Su Minjing, Yuan Feimin, Li Tiantian, Wei Cong
Key Laboratory of Plant Protection Resources and Pest Management, The Ministry of Education, College of Plant Protection, Northwest A&F University, Xianyang 712100, China.
Insects. 2022 Dec 16;13(12):1170. doi: 10.3390/insects13121170.
Insects' visual system is directly related to ecology and critical for their survival. Some cicadas present obvious differences in color and ultrastructure of compound eyes between nymphal and adult stages, but little is known about when cicadas obtain their visual ability to deal with the novel above-ground habitat. We use transcriptome analyses and reveal that cicada has a trichromatic color vision system and that the eyes undergo a non-gradual development process at the end of the 5th-instar nymphal stage. The white-eye 5th-instar nymphs (i.e., younger 5th-instar nymphs) have no visual ability because critical components of the visual system are deficient. The transformation of eyes toward possessing visual function takes place after a tipping point in the transition phase from the white-eye period to the subsequent red-eye period, which is related to a decrease of Juvenile Hormone. The period shortly after adult emergence is also critical for eye development. Key differentially-expressed genes related to phototransduction and chromophore synthesis play positive roles for cicadas to adapt to above-ground habitat. The accumulation of ommochromes corresponds to the color change of eyes from white to red and dark brown during the end of the 5th-instar nymphal period. Cuticle tanning leads to eye color changing from dark-brown to light-brown during the early adult stage. We hypothesize that the accumulation of ommochromes occurring at the end of 5th-instar nymphal stage and the early adult stage is not only for cicadas to obtain visual ability, but also is a secure strategy to cope with potential photodamage after emergence.
昆虫的视觉系统与生态学直接相关，对其生存至关重要。一些蝉在若虫期和成虫期的复眼颜色和超微结构存在明显差异，但对于蝉何时获得应对新的地上栖息地的视觉能力却知之甚少。我们通过转录组分析发现，蝉具有三色视觉系统，且眼睛在五龄若虫末期经历一个非渐进的发育过程。白眼五龄若虫（即较年轻的五龄若虫）没有视觉能力，因为视觉系统的关键组成部分存在缺陷。眼睛向具备视觉功能的转变发生在从白眼期到随后的红眼期的过渡阶段的一个临界点之后，这与保幼激素的减少有关。成虫羽化后的短时间内对眼睛发育也至关重要。与光转导和发色团合成相关的关键差异表达基因对蝉适应地上栖息地起到积极作用。在五龄若虫末期，眼色素的积累与眼睛从白色变为红色和深棕色相对应。在成虫早期，表皮鞣化导致眼睛颜色从深棕色变为浅棕色。我们推测，在五龄若虫末期和成虫早期发生的眼色素积累不仅是为了让蝉获得视觉能力，也是一种应对羽化后潜在光损伤的安全策略。
