Illustration by Jan Heuschele
Small-scale movements in response to global threats
Natural selection shapes behaviour, such as movement and migration in all organisms, but this is difficult to study in small, millimetre-sized, organisms. With novel labelling and tracking techniques, based on nanotechnology, we show in a recent paper published in Proc. R. Soc. B (enclosed), how movement in a common zooplankton species (Daphnia magna) is affected by size, morphology and previous exposure to detrimental ultraviolet radiation (UVR). As illustrated by the artwork (kindly provided by Jan Heuschele), all individuals responded with an immediate movment away from the UVR (sun) exposure, but when released from the threat they rapidly returned to the surface. Large individuals swam faster and generally travelled longer distances than small (young) individuals, suggesting ontogenetic differences in movement. Interestingly, individuals previously exposed to UVR (during several generations) showed a more relaxed response to UVR and travelled shorter total distances than those that were naive to UVR, suggesting induced tolerance to the threat. We also show that smaller individuals have lower capacity to avoid UVR which could explain patterns in natural systems of lower migration amplitudes in small individuals. The ability to change behavioural patterns in response to a threat, in this case UVR, adds to our understanding of how organisms navigate in the ‘landscape of fear’, and this has important implications for individual fitness and for interaction strengths in biotic interactions.
Lund University, Sweden