PT  - JOURNAL ARTICLE
AU  - Teofil Nakov
AU  - Jeremy M. Beaulieu
AU  - Andrew J. Alverson
TI  - Freshwater diatoms diversify faster than marine in both planktonic and benthic habitats
AID  - 10.1101/406165
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 406165
4099  - http://biorxiv.org/content/early/2018/08/31/406165.short
4100  - http://biorxiv.org/content/early/2018/08/31/406165.full
AB  - The marine–freshwater divide is a key determinant of the distribution and diversity of aquatic organisms. Many clades that span the salinity gradient are disproportionately more diverse in the younger, short-lived, and less abundant freshwater environments than they are in the marine realm, which covers most of the biosphere. Differences in the rates of accumulation and loss of diversity between marine and freshwaters contribute to these diversity imbalances. Assessing the salinity gradient together with other potential interacting variables can provide important additional insights. Diatoms, a species-rich lineage of photosynthetic protists, display a striking diversity imbalance across the marine–freshwater divide, but also between planktonic and benthic habitats, making them an excellent system to study such interactions. We used a novel set of state speciation and extinction models to show that the salinity–habitat interaction was important for diatom diversification and that both planktonic and benthic lineages turnover faster in freshwaters. Lineages occupying the same habitat (e.g., marine plankton) can diversify at substantially different rates in relation to the cumulative effect of unobserved variables implicitly accounted for by our models. Traversals of the salinity gradient were bidirectional, rejecting longstanding hypotheses about the permeability of the salinity barrier. The probability of colonization of freshwater (and the plankton) does, however, vary across the diatom phylogeny, indicating that phylogenetic diversity differs substantially between habitats (e.g., marine vs. freshwater plankton). Unlike metazoans, diatoms both speciate and go extinct at a faster rate in freshwater, suggesting an association between the rates of lineage and habitat turnover.