Light pollution and navigation in two nocturnal arthropod taxa

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Artificial light at night is a major anthropogenic pollutant. The area of artificially lit land is increasing at approximately 2% per year globally, and almost 90% of Europe is now affected by increased night sky luminance. The intensity, spectral composition, and timing of light pollution all affect different aspects of the physiology and behaviour of individual organisms. Ultimately, these changes can alter community structures and the ecology of different ecosystems.
Among nocturnal arthropods, research on the impacts of light pollution has largely focused on community-level effects or broader behavioural ecology. The effects of artificial light masking visual cues used in task-specific behaviours have received relatively little attention and there are indications that light pollution might obscure a major nocturnal cue, the skylight polarization pattern, but this has never been studied in any detail. Similarly, how light pollution might affect the timing of these behaviours is also under-studied. This PhD investigates how artificial light at night masks the skylight polarization pattern and how the loss of this cue, and the spectral composition and intensity of the artificial light, behaviourally impacts both nocturnal central-place foraging spiders of the genus Drassodes, and a long-distance migratory moth, Helicoverpa armigera. The major differences in the polarization pattern between dark and light-polluted skies across four moon phases and across a light pollution radiance gradient were established using imaging polarimetry. The ecological impact of the masking effect of light pollution to polarization-guided navigation was assessed using analysis of the tethered paths of animals exposed to polarized stimuli. Finally, the ecological impact of light pollution on the initiation and timing of nocturnal journeys was examined by observing patterns of activity under streetlights of different intensities and spectral compositions.
The skylight polarization pattern is significantly affected by light pollution which not only affects the strength of the polarization pattern, but its spatial and temporal extent. These impacts can occur even at low levels of light pollution and are exacerbated by changes in moon luminance across the phases of the lunar cycle. This has the potential to disorientate both H. armigera and Drassodes in the wild, as well as inhibit or alter time-sensitive navigational behaviour essential for survival with broader implications for dispersal, individual fitness, community composition and agroecosystems. Tuning the intensity and spectral composition of light pollution may alleviate the magnitude of these impacts through reductions in radiance and shifting the spectral character of the light away from short wavelengths.
Date of Award21 Mar 2023
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorNicholas W Roberts (Supervisor) & Lauren Sumner-Rooney (Supervisor)

Keywords

  • light pollution
  • polarization vision
  • navigation
  • arthropod

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