Polarization vision in crabs

  • Sam Smithers

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Many animals are sensitive to the polarization of light and use this visual information for a variety of behavioural tasks such as navigation, communication and habitat localisation. One group in particular, decapod crustaceans, are sensitive to the polarization of light across their whole visual field and use this information for object-based visually guided behaviours. The studies within this thesis investigated how crabs use polarization information, in combination with intensity, to detect objects and control visually guided behaviours. This thesis had three main aims. The first was to establish how polarization and intensity information are processed within the visual system of fiddler crabs to enhance object detection. Through a series of behavioural experiments, using a novel type of visual display technology that allowed polarization and intensity properties of visual stimuli to be adjusted independently and simultaneously, it was discovered that for a loom detection task, crabs process polarization and intensity information independently and in parallel. The second aim was to determine whether null points of polarization discrimination, which are inherent within the crab’s visual system, affect the ability of fiddler crabs to use their polarization vision to detect targets viewed against the sky. The findings of this study suggest that the null points did effect the detectability of polarization contrasts produced by targets viewed against the sky. Finally, a study was conducted to test whether fiddler crabs can detect second-order motion, which is defined by higher-order image properties such as flicker. It was discovered that fiddler crabs are able to detect second-order motion in both intensity and polarization. It is suggested that the presence of this motion may enhance the detection of certain predators. In addition to these three main studies, a fourth study attempted to test whether contrast sensitivity in dark adapted ghost crabs was affected by restrictions, imposed by circadian cycle, that limit the maximum light sensitivity achievable during the day. This caveat study found circadian cycle does not have a negative effect on the ability of dark adapted crabs to detect intensity and polarization contrasts during the day. Overall, the findings from this thesis shed light on the various ways that polarization vision can enhance object detection by providing a greater range of detectable contrast information for the receiver.
Date of Award28 Nov 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorAndrew N Radford (Supervisor) & Nicholas W Roberts (Supervisor)

Cite this

'