Signals in flux: Investigating the seasonal turnover of the diel vertical migration-inducing kairomone 5α-cyprinol sulfate

5α-cyprinol sulfate (CPS) is a chemical signal released by cyprinid fish
that plays a crucial role in predator-prey interactions by inducing diel
vertical migration (DVM) in Daphnia, a key process shaping freshwater
ecosystem dynamics. While CPS-mediated DVM has long been considered a
stable and predictable response to predation risk, this study challenges
previous assumptions by demonstrating that CPS undergoes rapid turnover in
aquatic systems. We show that CPS exudation is tightly linked to fish
feeding intensity, independent of fish size, while microbial degradation
emerges as the dominant removal process, with degradation rates reaching
up to 85.7% per day in lake water. Seasonal field data from a mesotrophic
lake reveal that CPS concentrations range from 40 to 900 ng/L over a
season, peaking in late summer, putatively indicating increased fish
feeding and shifts in prey availability. Using an integrated approach
combining laboratory feeding trials, field sampling, and predictive
modeling, we present a temperature-dependent framework that captures the
interplay between CPS exudation and degradation, revealing its transient
yet ecologically significant role. Our findings highlight a fundamental
reconsideration of CPS as an environmental cue: rather than reflecting
predator abundance, CPS concentrations primarily track predator feeding
activity, dynamically modulating the strength of DVM and its cascading
effects on freshwater food webs. This study provides the first in-situ
quantification of CPS turnover, offering new insights into the temporal
variability of chemical signaling and its ecosystem-wide consequences in
fluctuating aquatic environments.