大双角蝎蛉幼虫复眼超微结构及其在全变态类幼虫侧单眼演化中的意义

【目的】长翅目(Mecoptera)是全变态类昆虫中唯一在幼虫期具有复眼而无侧单眼的类群,是研究昆虫复眼与侧单眼之间演化关系的理想材料。本研究旨在阐明长翅目幼虫复眼的结构特征,为探讨长翅目幼虫复眼与其他全变态类幼虫侧单眼之间的进化关系提供依据。【方法】本研究运用光学显微镜、扫描和透射电子显微镜技术观察了蝎蛉科(Panorpidae)大双角蝎蛉Dicerapanorpa magna(Chou)幼虫复眼的超微结构,并依据其结构特征对长翅目幼虫复眼在全变态类幼虫侧单眼演化中的意义进行了探讨。【结果】结果表明,大双角蝎蛉幼虫复眼属于并列像眼,由50多个小眼组成。小眼由1个角膜、1个晶体、8个视网膜细胞、2个初级色素细胞和数个次级色素细胞等组成。视网膜细胞分为4个远端细胞和4个近端细胞。远端视网膜细胞的视小杆向上延伸包裹着晶体的基部,使视杆末端呈漏斗状。【结论】分层的视网膜细胞和漏斗状的视杆很可能是长翅目幼虫复眼的共有祖征。这两个特征不存在于长翅目成虫复眼中,但存在于许多渐变态类昆虫中。由此推测,长翅目幼虫复眼可能与渐变态类昆虫的复眼存在同源关系。我们认为,长翅目幼虫独有的复眼很可能是全变态类昆虫的祖征,其他全变态类幼虫的侧单眼可能是由复眼演化来的。     

蟋蟀视觉系统的解剖结构与生理机能

蟋蟀视觉系统由单眼、复眼、视叶三部分组成。蟋蟀的单眼为背单眼,由角膜、角膜生成细胞、视网膜等组成,是提高昆虫复眼所感知的视觉刺激的兴奋水平部位;复眼是最主要的视觉器官,由角膜、晶锥、感杆束和网膜细胞、基膜组成,是光电转导和视觉级联反应的中心;视叶由神经节层、外髓和内髓组成,是视觉神经系统的中心。     

亲土苔蛾成虫复眼超微结构

【目的】重叠型眼在昆虫复眼演化中起着重要作用。本研究旨在阐明夜出型亲土苔蛾Manulea affineola复眼类型及结构特征,以期填补灯蛾亚科昆虫复眼研究的空白,扩充夜出型昆虫复眼的特征数据,为探讨重叠型眼的变异趋势及复眼演化提供依据。【方法】运用光学和透射电子显微技术观察亲土苔蛾成虫复眼的超微结构。【结果】亲土苔蛾成虫复眼具有一个透明区,由6个次级色素细胞的透明胞质构成。小眼具8个视网膜细胞,其中1个视网膜细胞较短,仅位于小眼基部。在透明区内,7个视网膜细胞聚集成一束,其远端与晶体束末端相接,但并不形成视杆。在透明区下方,这7个视网膜细胞形成一个中心融合的视杆。在复眼背缘区的小眼的视杆具有近似矩形的横截面,而其余小眼的视杆具多分支状截面。【结论】亲土苔蛾成虫复眼属于重叠型眼;复眼背缘区的矩形视杆很可能与昆虫的偏振敏感性有关。     

