Comparative ultrastructure of coxal glands in unfed larvae of Leptotrombidium orientale (Schluger, 1948) (Trombiculidae) and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae)

Coxal glands of unfed larvae Leptotrombidium orientale (Schluger, 1948) (Trombiculidae), a terrestrial mite parasitizing vertebrates, and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae), a water mite parasitizing insects were studied using transmission electron microscopy. In both species, the coxal glands are represented by a paired tubular organ extending on the sides of the brain from the mouthparts to the frontal midgut wall and are formed of the cells arranged around the central lumen. As in other Parasitengona, the coxal glands are devoid of a proximal sacculus. The excretory duct, joining with ducts of the prosomal salivary glands constitutes the common podocephalic duct, opening into the subcheliceral space. The coxal glands of L. orientale are composed of a distal tubule with a basal labyrinth, an intermediate segment without labyrinth, and a proximal tubule bearing tight microvilli on the apical cell surface and coiled around the intermediate segment. The coxal glands of H. ruber mainly consist of the uniformly organized proximal tubule with apical microvilli of the cells lacking the basal labyrinth. This tubule shows several loops running backward and forward in a vertical plane on the side of the brain. In contrast to L. orientale , larvae of H. ruber reveal a terminal cuticular sac/bladder for accumulation of secreted fluids. Organization of the coxal glands depends on the ecological conditions of mites. Larvae of terrestrial L. orientale possess distal tubule functioning in re‐absorption of ions and water. Conversely, water mite larvae H. ruber need to evacuate of the water excess, so the filtrating proximal tubule is prominent.     

Expanding the ‘enemy-free space’ for oribatid mites: evidence for chemical defense of juvenile Archegozetes longisetosus against the rove beetle Stenus juno

Adult oribatid mites are thought to live functionally in ‘enemy-free space’ due to numerous morphological and chemical defensive strategies. Most juvenile oribatid mites, however, lack hardened cuticles and are thus thought to be under stronger predation pressure. On the other hand, the majority of oribatids have exocrine oil glands in all developmental stages, possibly rendering chemical defense the crucial survival strategy in juvenile Oribatida. We manipulated tritonymphs of the model oribatid mite Archegozetes longisetosus to completely discharge their oil glands and offered these chemically disarmed specimens to the polyphagous rove beetle Stenus juno. Disarmed specimens were easily consumed. By contrast, specimens with filled oil glands were significantly protected, being rejected by the beetles. This is the first direct evidence that oil gland secretions provide soft-bodied juvenile oribatids with chemical protection against large arthropod predators.     

Excretion in an oribatid mite Phthiracams sp. (Arachnida: Acari)

Phthiracams sp. has one pair of coxal glands. Each gland comprises a thin-walled sacculus which is specialized for the ultrafiltration of the haemolymph and a tubular labyrinth the ultrastructure of which indicates a specialization for the active resorption of material from the lumen.
In addition to its digestive function, the alimentary canal of this mite is also involved in excretion. Excretory material accumulates at the haemocoelic surface of the gut wall and, after endocytosis, passes through the cytoplasm of the cells as discrete bodies which appear in the faecal pellet.
The faecal pellet is covered with a peritrophic layer 250–500 nm thick which has no discernible structure and disintegrates in water.     

Vertical stratification of oribatid (Acari: Oribatida) communities in relation to their morphological and life-history traits and tree structures in a subtropical forest in Japan

