Diel Vertical Migration In Daphnia Research Articles

Modeling diel vertical migration with membrane computing

Diel vertical migration (DVM) is an important ecological phenomenon in which zooplankton migrate vertically to deal with trade-offs associated with greater food availability in shallow waters and lower predator risk in deep waters due to lower light availability. Because of these trade-offs, DVM dynamics are particularly sensitive to changes in light intensity at the water surface. Therefore, changes in the proportion of cloudy and sunny days have the potential to disrupt DVM dynamics. We propose a new membrane computing model that captures the effect of cloud cover on DVM in Daphnia, and we use it to explore the impacts of an increased proportion of cloudy days that are predicted to occur with climate change. Our 2-dimensional, spatially explicit model integrates multiple trophic levels from abiotic nutrients to Daphnia predators. We analyzed the effect that different proportions of cloudy and sunny days throughout the summer have on our model. The model simulations suggest that an increase in sunny days promotes a high phytoplankton concentration near the surface but does not necessarily promote an increased abundance of Daphnia. Our model also suggests that a higher proportion of cloudy days would increase Daphnia abundance due to a shift in the vertical distribution of Daphnia populations towards superficial waters. Our results highlight that climate changes in multiple regions will affect animal migrations leading to altered food web dynamics in freshwater ecosystems, and emphasize the potential of membrane computing as a modeling framework for spatially and temporally explicit ecological processes.

5α-cyprinol sulfate, a bile salt from fish, induces diel vertical migration in Daphnia

Prey are under selection to minimize predation losses. In aquatic environments, many prey use chemical cues released by predators, which initiate predator avoidance. A prominent example of behavioral predator-avoidance constitutes diel vertical migration (DVM) in the freshwater microcrustacean Daphnia spp., which is induced by chemical cues (kairomones) released by planktivorous fish. In a bioassay-guided approach using liquid chromatography and mass spectrometry, we identified the kairomone from fish incubation water as 5α-cyprinol sulfate inducing DVM in Daphnia at picomolar concentrations. The role of 5α-cyprinol sulfate in lipid digestion in fish explains why from an evolutionary perspective fish has not stopped releasing 5α-cyprinol sulfate despite the disadvantages for the releaser. The identification of the DVM-inducing kairomone enables investigating its spatial and temporal distribution and the underlying molecular mechanism of its perception. Furthermore, it allows to test if fish-mediated inducible defenses in other aquatic invertebrates are triggered by the same compound.

Diel vertical migration, size distribution and photoprotection in zooplankton as response to UV‐A radiation

AbstractThe transparency regulator hypothesis (TRH) proposes that ultraviolet radiation (UVR) is a main driving force behind diel vertical migration (DVM) of zooplankton in clearwater systems. While previous studies have mainly studied DVM in relation to the TRH on a spatial scale across systems we here focus on long‐term trends in a single system in order to assess if UVR explains observed patterns in DVM. We show that the strength of DVM in Daphnia is to a large extent explained by UVR and we demonstrate a tipping point at which the UVR intensity drastically affects the strength of DVM in Daphnia. In contrast, the strength of DVM could not be explained by the level of UVR among calanoid copepods. The amount of photoprotective compounds did not differ between zooplankton found at different depths indicating that zooplankton do not change their vertical position in relation to the amount of accumulated photoprotective compounds. In addition, we show that both Daphnia and calanoid copepods display patterns of size structured migration.

Research Article: Zooplankton diel vertical migrations in lakes of contrasting food webs

Abstract. Zooplankton diel vertical migration (DVM) is a defense mechanism used in planktivory avoidance. We evaluated zooplankton DVM in two lakes of contrasting food webs in Michigan's Upper Peninsula, USA to test the hypothesis that zooplankton follow normal DVM in the presence of a vertebrate zooplanktivore: Pumpkinseed sunfish, Lepomis gibbosus, and reverse DVM in the presence of an invertebrate predator; Chaoborus spp. We found normal DVM in Daphnia spp., cyclopoid copepods, and copepod nauplii populations in the vertebrate zooplanktivore dominated lake. In contrast, cyclopoid copepods and calanoid copepods exhibited reverse DVM in an invertebrate predator dominated lake. Although the magnitude of DVM was minimal in both lakes, our analysis demonstrated that large cladoceran zooplankton are more responsive to vertebrate predation while small size copepod zooplankton are more responsive to invertebrate predation.

