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.
Highlights
Tracking the motion and migration of individual organisms is of crucial importance for understanding their biology and ecology
In a broader perspective we suggest that this new technique will advance research on plankton ecology and that the use of quantum dots for tracking is applicable for tracking small organisms in water, and in air and on land
The binding of the poly-L-lysine coated quantum dots to the carapace was verified by placing a D. magna in a fluorescence microscope (Figure 3) were it is seen that the quantum dots are associated with the outside of the D. magna carapace
Summary
Tracking the motion and migration of individual organisms is of crucial importance for understanding their biology and ecology. Tracking of smaller, and in particular aquatic organisms, poses three considerable challenges. The size and weight of currently available transponders are a limiting factor to studying mm-scale organisms; the smallest tracking transponders available today are about 0.4 mm in size [5], which means that these devices drastically affect the behaviour of organisms at the mm length-scale. The size-limitation of current tracking devices has precluded studies focusing on movement of smaller organisms, such as crustacean zooplankton, in aquatic environments. In contrast to land-based, flight-less organisms, in which case a two-dimensional (2D) tracking approach is often satisfactory, tracking of aquatic organisms requires following organisms’ movement in a three-dimensional (3D) environment; to obtain accurate information regarding the position and speed of individual organisms, and allow reliable distinction between behaviours such as cruising and sinking [6]
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