Effects of stressors on growth and competition between different cryptic taxa affiliated with Ochromonadales (Chrysophyceae)

Morphologically similar flagellate taxa comprise a high cryptic diversity. This diversity evolved partly through parallel evolution in several phylogenetically distinct taxa. Here we investigate the effects of heat waves and salinization on growth and competition between cryptic taxa. For this purpose, we developed specific FISH probes targeting the phylogenetic clades comprising Pedospumella encystans, Spumella rivalis, and Poteriospumella lacustris, respectively. Exposure to salt resulted in a decreasing growth rate for all three taxa. In contrast, a sudden increase in temperature to 27 degrees C stimulated particularly the growth of P. lacustris. This species showed a high competitive strength and the taxon-specific responses to stressors lead to a shift of community composition. This tum-over of differently adapted cryptic species with presumably similar feeding preferences and predator-prey interactions may stabilize microbial food webs facing environmental change.