Journal of comparative physiology

, Volume 151, Issue 3, pp 295-310

First online:

The identification of spectral receptor types in the retina and lamina of the dragonflySympetrum rubicundulum

  • I. A. MeinertzhagenAffiliated withDepartment of Psychology, Life Sciences Centre, Dalhousie UniversityMarine Biological Laboratory
  • , R. MenzelAffiliated withInstitut für Tierphysiologie, Fachbereich Biologie, Freie Universität BerlinMarine Biological Laboratory
  • , G. KahleAffiliated withInstitut für Tierphysiologie, Fachbereich Biologie, Freie Universität BerlinMarine Biological Laboratory

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Photoreceptors and monopolar cells in the ventral eye ofSympetrum rubicundulum have been recorded from intracellularly and stained with Lucifer yellow. Units with four types of spectral sensitivity were found having λmax at 340, 410, 490–540 and 620 nm. On the basis of a significant difference in half bandwidth ofS(λ), the green receptors are separable into two subgroups with λmax at 490 and 540 nm. The fluorescence marking reveals that R5/8 and R2/3 are the green receptors; R1/4 is either a UV or an orange cell. Discrimination between the members of the three matched pairs R2 & 3, R5 & 8, and R1 & 4 has not been possible. R7 is the violet receptor, and R6 is probably an additional green receptor; these are the receptors with long visual fibres. No receptors in the ventral eye besides the orange (620 nm) are sensitive to polarized light, whereas UV receptors in the dorsal eye are highly sensitive to polarized light. The polarized light sensitivity of the orange receptors is interpreted as an adaptation to increase the contrast between a conspecific animal and shorter wavelength light with a predominantly horizontal E-vector, such as is provided by reflections on the water's surface.

Cell identification is complicated by the fact that in most cases more than one cell is dye-marked. We present evidence in favour of dye-coupling being functional and against it being any simple artifact. Most importantly, the cellular pattern of dye-coupling is related to the spectral sensitivity of the recorded unit.

Recordings from monopolar cells are interpretable in the light of the results of both receptor markings and the anatomical pattern of their synaptic connectivities. The significance of a previously described asymmetry of the synaptic connections of the lamina terminals from R1 and R4 is now most easily understood as the counterpart of a duality in the spectral properties of this receptor pair; whether UV- or orange-sensitive types coexist within a single ommatidium or are segregated between different ommatidia is, however, not known.