Divergent mating patterns and a unique mode of external sperm transfer in Zoraptera: an enigmatic group of pterygote insects.

A remarkable external sperm transfer is described for the first time in a species of a group of winged insects (Pterygota), the enigmatic Zoraptera. Mating and sperm transfer of two species of the order were examined in detail, documented, and compared with each other and with patterns described for other species belonging to the order. The behavior differs strikingly in Zorotypus impolitus and Zorotypus magnicaudelli. A copula is performed by males and females of the latter, as it is also the case in other zorapteran species and generally in pterygote insects. In striking contrast to this, males of Z. impolitus do not copulate but deposit small (100 µm in diameter) spermatophores externally on the abdomen of the female. Each spermatophore contains only one giant spermatozoon (3 mm long and 3 µm wide), a unique feature in the entire Hexapoda. External sperm transfer in Pterygota is a highly unusual case of evolutionary reversal. The very small relict group Zoraptera displays a uniform general morphology but exhibits very different reproductive structures and patterns of mating behavior. This may be an extreme form of a more general situation in insects, with a specific form of selection resulting in an accelerated rate of evolution in the reproductive system.

Beetles and flies collected on pig carrion in an experimental setting in Thuringia and their forensic implications.

Decomposition processes and insect succession were analysed on a total of eight pig (Sus scrofa) carcasses. The survey was carried out in four different periods between November 2007 and August 2008 and on two different substrates (meadow, concrete floor close to a building). The experiments were placed in a rural site in the surroundings of Jena, Thuringia. The duration and specificity of the different decomposition stages were dependent on season, weather and quality and quantity of insect colonization. Whereas the carrion maintained a bloated appearance even after 133 days in winter, it reached the dry stage within 8 days in the summer months. The type of substrate had few effects on the decaying process, but the insects were generally more abundant on the meadow. In total, more than 57 species of Diptera belonging to 17 families and 48 species of Coleoptera belonging to 14 families were identified. Dominant species belonged to the families of Calliphoridae (n = 11 spp.), Sarcophagidae (n = 8), Muscidae (n = 9), Piophilidae (n = 3), Silphidae (n = 6), Dermestidae (n = 3), Nitidulidae (n = 4), Cleridae (n = 3) and Histeridae (n = 2). Remarkably, the rather common Nicrophorus species were completely absent, whereas the usually rare Necrodes littoralis (L.) was present in larger numbers. No distinct coincidence between the occurrence of a single species and a certain decomposition stage could be confirmed. A main objective of the study is the establishment of a forensic entomological database for Central Europe, especially Thuringia.

The morphology and ultrastructure of salivary glands of Zoraptera (Insecta).

The salivary glands of two species of Zoraptera, Zorotypus caudelli and Zorotypus hubbardi, were examined and documented mainly using transmission electron microscopy (TEM). The results obtained for males and females of the two species are compared and functional aspects related to ultrastructural features are discussed. The salivary glands are divided into two regions: the secretory cell region and the long efferent duct, the latter with its distal end opening in the salivarium below the hypopharyngeal base. The secretory region consists of a complex of secretory cells provided with microvillated cavities connected by short ectodermal ducts to large ones, which are connected with the long efferent duct. The secretory cell cytoplasm contains a large system of rough endoplasmic reticulum and Golgi apparatus producing numerous dense secretions. The cells of the efferent duct, characterized by reduced cytoplasm and the presence of long membrane infoldings associated with mitochondria, are possibly involved in fluid uptaking from the duct lumen.

The fine structure of the rectal pads of Zorotypus caudelli Karny (Zoraptera, Insecta).

The rectal pads of a species of the controversial polyneopteran order Zoraptera were examined using histological sections and TEM micrographs. Six pads are present along the thin rectal epithelium. Each pad consists of a few large principal cells surrounded by flattened junctional cells, which extend also beneath the principal cells. The cells are lined by a thin apical cuticle. No basal cells and no cavity have been observed beneath the pad. Principal cells have a regular layer of apical microvilli and are joined by intercellular septate junctions, which are interrupted by short dilatations of the intercellular space. At these levels the two adjacent plasma membranes are joined by short zonulae adhaerentes. In the cytoplasm, a rich system of strict associations between lateral plasma membranes and mitochondria forms scalariform junctions. Rectal pads share ultrastructural features with similar excretory organs of several neopteran groups, in particular with Blattodea (roaches and termites) and Thysanoptera, and are involved in fluid reabsorption and ion regulation.