To clarify the effect of tree structure on the diversity of oribatid mites (Acari: Oribatida), we collected a total of 16,325 oribatids in 181 morphospecies from the leaves, branches, and trunk bark of trees and from the forest-floor soil and litter in a subtropical forest, Okinawa, Japan, and tested three predictions: (1) moisture stress in arboreal habitats would lead to larger body size (not supported); (2) morphological traits related to gripping a surface (number and size of claws) would be more developed in arboreal species (supported); and (3) advantages in colonization (no cost for searching mates and doubled population growth) would favor parthenogenesis in the arboreal oribatid communities (not supported). We observed vertical stratification among the five habitats in terms of mite density, species diversity, and species composition, but found no difference in the body length of oribatid species between the arboreal and forest-floor habitats. However, (homo-)tridactylous species predominated in the arboreal habitat, suggesting that this claw morphology facilitates adherence to and movement on arboreal substrates. Sexual species were common in the arboreal oribatid communities, whereas about half of the dominant species collected from the forest floor were likely to be parthenogenetic. It is unclear how these different reproductive systems may be advantageous for oribatid mites in arboreal and forest-floor habitats. Nevertheless, the structural complexity provided by trees appears to enhance and maintain the diversity of oribatid communities through vertical stratification in this subtropical forest.     

Taxonomic distribution of defensive alkaloids in Nearctic oribatid mites (Acari,Oribatida)

The opisthonotal (oil) glands of oribatid mites are the source of a wide diversity of taxon-specific defensive chemicals, and are likely the location for the more than 90 alkaloids recently identified in oribatids. Although originally recognized in temperate oribatid species, alkaloids have also been detected in related lineages of tropical oribatids. Many of these alkaloids are also present in a worldwide radiation of poison frogs, which are known to sequester these defensive chemicals from dietary arthropods, including oribatid mites. To date, most alkaloid records involve members of the superfamily Oripodoidea (Brachypylina), although few species have been examined and sampling of other taxonomic groups has been highly limited. Herein, we examined adults of more than 60 species of Nearctic oribatid mites, representing 46 genera and 33 families, for the presence of alkaloids. GC–MS analyses of whole body extracts led to the detection of 15 alkaloids, but collectively they occur only in members of the genera Scheloribates (Scheloribatidae) and Protokalumma (Parakalummidae). Most of these alkaloids have also been detected previously in the skin of poison frogs. All examined members of the oripodoid families Haplozetidae and Oribatulidae were alkaloid-free, and no mites outside the Oripodoidea contained alkaloids. Including previous studies, all sampled species of the cosmopolitan oripodoid families Scheloribatidae and Parakalummidae, and the related, mostly tropical families Mochlozetidae and Drymobatidae contain alkaloids. Our findings are consistent with a generalization that alkaloid presence is widespread, but not universal in Oripodoidea. Alkaloid presence in tropical, but not temperate members of some non-oripodoid taxa (in particular Galumnidae) deserves further study.     

The effect of different types of anthropogenic changes in soils on communities of oribatids in urban ecosystems

Communities of oribatids that inhabit the soils of urban ecosystems that have various degree of pollution with heavy metals and arsenic, recreational loads, and surface transformation were studied. The suppressing effect of the anthropogenic pressures on the communities of oribatids was investigated. The effect of the recreational load, the increase in the density of soil composition and elimination of the sod horizon, as well as the formation of urbanozems on oribatids are comparable to the effects of pollution. Among oribatids, species that indicate a disturbed states of communities and the purity of ecosystems were found.     

The fine structure of the coxal glands in Myobia murismusculi (Schrank) (Acari: Myobiidae)

The coxal glands of M. murismusculi consist of the proximal tubular portion (tubulus), the distal glandular sac and the terminal excretory duct. The tubulus comprises looped proximal and distal tubes that run in close association with each other. The cells of the proximal tube form numerous short protrusions that project into the neighbouring organs through the pores in their basal lamina. The sac is a distal part of the gland and so it cannot be considered as a homologue of the proximal filter sacculus of other arthropods. A large number of pinocytotic vesicles and lysosome-like bodies in the epithelial lining of the sac imply that the main functions of this organ may be the absorption of substances from the lumen of the gland and their subsequent intracellular transformation. In addition the sac of females was shown to produce dense secretory granules. The ultrastructural features of the glands are discussed and compared to other representatives of Acari.     

