Maintenance of Host Diversity

Daphnia dentifera experiences strong selective pressure to evolve resistance to its virulent fungal parasite Metschnikowia bicuspidata.  In fact, D. dentifera has been shown to evolve increased resistance over the course of a single large epidemic!  Despite the fact that we can detect this rapid evolution, host populations in the wild show a wide range in susceptibility; i.e. some Daphnia remain very susceptible to the fungus while other Daphnia remain totally resistant.  I’m interested in understanding how these little zooplankton retain such a huge range in susceptibility.

We’re exploring two factors that we believe are responsible for the maintenance of this diversity: 1) sexual reproduction, and 2) temporal gene flow from the egg bank of D. dentifera.  I’m working with undergraduate research assistant Haniyeh Zamani to assess how variation in susceptibility and genetic diversity change after Daphnia populations switch from asexual to sexual reproduction during late fall, and how they change again in the spring after Daphnia hatch from their egg bank (which allows them to overwinter in the freezing winters of Michigan).

We’ve found some very intriguing results that I’m excited to share.

Stay tuned!