Periodic Reporting for period 1 - PLACAV (Polarized light as an alternative to colour in animal vision)
Reporting period: 2015-03-01 to 2017-02-28
The project had two main objectives. First, to determine how polarization information is incorporated into the contrast vision system of fiddler crabs; and second, to investigate the use of polarization cues to fiddler crabs in their natural environment.
During the 10 month period funded by the Marie Curie fellowship, the second objective of the research was achieved as follows: Objective 2; to elucidate the function of the polarization vision of the fiddler crab Uca stenodactulus.
To determine whether fiddler crabs use their polarization vision to enhance the detection of neighbours in their mudflat habitat, I developed a novel system for manipulating their visual environment in situ. Work was conducted during a 3 month fieldtrip to the Republic of Panama, where I collaborated with staff scientist Dr John Christy at the Smithsonian Tropical Research Institute. Here I identified a suitable colony of fiddler crabs, located on the shore of the Pacific entrance to the Panama canal. Resident male fiddler crabs that were defending a home territory around a burrow were approached with a polarized dummy crab that was dragged along the mudflat surface via a pulley system. The response of the male to the approaching dummy was filmed using an overhead video camera. The distance of the dummy from the male crab was recorded to monitor various behavioural responses. This would allow me to identify whether the polarization characteristics of the dummy influenced the ability of the male to detect it. Two iterations of the experiment were conducted. First, polaroid filter was used to construct the stimulus. This proved unsuccessful due to the polarization being masked by silhouetting from the sun. The experiment was then repeated using transparent retarder filter, which alters the polarization but not the brightness of transmitted light. This experiment was successful, and I discovered that an increase in the polarization contrast of the dummy resulted its detection by resident males over a greater distance. The study concluded that this species of fiddler crab does indeed use polarization vision to detect neighbours on the mudflat surface.
These finding were found to be of sufficient quality and broad relevance to merit publication in a high-impact journal. I successfully published the study in the Journal of Current Biology:
How, Christy, Temple, Hemmi, Marshall and Roberts, 2015, Target detection is enhanced by polarization vision in a fiddler crab. Current Biology 25: 3069-3073. doi: 10.1016/j.cub.2015.09.073.
Additional data was collected during this fieldtrip, which has contributed to ongoing research into the polarization ecology of crustaceans. In particular, I started to gather photographic polarization images that quantify the distribution of polarized light in mudflat habitats. These, along with more recent examples, will be collated into a new study to describe the polarization patterns reflected from damp flat surfaces.
Attached to this form are two images: 1 - the fiddler crab Uca stenodactylus; 2 - the polarization pattern reflected from a mudflat panorama.
Findings have also been used to develop public engagement tools. In March 2017 I hosted a stand at the Science Museum Lates night, in which we presented a range of polarization-based interactive activities for the public to see.
I have also been successful in obtaining further funding to continue this work, including a Royal Society PhD studentship. I am also currently preparing a BBSRC New Investigator award on the topic.
My main aim for the future is to engage with industry partners, such as the BBC Natural History Unit, Roke Manor Research, and the Air Force Research Lab, to develop polarization imaging devices inspired by the visual system of fiddler crabs.