Catalogue of juvenile instars of oribatid mites (Acari: Oribatida)the next decade (20142023).

In its traditional, paraphyletic context (sans Astigmata), oribatid mites comprise more than 11,000 known species (Subas 2022). They are largely fungivores and decomposers in organic horizons of soil and have a plesiotypic ontogeny that includes four active, free-living juvenile instars. In a taxonomically organized 2014 catalogue, we summarized literature resources concerning the 805 species for which ontogenetic data (mainly morphological) were available. Herein, we supplement that catalogue with all data known to us that were published during the intervening decade. These relate to 267 species, of which 165 were described prior to 2014. As in the 2014 catalogue, representation is strongest among: the middle-derivative hyporder Nothrina; brachypyline superfamilies that are affiliated with aquatic, semiaquatic or intertidal environments (Limnozetoidea, Ameronothroidea); some eupheredermous groups (Plateremaeoidea, Damaeoidea); and Ceratozetoidea. Also as in 2014, groups that are underreprented, based on their high known diversity, are the ptyctimous Mixonomata (Euphthiracaroidea, Phthiracaroidea) and the brachypyline superfamilies Oppioidea and Oripodoidea.

Hunger for sex: Abundant, heterogeneous resources select for sexual reproduction in the field.

Major hypotheses on sex evolution predict that resource abundance and heterogeneity should either select for or against sexual reproduction. However, seldom have these predictions been explicitly tested in the field. Here, we investigated this question using soil oribatid mites, a diverse and abundant group of soil arthropods whose local communities can be dominated by either sexual or asexual species. First, we refined theoretical predictions by addressing how the effects of resource abundance, heterogeneity and abiotic conditions could modify each other. Then, we estimated the strength of selection for sexual species in local communities while controlling for phylogeny and neutral processes (ecological drift and dispersal), and tested its relation to resource and abiotic gradients. We show that sexual species tended to be favoured with increasing litter amount, a measure of basal resource abundance. Further, there was some evidence that this response occurred mainly under higher tree species richness, a measure of basal resource heterogeneity. This response to resources is unlikely to reflect niche partitioning between reproductive modes, as sexual and asexual species overlapped in trophic niche according to a comparative analysis using literature data on stable isotope ratios. Rather, these findings are consistent with the hypothesis that sex facilitates adaptation by breaking unfavourable genetic associations, an advantage that should increase with effective population size when many loci are under selection and, thus, with resource abundance.

Redescriptions of North American Epidamaeus (Acari, Oribatida, Damaeidae) species proposed by N. Banks, H.E. Ewing, A.P. Jacot, and J.W. Wilson.

Early American acarologists proposed several species that have been recombined to the oribatid mite genus Epidamaeus (Damaeidae), but none has been redescribed to modern standards. These include E. puritanicus (Banks, 1906), E. michaeli (Ewing, 1909), E. globifer (Ewing, 1913), E. florida (Wilson, 1936), E. olitor (Jacot, 1937), and E. craigheadi (Jacot, 1939). We redescribe and illustrate these species, based on available type specimens and other material in various collections, and give an indication of their overall distributions. Juvenile instars are at least partly described for all except E. florida and E. olitor. Since these six collectively include the most encountered Epidamaeus species in the eastern USA, a diagnostic key is presented that also includes E. arcticola (Hammer, 1952), which is reliably recorded from eastern North America (New Hampshire) for the first time. A neotype is selected for E. michaeli, which is considered a senior subjective synonym of E. canadensis (Banks, 1909) [new syn.]. Synonymy of E. puritanicus with E. grandjeani (Bulanova-Zachvatkina, 1957) is rejected.

Modelling selection, drift, dispersal and their interactions in the community assembly of Amazonian soil mites.