螺旋粉虱成虫的复眼形态及其内部结构

采用扫描电镜和组织切片法,观察了螺旋粉虱Aleurodicus dispersus Russell成虫复眼的形态及其显微结构。结果表明,螺旋粉虱复眼半球状,呈“∞”形分布于头部两侧,单个复眼约由253个小眼组成;各小眼面微凸,复眼中心区域小眼多为规则的六边形,密集排列似蜂窝状;近背区边缘小眼多为五边形或近圆形,小眼排列疏松,且少量相邻小眼的间距较大。雌、雄复眼小眼面积约为85μm2。单个小眼由角膜、晶体、网膜细胞及其特化产生的视杆和基细胞等几部分组成。晶体有四个晶锥细胞构成,晶体、视杆周围和色素细胞内均含有大量的色素颗粒。螺旋粉虱的复眼属于并置复眼。光、暗条件下,小眼的色素颗粒分布有所不同。光适应条件下,色素颗粒较均匀地分布于视杆上下两侧;暗适应状态下,色素颗粒则主要分布在视杆上侧和晶体下侧。而在相同的明、暗适应条件下,性别对色素颗粒的分布无显著影响。     

南五台蝎蛉成虫复眼的超微结构

采用扫描电镜和组织切片法,观察南五台蝎蛉Panorpa nanwutaina Chou成虫复眼的超微结构。南五台蝎蛉复眼近半椭球形,包括1500～1600个小眼。小眼表面光滑,由角膜、晶体、2个初级和12个次级色素细胞、视杆、以及基膜组成。角膜为多层片状纤维结构;晶体含有4个晶锥细胞;视杆由若干个视网膜细胞组成。晶体、视杆周围、和色素细胞内含有大量的色素颗粒,基膜两侧也有色素颗粒分布。南五台蝎蛉的复眼属于并列像眼。与普通蝎蛉P.communis L.小眼的次级色素细胞数目不同。讨论了南五台蝎蛉角膜的功能以及感觉毛和次级色素细胞在分类中的作用。     

柚木野螟成虫复眼外部形态和超微结构观察

【目的】柚木野螟Eutectona machaeralis主要取食危害珍贵树种柚木。本研究旨在观察研究柚木野螟成虫复眼的形态、组织结构和超微结构,分析其复眼结构特征,为更好了解该物种复杂的视觉行为与感光、趋光机制的关系奠定基础。【方法】运用光学显微镜以及扫描和透射电子显微镜技术观察了柚木野螟成虫复眼的形态、组织结构和超微结构。【结果】柚木野螟成虫复眼着生于头部触角基部,呈椭球形,属对称性复眼。雌、雄成虫复眼分别有2 300~2 755和1 950~2 316个小眼。小眼呈正六边形,表面密被角膜乳突,间隙偶有感觉毛。每个小眼由1个角膜、4个晶锥细胞、1对初级色素细胞,6个次级色素细胞、不同水平面分布的12个视网膜细胞和基膜等组成。沿小眼纵轴11个视网膜细胞的向心侧细胞膜特化成细丝状微绒毛,形成放射状排列的视小杆,组合呈融合型视杆;第12个视网膜细胞位于小眼基部。基膜上方,视网膜细胞和次级色素细胞末端膨大,以轴突形式穿过基底膜。【结论】柚木野螟复眼为典型的重叠像眼,雌、雄成虫小眼排列方式及内部结构无明显差异,但雌、雄虫小眼数量和大小具有明显的性二型现象。     

东方蜜蜂背单眼的结构和胚后发育

本研究通过形态解剖和BrdU免疫组织化学方法对东方蜜蜂Apis cerana Fabricius背单眼的胚后发育过程进行了比较研究,结果表明:东方蜜蜂的每一个背单眼都包括角膜晶体、角膜生成细胞、小网膜细胞以及后部的单眼神经。蜜蜂的背单眼起源自头壳上皮;其胚后发育的高峰期集中在蛹发育的前3d;其新细胞主要来源于上皮细胞和圆锥形单眼囊周围细胞的有丝分裂;单眼同脑的联系在P1期前后就已经建立;角膜晶体的形成在P5以后。说明单眼的结构和发育同其功能密切相关。     

