Molecular analysis of geographic patterns of eukaryotic diversity in Antarctic soils

Abstract

We describe the application of molecular biological techniques to estimate eukaryotic diversity (primarily fungi, algae, and protists) in Antarctic soils across a latitudinal and environmental gradient between approximately 60 and 87 degrees S. The data were used to (i) test the hypothesis that diversity would decrease with increasing southerly latitude and environmental severity, as is generally claimed for "higher" faunal and plant groups, and (ii) investigate the level of endemicity displayed in different taxonomic groups. Only limited support was obtained for a systematic decrease in diversity with latitude, and then only at the level of a gross comparison between maritime (Antarctic Peninsula/Scotia Arc) and continental Antarctic sites. While the most southerly continental Antarctic site was three to four times less diverse than all maritime sites, there was no evidence for a trend of decreasing diversity across the entire range of the maritime Antarctic (60 to 72 degrees S). Rather, we found the reverse pattern, with highest diversity at sites on Alexander Island (ca. 72 degrees S), at the southern limit of the maritime Antarctic. The very limited overlap found between the eukaryotic biota of the different study sites, combined with their generally low relatedness to existing sequence databases, indicates a high level of Antarctic site isolation and possibly endemicity, a pattern not consistent with similar studies on other continents.

FIG. 1.

Map showing the study region and indicating locations of collection sites.

FIG. 2.

Example of consensus tree of aligned complete sequences, showing major kingdom and subkingdom groups present in Signy Island samples. Bootsrap replications are shown for major groupings.

FIG. 3.

Rarefaction curves constructed for eukaryotic clone libraries from each of the six collection sites. Clones were grouped into OTUs at a level of sequence similarity of >97.5%. The “Signy without nematodes” curve has had a dominating clone removed (see text).

FIG. 4.

Principal-coordinate analysis of sites based on the percentage of sequences obtained for each taxonomic group at each site (original data are in Table 3).

FIG. 5.

Numbers of sites at which different OTUs were found. Fungal, algal, and nonalgal protist groups and a combination of all groups (including metazoans, plants, and uncultured clones) are shown. Numbers above the bars indicate the total number of OTUs in each group found at a given number of sites.