1. Analysis of Multiple Species Presence on Diatom Motility
S.A. Cohn, K. Patterson, A. Wolske;
Biological Sciences, DePaul Univ, Chicago, IL
Diatoms, like other algae, ordinarily live within complex multi-species algal communities.
Diatoms are crucial components in these aquatic communities, providing one of the most
abundant primary food sources. In order to help manage the development of healthy
aquatic ecosystems it is important to understand the ecological stimuli that regulate the
ability of motile diatoms to successfully migrate through their local assemblages in order to
successfully exploit resources such as light and nutrients. Our lab has shown how several
large single-celled diatom species display characteristic responses to local conditions such as
temperature and light. We have also showed how several of these conditions such as
adhesion and directional responses can often be modified in the presence of other diatom
species. We have investigated this further to show that this effect can be dependent on the
relative abundance of diatom species present. For example, when exposed to high blue light
irradiations at their leading tip, Stauroneis cells (S. phoenicenteron) will reverse direction in
about 43±4 s. However, in the presence of Craticula cells (C. cuspidata) the direction change
increases in a concentration dependent manner, increasing to 172±39 s when the
Craticula:Stauroneis ratio is 10:1 (same approximate cell density for all experiments). This
type of effect can be generated quickly, and appears to be rapidly reversible. In a separate
experiment, Stauroneis cells alone reversed direction upon blue light irradiation in 34±3 s,
but when these cells were exposed to a large number of Craticula cells this response time
increased to 42±2 sec within just a few minutes of exposure. Upon removal from the
Craticula cells and rinsing in fresh medium, the cells returned to their initial response time of
35±3 sec. In both cases the direction change response of the Craticula cells seems
unaffected by the presence of Stauroneis. We are investigating such species-dependent
modulations of motile characteristics to better understand the ways in which species can
affect each other's motility and might be able to undertake resource partitioning within a
complex algal assemblage to gain even more ecological advantage. This work was
supported by grants through the DePaul College of Science and Health, the DePaul
University Research Council, and equipment purchased previously through NSF Grant IBN-
9982897.