生物通报道：中科院昆明动物研究所的张亚平院士早年毕业于复旦大学生物系，1991年获中国科学院昆明动物研究所博士学位，在他37岁的时候成为了中国科学院院士。主要的研究包括在国内较早地、系统地开展动物分子系统学的研究，深入研究灵长类、食肉类、兔形类和啮齿类的进化，在国际上建立了较为全面的熊超科分子系统树等。近期这一研究组的研究成果接连登上《PLOS one》杂志。

在第一篇文章：Parallel and Convergent Evolution of the Dim-Light Vision Gene RH1 in Bats (Order: Chiroptera)中，研究人员在之前研究的基础上，分析了暗视觉通路上游的CRX基因和下游的SAG基因。结果发现这两个基因也在墓蝠和果幅中发生了趋同进化。

之前动物研究所沈永义副研究员在张亚平院士的指导下，克隆了视网膜上视杆细胞视紫红质的RHO基因(Rhodopsin)，发现无论是眼睛退化的食虫蝙蝠还是眼睛发达的旧大陆果蝠的视杆细胞都有表达RHO基因，说明即使是那些眼睛高度退化的食虫蝙蝠，它们仍然具有暗视觉。

这一基因在果蝠与墓蝠（食虫蝙蝠，眼睛没退化）间发生了趋同进化，长翼蝠和菊头蝠（眼睛都退化）也发生了趋同进化。该结果揭示了在蝙蝠分化后，可能由于对暗视觉的趋同需求（有些种类趋向于更多依赖视觉，眼睛发达；而有些是趋向于较少依赖视觉，眼睛退化），导致了RHO基因在蝙蝠里面发生了多次趋同进化。

最新这一研究则发现了罕见的一条通路里面，多个基因同时发生趋同进化。这也反应了复杂的性状（大眼睛，好的暗视觉能力）不是单个基因就能完全左右的，需要一系列的基因来控制。

有意思的是，研究人员在蝙蝠回声定位的研究上，也发现这种复杂功能的趋同进化是多基因作用的结果（PLoS Genetics接收，目前minor revision）。这些研究说明了对复杂器官的进化需要从基因通路/网络的角度进行探索，其进化是多基因联合作用的结果。这对进一步研究复杂性状的起源和进化具有重要意义。

而另外一篇文章：Multiple Episodes of Convergence in Genes of the Dim Light Vision Pathway in Bats，则分析了蝙蝠视觉基因通路在昏暗环境下的变化。

研究人员指出视杆必需基因网络的多重趋同事件并不常见，这说明了分析途径，以及网络在表型趋同分子机制进化中的重要作用。

（生物通：万纹）

原文摘要：

Parallel and Convergent Evolution of the Dim-Light Vision Gene RH1 in Bats (Order: Chiroptera)

Rhodopsin, encoded by the gene Rhodopsin (RH1), is extremely sensitive to light, and is responsible for dim-light vision. Bats are nocturnal mammals that inhabit poor light environments. Megabats (Old-World fruit bats) generally have well-developed eyes, while microbats (insectivorous bats) have developed echolocation and in general their eyes were degraded, however, dramatic differences in the eyes, and their reliance on vision, exist in this group. In this study, we examined the rod opsin gene (RH1), and compared its evolution to that of two cone opsin genes (SWS1 and M/LWS). While phylogenetic reconstruction with the cone opsin genes SWS1 and M/LWS generated a species tree in accord with expectations, the RH1 gene tree united Pteropodidae (Old-World fruit bats) and Yangochiroptera, with very high bootstrap values, suggesting the possibility of convergent evolution. The hypothesis of convergent evolution was further supported when nonsynonymous sites or amino acid sequences were used to construct phylogenies. Reconstructed RH1 sequences at internal nodes of the bat species phylogeny showed that: (1) Old-World fruit bats share an amino acid change (S270G) with the tomb bat; (2) Miniopterus share two amino acid changes (V104I, M183L) with Rhinolophoidea; (3) the amino acid replacement I123V occurred independently on four branches, and the replacements L99M, L266V and I286V occurred each on two branches. The multiple parallel amino acid replacements that occurred in the evolution of bat RH1 suggest the possibility of multiple convergences of their ecological specialization (i.e., various photic environments) during adaptation for the nocturnal lifestyle, and suggest that further attention is needed on the study of the ecology and behavior of bats.

Multiple Episodes of Convergence in Genes of the Dim Light Vision Pathway in Bats
The molecular basis of the evolution of phenotypic characters is very complex and is poorly understood with few examples documenting the roles of multiple genes. Considering that a single gene cannot fully explain the convergence of phenotypic characters, we choose to study the convergent evolution of rod vision in two divergent bats from a network perspective. The Old World fruit bats (Pteropodidae) are non-echolocating and have binocular vision, whereas the sheath-tailed bats (Emballonuridae) are echolocating and have monocular vision; however, they both have relatively large eyes and rely more on rod vision to find food and navigate in the night. We found that the genes CRX, which plays an essential role in the differentiation of photoreceptor cells, SAG, which is involved in the desensitization of the photoactivated transduction cascade, and the photoreceptor gene RH, which is directly responsible for the perception of dim light, have undergone parallel sequence evolution in two divergent lineages of bats with larger eyes (Pteropodidae and Emballonuroidea). The multiple convergent events in the network of genes essential for rod vision is a rare phenomenon that illustrates the importance of investigating pathways and networks in the evolution of the molecular basis of phenotypic convergence.


 

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