Light adaptation mechanisms in the eye of the fiddler crab Afruca tangeri

Emelie A Brodrick*, Nicholas W Roberts, Lauren Sumner-Rooney, Christian M Schlepütz, Martin J How

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

2 Citations (Scopus)
72 Downloads (Pure)

Abstract

A great diversity of adaptations is found among animals with compound eyes and even closely related taxa can show large variation in their light-adaptation strategies. A prime example of a visual system evolved to function in specific light environments is the fiddler crab, used widely as a model to research aspects of crustacean vision and neural pathways. However, questions remain regarding how their eyes respond to the changes in brightness spanning many orders of magnitude, associated with their habitat and ecology. The fiddler crab Afruca tangeri forages at low tide on tropical and semi-tropical mudflats, under bright sunlight and on moonless nights, suggesting that their eyes undergo effective light adaptation. Using synchrotron X-ray tomography, light and transmission electron microscopy and in vivo ophthalmoscopy, we describe the ultrastructural changes in the eye between day and night. Dark adaptation at dusk triggered extensive widening of the rhabdoms and crystalline cone tips. This doubled the ommatidial acceptance angles and increased microvillar surface area for light capture in the rhabdom, theoretically boosting optical sensitivity 7.4 times. During daytime, only partial dark-adaptation was achieved and rhabdoms remained narrow, indicating strong circadian control on the process. Bright light did not evoke changes in screening pigment distributions, suggesting a structural inability to adapt rapidly to the light level fluctuations frequently experienced when entering their burrow to escape predators. This should enable fiddler crabs to shelter for several minutes without undergoing significant dark-adaptation, their vision remaining effectively adapted for predator detection when surfacing again in bright light.
Original languageEnglish
Pages (from-to)616-634
Number of pages19
JournalJournal of Comparative Neurology
Volume529
Issue number3
Early online date27 Jun 2020
DOIs
Publication statusPublished - 1 Feb 2021

Bibliographical note

Funding Information:
Many thanks to the electron microscopy team for technical support at the Wolfson Bioimaging Centre, Bristol and to José Ignacio Navas Triano at Instituto de Investigación y Formación Agraria y Pesquera Centro de Agua del Pino. Animal collection was carried out with the authorization of the Consejería de Medio Ambiente y Ordenación del Territorio de la Junta de Andalucía. We acknowledge the Paul Scherrer Institut, Villigen, Switzerland for provision of synchrotron radiation beamtime at the TOMCAT beamline X02DA of the SLS. Funding for the research was provided by The Royal Society. Thanks also go to Dr John Christy who provided valuable insight at the early stages of the study. This study was supported by The Royal Society (grant numbers UF140558 and RG150565).

Funding Information:
Many thanks to the electron microscopy team for technical support at the Wolfson Bioimaging Centre, Bristol and to Jos? Ignacio Navas Triano at Instituto de Investigaci?n y Formaci?n Agraria y Pesquera Centro de Agua del Pino. Animal collection was carried out with the authorization of the Consejer?a de Medio Ambiente y Ordenaci?n del Territorio de la Junta de Andaluc?a. We acknowledge the Paul Scherrer Institut, Villigen, Switzerland for provision of synchrotron radiation beamtime at the TOMCAT beamline X02DA of the SLS. Funding for the research was provided by The Royal Society. Thanks also go to Dr John Christy who provided valuable insight at the early stages of the study. This study was supported by The Royal Society (grant numbers UF140558 and RG150565).

Publisher Copyright:
© 2020 The Authors. The Journal of Comparative Neurology published by Wiley Periodicals LLC.

Keywords

  • fiddler crab
  • Dark Adaptation
  • Rhabdom
  • TEM
  • Ophthalmoscope
  • Synchrotron X-ray tomography
  • Afruca tangeri

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