Role of melatonin in the control of depth distribution of Daphnia magna

Previous studies confirmed the presence of melatonin in Daphnia magna and demonstrated diurnal fluctuations in its concentration. It is also known that in several invertebrate species, melatonin affects locomotor activity. We tested the hypothesis that this hormone is involved in the regulation of Daphnia diel vertical migration (DVM) behaviour that is well recognized as the adaptive response to predation threat. Using ‘plankton organs’, we studied the effect of three concentrations of exogenous melatonin (10−5, 10−7, 10−9 M) on DVM of both female and male D. magna in the presence or absence of chemical cue (kairomone) of planktivorous fish. Depth distribution was measured six times a day, using infrared-sensitive closed circuit television cameras. Our results showed a significant effect of melatonin on the mean depth of experimental populations, both males and females, but only when melatonin was combined with fish kairomone. Females stayed, on average, closer to the surface than males, both responding to the presence of kairomone by descending to deeper strata. In the presence of exogenous melatonin and with the threat of predation, Daphnia stayed closer to the surface and their distribution was more variable than that of individuals, which were exposed to the kairomone alone. Approaching the surface in the presence of predation threat seems to be maladaptive. We postulate the role of melatonin as a stress signal inhibitor in molecular pathways of response to predation threat in Cladocera.

Upward phosphorus transport by Daphnia diel vertical migration

Upward phosphorus transport by Daphnia diel vertical migration

Individual-based simulation of diel vertical migration of Daphnia: A synthesis of proximate and ultimate factors

Diel vertical migration (DVM) of Daphnia is a well-studied inducible defence mechanism against predation by fish. Our study is anchored in constructing an individual-based model of DVM in order to bring established knowledge about essential key processes into a synthesis. For that purpose, we combined information about both proximate and ultimate factors of DVM with the intention to unify published results from these historically separated lines of research. The model consists of three submodels: (i) movements, (ii) growth and reproduction, and (iii) mortality. The submodel “movements” includes algorithms for light-dependent migration behaviour of Daphnia that were able to reproduce spatiotemporal distribution patterns of DVM. By means of scenario analyses, we tested the predator avoidance hypothesis by comparing population growth rates of migrating and non-migrating populations over a range of fish biomasses in the habitat. This enabled us to quantify the adaptive value of DVM under various environmental settings. Simulation results supported the predator avoidance hypothesis and showed a particularly high adaptive value of DVM if fish predation is intense. However, since DVM is associated with costs, a certain predation pressure in the habitat has to be prevailing in order to turn DVM into an adaptive strategy. Otherwise, if fish predation is weak, migrating populations realize lower population growth rates than non-migrating populations. In a second scenario, we tested the influence of vertical gradients of temperature and food on the adaptive value of DVM. We found a great potential to maximize the adaptive value of DVM if daphnids are able to modify their migration amplitude in dependence of the vertical structure of their habitat. For example, a deep chlorophyll maximum (DCM) can be a strong attractor for Daphnia to modify the migration amplitude in such a way that the daytime depth corresponds to the depth of the DCM. However, flexibility of the migration amplitude is only advantageous if the predation intensity is moderate – if predation is intense, only maximum migration amplitudes maximize fitness.

The impact of diel vertical migration of Daphnia on phytoplankton dynamics

Diel vertical migration (DVM) of large zooplankton is a very common phenomenon in the pelagic zone of lakes and oceans. Although the underlying mechanisms of DVM are well understood, we lack experimental studies on the consequences of this behaviour for the zooplankton's food resource-the phytoplankton. As large zooplankton species or individuals migrate downwards into lower and darker water strata by day and upwards into surface layers by night, a huge amount of herbivorous biomass moves through the water column twice a day. This migration must have profound consequences for the phytoplankton. It is generally assumed that migration supports an enhanced phytoplankton biomass and a change in the composition of the phytoplankton community towards smaller, edible algae in the epilimnion of a lake. We tested this assumption for the first time in field experiments by comparing phytoplankton biomass and community assemblage in mesocosms with and without artificially migrating natural stocks of Daphnia hyalina. We show that DVM can enhance phytoplankton biomass in the epilimnion and that it has a strong impact on the composition of a phytoplankton community leading to an advantage for small, edible algae. Our results support the idea that DVM of Daphnia can have strong effects on phytoplankton dynamics in a lake.

Absence of typical diel vertical migration in Daphnia: varying role of water clarity, food, and dissolved oxygen in Lake Eymir, Turkey