Fine structure and function of the coxal glands of lithobiomorph centipedes: Lithobius forficatus and L. crassipes (Chilopoda,Lithobiidae)

The ultrastructure of the coxal glands and associated tissues in the centipedes Lithobius forficatus and Lithobius crassipes has been examined in the light of two contrasting functional hypotheses postulated by different authors. Lithobiomorph chilopods possess eight sets of pores on the posterioventral border of the coxal podomeres of leg pairs 12–15 in adult (maturus) and subadult (pseudomaturus) stadia. A modified cuticular hypodermis, known as the coxal gland, surrounds the distal portion of each blindended pore. Each gland is made up of cells which contain large numbers of hypertrophied mitochondria and a highly folded apical and basal plasma membrane. The similarity of the coxal gland to so called “transporting epithelia” is discussed and further comparisons are made between these and secretory glands in arthropods. A careful consideration of both functional hypotheses (osmoregulation or pheromone release) has revealed the possibility that the coxal gland may encompass both functions.     

Oribatid mites (Acari,Oribatei) of three fens in the northern part of European Russia

Oribatids from three oxbow fens in Kostroma, Kirov, and Arkhangelsk provinces were studied. A total of 2800 adult mites belonging to 74 species were collected. The similarity of the faunas and communities in these fens is rather low, the Jaccard and Naumov coefficients constituting 22–37% and 11–22%, respectively. From the central part of each fen to its periphery, the diversity of oribatids increased from 4–6 to 25–28 species, and abundance, from 59–123 to 451-737 ind./l. Some oribatid species demonstrated similar preferences within all the fens studied. The oribatid faunas of fens and raised bogs are compared, and their characteristic species are distinguished.     

Regulation of salt gland, gut and kidney interactions

Marine birds can drink seawater because their cephalic 'salt' glands secrete a sodium chloride (NaCl) solution more concentrated than seawater. Salt gland secretion generates osmotically free water that sustains their other physiological processes. Acclimation to saline induces interstitial water and Na move into cells. When the bird drinks seawater, Na enters the plasma from the gut and plasma osmolality (Osm(pl)) increases. This induces water to move out cells expanding the extracellular fluid volume (ECFV). Both increases in Osm(pl) and ECFV stimulate salt gland secretion. The augmented intracellular fluid content should allow more rapid expansion of ECFV in response to elevated Osm(pl) and facilitate activation of salt gland secretion. To fully utilize the potential of the salt glands, intestinally absorbed NaCl must be reabsorbed by the kidneys. Thus, Na uptake at gut and renal levels may constrain extrarenal NaCl secretion. High NaCl intake elevates plasma aldosterone concentration of Pekin ducks and aldosterone stimulates intestinal and renal water and sodium uptake. High NaCl intake induces lengthening of the small intestine of adult Mallards, especially males. High NaCl intake has little effect on glomerular filtration rate or tubular sodium Na uptake of birds with competent salt glands. Relative to body mass, kidney mass and glomerular filtration rate (GFR) are greater in birds with salt glands than in birds that do not have them. Birds with salt glands do not change GFR, when they drink saline. Thus, their renal filtrate contains excess Na that is, in some species, almost completely renally reabsorbed and excreted in a more concentrated salt gland secretion. Na reabsorption by kidneys of other species, like mallards is less complete and their salt glands make less concentrated secretion. Such species may reflux urine into the hindgut, where additional Na may also be reabsorbed for extrarenal secretion. During exposure to saline, marine birds maintain elevated aldosterone levels despite high Na intake. Marine birds are excellent examples of physiological plasticity.     

