Checklist of Oribatida from American peatlands In total, we list 156 species recorded for American peatlands (Table 1) including the 49 species recorded from the S1 Bog site, of which only 26 species have been previously recorded for peatlands in the country. Previous work by Belanger (1976) (41 species) and Donaldson (1996) (31 species), the two other studies with the highest species richness, only share nine species occuring at both sites, and there are only six species recorded from all three sites. New York State has the greatest number of species recorded (73 species), largely due to the pioneering work of Belenger, followed by Minnesota (S1 Bog), and New Hampshire (Donaldson 1996). Similarly, the 49 species listed for Minnesota from this one peatland site, and the 31 species recorded from Donaldson for a single site in New Hampshire, suggest the importance of intensive sampling that is required to obtain comprehensive species lists for single peatland sites, and also highlight that these single sample locations are possibly a small proportional sample of peatland habitats within each State. Beyond these three sites, the state with the highest species richness is Alaska (28 species) as sampled by Behan (1978) and electronic records from the Canadian National Collection of Insects, Arachnids and Nematodes, and Maine (10 species). The most frequent species on the checklist is Punctoribates palustris recorded from five states (New York, New Hampshire, Minnesota, Wisconsin, Alabama and Georgia), Nanhermannia dorsalis from four states (Maine, New Hampshire, Minnesota, Mississippi), and Carabodes granulatus (New York, New Hampshire, Alabama, Mississippi). Punctoribates palustris is a widespread species, commonly associated with Sphagnum and other aquatic mosses as well as pond margins and muskeg; Behan-Pelletier and Lindo (2023) list records of P. palustris from thirteen U.S. states as well as in Canada. Similarly, C. granulatus is the Carabodes with the widest distribution in eastern North America and is recorded from at least 23 states (Behan-Pelletier & Lindo 2023), found in Sphagnum and other mosses, as well as leaf litter, rotten wood, lichens and fungi. The genus Nanhermannia is in need of revision, especially with respect to N. dorsalis which is a possible synonymy of N. coronata Berlese, 1913 that is known from peatlands in Europe (see Jacot 1937; Norton & Kethley 1990). That said, N. dorsalis and N. nana coexist in North American peatlands, although it is also unclear which records of N. nana from North America are valid (Roy Norton 2021, pers. comm.). Of the S1 Bog species in Minnesota, 23 species are new records for peatlands in the U.S., including two new families (Trichthoniidae and Atopochthoniidae) and many new species in the Enarthronota Superfamily (i.e., within family Brachychthoniidae) for American peatlands, although these species have been previously recorded from peatlands in other countries. For instance, Barreto and Lindo (2021) found Liochthonius brevis, L. sellnicki, Sellnickochthonius zelawaiensis, G. majestus, Tyrphonothrus foveolatus and N. dorsalis in fen sites in Northern Ontario, Canada, which is only ~ 620 km away from the S1 Bog in Minnesota. The oribatid mite fauna of the U.S. peatlands is highly similar to the peatland fauna of Canada, sharing 92 of the 156 species with the neighbour country, where 188 species have been recorded from peatlands (Barreto & Lindo 2021, Behan-Pelletier & Lindo 2023). This pattern is in line with the “classical” approach of zoogeographical regions proposed by Wallace (1876) that groups most of North America as part of the Nearctic region due to their biogeographical similarities in fauna taxa. The oribatid mite fauna of peatlands in the U.S. is also similar, albeit probably to a lesser extent, to the fauna in European peatlands. For instance, Seniczak et al. (2020) collected Ceratoppia quadridentata and T. foveolatus from Sphagnum mosses in Norway, Starý (2006) and Lehmitz et al. (2020) found S. zelawaiensis and T. foveolatus in peat bogs in the Czech Republic and Germany, respectively, and Minor et al. (2016) found T. foveolatus in peat bogs in Eastern Russia. A comparison between the oribatid mite diversity from the Nearctic region and the Palearctic region (roughly, Europe, northern Africa, and northern Asia) shows that only 359 out of the ~4,700 species are shared between the regions (Schatz 2004). It is important to note, though, that this similarity includes species from all habitats, not only peatlands as we were unable to validate all European habitat records. Several species listed are found in a variety of habitats and considered cosmopolitan, such as Hypochthonius rufulus, Platynothrus peltifer, T. maior, Oppiella nova, and Tectocepheus velatus (Behan-Pelletier & Lindo 2019; Subías 2022), which reinforces the idea that the peatland oribatid mite fauna also comprises non-specialist species (Donaldson 1996; Barreto 2021). In fact, some species collected during the S1 Bog sampling in Minnesota were unexpected as they are typically found in drier environments (e.g., dry forests, dry montane regions, canopy habitats); these include Eueremaeus nr. proximus, Scapheremaeus