Three processes can explain contemporary community assembly: natural selection, ecological drift and dispersal. However, quantifying their effects has been complicated by confusion between different processes and neglect of expected interactions among them. One possible solution is to simultaneously model the expected effects of each process within species, across communities and across species, thus providing more integrative tests of ecological theory. Here, we used generalized linear mixed models to assess the effects of selection, drift and dispersal on the occurrence probability of 135 soil oribatid mite species across 55 sites over an Amazonian rainforest landscape (64 km2). We tested for interactions between process-related factors and partitioned the explained variation among them. We found that occurrence probability (1) responded to soil P content and litter mass depending on body size and reproductive mode (sexual or parthenogenetic), respectively (selection); (2) increased with community size (drift); and (3) decreased with distance to the nearest source population, and more so in rare species (dispersal limitation). Processes did not interact significantly, and our best model explained 67% of the overall variation in species occurrence probability. However, most of the variation was attributable to dispersal limitation (55%). Our results challenge the seldom-tested theoretical prediction that ecological processes should interact. Rather, they suggest that dispersal limitation overrides the signatures of drift and selection at the landscape level, thus rendering soil microarthropod species ecologically equivalent and possibly contributing to the maintenance of metacommunity diversity.

How land-use intensity affects sexual and parthenogenetic oribatid mites in temperate forests and grasslands in Germany.

Intensive land use has been shown to alter the composition and functioning of soil communities. Due to their low dispersal ability, oribatid mites are particularly vulnerable to land-use intensification and species which are not adjusted to management-related disturbances become less abundant. We investigated how different land-use parameters in forests and grasslands affect oribatid mite diversity and abundance, with a focus on: (1) species-level impacts, by classifying species as increasing ('winners') or decreasing ('losers') in abundance with higher land-use intensity, and (2) reproductive impact, by investigating whether sexual and parthenogenetic species react differently. We collected 32,542 adult oribatid mites in 60 forests and grasslands of known land-use intensity in two regions of Germany. Diversity and total abundance as well as the proportion of sexual species were higher in forests than in grasslands. Diversity declined with higher land-use intensity in forests, but increased with higher mowing and fertilization in grasslands. Depending on land-use parameter and region, abundance either declined or remained unaffected by increasing intensity. Gravidity was higher in sexual than in parthenogenetic species and sexuals had 1.6× more eggs per gravid female. Proportions of sexual species and gravid females decreased with land-use intensity in forests, but increased with mowing in grasslands. At the species level, 75% of sexuals and 87.5% of parthenogens were 'losers' of higher percentages of dead wood originating from management-related disturbances. Across land-use parameters and habitats, a similar proportion of sexual and parthenogenetic oribatid mite species were 'losers' of high land-use intensity. However, 'winner' species were more common among sexuals.

Anderemaeus (Acari, Oribatida)-overview, three new species from South America and reassessment of Anderemaeidae supported by ontogeny.

Anderemaeus is a genus of Gondwanan soil-dwelling oribatid mites with seven of the eight previously known species being South American. We propose two new species from Chile- A. sidorchukae sp. nov. and A. dentatus sp. nov.-and a third from Ecuador, A. mataderoensis sp. nov. Juveniles of the former two species are described, comprising the first such data for Anderemaeidae: nymphs notably lack both exuvial scalps and centrodorsal gastronotic setae, and the opisthonotal gland opens on a distinct stalk. The generic description is revised and expanded and a key to known species of Anderemaeus is presented, including A. tridactylus comb. nov. We reject the inclusion of Anderemaeus in a broad concept of Caleremaeidae and the implied subsumption of Anderemaeidae, as there are no synapomorphies linking the taxa. Anderemaeus species possess derived traits-e.g. adult with circumpedal carina and nymphs with smooth cuticle and no scalp retention-that are absent from Caleremaeus but are shared with more derived brachypyline taxa. The higher classification of Anderemaeus is reviewed: an analysis of known traits is inconclusive regarding both the generic composition of Anderemaeidae and its superfamilial relationships. However, on the strength of juvenile morphology, we propose the transfer of Anderemaeidae to Gustavioidea.

A tropical arthropod unravels local and global environmental dependence of seasonal temperature-size response.

In most ectotherms, adult body size decreases with warming, the so-called 'temperature-size rule' (TSR). However, the extent to which the strength of the TSR varies naturally within species is little known, and the significance of this phenomenon for tropical biota has been largely neglected. Here, we show that the adult body mass of the soil mite Rostrozetes ovulum declined as maximum temperature increased over seasons in a central Amazonian rainforest. Further, per cent decline per °C was fourfold higher in riparian than in upland forests, possibly reflecting differences in oxygen and/or resource supply. Adding our results to a global dataset revealed that, across terrestrial arthropods, the seasonal TSR is generally stronger in hotter environments. Our study suggests that size thermal dependence varies predictably with the environment both locally and globally.

