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.

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.

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.

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.

Oribatid mites as a major dietary source for alkaloids in poison frogs.

Alkaloids in the skin glands of poison frogs serve as a chemical defense against predation, and almost all of these alkaloids appear to be sequestered from dietary arthropods. Certain alkaloid-containing ants have been considered the primary dietary source, but dietary sources for the majority of alkaloids remain unknown. Herein we report the presence of approximately 80 alkaloids from extracts of oribatid mites collected throughout Costa Rica and Panama, which represent 11 of the approximately 24 structural classes of alkaloids known in poison frogs. Forty-one of these alkaloids also occur in the dendrobatid poison frog, Oophaga pumilio, which co-occurs with the collected mites. These shared alkaloids include twenty-five 5,8-disubstituted or 5,6,8-trisubstituted indolizidines; one 1,4-disubstituted quinolizidine; three pumiliotoxins; and one homopumiliotoxin. All but the last of these alkaloid classes occur widely in poison frogs. In addition, nearly 40 alkaloids of unknown structure were detected in mites; none of these alkaloids have been identified in frog extracts. Two of these alkaloids are homopumiliotoxins, five appear to be izidines, four appear to be tricyclics, and six are related in structure to poison frog alkaloids that are currently unclassified as to structure. Mites are common in the diet of O. pumilio, as well as in the diets of other poison frogs. The results of this study indicate that mites are a significant arthropod repository of a variety of alkaloids and represent a major dietary source of alkaloids in poison frogs.