棉铃虫蛾复眼的微细结构及其区域性差异

用电子显微镜观察棉铃虫蛾复眼的微细结构及其区域性差异。此复眼具有小网膜细胞柱的透明带。每个小眼包括一个外凸内平的角膜,一个晶锥,四个形成晶锥、晶束的晶锥细胞和两个围绕着晶锥的主虹膜细胞,六至八个小网膜细胞和一个基细胞。晶锥末端有一短小固定的晶束。小网膜细胞柱远侧中央有似微绒毛结构的视杆束。每个小眼被六个附色素细胞围绕。 微细结构的区域性差异:1.背方小眼视杆中段横切面近似矩形,主要由六个微绒毛平行排列的三角形视小杯组成,整个视杆包含两个互相垂直的微绒毛轴;腹方、前方、后方和侧方区域的小眼视杆中段横切面为风扇形,“V”字形视小杆内微绒毛排列不平行;2.前方区域小眼视杆中段的横切面要比后方大;3.前方、腹方区域内,有的相邻小眼的小网膜细胞柱互相连结,背方、后方区域未观察到这一现象。     

双斑蟋复眼和视叶的显微结构

【目的】为探索昆虫视觉信号处理的重要神经结构,详细观察和描述了直翅目(Orthoptera)蟋蟀科(Gryllidae)代表性昆虫双斑蟋Gryllus bimaculatus De Geer复眼和视叶的组织学结构特征。【方法】利用扫描电镜技术和组织学切片技术,观察分析了30只双斑蟋的复眼和视叶组织学结构。【结果】双斑蟋复眼约有3400个小眼,均为六边形结构,小眼间隙内分布有机械感受器——感觉毛和钟形感受器。每个小眼均由角膜、晶锥、感杆束、6个网膜细胞及基膜等构成。视叶呈两个扇形结构,由三大神经纤维网构成,分别为神经节层、外髓、内髓。【结论】双斑蟋复眼表面具有少量感觉毛和钟形感受器,每个小眼均由角膜、晶锥、感杆束、6个网膜细胞及基膜等构成,属并列像眼,视叶由三大神经纤维网构成。     

灰茶尺蠖成虫复眼的超微结构及其明暗适应中的变化

【目的】明确灰茶尺蠖Ectropis grisescens成虫复眼的超微结构及其明暗适应中的变化,探究其调光机制。【方法】采用超景深显微镜测定了灰茶尺蠖成虫复眼的小眼数量、间角、直径和曲率半径等外部参数,并通过组织切片、光学显微镜和透射电子显微镜等技术观察了复眼的内部超微结构;通过光学显微镜观察了灰茶尺蠖成虫复眼在明暗环境中分别适应2 h后晶锥结构及色素颗粒的位置变化。【结果】灰茶尺蠖成虫复眼呈半球形,雌、雄虫单个复眼分别有2 502±105和3 123±78个小眼。小眼自远端至近端由角膜、晶锥、透明区构成的屈光层和由15个视网膜细胞构成的感光层组成。2个初级色素细胞包裹着晶锥,自角膜近端延伸至视网膜细胞核区的远端;每个小眼外围由6个次级色素细胞围绕,自角膜近端延伸至基膜;在透明区内14个视网膜细胞聚集成束(非感杆束),远端与晶锥束末端连接,在感光层内形成闭合型感杆束,延伸至第15个视网膜细胞(基部视网膜细胞)。在明暗适应时,灰茶尺蠖复眼的晶锥细胞间出现开闭,色素颗粒进行纵向位移,以适应外界的光强度的变化。【结论】灰茶尺蠖成虫复眼属于重叠像眼,感杆束为“14+1”模式;屏蔽色素颗粒的移动是其复眼适应外界光强度变化的重要机制。     

Ultrastructure of the single-chamber stemmata of Arge pagana (Panzer, 1798) (Hymenoptera: Argidae)