INSECT PHYLOGENOMICS. Response to Comment on "Phylogenomics resolves the timing and pattern of insect evolution".

Tong et al. comment on the accuracy of the dating analysis presented in our work on the phylogeny of insects and provide a reanalysis of our data. They replace log-normal priors with uniform priors and add a "roachoid" fossil as a calibration point. Although the reanalysis provides an interesting alternative viewpoint, we maintain that our choices were appropriate.

Discovery of Aspidytidae, a new family of aquatic Coleoptera.

The six extant aquatic families of Hydradephaga (Coleoptera) known so far represent a diverse group of beetles morphologically highly modified for life in the water. We report the discovery of a new genus with two species from South Africa and China, which differ greatly from all extant families, but resemble the Jurassic-Cretaceous dagger Liadytidae (the dagger symbol indicates that the taxa are known only as fossils). Based on a combined phylogenetic analysis of molecular and morphological data we erect a new family, Aspidytidae, which is the sister group of Dytiscidae plus Hygrobiidae. We propose a new scenario for the evolution of swimming behaviour in adephagan beetles, in which the transition into the aquatic environment is followed by complex and repeated changes in lifestyles, including the secondary complete loss of swimming ability in Aspidytidae.

Head-capsule design and mandible control in beetle larvae: a three-dimensional approach.

This work provides the morphological basis of mandible kinematics of beetle larvae with different types of head capsules, orientation of mouthparts, mandible design, and feeding behavior. Short descriptions are provided for the hypognathous head of Liocola marmorata (Scarabaeidae), the prognathous head of Cybister lateralimarginalis (Dytiscidae), and the hyperprognathous head of Hydrophilus piceus (Hydrophilidae). Using 3D measurements of a set of points selected on the head, 3D models of head capsules and mandible articulations were made for the larvae of these three species. Further calculations of the models showed differences in spatial positions of mandible axes and insertion points of mandible muscles. Functional consequences of these differences and evolutionary aspects of changes in head design and mandible articulations are discussed. It is suggested that the approach used in this study may be useful for further comparative studies of mandible mechanics of a broad variety of insect taxa.

Wing folding and the functional morphology of the wing base in Coleoptera.

The wing unfolding of Pachnoda marginata was examined using digital video (50 half-fps) and high speed video sequences (1000 fps), and the skeleto-muscular apparatus of the metathorax was described. Left and right hind wing are able to promote independently of each other. The hind wings do not unfold instantly when the elytra are lifted and may also reach the flight position (and beat) while still folded. Wing promotion is exhaustible and the time needed for unfolding varies considerably. These observations strongly suggest a muscular control. Wing unfolding is probably triggered by contraction of M. pleura alaris and a resulting proximad movement of the 3rd axillary sclerite, pulling the Media posterior backwards, while the Radius anterior is held by the basalar muscle as the antagonist. Our findings are in clear contrast to the earlier assumption that the hind wings of Coleoptera either unfold or fold due to intrinsic elasticity. The specific wing folding and unfolding mechanisms are autapomorphic character states of Coleoptera. They were maintained during evolution even though considerable variations of skeletal thoracic structures, musculature and venation occurred. (Additional material is available from the Zoology web page: http://www.urbanfischer.de/journals/zoology).

Vectors and vector-borne diseases of horses.

