Morphological diversity of the skeletal structures of fleas (Siphonaptera). Part 2: The general characteristic and features of the thorax

Analysis of a considerable amount of data on the anatomy of 27 structures of the thorax in 96 genera of fleas (over 90% of the genera in the world fauna) shows that different flea taxa can be described based on 48 universal and specific characters, whose 203 states reflect the entire known diversity of the flea morphology. Of them, 26 characters with 96 states can be formulated based on universal terms; 22 universal characters with 88 states describe the proportions of the segments and their parts, and also proportions and shapes of their sclerites; 23 specific characters with 107 states describe the structure of the thoracic sclerites and ridges as well as the patterns of their junctions. Judging by the number of characters and their states, the most evolutionarily flexible structures in fleas are the mesosternite and its apodeme together with the upper part of the mesopleural rod. Homoplasies at various levels comprise less than half (40%) of all the character states in the thorax structure. The character states reflecting the phylogenetic closeness of taxa make up about 15%.     

Extremely miniaturised and highly complex: The thoracic morphology of the first instar larva of Mengenilla chobauti (Insecta,Strepsiptera)

Thoracic structures of the extremely small first instar larva of the strepsipteran species Mengenilla chobauti (ca. 200 μm) were examined, described and reconstructed 3-dimensionally. The focus is on the skeletomuscular system. The characters were compared to conditions found in other insect larvae of very small (Ptiliidae) or large (Dytiscus) size (both Coleoptera) and features of “triungulin” larvae, first instar larvae of Rhipiphoridae, Meloidae (both Coleoptera), and Mantispidae (Neuroptera).The specific lifestyle and the extreme degree of miniaturisation result in numerous thoracic modifications. Many sclerites of the exo- and endoskeleton are reduced. Cervical sclerites, pleural ridges, furcae and spinae are absent. Most of the longitudinal muscles are connected within the thorax, and a pair of ventral longitudinal muscles is present in the pleural region of the meso- and metathorax. This results in a high intersegmental flexibility. Due to the size reduction and the correlated shift of the brain to the thorax, with 94 identified muscles the thoracic musculature appears highly compact. Compared to larger larvae the number of both the individual muscles and the muscle bundles are distinctly reduced. The thorax of the first instar larvae displays many additional strepsipteran autapomorphies. At least partly due to the highly specialised condition, potential synapomorphies with other groups were not found.     

AUTOMATIC ACOUSTIC IDENTIFICATION OF SINGING INSECTS

ABSTRACT

We report on our research efforts towards developing efficient equipment for the automatic recognition of insects using only the acoustic modality. Specifically, we deal with three groups of insects, namely the crickets, cicadas and katydids. Inspired by well-documented tactics of speech processing, the signal processing employed in the present work is elaborated further with respect to the sound production mechanisms of insects. In order to improve the practical efficacy of our equipment, we adopt a score-level fusion of classifiers with non-parametric (probabilistic neural network) and parametric (Gaussian mixture models) estimation of the probability density function. An efficient hierarchic classification scheme is introduced, where the identification of unlabelled input takes place at various levels of hierarchy, such as suborder, family, subfamily, genus and species. We evaluate the practical significance of our approach on a large and well-documented catalogue of recordings of crickets, cicadas and katydids. For the hierarchic classification scheme, we report identification accuracy that exceeds 99% at suborder and family levels. In the straight classification scheme, we report accuracy of 90% for 307 species.     

