The sternal glands of termites: segmental pattern,phylogenetic implications

Summary In Mastotermitidae, 3 sternal glands are observed on the 3rd, 4th and 5th abdominal segments. All other families only bear one gland, set on the 4th segment in Termopsidae and Hodotermitidae, and on the 5th in Kalotermitidae, Rhinotermitidae, Serritermitidae and Termitidae. This character may be useful for a phylogenetic analysis.     

白蚁踪迹信息素研究进展

近年来, 固相微萃取技术的使用显著促进了白蚁踪迹信息素研究的开展。目前, 已有77种白蚁的踪迹信息素得到研究, 常见化学成分为十二碳单烯醇、 十二碳二烯醇和十二碳三烯醇, 其次为新松柏烯。已经鉴定的踪迹信息素主要为单组分或双组分系统。白蚁踪迹信息素由腹板腺分泌, 除澳白蚁科的达氏澳白蚁Mastotermes darwiniensis具有3个腹板腺外, 现存的白蚁均具有1个腹板腺, 位于第4或第5腹节。所有腹板腺都具有类型Ⅰ和Ⅱ两类细胞, 原白蚁亚科（Termopsinae）、 齿白蚁科（Serritermitidae）、 鼻白蚁科（Rhinotermitidae）种类的腹板腺还具有类型Ⅲ细胞。踪迹信息素的生物合成还缺乏研究, 推测有甲羟戊酸、 脂肪醇和饱和表皮烃3种途径。白蚁踪迹信息素的简约性十分显著, 不同地理分布、 生物生态习性以及一些系统距离较远的种类具有相同和密切相关的踪迹信息素。对于许多种类, 相同的信息化合物具有踪迹信息素和配对性信息素双重功能。白蚁踪迹信息素种特异性和简约性的适应意义和进化机制需要进一步研究。     

白蚁信息素研究进展

白蚁是最古老的社会性昆虫, 其社会性的维持需要信息素的相互作用。本文回顾了近年来国内外白蚁信息素研究的最新进展, 内容涉及白蚁踪迹信息素、 性信息素、 告警信息素和促食信息素的功能、 化学成分及产生信息素的外分泌腺。白蚁分泌信息素的腺体主要有背板腺、 腹板腺、 后腹板腺、 额腺和唾腺。绝大多数白蚁信息素是挥发性物质。白蚁在化学通讯上存在节俭策略, 即同一种化合物由不同的白蚁种类的不同外分泌腺分泌, 可具有不同的功能。总结了各类信息素在白蚁物种间、 同一物种的品级间和性别间的异同和作用方式, 强调了白蚁信息素的反应阈值、 最佳浓度、 有效期和物种特异性对其功能的影响。目前对白蚁信息素的研究尚处于起步阶段, 其研究成果对等翅目系统发育研究和白蚁防治具有重要的意义。文章最后展望了白蚁信息素在白蚁防治上的应用前景。     

八种白蚁的兵蚁和工蚁消化道形态比较研究(等翅目)

为探讨白蚁消化道形态品级差异及其系统学意义,对4个科8种白蚁兵蚁和工蚁的消化道进行比较形态学研究.结果表明:低等白蚁的兵蚁和(拟)工蚁形态较为相似,高等白蚁的兵蚁与工蚁局部特征存在明显差异.由低等到高等兵蚁和工蚁消化道各部分差异呈增多趋势.前、中、后肠占消化道的百分比在山林原白蚁Hodotermopsis sjoest...     