The Neotropical mite genus Neopilizetes (Oribatida: Galumnidae): redescription of N. neotropicus, rediagnosis of the genus, and descriptions of four new species.

Neopilizetes is a genus of the oribatid mite family Galumnidae that was first characterized by having well-developed setae, a dorsosejugal suture, and raised striae on the prodorsum and notogaster. It was proposed to accommodate Pilizetes neotropicus Balogh Mahunka 1978 from Brazil-the only supposed Pilizetes species known outside the Ethiopian Region-and it has remained monotypic. We found adults of N. neotropicus and four related species in soil-litter interface samples of a single cacao plantation in Ilhéus, Bahia, Brazil. Herein we: redescribe N. neotropicus; describe Neopilizetes thoracicus n. sp., Neopilizetes tigris n. sp., Neopilizetes triumnasus n. sp. and Neopilizetes unumnasus n. sp., and use this information to develop a new concept and expanded diagnosis of Neopilizetes. A key to the five species is provided, and we offer reasons for rejecting the classification of Neopilizetes as a subgenus of Pilizetes.

A checklist of the oribatid mite species (Acari: Oribatida) of Brazil.

A checklist of the oribatid mite species reported in Brazil is presented, including all published records up to 2015. A total of 576 described species in 206 genera and 83 families is presented. Information includes the names by which each species was reported in the Brazilian literature, its general known distribution and by Brazilian States, references, and remarks, when needed. As with most countries, there was a slow early accumulation of knowledge but in recent decades the pace of description has been relatively high. A graphical overview of the number of described oribatid mite species from Brazil in different decades is given. The proportion contributed by each of the major oribatid groups is generally similar to that of the overall world fauna, with a composition that reflects the South American fauna and all of the Neotropics in general. There is a relatively low percentage of primitive mites (Palaeosomata, Enarthronota) other than Lohmanniidae and Mesoplophoridae, which are quite diverse. The Brachypylina comprises about 68% of the oribatid mite fauna. In the checklist, 41% of the species are known only from Brazil, 37% from the Neotropical region, 13.5% have a wider distribution in the global tropical and subtropical regions, and 8.5% are considered cosmopolitan or semicosmopolitan species. The number of descriptions of new species since 2000 from Brazil (73 spp.) and South America (230) is high, but the oribatid mite fauna of these countries remains poorly known. Only continued studies can determine if the high number of species known only from Brazil is an indication of high endemism.

Identity of the oribatid mite Oribata curva and transfer to Trichogalumna (Acari, Oribatida, Galumnidae), with discussion of nomenclatural and biogeographical issues in the 'curva' species-group.

Based on the study of type material, other historical specimens, and new collections, the adult of the thelytokous oribatid mite Oribata curva Ewing, 1907 (Galumnidae) is redescribed and the name is recombined to Trichogalumna curva (Ewing, 1907) comb. nov. A confusing history of synonymies and misidentifications is traced in detail, and their effect on published statements about biogeography is assessed. Reliable records of T. curva are only those from North America. The tropical mite Pergalumna ventralis (Willmann, 1932) is not a subspecies of T. curva. The widely-reported Trichogalumna nipponica (Aoki, 1966) and other similar species form a complex with T. curva that needs further morphological and molecular assessment.

Storage and release of hydrogen cyanide in a chelicerate (Oribatula tibialis).

Cyanogenesis denotes a chemical defensive strategy where hydrogen cyanide (HCN, hydrocyanic or prussic acid) is produced, stored, and released toward an attacking enemy. The high toxicity and volatility of HCN requires both chemical stabilization for storage and prevention of accidental self-poisoning. The few known cyanogenic animals are exclusively mandibulate arthropods (certain myriapods and insects) that store HCN as cyanogenic glycosides, lipids, or cyanohydrins. Here, we show that cyanogenesis has also evolved in the speciose Chelicerata. The oribatid mite Oribatula tibialis uses the cyanogenic aromatic ester mandelonitrile hexanoate (MNH) for HCN storage, which degrades via two different pathways, both of which release HCN. MNH is emitted from exocrine opisthonotal oil glands, which are potent organs for chemical defense in most oribatid mites.

Nanohystricidae n. fam., an unusual, plesiomorphic enarthronote mite family endemic to New Zealand (Acari, Oribatida).