Most diseases of horses with zoonotic importance are transmitted by arthropods. The vectors belong to two very distantly related groups, the chelicerate Ixodidae (Acari = ticks) and the hexapod Diptera (true flies). Almost all relevant species are predestined for transmitting pathogens by their blood-sucking habits. Especially species of Diptera, one of the megadiverse orders of holometabolan insects (ca. 150.000 spp.), affect the health status and performance of horses during the grazing period in summer. The severity of pathological effect depends on the pathogen, but also on the group of vectors and the intensity of the infection or infestation. Dipteran species but also blood-sucking representatives of Acari (Ixodidae) can damage their hosts by sucking blood, causing myiasis, allergy, paralysis and intoxication, and also transmit various bacterial, viral, parasitic, spirochetal and rickettsial diseases to animals and also humans. The aim of this review was to provide extensive information on the infectious diseases transmitted by members of the two arthropod lineages (Ixodidae, Diptera) and a systematic overview of the vectors. For each taxon, usually on the ordinal, family, and genus level a short characterisation is given, allowing non-entomologists easy identification. Additionally, the biology of the relevant species (or genera) is outlined briefly.

The fine structure of the female reproductive system of Zorotypus caudelli Karny (Zoraptera).

The general structure of the female genital system of Zorotypus caudelli is described. The ovarioles are of the panoistic type. Due to the reduction of the envelope (tunica externa) the ovarioles are in direct contact with the hemolymph like in some other insect groups, Plecoptera included. The calices are much larger in Z. caudelli then in Zorotypus hubbardi and their epithelial cells produce large amounts of secretions, probably protecting the surface of the eggs deposited on the substrate. Eggs taken from the calyx bear a series of long fringes, which are missing in the eggs found in the ovariole, and in other zorapteran species. The long sperm of Z. caudelli and the long spermathecal duct are likely related to a sexual isolating mechanism (cryptic female choice), impeding female re-mating. The apical receptacle and the spermathecal duct - both of ectodermal origin - consist of three cell types. In addition to the cells beneath the cuticle lining the lumen, two other cell types are visible: secretory and canal cells. The cytoplasm of the former is rich in rough endoplasmic reticulum cisterns and Golgi complexes, which produce numerous discrete dense secretory bodies. These products are released into the receiving canal crossing the extracellular cavity of secretory cells, extending over a series of long microvilli. The secretion is transported towards the lumen of the apical receptacle of the spermatheca or to that of the spermathecal duct by a connecting canal formed by the canal cells. It is enriched by material produced by the slender canal cells. Before mating, the sperm cells are enveloped by a thick glycocalyx produced at the level of the male accessory glands, but it is absent when they have reached the apical receptacle, and also in the spermathecal duct lumen. It is likely removed by secretions of the spermatheca. The eggs are fertilized at the level of the common oviduct where the spermathecal duct opens. Two micropyles at the dorsal side of the equator level possibly facilitate fertilization. The presence of these two micropyles is a presumably derived feature shared with Phasmatodea. The fine structure of the female reproductive system of Z. caudelli does not allow to assess the phylogenetic position at the present stage of knowledge. The enlarged calyx and the temporary presence of long fringes on the eggs are potential autapomorphies of Z. caudelli or may indicate relationships with other Zorotypus species.

The male and female reproductive systems of Zorotypus hubbardi Caudell, 1918 (Zoraptera).

Here we present an ultrastructural study of the male and female reproductive systems of Zorotypus hubbardi and compare the findings to those presented in an earlier study. The male reproductive system consists of small testes and thin and short deferent ducts opening into a huge seminal vesicle. At the end of the deferent duct a wiredrawer structure is present which initiates the spermatophore formation. A long ejaculatory duct, originating from the seminal vesicle, receives the secretions of three accessory glands. The copulatory organ is a relatively stout structure consisting of two cuticular claspers connected to a ventral sclerite. The testes contain very large and few germ cells (32 sperm in each cyst) which give rise to large sperm characterized by two giant mitochondrial derivatives, two large accessory bodies, and an axoneme with accessory tubules with 17 protofilaments in their tubular wall. In the seminal vesicle the sperm are joined by a secretion to form an elongate spermatophore. The female system consists of panoistic ovarioles, two lateral oviducts, and a common oviduct which receives the spermathecal duct of a huge spermathecal sac in the terminal part of the vagina. The duct is an anterior prolongation of the sac. Its distal part turns back twisting around its proximal portion. At this level a conspicuous muscle layer gives rise to a valve. The bent spermatophore is hosted in the spermathecal sac, with the sperm heads placed in the proximal part of the spermathecal duct. The opening of the duct is close to the female genital opening. The reproductive systems of Zorotypus caudelli and Z. hubbardi, apart from a distinctly different general organization, also have a different sperm structure: those of the former species are free long-moving cells, while the sperm of Z. hubbardi are giant cells joined in a spermatophore. This allows to hypothesize and discuss a different reproductive behaviour in the two species: monandric in Z. hubbardi and polyandric in Z. caudelli. Apparently different forms of selection have resulted in a very uniform general morphology in Zoraptera, and in highly divergent features related to the reproductive system. The presence of 17 protofilaments in the accessory microtubules of the flagellar axoneme is a potential synapomorphy of Zoraptera and Phasmatodea.