Stemmata are peculiar visual organs of most larvae in holometabolous insects. In Hymenoptera, Symphyta larvae exclusively possess a pair of stemmata, whose cellular organizations have not been thoroughly elucidated to date. In this paper, the morphology and fine structure of stemmata were investigated in the large rose sawfly Arge pagana (Panzer, 1798) using light and electron microscopy. The larvae possess a pair of stemmata, which belong to the “unicorneal composite eye” or single-chamber stemmata. Each stemma is composed of a biconvex cornea lens, a layer of corneagenous cells, numerous pigment cells, and hundreds of retinula cells. According to the number of retinula cells forming a rhabdom, the stemma can be divided into two regions, the larger Region I and the smaller Region II. The former occupies the largest area of the stemma and contains the majority of rhabdoms, each of which is formed by the rhabdomeres of eight retinula cells. The latter occupies a narrow posterior margin, where each rhabdom consists of nine retinula cells. Based on the different cellular organizations of rhabdoms, the stemma of Argidae is likely developed by the fusion of two types of ommatidial units.     

Ultrastructure of the larval eye of the scorpionfly Panorpa dubia (mecoptera: Panorpidae) with implications for the evolutionary origin of holometabolous larvae

The evolutionary origin of holometabolous larvae is a long‐standing and controversial issue. The Mecoptera are unique in Holometabola for their larvae possessing a pair of compound eyes instead of stemmata. The ultrastructure of the larval eyes of the scorpionfly Panorpa dubia Chou and Wang, 1981 was investigated using transmission electron microscopy. Each ommatidium possesses a cornea, a tetrapartite eucone crystalline cone, eight retinula cells, two primary pigment cells, and an undetermined number of secondary pigment cells. The rhabdomeres of the eight retinula cells form a centrally‐fused, tiered rhabdom of four distal and four proximal retinula cells. The rhabdomeres of the four distal retinula cells extend distally into a funnel shape around the basal surface of the crystalline cone. Based on the similarity of the larval eyes of Panorpidae to the eyes of the hemimetabolous insects and the difference from the stemmata of the holometabolous larvae, the evolutionary origin of the holometabolous larvae is briefly discussed. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

Optic lobes of the larval and imaginal scorpionfly Panorpa vulgaris (Mecoptera,Panorpidae): A neuroanatomical study of neuropil organization,retinula axons,and lamina monopolar cells

Panorpa larvae possess stemmata (lateral ocelli), which have the structure of compound eyes, and stemma lamina and stemma medulla neuropils. A distinct lobula neuropil is lacking. The stemma neuropils have a columnar organization. They contain lamina monopolar cells, and both short and long visual fibers. All the identified larval monopolar neurons have radially arranged dendrites along the entire depth of the lamina neuropil and a single terminal arborization within the medulla (L1/L2-type). The terminals of visual fibers have short spiny lateral projections. Long fibers possess en passant synapses within the lamina. The same principles of organization of first and second order visual neuropils are found in Panorpa imagines. In contrast to the larvae, a lobula neuropil is present. Adults have monopolar cells of the L1-type that are similar to the L1-neurons found in Diptera. The columnar organization, the presence of short and long visual fibers, and lamina monopolar neurons are thus features common to both visual systems, viz., the larval (stemmata) and the imaginal (compound eyes).     

Structure and development of the larval visual system in embryos of Lytta viridana leconte (coleoptera,meloidae)

At hatching (252–264 hr. at 25 ± 0.5°C), the visual system in larvae of Lytta viridana consists of paired stemmata, stemmatal nerves, optic neuropiles, and inner and outer imaginal optic lobe anlagen. It originates between 64 and 72 hr. with invagination of an optic lobe primordium in the side of each protocephalic lobe. These primordia later differentiate into protocerebral ganglion cells and the imaginal optic lobe anlagen. Each stemma arises at 72 hr. from epidermis below and behind the optic lobe invagination and subsequently becomes cupshaped, closes over, and differentiates. At hatching, it consists of a planoconvex corneal lens, a corneagenous layer, and an everse retina of numerous, pigmented retinular cells, each with a terminal rhabdomere. Between 96 and 104 hr, proximal ends of the retinular cells grow posteromedially into a transverse, horizontal fold in the posterior wall of each optic lobe invagination and along its length to the protocerebral neuropile, which they contact by 112 hr. As the brain withdraws posteriorly within the head, these axons elongate correspondingly. Sheath cells of stemmata and stemmatal nerves descend either from protocerebral perineurium or the optic lobe primordia. Structure and development of the larval visual system in L. viridana are compared with those of other insects and its various components are shown to be homologous throughout the Insecta. However, the stemmata of this insect more closely resemble the atypical imaginal eyes of male scale insects than the photoreceptors of other holometabolous larvae–a similarity arising through convergence.     