Nanohystrix hammerae n. gen., n. sp.--proposed on the basis of numerous adults and a few juveniles--is a new oribatid mite of the infraorder Enarthronota that appears to be phylogenetically relictual and endemic to northern New Zealand, in habitats ranging from native shrublands to native and semi-native forests. With an adult body length of 1-1.2 mm, the species is the largest known enarthronote mite outside Lohmanniidae, and it has an unusual combination of plesiomorphic and apomorphic traits. Plesiomorphies include: a well-formed median (naso) eye and pigmented lateral eyes; a bothridial seta with a simple, straight base; a vertically-oriented gnathosoma; a peranal segment; adanal sclerites partially incorporated in notogaster (uncertain polarity); three genu I solenidia and a famulus on tarsus II. Autapomorphies include: five pairs of pale cuticular disks on the notogaster, with unknown function; six pairs of long, erectile notogastral setae, including pair h2 incorporated in the second transverse scissure along with the f-row, and pair h1 in a third scissure; chelicerae that are unusually broad, creating a flat-faced appearance; legs I that are inferred to have an unusually wide range of motion. Further, it is the only enarthronote species known to have an elongated ovipositor, and one of few to have glassy, luminous notogastral setae. The gastronotum of juveniles lacks transverse scissures, but has isolated sclerites supporting setae, including erectile setae. The large character gaps between N. hammerae and other enarthronote taxa justifies proposal of a monotypic new family--Nanohystricidae n. fam.--which is tentatively grouped with several other relictual families in the paraphyletic Heterochthonioidea. Small muscles appear to be involved in the operation of all erectile setae, but seem to be only depressors, with erection effected by hysterosomal distension. Based on gut contents, its food is primarily fungal hyphae and spores, though ingestion of small arthropods also occurs (perhaps by necrophagy). Collections were made by Berlese-funnel samples of litter, by sweeping low vegetation, and (mainly) by pitfall traps; the latter two suggest that adults are surface-active. Tritonymphs were collected by pitfall traps, but earlier juveniles were collected only by Berlese-funnels. Adults are frequently infected with a eugregarine parasite, which can entirely fill the digestive caeca; immature trophozoites were also seen in tritonymphs. Adults also can serve as hosts for dispersal of secondary capilliconidia of the fungal genus Basidiobolus.

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.

Catalogue and historical overview of juvenile instars of oribatid mites (Acari: Oribatida).

Oribatid mites (Acari: Oribatida) comprise a taxonomically and morphologically diverse suborder of about 10,000 described species, not including the hyporder Astigmata, with collectively a global distribution. They are primarily soil and litter inhabitants, feeding on fungi and decaying plant remains with various levels of specificity. Though all five active instars are important for reasons that relate to both ecology and systematics, most species are known only as adults. Our purpose was to gather the existing world literature on the active juvenile instars (i.e., excluding prelarva) of oribatid mites, to put classifications and nomenclature in a current context, and to identify the nature of the information in each paper. A selected historical overview identifies the contributions of 19th century authors C.L. Koch, H. Nicolet and A.D. Michael, and summarizes errors that resulted in various oribatid mite juveniles being classified in genera, families and even suborders that were different from those of their adult instars. The catalogue includes all species known to us for which juveniles have been described: 805 species in 310 genera, representing only about 8% of the known oribatid mite species and 30% of genera. These represent 118 families, about 70% of those known. At the superfamily level, representation is weakest among the diverse Oppioidea and Oribatuloidea, and those superfamilies with juveniles that are endophagous in organic substrates, such as Phthiracaroidea, Euphthiracaroidea and Carabodoidea. Representation is strongest in the middle-derivative hyporder Nothrina, in which adults and juveniles are more easily associated, and in brachypyline superfamilies that are mostly affiliated with aquatic, semiaquatic or intertidal environments, such as Limnozetoidea and Ameronothroidea. Juvenile instars remain unknown for 45 families of Brachypylina. Four new nomenclatural actions were proposed: Ojaithrus nymphoides Habeeb, 1982 is a junior synonym of Hydrozetes californiensis Habeeb, 1974, Cepheus feideri Suciu & Panu, 1972 is a junior synonym of Conoppia palmicincta (Michael, 1880). Two species are recombined: Ceratozetes kirgisicus (Shaldybina, 1970) comb. nov. (from Ceratozetella); Scheloribates (Hemileius) nicki (Denmark & Woodring, 1965) comb. nov. (from Hemileius).

