Diversidade e distribuição de ciliados da Família Strombidiidae (Ciliophora) no oceano global
Abstract
Ciliates dominate microzooplankton and play an essential role in marine food
webs. By ingesting flagellates, bacteria and other organisms from pico and
nano-plankton, and then being consumed by zooplankton, ciliates are the main
pathway of carbon flow that links the microbial loop to the classical trophic
chain. However, the diversity and distribution of ciliates in the global ocean is
still poorly understood due to the difficulty of observing and classifying these
organisms under light microscopy. When fixed, most ciliates are lost or change
their morphology, making their identification difficult. Thus, the use of molecular
tools represents an opportunity to study the ciliate community in the ocean.
Within ciliates, the Strombidiidae family is amongst the most abundant, but
there are still few systematic studies at the global scale on the distribution,
abundance and phylogeny of this important group in the ocean. This study aims
to: 1) evaluate the phylogenetic diversity of Strombidiidae, 2) understand its
distribution in the global ocean, 3) determine the ecological niche of the most
abundant clades. We used a metabarcoding dataset (region V4 18S rRNA) of
1008 samples from the TARA Oceans and TARA Polar circum-navigation
expeditions. We constructed a Strombidiidae reference tree with complete 18S
rRNA gene sequences from the literature and inserted the metabarcoding
sequences for phylogenetic assignment. Then we related the distribution data of
these clades with environmental data to define ecological niches. The
phylogeny of Strombidiidae revealed 20 distinct clades, almost all of them
widely distributed in most oceanic regions. The most abundant clade
(Strombidium_clade2) is cosmopolitan. Furthermore, we obtained 12
environmental clades whose sequences (V4 18S rRNA region) are not identical
to those described in the reference tree, and thus, may represent new clades.
Niche analysis showed that the different clades of the Strombidiidae family had
different distribution patterns in the global ocean, determined by temperature,
salinity and oxygen. The Arctic Ocean had greater abundance among the
Strombidiidae clades and very characteristic niches were observed for these
oceanographic regions. This work represents the first study of the taxonomic
and phylogenetic diversity of the Strombidiidae family in the global ocean, thus
contributing to the knowledge of the ecology of marine ciliates.
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