title: Functional preservation and variation in the cone opsin genes of nocturnal tarsiers.
abstract: The short-wavelength sensitive (S-) opsin geneOPN1SWis pseudogenized in some nocturnal primates and retained in others, enabling dichromatic colour vision. Debate on the functional significance of this variation has focused on dark conditions, yet many nocturnal species initiate activity under dim (mesopic) light levels that can support colour vision. Tarsiers are nocturnal, twilight-active primates and exemplary visual predators; they also express different colour vision phenotypes, raising the possibility of discrete adaptations to mesopic conditions. To explore this premise, we conducted a field study in two stages. First, to estimate the level of functional constraint on colour vision, we sequencedOPN1SWin 12 wild-caught Philippine tarsiers (Tarsius syrichta). Second, to explore whether the dichromatic visual systems of Philippine and Bornean (Tarsius bancanus) tarsiers-which express alternate versions of the medium/long-wavelength sensitive (M/L-) opsin geneOPN1MW/OPN1LW-confer differential advantages specific to their respective habitats, we used twilight and moonlight conditions to model the visual contrasts of invertebrate prey. We detected a signature of purifying selection forOPN1SW, indicating that colour vision confers an adaptive advantage to tarsiers. However, this advantage extends to a relatively small proportion of prey-background contrasts, and mostly brown arthropod prey amid leaf litter. We also found that the colour vision ofT. bancanusis advantageous for discriminating prey under twilight that is enriched in shorter (bluer) wavelengths, a plausible idiosyncrasy of understorey habitats in Borneo.This article is part of the themed issue 'Vision in dim light'.
authors.affiliation: Department of Evolutionary Anthropology, Duke University, 104 Biological Sciences Building, Campus Box 90383, Durham, NC 27708, USA gillian.moritz@duke.edu.
authors.forename: Gillian L
authors.identifier: http://orcid.org/0000-0002-5499-6793
authors.initials: GL
authors.lastname: Moritz
authors.affiliation: Institute of Biology, University of the Philippines Diliman, Quezon City, Philippines.
authors.forename: Perry S
authors.initials: PS
authors.lastname: Ong
authors.affiliation: Departments of Anthropology and Biology, Pennsylvania State University, 513 Carpenter Building, University Park, PA 16802, USA.
authors.forename: George H
authors.initials: GH
authors.lastname: Perry
authors.affiliation: Department of Anthropology, Dartmouth College, 6047 Silsby Hall, Hanover, NH 03755, USA nathaniel.j.dominy@dartmouth.edu.|Department of Biological Sciences, Dartmouth College, Class of 1978 Life Sciences Center, 78 College Street, Hanover, NH 03755, USA.
authors.forename: Nathaniel J
authors.identifier: http://orcid.org/0000-0001-5916-418X
authors.initials: NJ
authors.lastname: Dominy
mesh_terms: D000818:Animals; D001893:Borneo; D055253:Color Vision; D003624:Darkness; D004777:Environment; D065928:Forests; D017299:Rod Opsins / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D016699:Tarsiidae / Q000235:genetics / Q000502:physiology*
chemical_list: D017299:Rod Opsins; C095855:long-wavelength opsin; C095854:middle-wavelength opsin; C095853:short-wavelength opsin
keywords: Tarsius; colour vision; nocturnality; opsins