The oldest known mastotermitids (Blattodea: Termitoidae) and phylogeny of basal termites

Five finely preserved termites from the mid‐Cretaceous (Cenomanian) amber of Myanmar provide new information allowing a reanalysis of the phylogeny of basal termites. The Mastotermitidae family is recovered as monophyletic, and a redefined Hodotermitidae sensu lato is also monophyletic to include Archotermopsidae, Hodotermitidae and Stolotermitidae. Such a phylogenetic relationship agrees with the results from previous molecular phylogeny. Alongside these findings, there are many taxa that can only be shown to be termites with no other phylogenetically informative data. These form a comb of ‘grade groups’ emerging in the Late Jurassic. The new amber specimens are described as two new species. Anisotermes xiai gen. et sp.n. is described from multiple castes and has symplesiomorphic characteristics: large body size, a broad pronotum, well‐developed reticulated veins, and a large anal lobe of the hindwings. It shares wing features with the other new species, Mastotermes monostichus sp.n. Both new taxa are assigned to the Mastotermitidae, as they are shown to have synapomorphies that unite the family. This published work has been registered on ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:1AD5CECA‐27B7‐48D5‐88DC‐CEC5150962D7 .     

Species-specific sex pheromones secreted from new sexual glands in two sympatric fungus-growing termites from northern Vietnam, <Emphasis Type="Italic">Macrotermes annandalei</Emphasis> and <Emphasis Type="Italic">M. barneyi</Emphasis>

Summary Reproductive isolation in termites is not well known. Our study carried out on two sympatric species from northern Vietnam, Macrotermes annandalei and M. barneyi, showed that dispersal flights and sex pheromones were two important factors in their reproductive isolation. These fungus-growing termites were isolated, partially due to the timing of their respective dispersal flights. M. annandalei flew the first day after rain, while the flights of M. barneyi occurred the second day after rain. However, the flights can also be simultaneous in the two species. Sex pheromones of M. annandalei and M. barneyi were shown to be species-specific. In both species, they were secreted by females from two glandular sources, from tergal glands located on tergite 6 to 10 in M. annandalei and tergite 5 to 10 in M. barneyi, and from posterior sternal glands located on sternite 6 and 7 in both species. These posterior sternal glands, found for the first time in the Termitidae, were sex-specific glands. Although not fully identified, sex pheromones of M. annandalei and M. barneyi were clearly different from the trail-following pheromone secreted by the sternal gland stricto sensu located on the sternite 5. These results show that in termites, the sexual behaviour, the glandular origin of sex pheromones and their role in reproductive isolation greatly vary depending on the species and deserve to be more extensively studied.Received 8 April 2003; revised 1 September 2003; accepted 10 September 2003.     

A mitochondrial genome phylogeny of termites (Blattodea: Termitoidae): Robust support for interfamilial relationships and molecular synapomorphies define major clades

Despite their ecological significance as decomposers and their evolutionary significance as the most speciose eusocial insect group outside the Hymenoptera, termite (Blattodea: Termitoidae or Isoptera) evolutionary relationships have yet to be well resolved. Previous morphological and molecular analyses strongly conflict at the family level and are marked by poor support for backbone nodes. A mitochondrial (mt) genome phylogeny of termites was produced to test relationships between the recognised termite families, improve nodal support and test the phylogenetic utility of rare genomic changes found in the termite mt genome. Complete mt genomes were sequenced for 7 of the 9 extant termite families with additional representatives of each of the two most speciose families Rhinotermitidae (3 of 7 subfamilies) and Termitidae (3 of 8 subfamilies). The mt genome of the well supported sister-group of termites, the subsocial cockroach Cryptocercus, was also sequenced. A highly supported tree of termite relationships was produced by all analytical methods and data treatment approaches, however the relationship of the termites+Cryptocercus clade to other cockroach lineages was highly affected by the strong nucleotide compositional bias found in termites relative to other dictyopterans. The phylogeny supports previously proposed suprafamilial termite lineages, the Euisoptera and Neoisoptera, a later derived Kalotermitidae as sister group of the Neoisoptera and a monophyletic clade of dampwood (Stolotermitidae, Archotermopsidae) and harvester termites (Hodotermitidae). In contrast to previous termite phylogenetic studies, nodal supports were very high for family-level relationships within termites. Two rare genomic changes in the mt genome control region were found to be molecular synapomorphies for major clades. An elongated stem-loop structure defined the clade Polyphagidae + (Cryptocercus+termites), and a further series of compensatory base changes in this stem-loop is synapomorphic for the Neoisoptera. The complicated repeat structures first identified in Reticulitermes, composed of short (A-type) and long (B-type repeats) defines the clade Heterotermitinae+Termitidae, while the secondary loss of A-type repeats is synapomorphic for the non-macrotermitine Termitidae.     

