【作者】 王波；

【导师】 黄大卫；

【作者基本信息】 山东农业大学 ， 农业昆虫与害虫防治， 2009， 硕士

【摘要】 视觉是动物感知周围环境最重要的途径之一,为了适应各自的环境,动物的视觉系统也进化出多种多样的形态。虽然视觉系统存在形态上的多样性,但动物对环境中光信号的敏感性都依赖于一类相似的物质,即视觉色素。视觉色素由一分子视蛋白脱辅蛋白和一分子来源于维生素A的衍生物的发色团组成,发色团以希夫碱的形式共价连接在视蛋白脱辅蛋白第七个跨膜区的一个赖氨酸残基上,起到感受光的作用。一般通过最大吸收光波波长(λmax)来描述视觉色素。视觉色素的光谱敏感性是由视蛋白跨膜区α螺旋的氨基酸侧链与发色团的专一性相互作用来调节的,由于大多数视觉色素含有相同的发色团,所以视觉色素最大吸收光波波长值是由视蛋白序列上的变化引起的。视蛋白家族成员很多,既有与视觉系统相关的视蛋白,也有许多非视觉系统成员的视蛋白被发现在动物的不同组织内表达。在脊椎动物中,根据最大吸收光波波长的不同,视觉系统视蛋白主要分LWS、SWS1、SWS2、Rh2和Rh1,昆虫视觉系统视蛋白的区分与脊椎动物的类似。新基因是由已存在的基因通过序列和功能上的分化产生的,视蛋白基因也是如此。7亿年前开始,伴随着脊椎动物和无脊椎动物物种的分化,祖先视蛋白基因历经了一系列独立的基因复制事件,产生了几类视蛋白基因。在动物进化过程中,不同种类的视蛋白基因经历了基因复制、基因丢失和引起功能改变的氨基酸替代,使得不同物种视蛋白组成出现多样化的状态。昆虫在大自然中占据多种多样的生态位,拥有不同的行为方式,它们的视觉系统也会发生相应的适应性进化。在榕树与榕小蜂这一典型的互利共生体系中,榕小蜂一生所处的光环境非常特殊。一般情况下,榕小蜂的雄蜂终生生活在果内,复眼退化、单眼缺失,而雌蜂需要出果寻找其它榕果完成传粉或产卵的使命,它们复眼发达。榕果是一个密闭的结构,在榕果内黑暗的空间内,应当没有什么光信息,特别是穿透力很弱的紫外线。一些研究中发现紫外线对很多动物都有重要意义,在与榕小蜂亲缘关系较近的蜜蜂中被证明的有对花的寻找和识别、偏振视觉和飞行定向。与自身所处的光环境的特殊性相适应,榕小蜂紫外线敏感视蛋白基因的进化必然有自身的规律。紫外线对榕小蜂视觉是否有意义?榕小蜂紫外线敏感视蛋白基因会不会有榕果特异性?在传粉榕小蜂与非传粉榕小蜂中是否有差别?为了解决这些问题,我们扩增了分布于4种榕树上的13种榕小蜂的紫外线敏感视蛋白基因cDNA片段和一种榕小蜂的紫外线敏感视蛋白基因cDNA全长。对这些序列的比较及系统发育分析表明,它们都属于紫外线敏感视蛋白支系,编码有紫外线敏感功能的视蛋白。大部分榕小蜂的紫外线敏感视蛋白基因序列高度保守,且表现出了某种程度上的趋同进化,因此该基因片段无法被用来做系统发育分析的分子标记。我们也对这些序列进行了选择压力的分析和祖先状态重建,筛选出了2个正选择位点,没有发现任何平行变化或趋同变化位点。这说明榕小蜂紫外线敏感视蛋白基因可能接受较弱的正选择。更多还原

【Abstract】 Vision is one of the most important ways to perceive ambient enviorenment in animals. The visual systems in animals vary among species as a consequence of adaptive evolution. Although the visual systems are phenotypically diverse, the sensitivity of animals to visual signals is based on the same kind of substance, the visual pigements. A visual pigment is composed of an opsin apoprotein and a Vitamin A-derived chromophore, the chromophore attach to Lys residue covalently in the seventh transmembrane of the opsin apoprotein through a Schiff’s base linkage, responses for light activation. Visual pigments are often characterized by the wavelength of maximal absorption(λmax). The spectral sensitivity of a visual pigment is tuned by specific interactions between the chromophore and the side chains of transmembraneα-helixes of opsin apoprotein. As most visual pigments recruit the same chromophore in animals, observed variation inλmax of a visual pigement is caused by variation in opsin sequence.The opsin family holds a lot of members, with some related to the visual system, and many non-visual opsins expressed in different tissues of animals. According to the wavelength of maximal absorption, vertebrate opsins could be distinguished as five classes: LWS, SWS1, SWS2, Rh2 and Rh1. Insect opsins are characterized in a similar way. Following the divergence of the ancestral vertebrate and invertebrate species, about 700 millions years ago, the ancestral opsin gene underwent a series of independent duplication events, producing several kinds of genes encoding different opsins. In the evolutionary history of animals, diffrent opsin gene lineages diversified by gene losses, gene duplications and function-altering amino acid substitutions.Insects occupy diverse niches in nature and have different behaviour patterns, and relevant adaptive evolution arises in their visual systems. In the mutualism system of fig wasps and their host figs, the light environment in which fig wasps live is very special. Generally, male fig wasps spend all their lives in the syconium of fig, and they have vestigial eyes and no ocelli. However, the female fig wasps have to emerge from the fig syconium and search for another syconium to finish the process of pollination and oviposition, and they have developed compound eyes. The enclosed syconium seems to be a complete dark cavity, with no light signals existing inside, especially for the weak-penetrable UV light. UV light plays a great role in many animals. For example in the bees, which are phylogenetically close related to fig wasps, UV is proved to be responsible for flowers detecting and recognizing, polarized vision and flying orientation. As a consequence of adaptation to the light environment in which they live, the UV sensitive opsins of fig wasps may have evolved in a special way.Does UV light play a role in the vison of fig wasps? Are the UV sensitive opsin genes restricted to figs? Is there any diference in this gene between the pollinators and non-pollinating fig wasps? To figure out these questions, we cloned a full-length UV sensitive opsin gene cDNA from a fig wasp species and partial UV sensitive opsin gene cDNA sequences from other 13 fig wasp species. These 14 fig wasp species are hosted in four different fig species. Comparision and phylogenetic analysis of these sequences indicates they belong to the UV sensitive opsin gene lineage, encode opsins which are responsible for UV light. Most of the UV opsins in fig wasps are too conservative and show a pattern of convergent evolution, so they seem to be unsuitable as a molecular marker for phylogenetic analysis. We also conducted selection test analysis and ancestral-state reconstruction. Two sites were found to be under positive selection, but no parallel or convergent change was observed. This suggests that UV sensitive opsin genes in fig wasps are under weak positive selection.更多还原