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Euxinic Freshwater Hypolimnia Promote Bacterial Endemicity in Continental Areas
8 páginas, 3 figuras, 1 tabla.Bacteria and archaea represent the vast majority of
biodiversity on Earth. The ways that dynamic ecological and
evolutionary processes interact in the microbial world are,
however, poorly known. Here, we have explored community
patterns of planktonic freshwater bacteria inhabiting stratified
lakes with oxic/anoxic interfaces and euxinic (anoxic and
sulfurous) water masses. The interface separates a welloxygenated
upper water mass (epilimnion) from a lower
anoxic water compartment (hypolimnion). We assessed
whether or not the vertical zonation of lakes promoted
endemism in deeper layers by analyzing bacterial 16S rRNA
gene sequences from the water column of worldwide
distributed stratified lakes and applying a community ecology
approach. Community similarity based on the phylogenetic
relatedness showed that bacterial assemblages from the same
water layer were more similar across lakes than to communities
from different layer within lakes and that anoxic hypolimnia
presented greater β-diversity than oxic epilimnia. Higher β-
diversity values are attributable to low dispersal and small
connectivity between community patches. In addition, surface
waters had significant spatial but non-significant environmental
components controlling phylogenetic β-diversity patterns,
respectively. Conversely, the bottom layers were significantly
correlated with environment but not with geographic distance.
Thus, we observed different ecological mechanisms simultasimultaneously
acting on the same water body. Overall, bacterial
endemicity is probably more common than previously thought,
particularly in isolated and environmentally heterogeneous
freshwater habitats. We argue for a microbial diversity
conservation perspective still lacking in the global and local
biodiversity preservation policies.This research was supported by grant
AERBAC 079/2007 from the Spanish Ministerio de Medio Ambiente
(MARM) and grants CONSOLIDER-INGENIO 2010 GRACCIE
CSD2007-00067 and PIRENA CGL2009-13318-CO2-01/BOS from
the Spanish Ministerio de Ciencia e Innovación (MICINN) to EOC.
AB is supported by the Spanish FPU predoctoral scholarship program.Peer reviewe