Location,morphology and function of nephrocytes in termites

Insect nephrocytes are cells bathed in hemolymph and considered to have an excretory function. These cells have ambiguous nomenclature and are understudied in termites. This study is the first report on the occurrence, morphology and function of nephrocytes in different termite castes. Cytological characteristics in specific developmental stages and castes enable physiological functions to be inferred. Perforate diaphragms indicate a role in filtration, while the extensive peripheral invaginations of the cell membrane suggest active endocytosis. A sequence of morphologies in putative digestive vacuoles infers a lysosomal system and the occurrence of phosphatases suggests a function involving detoxification of substances sequestered from hemolymph. Pericardical nephrocytes took up the dye trypan blue injected in live termites, suggesting their activity connected to the filtration of the hemolymph. Additionally, histochemical tests showed the existence of stored proteins in their cytoplasm. These cells present a well-developed Golgi apparatus and abundant rough endoplasmic reticulum, consistent with protein synthesis. This study highlights the importance of nephrocytes in Isoptera and opens perspectives for further research of these cells.     

Colony-dependent sex differences in protozoan communities of the lower termite <Emphasis Type="Italic">Reticulitermes speratus</Emphasis> (Isoptera: Rhinotermitidae)

In many animals, sex differences in hormones, behavior, and immunity lead to differences in their gut microbial communities. One of the best-known examples of mutualistic symbiosis is that between lower termites and their intestinal protozoa. Although differences in the protozoan communities of different castes have been studied in lower termites, nothing is known about the sex differences in protozoan communities in neuter castes. Here, we show that termite workers have different protozoan communities according to sex depending on the colony. We investigated the communities of symbiotic protozoa living in lower termites, Reticulitermes speratus, and how they are affected by sex and caste. Workers had the largest numbers of protozoa, followed by soldiers, whereas reproductives (primary kings and secondary queens) had no protozoa. Workers showed colony-dependent sex differences in the total abundance of protozoa, whereas soldiers showed no such sex differences. There were significant sex effect and/or interaction effect between colony and sex in abundances of five species of protozoa in workers. Workers also showed significant sex differences and/or colony-dependent sex differences in proportion of six species of protozoa. These may result in sex differences in the host–symbiont interaction due to physiological or behavioral sex differences in workers that have not been recognized previously. This study has an important implication: although workers are not engaged in reproduction, their potential sex difference may affect various aspects of social interactions.     

Arolia in termites (Isoptera): functional significance and evolutionary loss

Summary. Termite workers from all families examined had no arolia (=adhesive pads) on their tarsi and are unable to climb smooth vertical surfaces such as glass or polypropylene plastic. This contrasts with ants where both workers and alates of most species possess arolia and are able to climb these surfaces. Arolia were present in alates of the majority of species investigated from three of the four most basal termite families (Mastotermitidae, Termopsidae and Kalotermitidae), though absent from the basal family Hodotermitidae that contains only three genera. Alates in the two kalotermitid species tested readily climbed glass walls. The complete evolutionary loss of arolia from alates in the specious two most apical termite families (Rhinotermitidae and Termitidae) suggests paedomorphosis. Very smooth surfaces probably cannot be used to completely prevent entry of rhinotermitid termites into buildings because these termites can eventually build galleries of feces and soil over these surfaces. However, an experiment with Coptotermes formosanus showed that a smoother surface significantly slows down the rate of gallery building.Received 12 February 2004; revised 17 June 2004; accepted 29 June 2004.     

