title: Induced tolerance expressed as relaxed behavioural threat response in millimetre-sized aquatic organisms.
abstract: Natural selection shapes behaviour in all organisms, but this is difficult to study in small, millimetre-sized, organisms. With novel labelling and tracking techniques, based on nanotechnology, we here show how behaviour in zooplankton (Daphnia magna) is affected by size, morphology and previous exposure to detrimental ultraviolet radiation (UVR). All individuals responded with immediate downward swimming to UVR exposure, but when released from the threat they rapidly returned to the surface. Large individuals swam faster and generally travelled longer distances than small individuals. 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. In addition, animals previously exposed to UVR also had smaller eyes than the naive ones, whereas UVR-protective melanin pigmentation of the animals was similar between populations. Finally, we 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.
authors: Centre for Ecology and Evolution in Microbial Model Systems-EEMiS, Linnaeus University, 39182 Kalmar, Sweden samuel.hylander@lnu.se.
authors: Samuel
authors: S
authors: Hylander
authors: Department of Biology, Aquatic Ecology Unit, Lund University, Lund, Sweden.
authors: Mikael T
authors: MT
authors: Ekvall
authors: Department of Biology, Aquatic Ecology Unit, Lund University, Lund, Sweden.
authors: Giuseppe
authors: G
authors: Bianco
authors: Department of Biology, Aquatic Ecology Unit, Lund University, Lund, Sweden.
authors: Xi
authors: X
authors: Yang
authors: Department of Biology, Aquatic Ecology Unit, Lund University, Lund, Sweden.
authors: Lars-Anders
authors: LA
authors: Hansson
mesh_terms: D000818:Animals; D049628:Body Size; D003621:Daphnia / Q000502:physiology* / Q000528:radiation effects; D004924:Escape Reaction; D008543:Melanins / Q000502:physiology; D010858:Pigmentation; D014466:Ultraviolet Rays / Q000009:adverse effects*; D015048:Zooplankton / Q000502:physiology* / Q000528:radiation effects
chemical_list: D008543:Melanins
keywords: Daphnia; behavioural ecology; swimming speed; tracking; ultraviolet radiation; zooplankton