Diatoms do radiate: evidence for a freshwater species flock

Abstract

Due to the ubiquity and high dispersal capacity of unicellular eukaryotes, their often extraordinary diversity found in isolated and long-lived ecosystems such as ancient lakes is typically attributed to multiple colonization events rather than to in situ speciation. However, respective evolutionary studies are very scarce and the often high number of species flocks in ancient lakes across multicellular taxa raises the question whether unicellular species, such as diatoms, may radiate as well. Here, we use an integrative approach that includes molecular data from benthic diatom species of the genus Aneumastus endemic to ancient Lake Ohrid, fossil data obtained from the sediment record of a recent deep-drilling project and biogeographical information to test if this group, indeed, constitutes a species flock. Molecular-clock and phylogenetic analyses indicate a young monophyletic group of several endemic species. Molecular, fossil and biogeographical data strongly suggest a rapid intralacustrine diversification, which was possibly triggered by the emergence of novel habitats. This finding is the first evidence for a species flock in diatoms and suggests that in situ speciation is also a relevant evolutionary process for unicellular eukaryotes in isolated ecosystems.

Phylogenetic diversity and environment form assembly rules for Arctic diatom genera—A study on recent and ancient sedimentary DNA

“…This effect is driven by environmental filtering resulting in the co‐occurrence of lineages due to their similar ecological requirements. This signal tends to be strongest in the genus Staurosira , which could be a result of either multiple invasions of minute staurosiroid diatoms into the lakes with a subsequent selection of lineages adapted to the current environment or in situ radiation, which has been explored for diatoms in isolated ecosystems (Stelbrink et al, ). A significant (after Bonferroni correction) clustering signal in space as well as through time is also most obvious for Staurosira , supporting its affinity to diversify along the ecological gradient of the Siberian tree line (Stoof‐Leichsenring et al, ).…”

Characteristics, Main Impacts, and Stewardship of Natural and Artificial Freshwater Environments: Consequences for Biodiversity Conservation

“…One of the prominent features of ancient lakes is "species flocks" or closely related species that evolve sympatrically and coexist [215]. Species flocks have been documented in many groups, including invertebrates [216], fish [215,217], and photosynthetic organisms like diatoms [218]. These flocks are characterized by elevated species richness, shared origins, high levels of endemicity, and restricted geographic occurrence [219].…”

“…It is also evident that more basal "primitive" organisms have higher percentages of endemism. For instance, triclads (Order: Tricladida) are diverse in Lake Baikal with 74 species recorded, and almost 100% are endemic [218]. Nematodes are species rich and characterized with high levels of endemism in Lake Baikal [224].…”

Tracing the Origin of Planktonic Protists in an Ancient Lake

“…Yet, much less is known about the operation of this process in protists. Recent radiation has been proposed for dinoflagellates in Lake Baikal [26] as well as for a diatom species flock in Lake Ohrid [67]. Furthermore, the existence of species flocks in diatoms has been extensively discussed in a number of ecosystems [68,69,70].…”