The phylogeny of termites (Dictyoptera: Isoptera) based on mitochondrial and nuclear markers: Implications for the evolution of the worker and pseudergate castes, and foraging behaviors

A phylogenetic hypothesis of termite relationships was inferred from DNA sequence data. Seven gene fragments (12S rDNA, 16S rDNA, 18S rDNA, 28S rDNA, cytochrome oxidase I, cytochrome oxidase II and cytochrome b) were sequenced for 40 termite exemplars, representing all termite families and 14 outgroups. Termites were found to be monophyletic with Mastotermes darwiniensis (Mastotermitidae) as sister group to the remainder of the termites. In this remainder, the family Kalotermitidae was sister group to other families. The families Kalotermitidae, Hodotermitidae and Termitidae were retrieved as monophyletic whereas the Termopsidae and Rhinotermitidae appeared paraphyletic. All of these results were very stable and supported with high bootstrap and Bremer values. The evolution of worker caste and foraging behavior were discussed according to the phylogenetic hypothesis. Our analyses suggested that both true workers and pseudergates (“false workers”) were the result of at least two different origins. Our data support a traditional hypothesis of foraging behavior, in which the evolutionary transition from a one-piece type to a separate life type occurred through an intermediate behavioral form.     

Ultrastructure of posterior sternal glands of Macrotermes annandalei (Silvestri): new members of the sexual glandular set found in termites (Insecta)

In female alates of Macrotermes annandalei, two types of abdominal glands are involved in the secretion of sex pheromone. Tergal glands are found at the anterior margin of tergites 6-10 and posterior sternal glands (PSGs) are located at the anterior margin of sternites 6-7. The cytological features of both types of glands are quite similar. The fine structural organization of PSGs is studied more precisely and described for the first time. The glandular cuticle is pitted with narrow apertures corresponding to the openings of numerous subcuticular pouches. Several Class 3 glandular units open in each pouch. One canal cell and one secretory cell make an individual glandular unit. The canal cell is enlarged apically and is connected with the other canal cells to form a common pouch. Based on the structural features found in these glands, we propose a common secretory process for PSGs and tergal glands. During the physiological maturation of alates inside the nest, secretory vesicles amass in the cytoplasm of secretory cells, while large intercellular spaces collapse the cuticular pouches. At the time of dispersal flight, pouches are filled with the content of secretory vesicles while intercellular spaces are sharply reduced. After calling behavior, no secretion remains in the glands and pouches collapse again, while secretory cells are drastically reduced in size. The structure and the secretory processes of PSGs and tergal glands are compared to those of abdominal sexual glands known in termites.     

Morphological phylogenetics of termites (Isoptera)

Isoptera (termites) are an ecologically important order, with both a high abundance and biomass in tropical ecosystems. However, there have been few phylogenetic hypotheses for termites, and we present here the first comprehensive cladistic analysis for the group. We analysed relationships between all seven termite families, including representatives of all known feeding group, plus a number of systematically critical taxa. Termite species richness is biased towards the higher termites (Termitidae), and our taxon sampling reflects this. Our analysis was based essentially on morphological characters (96 workers, 93 soldiers) plus seven biological characters. The cladistic analysis gave four equally parsimonious trees, representing two islands of topologies. The strict consensus tree is fully resolved for the higher termites, but less so for the lower termites. Overall there is low statistical support for the suggested topology, and this can be explained by the high incongruence between the data sets (worker, soldier and biological). This study highlights the particular problems of coding morphological characters in social insects with multiple castes. Without the input of additional data sets, e.g. alates, biological, behavioural and molecular, it will not be possible to obtain a well-supported termite phylogeny.     

