In their natural environments, organisms are unlikely to be distributed randomly but instead they are constantly faced with multiple and variable threats. In order to maximise survival, they need to be able to perceive the present threat level and respond accordingly. In aquatic ecosystems, two common threats for crustacean zooplankton are predation and ultraviolet radiation (UVR). Despite the growing recognition that zooplankton can plastically respond to predation and UVR within a single generation, little is known on how they evolutionarily cope with these simultaneously occurring multiple threats over generations. In this thesis, I investigate the threat responses in zooplankton when exposed to multiple threats from predation and UVR based on short-term (within a single generation) and multigenerational exposure experiments.
Alteration in behavioural traits is generally the first reaction in zooplankton to changed conditions, which allows them to escape from the threats instantly after exposure. One example of a common behavioural response in zooplankton is diel vertical migration (DVM), where they spend the day in deep, dark waters and migrate up to surface waters at night. I found that low-latitude copepods in Bahamian blue holes exhibited DVM to reduce predation risk from visually hunting fish, whereas no response was found to lake-specific differences in UVR transparency. Moreover, copepods also follow their food resources, so that they stay at the depth with rich food where predation risk and UVR may decrease to a negligible level. When exposed to conflicting threats from UVR and predation from either moving pelagic or benthic predators, Daphnia are able to make different risk assessments and thereby alter their behaviour in accordance with the actual threat level. I show that two Daphnia species respond strongly to UVR, whereas only the large prey species D. magna express a predator avoidance behaviour.
In addition to alterations in behaviour, D. magna can also change its body size and life-history to deal with multiple threats from predation and UVR. I demonstrate that D. magna become smaller through generations in response to fish predation, whereas they change their behaviour to avoid UVR. Individuals who have previously experienced UVR respond more relaxed when exposed to such radiation again. These individuals also produce less offspring during the first generation after exposure but the number of offspring then gradually increases through generations. Therefore, D. magna adopt divergent strategies over generations and become adapted to the local environmental conditions after about three generations. Exposure to UVR can induce plastic phenotypic changes in D. magna including alterations in behaviour and life-history shifts. However, such transgenerational effects may be modified by the evolutionary history of stress that lead to different plastic responses to UVR across generations.
- Naturvetenskapliga fakulteten
- Hansson, Lars-Anders, handledare
- Brönmark, Christer, Biträdande handledare
|Sponsorer för avhandling|
|Tilldelningsdatum||2021 jan 15|
|Status||Published - 2021|
Place: Blå hallen, Ekologihuset, Sölvegatan 35A, Lund. Join via zoom: https://lu-se.zoom.us/j/64588294094?pwd=NE52c0VDV3FnMzlYVlNoM1NNZCthdz09
Name: Declerc, Steven
Title: Associate Professor
Affiliation: Netherlands institute of Ecology