Phylogeny of Ensifera (Hexapoda: Orthoptera) using three ribosomal loci, with implications for the evolution of acoustic communication

Representatives of the Orthopteran suborder Ensifera (crickets, katydids, and related insects) are well known for acoustic signals produced in the contexts of courtship and mate recognition. We present a phylogenetic estimate of Ensifera for a sample of 51 taxonomically diverse exemplars, using sequences from 18S, 28S, and 16S rRNA. The results support a monophyletic Ensifera, monophyly of most ensiferan families, and the superfamily Gryllacridoidea which would include Stenopelmatidae, Anostostomatidae, Gryllacrididae, and Lezina. Schizodactylidae was recovered as the sister lineage to Grylloidea, and both Rhaphidophoridae and Tettigoniidae were found to be more closely related to Grylloidea than has been suggested by prior studies. The ambidextrously stridulating haglid Cyphoderris was found to be basal (or sister) to a clade that contains both Grylloidea and Tettigoniidae. Tree comparison tests with the concatenated molecular data found our phylogeny to be significantly better at explaining our data than three recent phylogenetic hypotheses based on morphological characters. A high degree of conflict exists between the molecular and morphological data, possibly indicating that much homoplasy is present in Ensifera, particularly in acoustic structures. In contrast to prior evolutionary hypotheses based on most parsimonious ancestral state reconstructions, we propose that tegminal stridulation and tibial tympana are ancestral to Ensifera and were lost multiple times, especially within the Gryllidae.     

Coping with the cold: temperature and mating activity of male sagebrush crickets Cyphoderris strepitans (Orthoptera: Haglidae)

Abstract. The effect of temperature on male sexual displays is well documented but its role in mediating the differential mating success of males is less well established. Male sagebrush crickets Cyphoderris strepitans Morris and Gwynne occur in high‐elevation sagebrush meadows in mountainous areas of the western U.S.A., and often are observed singing at temperatures as low ?8 to ?4 °C to attract sexually receptive females. Males exhibit differential mating success based on their previous mating experience: virgin males have a higher probability of obtaining a mating than do non‐virgin males of securing an additional mating. This differential mating success is mediated in part by an unusual form of nuptial feeding behaviour. Females feed on males’ hind wings at mating and the costs imposed on males as a consequence of this behaviour constrain male mating success. In the present study, to determine whether sagebrush crickets are capable of some degree of thermoregulation, and also to investigate whether this ability is influenced by male mating experience, thoracic temperatures of males of varying mating status were measured in relation to ambient temperature throughout the breeding season. A full factorial model examining the effect of site of capture, mating status, body mass and ambient temperature reveals that only ambient temperature has a significant effect on thoracic temperature after controlling for all other factors. It is concluded that differences in the calling times of virgin and non‐virgin males and their ability to secure mates does not result from differences in their ability to cope physiologically with low temperatures.     

Selection against Aerial Dispersal in Ants: Two Non-Flying Queen Phenotypes in Pogonomyrmex laticeps

The South American seed-harvester ant Pogonomyrmex laticeps has dimorphic queens: ergatoid (permanently wingless) and brachypterous (short, non-functional wings). Surveys in western Argentina indicated that colonies near Chilecito, La Rioja Province, produced only ergatoid queens, while those near Punta Balasto, Catamarca Province (263 km away), produced only brachypterous queens. Brachypterous queens were significantly larger than ergatoid queens for 10 of 11 external characters, but both phenotypes had comparable reproductive potential, i.e., a spermatheca and a similar number of ovarioles. Using normal winged queens of the closely related P. uruguayensis for comparison, we determined that both queen phenotypes in P. laticeps had a full set of dorsal thoracic sclerites, albeit each sclerite was much reduced, whereas workers had a thorax without distinct dorsal sclerites. Sclerites were fused and immobile in ergatoid queens, while they were separable and fully articulated in brachypterous queens. Both phenotypes lacked the big indirect flight muscles, but brachypterous queens retained the tiny direct flight muscles. Overall, this dimorphism across populations indicates that there are alternative solutions to selective pressures against flying queens. We lack field data about colony founding strategy (independent or dependent) for either queen phenotype, but colonies at both sites produced numerous gynes, and we infer that all foundresses initiate colonies independently and are obligate foragers.     