Phylogenetic evidence for a single,ancestral origin of a ‘true’ worker caste in termites

Phylogenetic analysis based on sequence variation in mitochondrial large‐subunit rRNA and cytochrome oxidase II genes was used to investigate the evolutionary relationships among termite families. Maximum likelihood and parsimony analyses of a combined nucleotide data set yield a single well‐supported topology, which is: (((((Termitidae, Rhinotermitidae), Serritermitidae), Kalotermitidae), (Hodotermitidae, Termopsidae)), Mastotermitidae). Although some aspects of this topology are consistent with previous schemes, overall it differs from any published. Optimization of ‘true’ workers onto the tree suggests that this caste originated once, early in the history of the lineage and has been lost secondarily twice. This scenario differs from the more widely accepted notion that workers are derived and of polyphyletic origin and that extant pseudergates, or ‘false’ workers, are their developmentally unspecialized ancestor caste. Worker gains and losses covary directly in number and direction with shifts in ‘ecological life type’. A test for correlated evolution which takes phylogenetic structure into account indicates that this pattern is of biological significance and suggests that the variable occurrence of a worker caste in termites has ecological determinants, apparently linked to differences in feeding and nesting habits.     

The Soldiers in Societies: Defense,Regulation, and Evolution

The presence of reproductively altruistic castes is one of the primary traits of the eusocial societies. Adaptation and regulation of the sterile caste, to a certain extent, drives the evolution of eusociality. Depending on adaptive functions of the first evolved sterile caste, eusocial societies can be categorized into the worker-first and soldier-first lineages, respectively. The former is marked by a worker caste as the first evolved altruistic caste, whose primary function is housekeeping, and the latter is highlighted by a sterile soldier caste as the first evolved altruistic caste, whose task is predominantly colony defense. The apparent functional differences between these two fundamentally important castes suggest worker-first and soldier-first eusociality are potentially driven by a suite of distinctively different factors. Current studies of eusocial evolution have been focused largely on the worker-first Hymenoptera, whereas understanding of soldier-first lineages including termites, eusocial aphids, gall-dwelling thrips, and snapping shrimp, is greatly lacking. In this review, we summarize the current state of knowledge on biology, morphology, adaptive functions, and caste regulation of the soldier caste. In addition, we discuss the biological, ecological and genetic factors that might contribute to the evolution of distinct caste systems within eusocial lineages.     

Soldier-specific modification of the mandibular motor neurons in termites

Social insects exhibit a variety of caste-specific behavioral tendencies that constitute the basis of division of labor within the colony. In termites, the soldier caste display distinctive defense behaviors, such as aggressively attacking enemies with well-developed mandibles, while the other castes retreat into the colony without exhibiting any aggressive response. It is thus likely that some form of soldier-specific neuronal modification exists in termites. In this study, the authors compared the brain (cerebral ganglion) and the suboesophageal ganglion (SOG) of soldiers and pseudergates (workers) in the damp-wood termite, Hodotermopsis sjostedti. The size of the SOG was significantly larger in soldiers than in pseudergates, but no difference in brain size was apparent between castes. Furthermore, mandibular nerves were thicker in soldiers than in pseudergates. Retrograde staining revealed that the somata sizes of the mandibular motor neurons (MdMNs) in soldiers were more than twice as large as those of pseudergates. The enlargement of MdMNs was also observed in individuals treated with a juvenile hormone analogue (JHA), indicating that MdMNs become enlarged in response to juvenile hormone (JH) action during soldier differentiation. This enlargement is likely to have two functions: a behavioral function in which soldier termites will be able to defend more effectively through relatively faster and stronger mandibular movements, and a developmental function that associates with the development of soldier-specific mandibular muscle morphogenesis in termite head. The soldier-specific enlargement of mandibular motor neurons was observed in all examined species in five termite families that have different mechanisms of defense, suggesting that such neuronal modification was already present in the common ancestor of termites and is significant for soldier function.     

Ultrastructure of the sternal glands inThrips validus uzel (Thysanoptera,terebrantia)

Summary The ultrastructure of the sternal glands of the males ofThrips validus is consistent with the hypothesis that they are involved in pheromone production. The secretory cells, which are strongly modified epidermal cells, are characterized by the abundance of mitochondria and the presence of agranular, tubular endoplasmic reticulum (ATER) and microbodies. Each of the numerous apical microvilli encloses one or several tubular extensions of ATER. Some mitochondria are in close contact with ATER tubules. The mitochondrial matrix is probably involved in the elaboration of the secretory product, which is extruded and possibly modified by the agranular reticulum. The secretion is sudanophilic, but not osmiophilic. No lipid droplets are found in the cytoplasm. After storage in the strongly dilated subcuticular space, the secretion is released by epicuticular ductules with a diameter of about 120 å.I should like to thank the staff of the EM laboratory of the Zoological Institute for technical assistance, especially the photographer, Mrs. M. Ullmann     

