Data from: Variation in opsin genes correlates with signaling ecology in North American fireflies

Genes underlying signal reception should evolve to maximize signal detection in a particular environment. In animals, opsins, the protein component of visual pigments, are predicted to evolve according to this expectation. Fireflies are known for their bioluminescent mating signals. The eyes of nocturnal species are expected to maximize the detection of conspecific signal colours emitted in the typical low-light environment. This is not expected for species that have transitioned to diurnal activity in bright daytime environments. Here, we test the hypothesis that opsin gene sequence plays a role in modifying firefly eye spectral sensitivity. We use genome and transcriptome sequencing in four firefly species, transcriptome sequencing in six additional species and targeted gene sequencing in 28 other species to identify all opsin genes present in North American fireflies and to elucidate amino acid sites under positive selection. We also determine whether amino acid substitutions in opsins are linked to evolutionary changes in signal mode, signal colour and light environment. We find only two opsins, one long wavelength and one ultraviolet, in all firefly species and identify 25 candidate sites that may be involved in determining spectral sensitivity. In addition, we find elevated rates of evolution at transitions to diurnal activity, and changes in selective constraint on long wavelength opsin associated with changes in light environment. Our results suggest that changes in eye spectral sensitivity are at least partially due to opsin sequence. Fireflies continue to be a promising system in which to investigate the evolution of signals, receptors and signalling environments.

介导信号接收的基因应在特定环境中进化以最大化信号检测效能。在动物体内，视蛋白（opsin）作为视觉色素的蛋白组分，其演化模式符合这一预期。萤火虫以其生物发光的求偶信号闻名。夜行性物种的眼睛应最大化对典型弱光环境下同种个体发出的信号色彩的检测能力；而对于已过渡到昼间活动、暴露于明亮日间环境的物种而言，这一演化趋势则不成立。本研究检验了视蛋白基因序列参与调控萤火虫眼睛光谱敏感性的假说。我们对4个萤火虫物种开展基因组（genome）与转录组（transcriptome）测序，对另外6个物种进行转录组测序，并对其余28个物种实施靶向基因测序（targeted gene sequencing），以此鉴定北美萤火虫体内存在的全部视蛋白基因，并阐明处于正选择（positive selection）压力下的氨基酸位点。此外，我们还分析了视蛋白的氨基酸替换是否与信号模式、信号色彩及光照环境的演化改变存在关联。研究发现，所有萤火虫物种仅存在两种视蛋白：一类为长波长视蛋白，另一类为紫外视蛋白；同时鉴定出25个可能参与调控光谱敏感性的候选位点。此外，我们观察到在向昼行活动过渡的类群中，进化速率显著升高，且长波长视蛋白的选择约束随光照环境改变而发生变化。本研究结果表明，萤火虫眼睛光谱敏感性的变化至少部分源于视蛋白基因序列的改变。萤火虫依然是研究信号、受体及信号环境演化的极具潜力的实验体系。