Abdominal Tubercles of Adult Male Camel Crickets, Pristoceuthophilus marmoratus Rehn (Orthoptera: Rhaphidophoridae), Produce Cues Attractive to Females

In contrast to many crickets and katydids, adult male camel crickets (Orthoptera: Raphidophoridae) do not stridulate and do not produce audible air-borne calling songs to attract females for mating. The mating behavior of most camel cricket species is undescribed; how pair-formation occurs is unknown, but chemical cues seem one likely possibility. In the camel cricket Pristoceuthophilus marmoratus Rehn, we test (1) the role of chemical cues in conspecific attraction, and (2) the role of the abdominal tubercles of adult males in producing those cues. We show (1) that virgin adult females are attracted to paper towels previously exposed to adult males, and (2) that paper towels previously exposed to adult males with exposed tubercles are more attractive than paper towels previously exposed to adult males with experimentally closed tubercles. In addition, we present Scanning Electron Microscope photos of adult male tubercle structure that are consistent with their putative role in producing chemical cues.     

The thoracic morphology of cave-dwelling and free-living ground beetles from China (Coleoptera,Carabidae, Trechinae)

External and internal thoracic structures of two carabid species (Trechini) were examined and documented with different techniques. The study has a main focus on the eyeless cave-dwelling specialist Sinaphaenops wangorum, but detailed information is also provided for a species occurring in cave entrances. The phylogenetic background of the structural features of the thoracic skeletomuscular system was addressed. The thoracic morphology of the examined species was compared to conditions observed in previously studied carabids and non-related subterranean leiodids (Staphylinoidea) in order to identify cave adaptations. Main thoracic character complexes linked with cavernicolous habits in Trechini are elongation of the pro- and mesothorax and the legs, and a complete and irreversible reduction of the flight apparatus. The lost flight capacity is linked with a far reaching modification of skeletal elements of the metathorax including a strongly shortened and simplified metanotum, a shortened metaventrite, and completely reduced wings and sclerites of the wing base. The elongate prothorax together with the long and slender head and elongated legs distinctly increases the activity range in the subterranean lightless environment, which likely facilitates foraging of the carnivorous beetles. Some of the observed features like wing loss and elongation of the anterior thorax and legs are also found in some cave-dwelling Leiodidae (Leptodirini), whereas some other subterranean members of the staphylinoid family have a compact body and legs of normal length. In contrast to the predaceous Trechini, Leptodirini are scavengers.     

The type species of the ordovician trilobitesymphysurus: systematics,functional morphology and terrace ridges

The type of the widespread Ordovician trilobiteSymphysurus, S. palpebrosus Dalman, 1827, is redescribed from the type Swedish material; its distribution is documented.Symphysurus is one of very few trilobite genera to be found in both Ordovician Baltica and Gondwana, in more peripheral sites relative to the platform areas.S. palpebrosus has complex coaptative devices to ensure tight enrollment. Analysis of the functional morphology shows that it spent at least part of its life with thorax and pygidium buried in the sediment in the bumastoid stance, although it may have fed outside its burrow. Terrace ridges are well developed on certain parts of the cuticle; their positioning and geometry shows that only a few of them could have functioned in direct engagement with the sediment. Those associated with petaloid thoracic facets may have permitted respiration in the enrolled condition.     

Constant light disrupts the circadian but not the circatidal rhythm in mangrove crickets

Mangrove crickets have a circatidal activity rhythm (~12.6 h cycles) with a circadian modulation under constant darkness (DD), whereby activity levels are higher during subjective night low tides than subjective day low tides. This study explored the locomotor activity rhythm of mangrove crickets under constant light (LL). Under LL, the crickets also exhibited a clear circatidal activity rhythm with a free-running period of 12.6 ± 0.26 h (mean ± SD, n = 6), which was not significantly different from that observed under DD. In contrast, activity levels were almost the same between subjective day and night, unlike those under DD, which were greater during subjective night. The loss of circadian modulation under LL may be explained by the suspension of the circadian clock in these conditions. These results strongly suggest that the circatidal activity rhythm is driven by its own clock system, distinct from the circadian clock.     

