Evolution of opsin genes reveals a functional role of vision in the echolocating little brown bat (Myotis lucifugus) Huabin Zhao a, b, c , Dong Xu c , Yingying Zhou c , Jon Flanders c , Shuyi Zhang c, * a Institute of Zoology, Chinese Academy of Sciences, Beijing 100080, China b Graduate University of Chinese Academy of Sciences, Beijing 100080, China c School of Life Science, East China Normal University, Shanghai 200062, China article info Article history: Received 19 August 2008 Accepted 15 March 2009 Keywords: Opsin Vision Echolocation Evolution Purifying selection Little brown bat Echolocating bat abstract Echolocating bats are able to orientate, navigate and forage without visual cues. To probe the role of vision in bats, we studied the visual opsin genes from the echolocating little brown bat (Myotis lucifugus). Short-wavelength sensitive (SWS1) opsin, middle/long- wavelength sensitive (M/LWS) opsin and rhodopsin cDNA sequences were identified from the Ensembl database and validated by the sequencing of genomic DNA. We retrieved the published orthologous genes from eleven additional representative species of mammals from GenBank and conducted an evolutionary analysis. We found that the M/LWS opsin and rhodopsin genes were both under strong purifying selection, whereas the SWS1 opsin gene has undergone positive selection at two amino acid sites and one lineage, though the main evolutionary force is still purifying selection. Two-ratio model of the SWS1 opsin gene revealed that the u ratio for the little brown bat lineage was nearly three times lower than the background ratio, suggesting a much stronger functional constraint. Our relative rate tests show the little brown bat has a lower nonsynonymous substitution rate than those in other mammals (on average 32% lower) for the SWS1 opsin gene. However, no such significant differences were detected for the M/LWS opsin and rhodopsin genes. The results of the relative ratio tests are consistent with that of tests for selection, showing a history of purifying selection on the little brown bat opsin genes. These findings suggest a functional role of vision in the little brown bat despite being nocturnal and using echolocation. We speculate that this echolocating bat may be able to use visual cues to orientate, navigate and forage at night, to discriminate color under moonlight and starlight conditions, or to avoid predation by diurnal raptors. Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. 1. Introduction Vertebrate vision, consisting of chromophores and opsins, is reliant upon visual pigments to absorb different spectrums of light (Wald, 1968; Yokoyama, 2000; Yokoyama and Yokoyama, 1996). These opsins determine the spectral tuning properties of each visual pigment (Yokoyama and Yokoyama, 1990, 1996). Three classes of visual opsin genes exist in most mammals, namely SWS1 (short-wavelength sensitive type 1), M/LWS (middle/long-wavelength sensitive) and rhodopsin. SWS1 and M/ LWS opsins are localized within cones which are typically responsible for color vision in bright light, whereas rhodopsins reside in rods, enabling non-color vision in dim light (Yokoyama and Yokoyama, 1990, 1996; Yokoyama, 2000). * Corresponding author. Tel./fax: þ86 21 62235786. E-mail address: syzhang@bio.ecnu.edu.cn (S. Zhang). Contents lists available at ScienceDirect Biochemical Systematics and Ecology journal homepage: www.elsevier.com/locate/biochemsyseco 0305-1978/$ – see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.bse.2009.03.001 Biochemical Systematics and Ecology 37 (2009) 154–161