Microbial biogeography through the lens of an invasive species: The intercontinental disjunction of Discostella asterocostata as a case study

The large population sizes and unlimited dispersal potential of microbes has led to the hypothesis that microbial species should be found in all suitable open habitats worldwide. Consequently, microbes should not exhibit the kinds of biogeographic patterns seen in macroorganisms. This paradigm is challenged by the growing list of invasive microbes with biogeographic disjunctions that highlight natural limitations on microbial dispersal. We sampled water bodies in the United States and compiled records from the literature and public databases to characterize the distribution of Discostella asterocostata, a freshwater planktonic diatom that was thought to be restricted to the Far East. We report its presence in ecologically similar water bodies in the United States. Populations from the U.S. and China are indistinguishable morphometrically, suggesting a recent separation. This hypothesis is supported by paleolimnological data, which point to an introduction into the U.S. as recently as the mid-1980s. Discostella asterocostata appears to be a recent invasive that has rapidly spread across the eastern U.S. The overlapping distributions of D. asterocostata and invasive carp species, both globally and in the U.S., highlighted Asian carp as a possible vector for the introduction. The growing list of invasive diatoms highlights natural constraints on microbial dispersal, resulting in biogeographic distributions that can be upended through human activity.

Target Audience: This presentation is intended for those interested in the geographic distribution of diatoms and the introduction of an increasing number of diatoms as invasive species. The presentation is directed to a general audience and does not require specialized expertise.