Isolation of the abdomen releases oviposition behaviour in females of the cricket, Acheta domesticus

Upon isolation, abdomens of adult female house crickets (Acheta domesticus) produced abdominal and ovipositor movements characteristic of normal oviposition. Oviposition behaviour was thus released even in reproductively mature or immature virgins where under normal conditions it was never observed. Decapitation was not sufficient to release oviposition behaviour but transection of the ventral nerve cord between the thorax and the abdomen of immobilized females evoked the response. These observations indicate that the motor programmes for certain components of the oviposition sequence reside in the abdominal ganglia. Moreover, the prerequisite circuitry for ovipositional posturing of the abdomen and ovipositor appears to be functional prior to sexual maturity and insemination, primed by mating, and subject to inhibition by the thoracic ganglia.     

Landscape and weather determinants of prey availability: implications for the Lesser Kestrel Falco naumanni

Spatial and temporal variation in prey abundance have been shown to impact the time of breeding and breeding success of birds. Understanding the ecological requirements of preferred prey can help develop management measures to improve food supply for target species. For the colonial Lesser Kestrel Falco naumanni, mole crickets Gryllotalpa spp. are one of the most important prey items during the mate‐feeding period. Lesser Kestrel colonies with higher mole cricket consumption had earlier egg‐laying dates, suggesting that differences between individuals in the time of breeding could be caused by differences in the diet. Moreover, the mean number of mole crickets in pellets was significantly correlated with clutch size (in one of the studied years) and egg volume. Thus, the impact of environmental variables and land use on mole crickets is likely to be relevant to Lesser Kestrel conservation. Weekly consumption of mole crickets was higher following an increase in either precipitation or minimum temperature values. Furthermore, mole cricket consumption was higher in colonies surrounded by higher quality soils and in wetter areas and years. Predicted probability of mole cricket occurrence in surveyed watercourse margins suggested a positive relationship between soil penetrability and mole cricket occurrence. Among variables that might be the target of management, the presence of riparian vegetation positively influenced the occurrence of mole crickets, whilst tillage and sowing of streambeds were revealed as the most important threats. We suggest that the maintenance of native vegetation in the margins of watercourses could improve soil resilience to erosion, increase water retention, soil penetrability and fertility, and provide a food supply and shelter for mole crickets. Overall, the implementation of such recommendations is likely to benefit other farmland species known to consume mole crickets, including several endangered species.     

The female postabdomen and genitalia of the basal moth family Heterobathmiidae (Insecta: Lepidoptera): Structure and phylogenetic significance

Female Heterobathmia have the segments behind VIII forming a compact ‘terminal unit’ with a large saddle-shaped dorsal plate and a membranous ventroposterior surface bearing the separate gonopore and anus. While females of most of the nine known species are overall similar, Heterobathmia valvifer is unique amongst lepidopterans in possessing paired ventral appendages (‘ovipositor valves’) arising from the intersegmental groove following segment VIII; evidence from musculature contradicts an interpretation of these appendages structures as ‘true’ ovipositor valves. The ventroposterior wall of the terminal unit in H. valvifer bears paired sclerites, possible homologues of the ‘ventral rods’ in basal Lepidoptera-Glossata. In Heterobathmia megadecella sclerites on paired longitudinal elevations in comparable positions probably are/include homologues of these sclerites. Their similarity with paired sclerotizations in the corresponding region of hydrobiosid caddisflies is noted. A prominent frame-like sclerotization in the genital chamber, located in front of the spermathecal duct origin, is present only in H. megadecella.Putative heterobathmiid autapomorphies include an enlarged ‘subgenital plate’ on venter VIII, absence of apophyses on segment VIII, shortened apophyses on the terminal unit, multilobed accessory glands (but their ‘type 1’ secretory epithelium is plesiomorphic at this level), a conspicuous papilla in the chamber cuticle bearing the opening of the ductus bursae on its apex, and inwards-pointing spines in the ductus bursae. A variably developed thickening of the anterior genital chamber intima is another putative family autapomorphy, while an extreme thickening of the posterior intima seen in Heterobathmia pseuderiocrania is not of general occurrence in heterobathmiids. A sistergroup relationship between Heterobathmiidae and Glossata is supported by their fully developed ‘2-compartment section’ of the spermathecal duct and losses of some likely lepidopteran groundplan muscles.     

