The ecological assembly of bacterial communities in Antarctic wetlands varies across levels of phylogenetic resolution

Abstract

Summary As functional traits are conserved at different phylogenetic depths, the ability to detect community assembly processes can be conditional on the phylogenetic resolution; yet most previous work quantifying their influence has focused on a single level of phylogenetic resolution. Here, we have studied the ecological assembly of bacterial communities from an Antarctic wetland complex, applying null models across different levels of phylogenetic resolution (i.e. clustering ASVs into OTUs with decreasing sequence identity thresholds). We found that the relative influence of the community assembly processes varies with phylogenetic resolution. More specifically, selection processes seem to impose stronger influence at finer (100% sequence similarity ASV) than at coarser (99%–97% sequence similarity OTUs) resolution. We identified environmental features related with the ecological processes and propose a conceptual model for the bacterial community assembly in this Antarctic ecosystem. Briefly, eco‐evolutionary processes appear to be leading to different but very closely related ASVs in lotic, lentic and terrestrial environments. In all, this study shows that assessing community assembly processes at different phylogenetic resolutions is key to improve our understanding of microbial ecology. More importantly, a failure to detect selection processes at coarser phylogenetic resolution does not imply the absence of such processes at finer resolutions.

Microdiverse bacterial clades prevail across Antarctic wetlands

“…In line with the high contribution of ecological homogeneous selection in the bacterial community assembly at CPWC (Quiroga et al., 2022), we consistently identified five bacterial HoS clades driving these assemblages. As expected, the HoS clades showed high relative abundance across all samples, resembling ecologically successful clades that thrive in the extreme CPWC.…”

“…Furthermore, the ASVs within HoS clades displayed, on average, 1.8 and 3.6 times higher number of reads per sample than those from non‐S and HeS clades respectively. In addition, the identified HeS clade showed distinctly low relative abundance per sample, potentially explaining the overall strong homogeneous selection detected at the community level (Quiroga et al., 2022). Signs of strong homogeneous selection were previously reported for bacterial communities from other extreme ecosystems, such as Antarctic lakes (Logares et al., 2018), glacier‐fed streams (Fodelianakis et al., 2022), proglacial floodplain streams (Brandani et al., 2023) and the oligotrophic South Pacific Gyre (Allen et al., 2020).…”

“…Considering that community-wide lower than expected phylogenetic turnover dominates the bacterial metacommunity within the CPWC (Quiroga et al, 2022), we expect to find numerous HoS clades with high relative abundances. Furthermore, we hypothesize that these HoS clades are ubiquitously distributed across multiple habitats.…”

“…We analysed a set of 64 samples (i.e. 64 communities) from the CPWC surveyed over the early 2018 Antarctic summer (Quiroga et al., 2022). Each sample was collected and processed individually as previously described (Quiroga et al., 2022).…”

“…Its bacterial metacommunity consists of a set of local communities, inhabiting lentic (ponds, lakes), lotic (streams, seepages, wet rocks) and terrestrial (soils, mosses, snow) environments, spatially connected by species dispersal (Leibold et al., 2004). A previous study revealed that bacterial assemblages at CPWC are shaped by strong homogeneous selection, which together with dispersal limitation acting in concert with drift and microdiversification, appear to be leading to different but very closely related bacterial amplicon sequence variants (ASVs, 100% sequence similarity operational taxonomic units; Callahan et al., 2016) across lentic, lotic and terrestrial environments (Quiroga et al., 2022). However, we still do not know which bacterial taxa or phylogenetic clades are shaped by selection processes in the CPWC nor their ecological strategies to thrive in such extreme conditions.…”