Distribution and Diversity of Soil Microfauna from East Antarctica: Assessing the Link between Biotic and Abiotic Factors

Abstract

Terrestrial life in Antarctica has been described as some of the simplest on the planet, and mainly confined to soil microfaunal communities. Studies have suggested that the lack of diversity is due to extreme environmental conditions and thought to be driven by abiotic factors. In this study we investigated soil microfauna composition, abundance, and distribution in East Antarctica, and assessed correlations with soil geochemistry and environmental variables. We examined 109 soil samples from a wide range of ice-free habitats, spanning 2000 km from Framnes Mountains to Bailey Peninsula. Microfauna across all samples were patchily distributed, from complete absence of invertebrates to over 1600 specimens/gram of dry weight of soil (gdw), with highest microfauna abundance observed in samples with visible vegetation. Bdelloid rotifers were on average the most widespread found in 87% of sampled sites and the most abundant (44 specimens/gdw). Tardigrades occurred in 57% of the sampled sites with an abundance of 12 specimens/gdw. Nematodes occurred in 71% of samples with a total abundance of 3 specimens/gdw. Ciliates and mites were rarely found in soil samples, with an average abundance of 1.3 and 0.04 specimens/gdw, respectively. We found that microfaunal composition and abundance were mostly correlated with the soil geochemical parameters; phosphorus, NO3 − and salinity, and likely to be the result of soil properties and historic landscape formation and alteration, rather than the geographic region they were sampled from. Studies focusing on Antarctic biodiversity must take into account soil geochemical and environmental factors that influence population and species heterogeneity.

Impacts of DNA extraction and PCR on DNA metabarcoding estimates of soil biodiversity

“…The 15 g indirect extractions tended to produce lower estimates of metazoan biodiversity than the 15 g phosphate buffer extractions, despite the former method being targeted at microfauna (Velasco-Castrillón et al, 2014). This suggests that the sieving and centrifugation steps involved in this method may have resulted in the exclusion of metazoans that are represented as body fragments or free DNA molecules, rather than whole organisms.…”

“…Of course, this may be due to each set of 1.5 g direct extracts and PCRs representing 10 small subsamples of soil, whereas the results from the larger extraction methods represent replicate PCRs from one (or two) large samples, resulting in greater heterogeneity among the former than the latter. The 15 g indirect extractions tended to produce lower estimates of metazoan biodiversity than the 15 g phosphate buffer extractions, despite the former method being targeted at microfauna (Velasco‐Castrillón et al., ). This suggests that the sieving and centrifugation steps involved in this method may have resulted in the exclusion of metazoans that are represented as body fragments or free DNA molecules, rather than whole organisms.…”

Ground-truthing Phylotype Assignments for Antarctic Invertebrates

“…Sampling locations of Antarctic soils are shown in Fig. 1, invertebrate isolation and taxonomic descriptions are detailed elsewhere [14]. Invertebrate morphotype composition of these soils is provided in Fig.…”

“…This limitation somewhat constrains comparisons between sequence-based and morphology based taxonomy assignments as performed here. Regardless, metabarcoding approaches are preferable in the first instance over morphological techniques for taxonomic identification of highly abundant and cryptic Antarctic nematodes and rotifers in Antarctic bulk soil samples, and provide some attractive benefits: (1) The high abundance of those taxa constitutes a constraint to morphological approaches and increases their DNA contributions to low-diverse Antarctic soil extracts, leading to higher success of metabarcoding approaches [14,61,62]; (2) both nematodes and rotifers are often missed in morphological approaches due to constraints of extraction methods, their small size and conserved morphology [61,62,71]; and (3) both markers employed here were able to provide family level assignments to nematodes and rotifers with reasonable workload (Fig. 6), despite the fact that all metabarcoding markers perform differently in detecting expected phylotypes from DNA mixtures [24].…”

“…Antarctic springtails, mites, tardigrades, nematodes and rotifers are morphologically conserved, but still frequently analyzed with morphological approaches, requiring highly skilled taxonomists -time required to identify such invertebrates can be considered inversely proportional to their size [11][12][13][14]. Not reliant on morphological identification, DNA- Abstract: Biodiversity information from Antarctic terrestrial habitats helps conservation efforts, but the distribution and diversity particularly of microinvertebrates remains poorly understood.…”