The Theme
Rotifers are microscopically small animals that live in freshwater, brackish water and other moist environments such as mosses. Some planktonic species are ideal model organisms because they are the fastest reproducing metazoans (rotifers have about 1000 cells) and can be cultured in controlled laboratory environments such as bubbled chemostats.
Rotifers are also great study objects because they have an extremely interesting natural history. Many exciting ecological and evolutionary phenomena can be investigated in rotifers.
Rotifers have three major sub-groups that differ in their sexual preferences. The Seisonidea are bisexual and produce about equally sized males and females. The monogononts (which we mostly study in the Fussmann lab) reproduce predominantly parthenogenetically with females only. Occasionally they can be stimulated to undergo meiosis, after which the females can produce dwarf males with which they have sex. Finally, the bdelloids reproduce only asexually and haven’t had sex nor males for more than 80 million years (as a taxonomic group, that is), which is sometimes called an evolutionary scandal.
The different propensities to produce males among the different rotifer sub-groups and within the monogononts are an ideal test bed for evolutionary theories about the importance of sex.
Other interesting topics that can be studied using rotifers are predator-prey relationships, the chemical induction of defensive morphologies, movement and aggregation of animals - to name just a few.
The Questions
Here are some examples of rotifer-related questions that undergraduate researchers have investigated in the Fussmann lab:
- Does predator-induced spine formation affect the competitive dynamics of rotifers? (Matthew Feeley)
- Is competition a factor that stimulates rotifers to disperse? (Xiao Xiao)
- Why do never 100% of rotifer females switch to sexual reproduction when exposed to the appropriate stimulus? (Greg Kramer, Mahmoud Labib; published in Hydrobiologia 2007)
The System
We are trying to keep a rotifer zoo alive in the lab. Currently we have cultures of the rotifers Brachionus calyciflorus (several clones), B. havanaensis, B. rubens, Proales sp., Asplanchna priodonta, plus some non-rotifer zooplankton such as Daphnia and ciliates.
We started some of these cultures ourselves from lake plankton, others get passed around by the community of rotifer researchers. We are thankful to Martin Boraas, S.S.S. Sarma and A. Verschoor.
Did You Know?
Rotiferologists around the world are an active community. We have an international meeting every three years in places like Mexico, Thailand, Austria, where we talk about all aspects of rotifer science.
The most recent meeting, ROTIFERA XII, took place in Berlin, Germany, in August 2009. G. Fussmann organized a session on the “Evolution of Rotifers”.