Diversity and Biogeography as Revealed by Morphologies and DNA Sequences

Abstract

Zooplankton diversity and biogeography have been based on morphological identifications for over 200 years but are increasingly being studied by DNA sequences. To better integrate these data, a clear understanding on how phenotypes and genotypes relate is required. Knowledge of inter- and intraspecific genetic variability, in correlation with morphological traits, is the key to elucidate zooplankton diversity and distribution, and how these variables respond to the environment. Within the smallest size fractions of zooplankton, tintinnid ciliates have been the subject of such comparisons, at the level of both species (by DNA barcoding of identified isolates) and assemblages (by concurrent metabarcoding and microscopy). Synthesis of these comparisons shows that: (1) like other organisms, tintinnids include both cryptic and polymorphic species; (2) the global number of species, as well as the species richness in a given sample, cannot be accurately estimated with the available methods; (3) the decoupling between morphological and molecular signals does not mask the bulk of assemblage fluctuations in space and time; and (4) DNA sequences reveal distributions linked to salinity, in addition to known bathymetric and latitudinal patterns.

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