Three-Dimensional Tracking of Small Aquatic Organisms Using Fluorescent Nanoparticles

Abstract

Tracking techniques are vital for the understanding of the biology and ecology of organisms. While such techniques have provided important information on the movement and migration of large animals, such as mammals and birds, scientific advances in understanding the individual behaviour and interactions of small (mm-scale) organisms have been hampered by constraints, such as the sizes of existing tracking devices, in existing tracking methods. By combining biology, chemistry and physics we here present a method that allows three-dimensional (3D) tracking of individual mm-sized aquatic organisms. The method is based on in-vivo labelling of the organisms with fluorescent nanoparticles, so-called quantum dots, and tracking of the organisms in 3D via the quantum-dot fluorescence using a synchronized multiple camera system. It allows for the efficient and simultaneous study of the behaviour of one as well as multiple individuals in large volumes of observation, thus enabling the study of behavioural interactions at the community scale. The method is non-perturbing – we demonstrate that the labelling is not affecting the behavioural response of the organisms – and is applicable over a wide range of taxa, including cladocerans as well as insects, suggesting that our methodological concept opens up for new research fields on individual behaviour of small animals. Hence, this offers opportunities to focus on important biological, ecological and behavioural questions never before possible to address.

Induced tolerance expressed as relaxed behavioural threat response in millimetre-sized aquatic organisms

“…In all, this resulted in a 9 min long footage for each individual. For standard camera settings and radiation regime, see Ekvall et al [8]. Each individual Daphnia was then tracked in three dimensions and the mean depth in the aquaria, the three-dimensional speed and the total distance travelled (i.e.…”

The evolution of the molecular response to stress and its relevance to trauma and stressor-related disorders

“…Research will have to focus beyond the molecular to the atomic and it is therefore probable that the assistance of quantum biology will be required for an ultimate explanation of the physicochemistry of these reactions (Arndt et al, 2009;Li et al, 2016). Quantum biology has already proved helpful in tracking small animals (Ekvall et al, 2013) and explaining magnetoreception in the migration of birds and molecular mechanisms enabling the sense of smell (Brookes et al, 2012;McFadden and Al-Khalili, 2014).…”

Characterisation of variables associated with the flight behaviour of the rust-red flour beetle (Tribolium castaneum)

“…The smaller size of QDs and the ability to tune them to different colours makes them a desirable candidate for external as well as internal marking. This has already been demonstrated by studies on Daphnia magna (Daphniidae) where the zooplankton was successfully marked both externally and internally by functionalized QDs and could be tracked for 2D and 3D movement in large aquaria (Lard et al, 2010;Ekvall et al, 2013).…”

“…The study was, however, limited by the ability to detect QDs for periods longer than 2 days because D. magna frequently sheds its carapace. A successful demonstration of 3D tracking of D. magna has been made by using poly-L-lysine coated QDs for in vivo marking (Ekvall et al, 2013). The QDs had no negative effects on the organisms' behaviour and the individuals could be easily detected under the camera in an aquarium.…”

“…Daphniidae) in water currents (Ekvall et al, 2013). The QDs were also shown to have no negative effects on the behavioural responses of two types of aquatic insect larvae (mayfly and glass worm), along with D. magna.…”