Internal extraocular photoreceptors in a dipteran insect

Within the head capsule of the moth-fly Psychoda cinerea, underlying each of the two compound eyes, are two internal ocelli of different sizes. There are seven photoreceptor cells in Ocellus I and two in Ocellus II. The internal Ocellus I appears clearly different from the retina of the compound eye, by different rhabdom structure, different size of pigment granules and different stability of these pigments to solvents. Ocellus II does not contain any pigment granules. The physiological activity of these photoreceptors is indicated by their well-developed axons, the rhabdom structure, organelles produced by membrane reorganization, and Actaptation phenomena. The internal ocelli are former larval stemmata that have been displaced inward during metamorphosis. Presumably they have a stimulatory action on the CNS, in analogy with the dorsal ocelli, which are lacking in Psychoda. It is plausible to credit the internal ocelli with a photosensitive role in the functional complex of pacemakers and circadian rhythm.     

Phylogeny of the Myriapoda – Crustacea – Insecta: a new attempt using photoreceptor structure*

According to molecular sequence data Crustacea and not Myriapoda seem to be the sister‐group to Insecta. This makes it necessary to reconsider how the morphology of their eyes fit with these new cladograms. Homology of facetted eye structures in Insecta (Hexapoda in the sense of Ento‐ and Ectognatha) and Crustacea is clearly supported by identical numbers of cells in an ommatidium (two corneageneous or primary pigment cells, four Semper cells which build the crystalline cone and primarily eight retinula cells). These cell numbers are retained even when great functional modification occurs, especially in the region of the dioptric apparatus. There are two different possibilities to explain differences in eye structure in Myriapoda depending on their phylogenetic position in the cladogram of Mandibulata. In the traditional Tracheata cladogram, eyes of Myriapoda must be secondarily modified. This modification can be explained using the different evolutionary pathways of insect facetted eyes to insect larval eyes (stemmata) as an analogous model system. Comparative morphology of larval insect eyes from all holometabolan orders shows that there are several evolutionary pathways which have led to different types of stemmata and that the process always involved the breaking up the compound eye into individual larval ommatidia. Further evolution led on many occasions to so‐called fusion‐stemmata that occur convergently in each holometabolic order and reveals, in part, great structural similarities to the lateral ocelli of myriapods. As myriapodan eyes cannot be regarded as typical mandibulate ommatidia, their structure can be explained as a modified complex eye evolved in a comparable way to the development to the fusion‐stemmata of insect larvae. The facetted eyes of Scutigera (Myriapoda, Chilopoda) must be considered as secondarily reorganized lateral myriapodan stemmata, the so‐called ‘pseudo‐compound eyes’. New is a crystalline cone‐like vitreous body within the dioptric apparatus. In the new cladogram with Crustacea and Insecta as sister‐groups however, the facetted eyes of Scutigera can be interpreted as an old precursor of the Crustacea – Insecta facetted eye with modified ommatidia having a four‐part crystalline cone, etc. as a synapomorphy. Lateral ocelli of all the other Myriapoda are then modified like insect stemmata. The precursor is then the Scutigera‐Ommatidium. In addition further interpretations of evolutionary pathways of myriapodan morphological characters are discussed.     

