William (Bill) Lamberts, Biology
Daphnia pulex have been shown to respond to kairomones emitted by predatory Chaoborus and planktivorous fish, though these two groups of predators differ significantly in their predation styles. The effects of predation vary across Daphnia size range, and heart rate response to Chaoborus kairomones has been shown to vary across size. I found that heart rate of individuals in the small size class in a clonal population of Daphnia pulex respond more strongly to bluegill (Lepomismacrochirus) kairomones than heart rate of medium or large size classes. The two largest classes showed no difference in heart rate between control and fish kairomone treatments. This is possibly due to physiological differences between small and large Daphnia pulex, or it could be an adaptive response based on the futility of escape from fish predation for large Daphnia and the lower detection rates for small Daphnia.
Culshaw-Maurer, Michael J., "The Induced Heart Rate Response to Fish Kairomones in Daphnia pulex" (2015). Honors Theses, 1963-2015. 79.