贵州施秉喀斯特地区林地土壤甲螨的群落组成及多样性（英文）

【目的】为了解施秉喀斯特地区林地土壤甲螨的分布和群落组成特点,明确中国西南喀斯特地区林地类型对土壤甲螨群落密度、组成和物种多样性的影响,对该区林地土壤甲螨的群落结构及多样性进行了的调查和分析。【方法】2012年8月选取了中国西南施秉喀斯特地区典型生境中的8个样地,每个样地9个取样点,用Berlese-Tullgren装置分离土样24 h。多样性分析采用常见的多样性指数;群落相似性分析采用Jaccard相似性系数(C_J);群落聚类分析分别采用Marczewski Steinhaus 距离(C_ms)和Bray-Curtis距离,应用R 2.11程序进行类平均法聚类。【结果】结果显示,中国西南喀斯特8个样地中土壤甲螨由少数的优势属和数量众多的稀有属组成。其中全菌甲螨属 Perscheloribates (22.48%)和长单翼甲螨属 Protoribates (11.45%)个体数量最为丰富。长单翼甲螨属 Protoribate、上罗甲螨属Epilohmannia、小奥甲螨属 Oppiella、小盾珠甲螨属 Suctobelbella 和盖头甲螨属 Tectocepheus 分布广泛。本区的甲螨组成（属级水平）表现出明显热带和亚热带地区特点。在天然常绿落叶阔叶林中,甲螨的个体数量和种类数较多,但多样性不高,而在人工针叶林中甲螨多样性最高。甲螨群落组成和分布特征多样,异质性高,特别是在天然常绿落叶阔叶林中突出。【结论】研究表明,施秉喀斯特生态系统的不同林分影响甲螨的物种多样性和群落稳定性,天然常绿落叶阔叶混交林是甲螨的“避难所”。     

Internal anatomy of Hypochthonius rufulus (acari: Oribatida)

The internal anatomy of juveniles and adults of Hypochthonius rufulus selected as a model species representing the lower Oribatida was investigated histologically and compared with the published characteristics of higher oribatid internal anatomy. In this species, the cuticle is weak and flexible, consisting of epicuticle and endocuticle on the body, but including an exocuticle between the epicuticle and endocuticle of the legs. Walls of the mesenteron in the digestive tract are of uniform thickness and structure without any regional thickening, and there are no proventricular glands. The hindgut is apparently divided into five parts: colon 1 and 2, rectum 1 and 2, and anal atrium; food bolus exhibits a multilamellar structure in this section. The glandular system is less diversified than in some other oribatids. Tracheae are apparently lacking. Females possess only two relatively large eggs, filling one-half of opistosoma, and they lack ovipositors. Eggs are present in females during the whole year. Gonad buds appear first in the protonymph stage. Only one male was found among 146 adults studied. No male external organ (aedeagus or penis) is present.     

EVOLUTIONARY MORPHOLOGY AND PHYLOGENY OF ARAGHNIDA

Abstract— This paper reports results from a cladistic analysis of the 11 Recent arachnid orders. The polarities of 64 newly discovered and traditional characters were determined through outgroup comparisons that included Eurypterida, Xiphosura, Trilobita and Crustacea. A branch-and-bound algorithm was used to discover a single tree (consistency index 0–59). The relationships suggested by this analysis differ substantially from previous interpretations of arachnid phylogeny, and a new taxonomic system is introduced to accommodate these results. This analysis suggests that Arachnida is monophyletic and composed of two principal lineages, Micrura and Dromopoda. Possible synapomorphies of Micrura include a pygidmm, tntosternum, six principal lateral eyes, poorly sclerotized postgenital appendages, coxal gland orifices near leg 1, an array of micxotubules associated with the spermatozoan nucleus, and absence of coxal endites on the walking legs. The micruran orders appear to have the following relationships: (Palpigradi (Araneae (Amblypygi (I helyphonida, Schizomida)))) (Ricinulei, Acari). Possible synapomorphies of Dromopoda include transverse carapaeal furrows, greatly reduced prosomal sternum, prosomal endosternite with two segmental components, stomotheca, bicondylar femoropatellar and patellotibial joints and extensor muscles. The dromopodan orders appear to have the following relationships: Opiliones (Scorpioncs (Pscudo-scorpiones, Solifugae)).     