Diel vertical migration (DVM) is a complex and dynamic behaviour against predation because the reaction of migrating organisms to light intensity plays a primary role, but is modified by other factors. In the relatively shallow but thermally stratified Lake Eymir, Daphnia pulex de Geers utilized vertical refugia afforded by the hypolimnion during both day and night. Differences in general vulnerability to fish predation determined the differences in their mean residence depths (MRDs) of different population categories such as most conspicuous and vulnerable individuals of adult with eggs inhabited the deepest depth, whereas juveniles stayed close the thermocline. In late spring, profoundly high amplitude of displacement within the hypolimnion, probably due to the hypolimnion being well-lit and relatively well-oxygenated for the fish and rather unsafe for the large-sized daphnids, was recorded. Therefore, the large-sized daphnids daytime refuge was close to the bottom whereas at night they moved upward to benefit from warmer water temperature along with food availability in the presence of fish predation but still remained below the thermocline. In summer, the insignificant amplitude of the hypolimnetic, which later became epilimnetic, displacements were probably due to the near-anoxic condition found below the thermocline. This might have deterred the fish, thus providing a safer refuge for daphnids in the below thermocline, which afterwards became the above thermocline. Low oxygen availability was regarded as the summer proximate factor. The abundant food and warmer water conditions found in the below/above thermocline also accounted for absence of DVM in summer. Consequently, this study suggests that DVM by Daphnia is an adaptation that is plastic to changing environmental conditions.

On the combined analysis of proximate and ultimate aspects in diel vertical migration (DVM) research

Although evolutionary ecologists agree that proximate and ultimate aspects are two sides of one coin, they are seldom interested in studies on physiological and behavioural mechanisms at the base of ecological phenomena. Nevertheless, these mechanisms are objects of selection and evolved to realise adaptive significances. This paper is a plea to bring both fields closer together, and, by means of an example of Diel Vertical Migration of Daphnia, some proximate and ultimate aspects are discussed. It is argued that light changes, not fish kairomone, is the primary cause for an individual to swim downwards at dawn and upwards at dusk. However, what is called a causal factor might differ when ecosystems or individuals are studied. In addition, causality in ecology is not simple, and has the character of a `set of necessary conditions'. To illustrate the importance of proximate analyses in DVM, two basic response mechanisms are discussed: Photobehaviour system 1 and 2. The physiological character of these systems leads to a fixed type of migration or to a phenotypically induced DVM, respectively. The adaptive significance of the first might be a reduction of the hazardous effects of UV radiation and of the second a lowering of mortality due to visually hunting predators.

Predator-induced diel vertical migration inDaphnia: Enrichment and preliminary chemical characterization of a kairomone exuded by fish

Planktivorous fish release a cue of an unknown chemical nature into the water that induces diel vertical migration inDaphnia as predator avoidance response. We used a bioassay to obtain information about the chemical nature of the kairomone. We present a method to enrich the cue from holding water of fish by sorbent extraction. The kairomone exuded byLeucaspius delineatus can be characterized as a nonolefinic low-molecular-weight anion of intermediate lipophilicity. The presence of amino groups in the molecule can be excluded, whereas hydroxy groups are essential for activity. Separation by HPLC yielded only one active fraction. The kairomones released byCarassius carassius andRutilus rutilus showed the same chemical characteristics, suggesting that the kairomones from different species of fish, sensed byDaphia, are very similar, if not identical.

Trade‐Offs in Diel Vertical Migration by Zooplankton: The Costs of Predator Avoidance

Diel vertical migration (DVM) of zooplankton is a behavioral antipredator defense that is shaped by the trade—off between higher predation risk in surface waters and reduced growth in deeper waters. We conducted two laboratory experiments to quantify the costs connected with DVM. In the first experiment, Daphnia magna were kept individually in thermally stratified flow—through tubes and exposed to seven different concentrations of fish—exuded kairomones. Above a threshold concentration, the strength of migration increased with increases in the concentration of fish exudates. Enhancement of migration resulted in a lower mean ambient temperature experienced by the animals and marked decreases in individual growth and reproduction rates. In order to separate costs due to low hypolimnetic temperatures in a stratified system from costs due to reduced food concentrations in deeper waters, we conducted an experiment with a 2 ° 2 factorial design (fish presence vs. absence and high vs. low food conditions). Differences in mean ambient temperature between Daphnia that performed DVM and nonmigrating animals were found to have a much stronger impact on life history parameters than food effects. A reevaluation of field data on DVM in Daphnia further supports the view that vertical gradients are more important than food gradients.

Lack of endogenous rhythmicity in Daphnia diel vertical migration

A population of Daphnia Galeata × hyalina was induced to perform diel vertical migration (DVM) by the addition of fish‐kairomones to a large plankton tower. Vertical profiles of zooplankton abundance were measured every 12 h. When the tower was covered to shield the water column from the light, DVM ceased, and vertical distributions were not statistically different from the night profiles that had been observed before the tank was covered. This result suggests that endogenous rhythms do not trigger DVM, but that a change in light intensity must occur.

Chemically-induced diel vertical migration in Daphnia: a new bioassay for kairomones exuded by fish

Chemically-induced diel vertical migration in Daphnia: a new bioassay for kairomones exuded by fish

Fish predators, food availability and diel vertical migration in Daphnia

Fish predators, food availability and diel vertical migration in <i>Daphnia</i>