Transcriptome Analyses Reveal Circadian-Related Expression Features in the Visual Systems of Two Snakes

Chen-Yang Tang,Kong Yang,Jia-Tang Li,Changjun Peng,Meng-Huan Song,Wei Wu,Zhong-Liang Peng

doi:10.3390/d13120621

Abstract

The visual characteristics of animals with different circadian habits, especially colubrid snakes, exhibit highly variable photoreceptor morphology. While studies have reported on the diversity in retinal cell morphology among snakes with different circadian patterns, few studies have examined the expression of genes related to vision. To explore gene expression patterns in the eyes between diurnal and nocturnal snakes, we carried out RNA sequencing of six tissues (eye, heart, liver, lung, kidney, and muscle) in two colubrids with disparate circadian activities, i.e., diurnal Ahaetulla prasina and nocturnal Lycodon flavozonatum, followed by weighted gene co-expression network analysis (WGCNA). The genes in the two most correlated modules were primarily enriched in different functional pathways, thus suggesting different biological functions. Three opsin genes (RH1, LWS, and SWS) were differentially expressed between the two species. Moreover, in the phototransduction pathway, different genes were highly expressed in the eyes of both species, reflecting specific expression patterns in the eyes of snakes with different circadian activity. We also confirmed the dominance of cone- and rod-related genes in diurnal and nocturnal adaptation, respectively. This work provides an important foundation for genetic research on visual adaptation in snakes and provides further insight into the adaptive evolution of such species.

Highlights

The evolution of perception has long fascinated evolutionary biologists, especially the complex visual systems that have evolved over millions of years to adapt to diverse habitats with various spectral ranges and illumination intensities [1]
To understand the genetic mechanisms underlying the visual adaption between two snakes with different habits, we collected a total of six individuals for transcriptome sequencing
Activity patterns can be well discriminated based on morphometric analysis and signatures of selection [15,16,29]

Summary

Introduction

The evolution of perception has long fascinated evolutionary biologists, especially the complex visual systems that have evolved over millions of years to adapt to diverse habitats with various spectral ranges and illumination intensities [1]. Visual pigments (or opsins) play a core role in visual photosensitivity. Photons are absorbed by visual pigments, i.e., G protein-coupled receptors [3]. Rhodopsin visual pigments are found in rod cells, whereas color visual pigments are found in cone cells [4]. Animal lifestyle often reflects the content of cones and rods [5]. Nocturnal terrestrial animals have an abundance of rods, which mediate dim-light vision, whereas diurnal vertebrates contain more cones with good color vision [6]. Daytime visual capabilities, including cone densities, cone: rod ratios, and photopic a-wave amplitudes, can discriminate wading bird species [7]; among reptiles, the nocturnal gecko (Gekko gekko) has pure rod retinas [8] while the diurnal chameleon (Anolis carolinensis) has pure cone retinas [9]

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Results

Conclusion