Eye and optic lobe metamorphosis in the sunburst diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae)

Nearly nothing is known about the transition that visual brain regions undergo during metamorphosis, except for Drosophila in which larval eyes and the underlying neural structure are strongly reduced. We have studied the larvae of the sunburst diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae), which are sophisticated visually oriented predators characterized by six elaborate stemmata on each side of the head and an associated large optic lobe. We used general neurohistological staining and 3D reconstruction to determine how the eyes and optic lobe of T. marmoratus change morphologically during metamorphosis. We find that in third (last) instar larvae, the adult neuropils are already forming de novo dorsally and slightly anteriorly to the larval neuropils, while the latter rapidly degenerate. Larval eyes are eventually reduced to distinct areas with dark pigmentation. This complete reorganization, which may be an evolutionarily conserved trait in holometabolous insects, occurs despite the considerable costs that must apply to such a visually complex animal. Our findings are consistent with the concept that stemmata are homologous to the most posterior ommatidia of hemimetabolous insects, an idea also recently supported by molecular data.     

Opsin evolution and expression in Arthropod compound Eyes and Ocelli: Insights from the cricket Gryllus bimaculatus

ABSTRACT: BACKGROUND: Opsins are key proteins in animal photoreception. Together with a light-sensitive group, the chromophore, they form visual pigments which initiate the visual transduction cascade when photoactivated. The spectral absorption properties of visual pigments are mainly determined by their opsins, and thus opsins are crucial to understand the adaptations of animal eyes. Studies on the phylogeny and expression pattern of opsins have received considerable attention, but our knowledge about insect visual opsins is still limited. Up to now, researchers have focused on holometabolous insects, while general conclusions require sampling from a broader range of taxa. We have therefore investigated visual opsins in the ocelli and compound eyes of the two-spotted cricket Gryllus bimaculatus, a hemimetabolous insect. RESULTS: Phylogenetic analyses place all identified cricket sequences within the three main visual opsin clades of insects. We assign three of these opsins to visual pigments found in the compound eyes with peak absorbances in the green (515 nm), blue (445 nm) and UV (332 nm) spectral range. Their expression pattern divides the retina into distinct regions: (1) the polarization-sensitive dorsal rim area with blue- and UV-opsin, (2) a newly-discovered ventral band of ommatidia with blue- and green-opsin and (3) the remainder of the compound eye with UV- and green-opsin. In addition, we provide evidence for two ocellar photopigments with peak absorbances in the green (511 nm) and UV (350 nm) spectral range, and with opsins that differ from those expressed in the compound eyes. CONCLUSIONS: Our data show that cricket eyes are spectrally more specialized than has previously been assumed, suggesting that similar adaptations in other insect species might have been overlooked. The arrangement of spectral receptor types within some ommatidia of the cricket compound eyes differs from the generally accepted pattern found in holometabolous insect taxa and awaits a functional explanation. From the opsin phylogeny, we conclude that gene duplications, which permitted differential opsin expression in insect ocelli and compound eyes, occurred independently in several insect lineages and are recent compared to the origin of the eyes themselves.     

The role of the ocelli in the phototactic behaviour of the haematophagous bug Triatoma infestans

In addition to compound eyes, most adult insects posses two or three simple eyes, the ocelli. The function of these photoreceptors remains elusive in most cases. Triatomine bugs posses two well-developed ocelli, located in a latero-dorsal position, behind the compound eyes. We tested the role of the ocelli in the phototactic behaviour of Triatoma infestans, by measuring the time spent by adult males in the dark half of an experimental arena, which had the other half illuminated. The occlusion of the ocelli or the compound eyes alone had little effect on the phototactic response of the bugs. Only those insects which had both their ocelli and compound eyes occluded showed a significant reduction in their negative response to light. The ability of the ocelli of T. infestans to mediate the phototactic response by themselves (i.e., not through the modulation of compound eyes sensitivity) constitutes the first report on this function in insects.