Neurosecretion

Summary Ultrastructural specializations characteristic of sites of release of neurosecretory material from axons were examined in several species of blattarian insects. Discharge of such material may take place within or outside of neurohemal organs and is not restricted to fiber terminals. Structurally distinctive areas serving this function occur intermittently and may be more or less transient. Many of these specialized zones face the extracellular stroma that forms sheaths and partitions of neurohemal organs (corpora cardiaca, perisympathetic organs), others contact various cellular elements (nerve fibers with or without neurosecretory granules, glial cells, non-neural endocrine cells).Irrespective of the milieu, these sites of release are characterized by small electron lucent vesicles clustered near the internal surface of the plasma membrane, and by variously shaped accumulations of electron dense material on either side of this membrane. These ultrastructural features are strikingly similar to those of the presynaptic component of conventional interneuronal junctions. However, the functional implications of this morphological resemblance seem to be limited. In neurosecretory systems, physiological phenomena comparable to chemical transmission are out of the question in the absence of postsynaptic cells.In peptidergic neurons of the insect species used in the present study, as in those of various mammals examined by other investigators, the small vesicles observed seem to be the result of fragmentation of neurosecretory granules prior to the discharge of their contents. The presence of variable intermediate stages speaks against a cholingergic role of these synapticlike vesicles at least some of which seem to contain neurosecretory material instead of a neurotransmitter. Furthermore, the variously shaped intra- and extracellular dense material in synaptoid areas seems to represent a neurosecretory product in transit and is therefore not equivalent to dense material customarily found within or on either side of the regular synaptic cleft.Sites of release not directly affiliated with the stroma often share a common narrow gap between adjoining neurosecretory fibers and face each other in mirror image fashion. It is here where the distinction from regular synapses is sometimes more difficult to make because the structural elements of one side of the paired complex may mimic postsynaptic dense material. A further source of difficulty in the interpretation of special contact areas of this sort is the existence of unusual junctions between two classes of neurosecretory neurons (B and A fibers) in which pre- and postsynaptic details are discernible. These, and synaptoid junctions with non-neural endocrine effector cells, seem to serve for the dispatch of local neurosecretory signals that resemble, but are nevertheless apart from, conventional neurohumoral communication. The special neurosesecretory products involved here do not qualify as neurohormones.Synaptoid neurosecretory contact areas with pre- and postsynaptic features should be classified as a group distinct from another group in which the postsynaptic component is absent.Supported by grants AM-3984, NB-00840, and NB-05219 from the U.S.P.H.S.I am greatly indebted to Mrs. Sarah Wurzelmann for her excellent technical assistance.     

The nasus gland: A new gland in soldiers of Angularitermes (Termitidae,Nasutitermitinae)

Termites have developed many exocrine glands, generally dedicated to defence or communication. Although a few of these glands occur in all termite species, or represent synapomorphies of larger clades, others are morphological innovations of a single species, or a few related species. Here, we describe the nasus gland, a new gland occurring at the base of the nasus of Angularitermes soldiers. The nasus gland is composed of class 1, 2, and 3 secretory cells, a rare combination that is only shared by the sternal and tergal glands of some termites and cockroaches. The ultrastructural observations suggest that the secretion is produced by class 2 and 3 secretory cells, and released mostly by class 3 cells. The base of the nasus has a rough appearance due to numerous pits bearing openings of canals conducting the secretion from class 3 secretory cells to the exterior. We tentatively assign a defensive function to the nasus gland, although further research is needed to confirm this function. Although the gland is described only from species of Angularitermes, other genera of Nasutitermitinae also present a rough nasus base, suggesting the presence of a similar, possibly homologous, gland.