Ultrastructural studies and Na+,K+-ATPase immunolocalization in the antennal urinary glands of the lobster Homarus gammarus (Crustacea, Decapoda).

Unlike in crustacean freshwater species, the structure and ultrastructure of the excretory antennal gland is poorly documented in marine species. The general organization and ultrastructure of the cells and the localization of Na(+),K(+)-ATPase were examined in the antennal gland of the adult lobster Homarus gammarus. Each gland is composed of a centrally located coelomosac surrounded ventrally by a labyrinth divided into two parts (I and II) and dorsally by a voluminous bladder. There is no differentiated nephridal tubule between them. The labyrinth and bladder cells have in common a number of ultrastructural cytological features, including basal membrane infoldings associated with mitochondria, apical microvilli, and cytoplasmic extrusions, and a cytoplasm packed with numerous vacuoles, vesicles, lysosome-like bodies, and swollen mitochondria. Each type of cell also presents distinctive characters. Na(+),K(+)-ATPase was detected through immunofluorescence in the basal part of the cells of the labyrinth and in the bladder cells with an increasing immunostaining from labyrinth I to the bladder. No immunoreactivity was detected in the coelomosac. The cells of the labyrinth and of the bladder present morphological and enzymatic features of ionocytes. The antennal glands of the lobster thus possess active ion exchanges capabilities.     

Convergent evolution of defense mechanisms in oribatid mites (Acari, Oribatida) shows no "ghosts of predation past"

Oribatid mites are diverse and abundant terrestrial soil arthropods that are involved in decomposition of organic matter and nutrient cycling. As indicated by fossils starting from the Devonian, they evolved varied mechanisms and structures for defense from predators. We investigated four of these defensive structures (ptychoid body, hologastry, mineralization and opisthonotal glands) and used ancestral character state reconstruction to determine whether they evolved convergently and how many times this may have happened. Phylogenetic trees based on 18S rDNA were constructed for 42 oribatid mite species and two outgroup taxa using likelihood and Bayesian algorithms. The results suggest that at least three of the four defensive structures evolved convergently several times; for opisthonotal glands convergent evolution remains equivocal. This high level of convergence indicates that predation has been an important factor throughout the evolution of oribatid mites, contributing to morphological diversity and potentially also to species richness, as there are indications that some taxa radiated after the evolution of defense structures. Despite the ancientness of oribatid mites, defense structures seems to have been rarely lost, suggesting that they still are functional and necessary to reduce predation, rather than being 'ghosts of predation past'.     

Geographic Variation in Plant Community Structure of Salt Marshes: Species,Functional and Phylogenetic Perspectives

In general, community similarity is thought to decay with distance; however, this view may be complicated by the relative roles of different ecological processes at different geographical scales, and by the compositional perspective (e.g. species, functional group and phylogenetic lineage) used. Coastal salt marshes are widely distributed worldwide, but no studies have explicitly examined variation in salt marsh plant community composition across geographical scales, and from species, functional and phylogenetic perspectives. Based on studies in other ecosystems, we hypothesized that, in coastal salt marshes, community turnover would be more rapid at local versus larger geographical scales; and that community turnover patterns would diverge among compositional perspectives, with a greater distance decay at the species level than at the functional or phylogenetic levels. We tested these hypotheses in salt marshes of two regions: The southern Atlantic and Gulf Coasts of the United States. We examined the characteristics of plant community composition at each salt marsh site, how community similarity decayed with distance within individual salt marshes versus among sites in each region, and how community similarity differed among regions, using species, functional and phylogenetic perspectives. We found that results from the three compositional perspectives generally showed similar patterns: there was strong variation in community composition within individual salt marsh sites across elevation; in contrast, community similarity decayed with distance four to five orders of magnitude more slowly across sites within each region. Overall, community dissimilarity of salt marshes was lowest on the southern Atlantic Coast, intermediate on the Gulf Coast, and highest between the two regions. Our results indicated that local gradients are relatively more important than regional processes in structuring coastal salt marsh communities. Our results also suggested that in ecosystems with low species diversity, functional and phylogenetic approaches may not provide additional insight over a species-based approach.     

