Adaptation in microcosms and the maintenance of sex in rotifers

Project Description

The ubiquity of sexual reproduction in Eukaryotes remains a long-standing question in evolutionary biology. Theory suggests that, compared to asexuality, sexual populations can more readily create genetic variation in fitness, facilitating adaptation. A recent study, using the facultatively sexual rotifer, Brachionus calyciflorus, has shown sex to be favourable within populations adapting to new environments. We will extend the previous study by utilizing more complex environments, similar to those found in nature. The seasonal dynamics of ponds and lakes create ample opportunity for adaptation in short-lived organisms like rotifers. Laboratory populations of rotifers will be subjected to water collected continuously from natural ponds over the summer. We will determine whether sex is favourable in these populations adapting to changing pond conditions relative to populations kept under constant lab conditions. We will also distinguish the relative importance of abiotic properties from those of the biotic community, particularly any potential food and competitors of the rotifers.

Additional Scientific Information

Recent work from our lab, using the facultatively sexual rotifer, Brachionus calyciflorus, showed that sex increased during adaptation to new environments, but decreased once the population is adapted. Complexity and temporal variation under natural conditions should favour sex over longer periods of time since populations are continuously adapting to new environments. This study aims to determine whether seasonal pond dynamics can favour sex by facilitating adaptation in rotifers. We will have three treatments, a constant lab condition and two utilizing pond water (abiotic and biotic). The abiotic treatment will be filtered and sterilized to remove all biotic components of the water. The biotic treatment will use filters to remove any large zooplankton that may predate on rotifers. Bacteria, small phytoplankton and small zooplankton will remain in this treatment and are potential sources of food, competitors and parasites. Pond water will be collected and exchanged into populations every two days to mimic natural conditions. We will measure abiotic and biotic components of the water throughout the season, such as pH, chlorophyll concentration and the plankton community. Several different components of fitness and rates of sex in the rotifer populations will be measured to determine the effects of the treatments.

Principal Investigator: Aneil Agrawal
Researcher(s): Eddie Ho, Pepijn Luijckx

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