One hundred years of instability in ensiferan relationships

Although Ensifera is a major insect model group, its phylogenetic relationships have been understudied so far. Few phylogenetic hypotheses have been proposed, either with morphological or molecular data. The largest dataset ever used for phylogeny reconstruction on this group is molecular (16S rRNA, 18S rRNA and 28S rRNA sequences for 51 ensiferan species), which has been used twice with different resultant topologies. However, only one of these hypotheses has been adopted commonly as a reference classification. Here we re‐analyse this molecular dataset with different methods and parameters to test the robustness and the stability of the adopted phylogeny. Our study reveals the instability of phylogenetic relationships derived from this dataset, especially for the deepest nodes of the group, and suggests some guidelines for future studies. The comparison between the different classifications proposed in the past 70 years for Ensifera and our results allows the identification of potential monophyletic clades (katydids, mole crickets, scaly crickets + Malgasia, true crickets, leaf roller crickets, cave crickets) and the remaining unresolved clades (wetas, Jerusalem crickets and most of the highest rank clades) in Ensifera phylogeny.     

Comparative morphology of the thorax musculature of adult Anisoptera (Insecta: Odonata): Functional aspects of the flight apparatus

Due to their unique flight mechanism including a direct flight musculature, Odonata show impressive flight skills. Several publications addressed the details of this flight apparatus like: sclerites, wings, musculature, and flight aerodynamics. However, 3D-analysis of the thorax musculature of adult dragonflies was not studied before and this paper allows for a detailed insight. We, therefore, focused on the thorax musculature of adult Anisoptera using micro-computed tomography. Herewith, we present a comparative morphological approach to identify differences within Anisoptera: Aeshnidae, Corduliidae, Gomphidae, and Libellulidae. In total, 54 muscles were identified: 16 prothoracic, 19 mesothoracic, and 19 metathoracic. Recorded differences were for example, the reduction of muscle Idlm4 and an additional muscle IIIdlm1 in Aeshna cyanea, previously described as rudimentary or missing. Muscle Iscm1, which was previously reported missing in all Odonata, was found in all investigated species. The attachment of muscle IIpcm2 in Pantala flavescens is interpreted as a probable adaption to its long-distance migration behaviour. Furthermore, we present a review of functions of the odonatan flight muscles, considering previous publications. The data herein set a basis for functional and biomechanical studies of the flight apparatus and will therefore lay the foundation for a better understanding of the odonatan flight.     

Morphology and ontogeny of the eodiscoid trilobite Sinodiscus changyangensis from the lower Cambrian of South China

Abstract: A large number of complete specimens together with numerous disarticulated sclerites of the eodiscinid trilobite Sinodiscus changyangensis Zhang in Zhou et al., 1977 have been collected from the lower Cambrian Shuijingtuo Formation in Changyang, Hubei Province, South China. An ontogenetic series is established based on the immature and mature exoskeletons including the previously unknown protaspides and meraspides, in particular. No further substages can be differentiated in the protaspid specimens herein. Changes that took place during the meraspid period include the addition of postcephalic segments and prominent pygidial larval notches in early meraspid development which became progressively less distinct and disappeared in degree 2. Two holaspid stages are recognized based on the addition of a new pygidial segment, indicating that the start of the holaspid phase preceded the onset of the epimorphic phase and accordingly, its developmental mode is attributed to the protarthrous pattern. The trunk segmentation schedule of S. changyangensis is discussed, which is similar to other primitive eodiscoid trilobites, that is, as the boundary between the thorax and pygidium migrated posteriorly, there is no change in the number of the trunk segments. The processes of liberation of the thoracic segment and segment insertion into the pygidium are separated from one another, and the two different mechanisms, somitogenesis and tagmosis, progress independently during the ontogenetic development of the postcephalic region of these primitive eodiscinids.     

