DNA barcodes expose unexpected diversity in Canadian mites

Abstract

Mites (Arachnida: Acariformes, Parasitiformes) are the most abundant and species‐rich group of arthropods in soil, but are also diverse in freshwater habitats, on plants, and as symbionts of larger animals. However, assessment of their diversity has been impeded by their small size and often cryptic morphology. As a consequence, published estimates of their species richness span more than two orders of magnitude (0.4–114 million). In this study we employ DNA barcoding and the Barcode Index Number (BIN) system to investigate mite diversity at over 1,800 sites across Canada, primarily from soil and litter habitats with smaller contributions from freshwater, plants, and animal hosts. Barcodes from 73,394 specimens revealed 7,077 BINs with representatives from all four orders (Ixodida, Mesostigmata, Sarcoptiformes, Trombidiformes) and 60% (186) of the known families. The BIN total is 2.4 times the number of species previously recorded from Canada (2,999), reflecting the unexpectedly high richness of several families. Richness projections suggest that more than 28,000 BINs occur at the sampled locations, indicating that the Canadian mite fauna almost certainly includes more than 30,000 species—a total similar to that for the most diverse insect order in Canada, Diptera. This unexpected diversity was partitioned into highly dissimilar, spatially‐structured assemblages that likely reflect dispersal limitation and environmental heterogeneity. Further sampling of a greater diversity of habitats will refine understanding of mite diversity in Canada, but similar analyses in other geographic regions will be essential to ascertain their diversity at a global scale.

The limited spatial scale of dispersal in soil arthropods revealed with whole-community haplotype-level metabarcoding

“…Broad surveys of invertebrate soil diversity using HTS have commonly relied on markers of low species-level resolution and via eDNA extracted from small soil samples (Bahram et al, 2016; Wu et al, 2011; Zinger et al, 2019). Other studies have characterise specific groups of mites or springtails by individualised processing of specimens and relying on morphological assignment to generate species-level data (Caruso, Schaefer, Monson, & Keith, 2019; Ingimarsdóttir et al, 2012), but see also Young, Proctor, DeWaard, & Hebert (2019) on molecular species assignment. HTS data now greatly increase the potential of expanding both the number of species studied and the level of detail at which intra-specific variation for each is captured.…”

“…However, they do not inform about colonisation and establishment success (effective dispersal) and possibly only pertain to a few highly dispersive species. Additionally, the dispersal potential may have been overestimated due to the low resolution of morphological species identification (Cicconardi et al, 2013) leading to perceived low turnover among sites, as evident from recent large-scale barcoding studies (Young et al, 2019). Our results at the community level thus raise doubts about a generalised dispersal advantage for small-bodied arthropods and instead indicate very small dispersal distances, even over evolutionary time scales, for the majority of species that make up the complex mesofauna communities of the soil.…”

Unexpected diversity in the host-generalist oribatid miteParaleius leontonychus(Oribatida, Scheloribatidae) phoretic on Palearctic bark beetles

“…Recent studies have shown that inconspicuous and/or small taxa, often with a reclusive life style, show particularly high levels of cryptic diversity ( Von Saltzwedel, Scheu & Schaefer, 2017 ; Wagner et al, 2019 ). Mites are no exception, and indeed, their actual diversity seems to be vastly underestimated, even in common and easily recognizable taxa ( Navia et al, 2013 ; Young et al, 2019 ; Schäffer, Kerschbaumer & Koblmüller, 2019 ).…”

“…Recent phylogenetic studies on mites and metabarcoding studies based on environmental DNA suggest that the number of mite species currently recognized is a considerable underestimation of the true diversity, even for common taxa allegedly easy to identify to species level ( Navia et al, 2013 ; Young et al, 2019 ; Schäffer, Kerschbaumer & Koblmüller, 2019 ). As P. leontonychus has been reported to be associated with a large number of bark beetles, which themselves tend to show some preferences to particular tree genera ( Raffa, Gregoire & Lindgren, 2015 ), the question arises whether P. leontonychus is a truly widespread species with no host preference at all or whether it is a complex of cryptic species with specialization to particular hosts and trees as has been previously documented for uropodoid mites phoretic on bark beetles ( Knee et al, 2012 ).…”

Discriminating larvae of two syntopic Cychramus species (Coleoptera, Nitidulidae) by means of bar-HRM analysis

“…However, taxonomic identification based only on morphology can be difficult to virtually impossible or very time consuming when two or more species are morphologically highly similar. Indeed, there is increasing evidence that the diversity of recognized morphospecies does by far not reflect the true species diversity, especially in inconspicuous and small taxa [ 1 , 2 ]. In addition, certain life stages (i.e., eggs and larvae) or sexes are often morphologically indistinguishable among species [ 3 ], complicating inferences about species richness and ecological interactions.…”