Diverging responses to threats across generations in zooplankton

Abstract

Our understanding on how organisms evolutionarily cope with simultaneously occurring, multiple threats over generations is still elusive. In a long‐term experimental study, we therefore exposed clones of a freshwater cladoceran, Daphnia magna, to threats from predation and ultraviolet radiation (UVR) during three consecutive parthenogenetic generations. We show that Daphnia can adapt to different sets of threats within three generations through modifying morphology, swimming behavior, or life‐history traits. When faced with predator cues, D. magna responded with reduced body size, whereas exposure to UVR induced behavioral tolerance when again exposed to this threat. Such UVR‐tolerant behavior was initially associated with a reduced clutch size, but Daphnia restored the reproductive output gradually through generations. The findings advance our understanding on how those common invertebrates, with a global distribution, are able to persist and rapidly become successful in a changing environment.

Population connectivity, dispersal, and swimming behavior inDaphnia

“…Their behavioral response consists in the increase of their swimming speed and distancing from the UVR source (Ekvall et al., 2015). Recent studies have shown that the swimming speed and behavior under UVR threat are inherited in D. magna across generations (Sha et al., 2020, this study). Moreover, the present study highlights a significant difference in swimming speed between populations under threat.…”

“…Sha et al. (2020) further demonstrated that D . magna adaption to different threats (predation, UVR) occurred within three generations.…”

“…A recent study demonstrated that D . magna can adapt rapidly (morphology, life history, swimming behavior) to different threats (predation, UVR) (Sha et al., 2020). We analyzed the adaptive genotypic diversity in D. magna using two markers associated with fish predation and general landscape stressors (i.e., fish predation, parasite infection, and land use)(Orsini et al., 2012).…”

“…No. Q21311MP) and then transferred to the monitoring aquarium, where their swimming behavior was recorded under three consecutive illumination phases, including one minute of LED illumination (Acclimation phase), followed by one minute of UVR (Stimulation phase) and by a one minute of LED illumination (Recovery phase) (Sha et al, 2020). From these video recordings, we extracted the 3D position of each individual at six frame per second in MATLAB V1.7 using the method described in Palmér et al (2016).…”

“…Such escape behavior affects the vertical pattern through the water column (Ekvall et al., 2015; Hansson & Hylander, 2009b), impacting its refuge demand (Hansson et al., 2016) and the ecology of the ecosystem (e.g., Grossart et al., 2010). Moreover, Daphnia can adapt to multiple environmental stressors by adjusting its morphology, swimming behavior, and life history traits within a few parthenogenic generations (Sha et al., 2020). In addition to phenotypic plasticity (Christjani et al., 2016), recent studies have suggested the occurrence of personalities among Daphnia individuals when exposed to UVR (Heuschele et al., 2017).…”