PATTERNS OF VARIATION AND LINKAGE DISEQUILIBRIUM IN A FIELD CRICKET HYBRID ZONE

The distribution of multilocus genotypes found within a natural hybrid zone is determined by the sample of genotypes present when the hybrid zone first formed, by subsequent patterns of genetic exchange between the hybridizing taxa, and by drift and selection within each of the hybrid zone populations. We have used anonymous nuclear DNA restriction fragment polymorphisms (RFLPs) to characterize the array of multilocus genotypes present within a well-studied hybrid zone between two eastern North American field crickets, Gryllus pennsylvanicus and Gryllus firmus. These crickets hybridize along a zone of contact that extends from New England to Virginia. Previous studies have shown that both premating and postmating barriers exist between the two cricket species, but the absence of diagnostic morphological and allozyme markers has made it difficult to assess the consequences of these barriers for genetic exchange. Analyses based on four diagnostic anonymous nuclear markers indicate that hybrid zone populations in Connecticut contain few F₁ hybrids, and that nonrandom associations persist among nuclear gene markers, between nuclear and cytoplasmic markers, and between molecular markers and morphology. Field cricket populations within the hybrid zone are not “hybrid swarms” but consist primarily of crickets that are very much like one or the other of the parental species. Despite ample opportunity for genetic exchange and evidence for introgression at some loci, the two species remain quite distinct. Such a pattern appears to be characteristic of many natural hybrid zones.     

Temperature coupling in cricket acoustic communication

Acoustic communication in Gryllus firmus is temperature-coupled: temperature induces parallel changes in male calling song temporal pattern, and in female preference for song. Temperature effects on song production and recognition networks were localized by selectively warming head or thorax or both head and thorax of intact crickets, then eliciting aggression song production (males) or phonotaxis to synthetic calling song (females). Because male song is produced by a thoracic central pattern generator (CPG), and because head ganglia are necessary for female song recognition, measurements of female phonotaxis under such conditions may be used to test the following competing hypotheses about organization of the song recognition network: 1. A set of neurons homologous to the male song CPG exist in the female, and are used as a template that determines preferred values of song temporal parameters for song pattern recognition (the common neural elements hypothesis), and 2. temporal pattern preference is determined entirely within the head ganglia. Neither selective warming of the head nor of the thorax was effective in changing female song preference, but simultaneous warming of head and thorax shifted preference toward a faster song in most preparations, as did warming the whole animal by raising ambient temperature. These results suggest that phonotactic preference for song temporal pattern is plurisegmentally determined in field crickets. Selective warming experiments during aggression song production in males revealed that syllable period is influenced but not completely determined by thoracic temperature; head temperature is irrelevant. The song CPG appears to receive some rate-setting information from outside the thoracic central nervous system.     

寒武纪叶足动物链状心网虫躯干骨板功能形态学研究*

链状心网虫(Cardiodictyon catenulum)是寒武纪澄江生物群中较为常见的叶足动物, 其躯干骨板的形态一直存在较大争议。本项研究显示该叶足动物的躯干具有一纵列马鞍状骨板, 每个体节具有单一的骨板, 每个骨板从背部延伸至躯干两侧。因此该叶足动物的骨板与其余具有成对或环状分布的躯干骨板的叶足动物存在显著的区别。骨板中央存在一个圆锥形凸起, 骨板边缘显著增厚且呈锯齿状。链状心网虫的躯干骨板边缘增厚和鞍点的凸起提升了整体的刚性; 锯齿状边缘也指示了更优的保护及防御功能。本项研究还发现链状心网虫骨板表面具有显微筛状结构, 筛孔被充填并保存为众多等距离分布的黄铁矿化瘤突, 与微网虫、怪诞虫及爪网虫躯干骨板的显微网状结构类似, 可能为纤细乳突的出口。本文认为: 寒武纪叶足动物的躯干骨板普遍具有显微筛状结构; 这些骨板除了保护与防御, 可能还有感觉的功能。每个躯干体节对应骨板为寒武纪叶足动物的独有衍征, 可能为背骨板的早期形态, 也可能由成对骨板愈合而来。