The extraretinal photoreceptors of non-mammalian vertebrates

Abstract

When John Lythgoe published The Ecology of Vision in 1979 he did not include any discussion of extraretinal or extraocular photopigments. However, during the 1980’s information about these photopigments emerged, and John’s research interests also began to encompass this field. In 1984 John considered the adaptive aspects of extraretinal photoreceptors and noted that ‘As yet there does not seem to be any reason to think that the spectral absorbance of extraretinal photo-pigments are located in the spectrum to maximise the capture of photons...’ (Lythgoe 1984). In this chapter we will review this statement, in the light of recent findings, and discuss the sensory ecology of these remarkable photoreceptor systems. Our discussion of extraretinal photoreceptors has been divided between two chapters, this and the one following. The first part of this chapter will consider the diversity and role of the extraretinal photoreceptors in the non-mammalian vertebrates, and the second part of the chapter will consider the sensory tasks of extraretinal photoreceptors and the extent to which the photo-pigments of these systems are ‘fine-tuned’ to their sensory role. In Chapter 7 we concentrate on the role of extraretinal and retinal photoreceptors in the regulation of biological clocks.