palustris, and Cepheus corae. Yet, to the best of our knowledge, we report the first record of Mycobates hyaleus and Atopochthonius artiodactylus for a peatland system, as they have been previously only collected in forests in North America (mosses, lichens, litter) (Behan-Pelletier & Lindo 2019). The presence of these species may be a result of the harvesting the site went through in 1969 and 1974 (Perala & Verry 2011) that led to a reduction in moisture. Drying has been documented as a major disturbance for peatland oribatid mite communities (Laiho et al. 2001; Lehmitz 2014) with soil fauna communities changing towards those of forests (Silvan et al. 2000). For instance, Lehmitz (2014) compared samples before and after a harvesting event in a German bog and concluded that harvesting favours terrestrial species. Indeed, based on the oribatid mite community from the Spruce Hole Bog, New Hampshire, Donaldson (1996) posited that only a small portion of species found in peatlands are specialists occurring in very high abundances, likely due to a semi-aquatic habitat association and preference for acidic environments. In our case, peatland specialist species included the abundant E. mahunkai, L. lustrum and Mainothrus badius. Interestingly, Norton and Behan-Pelletier (2007) note that all known sites inhabited by E. mahunkai are peatlands (fens or bogs), while the specific name ‘lustrum’ from L. lustrum is Latin for bog and refers to the habitat of this species. These three species (Barreto et al. 2021) and other oribatid mites (Minor et al. 2019; Lehmitz et al. 2020) have been shown to associate with high moisture levels. Oribatid mites have been noted to be better represented by thelytokous species in peatlands compared to other ecosystems (Behan-Pelletier & Bissett 1994; Maraun et al. 2019), both in terms of number of thelytokous species and their collective proportional abundance. This was evident at the S1 Bog, based on reproductive modes indicated by Norton et al. (1993), Fischer et al. (2010) and Maraun et al. (2019). Thelytokous species represented ~90% of S1 Bog species, and this number is reduced to ~79% if we disregard the species without confirmation of reproduction mode in literature (i.e., the ones believed to be thelytokous but lacking data to support it). Similar trend is seen for the abundance of thelytokous species, that represented ~66% of all individuals, but ~52% if removing the aforementioned cases. This pattern might be related to a lower efficacy of free-standing spermatophores produced by males in wet habitat like peatlands (Norton & Palmer 1991), and/or because high accumulation of dead organic matter provides ample resources that are easy to access in these systems (Maraun et al. 2019). Not surprisingly, peatland records for the thelytokous family Brachychthoniidae were extended, with five new species added to the checklist, similar to peatland sites in Canada (Barreto & Lindo 2021). A comparison between the species in the S1 Bog and the species previously recorded in American peatlands, highlights some species-poor families at our site. For instance, the predominantly sexual families Phthiracaridae (two records vs. eight from other peatlands) and Ceratozetidae (five records vs. 15 from other peatlands), and the predominantly thelytokous families Trhypochthoniidae (two records vs. seven records from other peatlands) and Nothridae (one record vs. six from other peatlands). We note that our site is surrounded by a predominantly deciduous forest, which could explain in part the low diversity in Phthiracaridae, as these mites are endophagous of decaying wood, including conifer needles, as immatures (Jacot 1939). Our sampling from the S1 Bog in Minnesota contains at least four undescribed species (Brachychthonius n. sp., Hoplophorella n. sp., Liebstadia n. sp., and Trichoribates n. sp.), and we predict that many more undescribed species are likely contained within peatlands of the U.S. For instance, Alaska contains extensive peatland habitats that formed early in deglacial periods and that are estimated to be>15,000 years old (Jones & Yu 2010) and undescribed species have been recorded, for example, in Behan (1978) that showed that 13.4% of the species found in Alaska, including species from peatlands, were undescribed. As not many peatland sites have been sampled in the U.S., this checklist has a geographical limitation. It is also important to note the relatively low area peatlands cover in the country, representing only ~2% of the landscape (Xu et al. 2018) with the vast majority concentrated in only two states in the country’s North region, Minnesota and Alaska (Minnesota Scientific and Natural Areas Patterned Peatlands 2022). Nonetheless, the high diversity sampled from peatlands in other States, often from only one sample location, highlights the understudied oribatid mite fauna of many habitats in the U.S.

Published as part of Barreto, Carlos & Lindo, Zoë, 2024, Checklist of oribatid mites (Acari: Oribatida) from peatlands in the United States with notes on oribatid mites from a bog in Minnesota, pp. 106-121 in Zootaxa 5556 (1) on pages 115-117, DOI: 10.11646/zootaxa.5556.1.10, http://zenodo.org/record/14595028