Multivariate trait analysis reveals diatom plasticity constrained to a reduced set of biological axes

Trait-based approaches to phytoplankton ecology have gained traction in
recent decades as phenotypic traits are incorporated into ecological and
biogeochemical models. Here, we use high-throughput phenotyping to explore
both intra- and interspecific constraints on trait combinations that are
expressed in the cosmopolitan marine diatom genus Thalassiosira. We
demonstrate that within Thalassiosira, phenotypic diversity cannot be
predicted from genotypic diversity, and moreover, plasticity can create
highly divergent phenotypes that are incongruent with taxonomic grouping.
Significantly, multivariate phenotypes can be represented in reduced
dimensional space using principal component analysis with 77.7% of the
variance captured by two orthogonal axes, here termed a ‘trait-scape’.
Furthermore, this trait-scape can be recovered with a reduced set of
traits. Plastic responses to the new environments expanded phenotypic
trait values and the trait-scape, however, the overall pattern of response
to the new environments was similar between strains and many trait
correlations remained constant. These findings demonstrate that
trait-scapes can be used to reveal common constraints on multi-trait
plasticity in phytoplankton with divergent underlying phenotypes.
Understanding how to integrate trait correlational constraints and
trade-offs into theoretical frameworks like biogeochemical models will be
critical to predict how microbial responses to environmental change will
impact elemental cycling now and into the future.