Fine structure and function of the prosomal glands of the two-spotted spider mite,Tetranychus urticae (Acari,Tetranychidae)

Summary The prosomal glands of Tetranychus urticae (Acari, Tetranychidae) were examined light and electron microscopically. Five paired and one unpaired gland are found both in females and males. The silk spinning apparatus consists of paired silk glands which extend laterally on both sides of the esophagus into the pedipalps. There, they enter the terminal silk gland bag which opens into a silk bristle at the apex of the pedipalps. The salivary secretions are formed in three paired glands which have an interconnecting duct, the podocephalic canal. The dorsal podocephalic glands may produce a serous secretion, the anterior podocephalic glands a mucous secretion, and the coxal organ may add a liquid, ion-rich secretion. These secretions pass the podocephalic canal and reach the mouth at the apex of the gnathosome. The function of the paired tracheal organs and the unpaired tracheal gland is still unclear. The tracheal gland may produce a secretion which facilitates the movement of the fused chelicerae and the stylets.This study was financed by a grant from the Deutsche Forschungsgemeinschaft (DFG Se 162/12)     

Triggering chemical defense in an oribatid mite using artificial stimuli

Most oribatid mites are well known for their exocrine oil gland secretions, from which more than a hundred different chemical components (hydrocarbons, terpenes, aromatics and alkaloids) have been described. The biological functions of these secretions have remained enigmatic for most species, but alarm-pheromonal and allomonal functions have been hypothesized, and demonstrated in some cases. Here, we tested different experimental stimuli to induce the release of defensive secretions in the model oribatid mite Archegozetes longisetosus Aoki. Whereas various mechanical stimuli did not result in a reproducible and complete expulsion of oil gland secretions, repeated treatments with hexane led to complete discharge. Life history parameters such as survival, development and reproduction were not influenced by the hexane treatment. Repeated hexane treatments also resulted in a complete depletion of oil glands in Euphthiracarus cribrarius Berlese.     

Secondary succession, soil formation and development of a diverse community of oribatids and saprophagous soil macro-invertebrates

Investigations into different stages of secondary succession (from a wheat field to a beechwood on Threstone; Northern Germany) demonstrated the formation of a carbon rich top soil in later successional stages. Parallel to changes in plant species and soil formation, there were also changes in species composition and diversity of saprophagous macro-invertebrates (Lumbricidae, Diplopoda, Isopoda) and oribatid mites (Acari: Oribatida). Diversity of diplopod and isopod species increased after cessation of cultivation, but in a late successional stage (ca 50 y-old fallow, ash-dominated wood) species number of diplopods and isopods declined strongly. In comparison with the other soil invertebrate groups, species composition of earthworms among the sites was more similar. Accumulation of soil C was assumed to be related to wood formation and occurrence of woody debris and recalcitrant leaf litter of beech trees. Incorporation of recalcitrant litter materials by earthworm species living in the upper mineral soil presumably contributed significantly to accumulation of soil C. Accumulation of soil C was accompanied by the development of an oribatid mite community rich in species. In early successional stages oribatids predominantly colonized the litter layer, while most oribatid mites of the beechwood inhabited the upper mineral soil. Maximum diversity of oribatid mites in the beechwood is assumed to be related to instability of the mineral soil caused by earthworm activity. Changes in species composition and diversity are discussed considering succession theory. Even soil invertebrates of similar trophic groups appear to respond very differently to successional changes. It is concluded that conservation strategies to maintain high diversity of soil invertebrates are most likely to be successful if a wide range of habitats of different successional stages is included.