Abstract:
Studies of microbial biogeography are often convoluted by extremely high diversity and
differences in microenvironmental factors such as pH and nutrient availability. Desert
endolithic (inside rock) communities are relatively simple ecosystems that can serve
as a tractable model for investigating long-range biogeographic effects on microbial
communities. We conducted a comprehensive survey of endolithic sandstones using
high-throughput marker gene sequencing to characterize global patterns of diversity
in endolithic microbial communities. We also tested a range of abiotic variables in
order to investigate the factors that drive community assembly at various trophic levels.
Macroclimate was found to be the primary driver of endolithic community composition,
with the most striking difference witnessed between hot and polar deserts. This
difference was largely attributable to the specialization of prokaryotic and eukaryotic
primary producers to different climate conditions. On a regional scale, microclimate and
properties of the rock substrate were found to influence community assembly, although
to a lesser degree than global hot versus polar conditions. We found new evidence
that the factors driving endolithic community assembly differ between trophic levels.
While phototrophic taxa, mostly oxygenic photosynthesizers, were rigorously selected
for among different sites, heterotrophic taxa were more cosmopolitan, suggesting that
stochasticity plays a larger role in heterotroph assembly. This study is the first to uncover
the global drivers of desert endolithic diversity using high-throughput sequencing. We
demonstrate that phototrophs and heterotrophs in the endolithic community assemble
under different stochastic and deterministic influences, emphasizing the need for studies
of microorganisms in context of their functional niche in the community.
