Global patterns of diversity and phylogenetic community structure in
free-living Nematodes: a metabarcoding meta-analysis
Abstract
Identifying and understanding patterns of biological diversity is
crucial at a time when even the most remote and pristine marine
ecosystems are threatened by resource exploitation such as deep-seabed
mining. Metabarcoding provides the means through which to perform
comprehensive investigations of diversity by examining entire
assemblages simultaneously. Nematodes commonly represent the most
abundant infaunal metazoan group in marine soft sediments. In this
meta-analysis, we compiled all publicly available metabarcoding datasets
targeting the 18S rRNA v1-v2 region from sediment samples to conduct a
global-scale examination of nematode Amplicon Sequence Variant (ASV)
alpha diversity patterns, evolutionary distinctiveness (ED) and
phylogenetic community structure at different depths and environments.
We found that nematode ASV richness followed a parabolic trend,
increasing from the intertidal to the shelf, reaching a maximum in the
bathyal and decreasing in the abyssal zone. No depth- or
environment-specific assemblages were identified as a large fraction of
genera were shared. Contrastingly, the vast majority of ASVs were unique
to each environment and/or depth zone; genetic diversity was thus highly
localised. The intertidal and abyssal samples had the highest ED values,
indicating that both a dynamic, fluctuating ecosystem, as well as a
relatively stable yet very old one, can produce highly diversified
assemblages. Overwhelmingly, nematode ASVs in all environments exhibited
phylogenetic clustering, pointing to environmental filtering as the
primary force defining community assembly rather than competitive
interactions. This finding stresses the importance of habitat
preservation for the maintenance of marine nematode diversity.