequences were reconstructed for three key nodes: Amniota, Mammalia, and Theria. When expressed in vitro, all sequences generated stable visual pigments with λMAX values similar to the well-studied bovine rhodopsin. Retinal release rates of mammalian and therian ancestral rhodopsins, measured via fluorescence spectroscopy, were significantly slower than those of the amniote ancestor, indicating altered molecular function possibly related to nocturnality. Positive selection along the therian branch suggests adaptive evolution in rhodopsin concurrent with therian ecological diversification events during the Mesozoic that allowed for an exploration of the environment at varying light levels.
authors.affiliation: Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, 10115, Berlin, Germany. constanze.bickelmann@mfn-berlin.de.
authors.forename: Constanze
authors.initials: C
authors.lastname: Bickelmann
authors.affiliation: Department of Cell and Systems Biology, University of Toronto, Toronto, ON, M5S 3G5, Canada.|Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada.
authors.forename: James M
authors.initials: JM
authors.lastname: Morrow
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada.
authors.forename: Jing
authors.initials: J
authors.lastname: Du
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada.
authors.forename: Ryan K
authors.initials: RK
authors.lastname: Schott
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada.
authors.forename: Ilke
authors.initials: I
authors.lastname: van Hazel
authors.affiliation: Department of Cell and Systems Biology, University of Toronto, Toronto, ON, M5S 3G5, Canada.
authors.forename: Steve
authors.initials: S
authors.lastname: Lim
authors.affiliation: Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, 10115, Berlin, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Müller
authors.affiliation: Department of Cell and Systems Biology, University of Toronto, Toronto, ON, M5S 3G5, Canada. belinda.chang@utoronto.ca.|Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada. belinda.chang@utoronto.ca.|Centre for the Analysis of Genome Evolution and Function, Toronto, ON, M5S 3B2, Canada. belinda.chang@utoronto.ca.
authors.forename: Belinda S W
authors.initials: BS
authors.lastname: Chang
mesh_terms: D000818:Animals; D005075:Biological Evolution; D003062:Codon; D005580:Fossils; D008027:Light; D008322:Mammals / Q000235:genetics* / Q000502:physiology; D055254:Night Vision / Q000235:genetics*; D012243:Rhodopsin / Q000235:genetics*; D012641:Selection, Genetic
chemical_list: D003062:Codon; D012243:Rhodopsin
keywords: Ancestral sequence reconstruction; codon-based likelihood models; dN/dS; mammalian evolution; nocturnality; rhodopsin evolution