Psammochthoniidae n. fam., a paedomorphic family of oribatid mites (Oribatida: Enarthronota) from sandy soil in Thailand, Brazil and the U.S.A.

A new genus and species of enarthronote oribatid mite, Psammochthonius kethleyi n.g., n. sp., is described and illustrated based on adult and immature specimens collected from coastal sandy soil in Thailand (Phangnga), Brazil (SAo Paulo) and the U.S.A. (Mississippi). Analysis shows that it is a member of Hypochthonioidea, but not of any named family, so the monobasic family Psammochthoniidae n. fain. is proposed. Traits that are unique among hypochthonioid mites include an adult body length under 250 microm, a functionally trichoid body form (postpedal flexing), strong lateral displacement of setae in row e, which insert on a unique form of transverse scissure, subcapitular stenarthry, leg IV vestiges and a possible precocious genital swelling in the larva, apparent absence of an anal segment, and a highly regressed leg setation. The latter two, and some other traits that were previously unknown in Hypochthonioidea, suggest that Psammochthoniidae represents the first clearly paedomorphic lineage in this diverse superfamily. Like all other known hypochthonioid mites, P. kethleyi appears to be thelytokous.

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'.

Tasty but protected--first evidence of chemical defense in oribatid mites.

Oribatid mites (Acari, Oribatida) represent one of the most abundant and speciose groups of microarthropods in the decomposer food webs of soils, but little is known of their top-down regulation by predators. Oribatids are relatively long-lived and have numerous morphological defensive adaptations, and so have been proposed to live in 'enemy-free space'. Most also possess a pair of large exocrine oil glands that produce species-specific mixtures of hydrocarbons, terpenes, aromatics, and alkaloids with presumably allomonal functions, although their adaptive value has never been tested empirically. We developed a protocol that discharges the oil glands of the model oribatid species, Archegozetes longisetosus. and offered 'disarmed' individuals as prey to polyphagous Stenus beetles (Staphylinidae), using untreated mites as controls. Stenus juno fed on disarmed mites with behavioral sequences and success rates similar to those observed when they prey on springtails, a common prey. In contrast, mites from the control group with full glands were almost completely rejected; contact with the gland region elicited a strong reaction and cleaning behavior in the beetle. This is the first evidence of an adaptive value of oribatid mite oil gland secretions for chemical defense. The protocol of discharging oil glands should facilitate future studies on top-down control of oribatid mites that aim to differentiate between morphological and chemical aspects of defensive strategies.

Fine structure of the gnathosoma of archegozetes longisetosus [corrected] aoki (acari: oribatida, trhypochthoniidae).

Oribatida are one of the main groups of Acari comprising mostly important decomposers in soils. Most species are particle feeders, an exceptional mode of nutrition in Arachnida. Hence, their feeding organs, the gnathosoma, are of special functional interest. We studied nearly all components using scanning and transmission electron microscopies as well as reconstructions based on synchrotron X-ray microtomography from the model oribatid Archegozetes longisetosus. Besides cuticular structures, we describe the full set of muscles and confirm the presence of a trochanter remnant at the base of the chelicera. Setae on the prodorsum and the anterior and posterior infracapitular setae are mechanoreceptors innervated by two dendrites ending with tubular bodies. Dendrites of adoral setae, anterior setae of the chelicerae, and the supracoxal setae show neither obvious tubular bodies nor wall or terminal pores. Thus their function remains obscure. For the first time, a muscular proprioreceptor has been found in Arachnida. It likely monitors the actions of muscles moving the movable digit of the chelicera. Glandular structures within and associated with the gnathosoma are described. Dermal glands represented by secretory porose areas are found within the infracapitulum. More complex associated glands comprise the podocephalic glands and the infracapitular glands, the ducts of which were traced completely for the first time. The components described are mostly fundamental for the gnathosoma of Actinotrichida (Acariformes), one of the two lineages of Acari, to which Oribatida belong. The gnathosoma is generally considered the most relevant putative synapomorphy of Acari. Since the monophyly of Acari has become more and more questionable during the last decades, a thorough reinvestigation of this body part is necessary for a comprehensive understanding of acarine and even arachnid phylogeny and evolution. This article provides a starting point of such a re-evaluation of the gnathosoma.