The male reproductive system of Zorotypus caudelli Karny (Zoraptera): Sperm structure and spermiogenesis.

Considering the overall uniformity of the morphology of Zoraptera, the structural diversity of the male genital system is remarkable. Structures related to the male reproductive system of Zorotypus caudelli differ profoundly from those of Zorotypus hubbardi. The testes are elongated rather than spherical, the seminal vesicle is apparently absent, and the deferent ducts are very long. A feature shared by these two species and other zorapterans examined is that the two accessory glands are closely adherent to each other and form a single large structure, from which the ejaculatory duct originates. This is a potential zorapteran autapomorphy. Another feature possibly present in the groundplan of the order is the strong elongation of the sperm cells. This may be connected with a reproductive strategy of males trying to avoid re-mating of females with other males after the first copulation. The extremely long and coiled spermathecal duct of Z. caudelli and other zorapteran species is possibly correlated with the sperm elongation, and both features combined may result in a sexual isolating mechanism. The short duration of mating of Zorotypus barberi and Zorotypus gurneyi suggests that the male introduces sperm into the female tract up to the opening of the spermathecal duct using their long coiled aedeagus. A thick glycocalyx around the sperm in the distal part of the deferent ducts probably protects the sperm cells during their forward progression towards the long spermathecal duct, and is removed when they reach the apical receptacle. The spermatogenesis of Z. caudelli follows a pattern commonly found in insects, but differs distinctly from that of Z. hubbardi in the number of spermatids in each sperm cyst. An unusual and possibly autapomorphic feature of Z. caudelli is a disconnection of sub-tubules A and B at the level of microtubule doublets 1 and 6 of the mature sperm cells. It is conceivable that this results in a shorter period of sperm motility. The character combination found in different zorapteran species supports the view that the sperm, a very compact functional unit, does not evolve as a unit, but like in other more complex body regions, sperm components can also be modified independently from each other. This results in different mosaic patterns of plesiomorphic and derived features in a very compact entity in different species of the very small and otherwise uniform order Zoraptera. In Z. caudelli, for instance, the bi-layered acrosome and small accessory bodies are plesiomorphic states among several others, whereas the mitochondrial derivatives and the elongate nucleus are apparently derived conditions. Other combinations likely occur in other zorapteran species. Only few but noteworthy sperm characters indicate possible phylogenetic affinities of Zoraptera. A possible synapomorphic feature, the presence of dense laminae radiating in a cartwheel array between neighbouring centriolar triplets, is shared with Phasmatodea and Embioptera. Another potential synapomorphy shared with Phasmatodea is the presence of 17 protofilaments in the tubular wall of the outer accessory microtubules.

Evolution of locomotory attachment pads of hexapods.

This study shows that, in their evolution, hexapods have convergently developed two distinctly different mechanisms to attach themselves to a variety of substrates during locomotion. The first mechanism is provided by hairy surfaces and the second one by smooth flexible pads. The main similarity of both mechanisms is that the structured pad surface or particular properties of pad materials guarantee a maximum real contact with diverse substrata, regardless of their microsculpture. Ten characters of the two alternative designs were coded and analyzed together with a data matrix containing 105 additional morphological characters of different stages and body parts. The analysis demonstrates that similar structures (arolium, euplantulae, hairy tarsomeres) have evolved independently in several hexapod lineages. The evolution of flight and the associated necessity of being able to cling to vegetation or other substrates are suggested to be major triggers for the evolution of attachment structures.