Niche features and assembly mechanisms of microeukaryotic generalists and specialists along a north-south gradient of a subtropical coastal sea

ABSTRACT: The assembly mechanisms of generalists and specialists have been extensively studied for prokaryotes but underexplored for microeukaryotes, the crucial players in marine ecosystems. In addition, the latitudinal gradient of biodiversity on the scale of the global ocean has been well documented, but is less studied at a regional scale. Here, we investigated plankton assemblages along a latitudinal gradient of a subtropical regional coastline using high-throughput sequencing of the 18S rRNA gene (rDNA) V4 region. We observed a trend of increasing diversity with decreasing latitudes in this provincial spatial scale, resembling the previously reported global-scale trend. Based on niche breadth, microeukaryotes in our samples were grouped into generalists, opportunists and specialists. Generalists were more influenced by selection than specialists, with temperature being an important factor. In addition, we found that dispersal limitation had a greater influence on the generalists than on the specialists. Interestingly, dinoflagellates, a major component in both generalist and specialist subcommunities, were important to stabilization in the generalist subcommunity. Chlorophyta, in contrast, had a crucial effect on network stability for specialists. Overall, this study verifies the latitudinal gradient of biodiversity at a mesoscale, and provides new insights into the ecotypic grouping and assembly mechanism of microeukaryotes. It also sheds light on the potential differential importance of Dinoflagellata and Chlorophyta.