Two Worlds on a Stone: Arctic Desert Hypoliths and Epiliths Show Spatial Niche Differentiation

Abstract

In Arctic polar deserts, rocks can be extensively colonized by phototrophic hypolithic communities that exploit periglacial sorting processes to grow beneath opaque rocks. These communities are distinguished by green bands that are distinctly and abruptly separated from the black-pigmented communities on the rock surface (epiliths). We used 16S and 18S rDNA culture-independent methods to address the hypothesis that the two communities are different. Although both communities were dominated by cyanobacterial species (Chroococcidiopsis and Nostoc spp.), we found that the hypolithic and epilithic habitats host distinct microbial communities. We found that eukaryotic hypolithic and epilithic communities were statistically similar but that the hypolithic habitats contained tardigrade DNA, showing that the more clement subsurface habitat supports animal life in contrast to the surface of the rocks. These results reveal the distinctive communities and sharp demarcations that can develop across small spatial scales in the Earth's rocky extreme environments.

FIGURE 1

Hypolithic communities of Devon Island, Canadian High Arctic. (A) Location of sampling site in Canadian High Arctic (Devon Island), (B) An example of patterned ground on Devon Island showing sorting of rocks and edges around which light can penetrate to the subsurface. The image is approximately two metres across in the foreground, (C) An example of a rock community inhabiting Arctic rocks. The hypolithic community is shown as a distinctive green region on the underside of the rock. The surface of the rock is covered by a black‐pigmented epilithic community. The rock is 21 cm tall.

FIGURE 2

Multi‐Dimensional Scaling plot showing the relative dissimilarity between prokaryotic communities from the hypolithic (blue) and eplithic (red) communities, informed by a Bray–Curtis dissimilarity matrix.

FIGURE 3

The mean abundance (bars) and statistical importance (line) of each prokaryotic taxa characteristic of hypolithic (upper graph) and epilithic (lower graph) communities. Importance determined by SIMPER analysis.

FIGURE 4

Univariate analysis of prokaryotic communities comparing hypolithic and epilithic communities. Data show the total number of species (S), total number of individuals (N), species richness (d), and Pielou's species evenness (J).

FIGURE 5

Multi‐Dimensional Scaling plot showing the relative dissimilarity between eukaryotic communities from the hypolithic (blue) and epilithic (red) communities of Arctic rock environments, informed by a Bray–Curtis dissimilarity matrix.

FIGURE 6

The mean abundance (bars) and statistical importance (line) of each eukaryotic taxa characteristic of hypolithic (upper graph) and epilithic (lower graph) communities from Arctic rock environments. Importance determined by SIMPER analysis.

FIGURE 7

Univariate analysis of eukaryotic communities comparing hypolithic and epilithic communities. Data showing the total number of species (S), total number of individuals (N), species richness (d) and Pielou's species evenness (J).

FIGURE 8

Phylogenetic trees of the characteristic taxa from hypolithic and epilithic communities, as determined by SIMPER analysis and shown alongside a pictorial illustration of the two communities (with animal DNA in the hypolithic community depicted using schematics of these organisms). Taken from SIMPER analysis of combined bacterial and eukaryotic datasets. Colours indicates phylogenetic groupings; Purple = cyanobacteria, Green = eukaryotes, Blue = animalia (Tardigrada) separated from other eukaryotes to emphasize their presence. All others are bacteria.