The Mess of Stress: Daphnia and Predator Response

Predation is one of the major factors driving natural selection. As a result, prey species have evolved a variety of defensive mechanisms to cope with the selection pressure exerted by predators. We are looking specifically at phenotypic plasticity of defense traits in daphnia magna produced in response to damselfly kairomones (chemical predator cues).

Phenotypic plasticity is defined as physical qualities that are subject to change due to environmental pressures. This study builds off of past research exploring the relationship between kairomones and stress on the development of daphnia defense mechanisms: helmets, neck teeth, and long tails.

What is fascinating about these antipredator defenses is that Daphnia develop them in response to their parents’ experience of predatory cues (transgenerational plasticity) and over evolutionary time—via genetic variation that is favored by natural selection. For example, 5α-cyprinol sulfate, a bile acid that fish release from their intestine, gills, and the urinary tract into the water, is detected by daphnia and recognized as a predator cue . In a similar fashion, kairomones released by damselflies can be sensed by daphnia magna.

We sought to find the effects of predator cues on reproductive and survival rates. We also measured the development of the defense mechanisms: neck teeth, helmet and tail spikes, and change in size and shape (cyclomorphosis) on daphnia magna transgenerationally.

We chose daphnia because they are a good model organism for seeing phenotypic changes that reveal changes in their gene expression. This can relate to humans because we can get more of an idea of how stressors of a parent affects the offspring and next generations.