The photobehaviour of Daphnia spp. as a model to explain diel vertical migration in zooplankton

Abstract

Many pelagic animal species in the marine environment and in lakes migrate to deeper water layers before sunrise and return around sunset. The amplitude of these diel vertical migrations (DVM) varies from several hundreds of metres in the oceans to approx. 5-20 m in lakes. DVM can be studied from a proximate and an ultimate point of view. A proximate analysis is intended to reveal the underlying behavioural mechanism and the factors that cause the daily displacements. The ultimate analysis deals with the adaptive significance of DVM and the driving forces that were responsible for the selection of the traits essential to the behavioural mechanism. The freshwater cladoceran Daphnia is the best studied species and results can be used to model migration behaviour in general. Phototaxis in Daphnia spp., which is defined as a light-oriented swimming towards (positive phototaxis) or away (negative phototaxis) from a light source, is considered the most important mechanism basic to DVM. A distinction has been made between primary phototaxis which occurs when light intensity is constant, and secondary phototaxis which is caused by changes in light intensity. Both types of reaction are superimposed on normal swimming. This swimming of Daphnia spp. consists of alternating upwards and downwards displacements over small distances. An internal oscillator seems to be at the base of these alternations. Primary phototaxis is the result of a dominance of either the upwards or the downwards oscillator phase, and the direction depends on internal and external factors : for example, fish-mediated chemicals or kairomones induce a downwards drift. Adverse environmental factors may produce a persistent primary phototaxis. Rare clones of D. magna have been found that show also persistent positive or negative primary phototaxis and interbreeding of the two types produces intermediate progeny : thus a genetic component seems to be involved. Also secondary phototaxis is superimposed on normal swimming : a continuous increase in light intensity amplifies the downwards oscillator phase and decreases the upwards phase. A threshold must be succeeded which depends on the rate and the duration of the relative change in light intensity. The relation between both is given by the stimulus strength versus stimulus duration curve. An absolute threshold or rheobase exists, defined as the minimum rate of change causing a response if continued for an infinitely long time. DVM in a lake takes place during a period of 1n5-2 h when light changes are higher than the rheobase threshold. Accelerations in the rate of relative increase in light intensity strongly enhance downwards swimming in Daphnia spp. and this enhancement increases with increasing fish kairomone and food concentration. This phenomenon may represent a ' decision-making mechanism ' to realize the adaptive goal of DVM : at high fish predator densities, thus high kairomone concentrations, and sufficiently high food concentrations, DVM is profitable but not so at low concentrations. Body axis or...

Hydroacoustic assessment of fish and Chaoborus (Diptera-Chaoboridae) distribution in three Neotropical lakes

“…Furthermore, the hydroacoustic technique Dom Helvécio Lake (Figure 4) and Nado reservoir echograms (Figure 6), corroborates with other studies on zooplankton diurnal vertical migration in these habitats (for instance, Fukuhara et al, 1993;Bezerra-Neto et al, 2009). One of the most accepted explanations to DVM of Chaoborus larvae is avoiding spatial overlap with the predator (Ringelberg, 1999), in the case fish individuals. In Carioca Lake, the absence of DVM may be a result of ecological release due to the introduction of exotics piscivorous fish (e.g.…”

Pigment-dispersing hormone in Daphnia interneurons, one type homologous to insect clock neurons displaying circadian rhythmicity

“…However, the identification of clock neurons satisfying criteria for autonomous pacemakers has not been easily forthcoming in any of the crustacean models investigated so far [17,76,77]. Daphnia and other cladoceran species have, as per many other planktonic organisms, developed escape strategies among which a light-entrained circadian behavior Pigment-dispersing hormone in Daphnia 3419 known as diel vertical migration (DVM) in the water body is probably the most important [78][79][80][81]. Furthermore, many other diel rhythmic and photoperiod-dependent behaviours are known for cladoceran species such as circadian eyepigment movements, growth and reproductive diapause control [82][83][84][85].…”

The Great Salt Lake's monimolimnion and its importance for mercury bioaccumulation in brine shrimp (Artemia franciscana)

“…Because Artemia were drawn to the focused light source, night distributions were difficult to obtain, but the attraction effect was minimized by measuring each interval randomly and not progressively along the column. Attraction to a focused bright light beam is common in zooplankton, as opposed to avoidance of a diffuse light source (Ringelberg 1999). Differences between day and night distributions were minimal, and only the mean distributions are reported here.…”