Polarized light detection in spiders
Marie Dacke1,*,
Thuy A. Doan2 and
David C. O’Carroll2
1 Department of Zoology, University of Lund, Helgonavägen 3, S-223 54 Lund, Sweden and
2 Department of Zoology, University of Washington, Box 351800 Seattle, WA 98195, USA
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Fig. 1. The simple eyes of spiders are named after their relative position on the head. The comparative size and layout of the anterio-median (AM), anterio-lateral (AL), posterio-median (PM) and posterio-lateral (PL) eyes does, however, vary with species.
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Fig. 2. (A) Diagram of the apparatus used to demonstrate that a dorsal region of the field of view is used for polarization analysis by lycosids. (B) Raw responses of spiders (Pardosa tristis) to rotation of a polarizer (right) and a neutral density filter (left). The filled circles indicate the starting point of the spider. The arrowheads indicate the commencement of filter rotation. For further details, see text.
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Fig. 3. Averaged responses of wolf spiders to the stimulus described in Fig.2. Responses before (open columns) and after (grey columns) rotation of either a neutral density filter (control) or a polarizer (test) are shown for either clockwise (N=9) or counterclockwise (N=11) rotation of the filter. In both cases, P values show the statistical significance of the difference in rotational response of the spider (Student’s paired t-test). Values are means ± S.E.M.
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Fig. 4. Light micrograph showing transverse sections through the ventral anterio-median retina of a lycosid wolf spider (species A). (A) Low-power view, showing type 1 receptors (1) and both distal (2d) and proximal (2p) type 2 receptors from the tiered region. The blind strip (bl) between these layers in clearly visible in this section. Scale bar, 55µm. D, dorsal; L, lateral. (B) A higher power view of the tiered region, showing orthogonal type 2 receptors in the distal (d) and proximal (p) layers and longitudinal, vertically extended intermediate segments of the distal receptors (arrowheads). Scale bar, 25µm.
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Fig. 5. Longitudinal sections through the anterio-lateral retinae of a lycosid (species A). (A) A low-power view of a vertical section showing the positions of type 1 (1) and type 2 (2) receptors and the blind region (bl). Dorsal is up, and ventral down in this figure. Scale bar, 35µm. (B) A higher power view of a horizontal section through the ventral tiered region. The distal (d) and proximal (p) layers are clearly visible, with no continuation of the intermediate segments of the distal layer through the proximal layer. Scale bar, 15µm. (C) Summary of the organization of the retina as seen in longitudinal section, showing the fields of view of each region. The shaded region shows an approximate projection through the nodal point of the lens of the blind region (bl) that divides the fields of view of the type 1 and type 2 receptor regions. VC, vitreous cells; SP, screening pigment; ON, optic nerve.
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Fig. 6. Structure of the posterio-median eye of Drassodes cupreus. (A) Tangential section (light micrograph; scale bar, 1µm) through the retina of the PM eye revealing a regular rhabdomeral arrangement. (B) Electron micrograph of the boxed region in A, showing the parallel microvillar arrangement found over the bigger part of the retina. Scale bar, 500nm. (C) Drawing of the ‘canoe-shaped tapetum’ and the retina, with one possible path of light through the eye (arrow). The front end of the eye is cut off to expose interior structures. Modified from (Dacke et al., 1999.)
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Fig. 7. Intracellular recordings in the retina of a posterio-median eye of the spider Drassodes cupreus. Left and right response–intensity curves are recorded with light polarized parallel (Para) and perpendicular (Perp) to the long axis of the eye, respectively. The log intensity shift of 0.96 between the two curves translates to a polarization sensitivity of 9.1 (a unitless quantity). (This figure was published as supplementary information in Dacke et al., 1999; http://www.nature.com/nature/journal/v401/n6752/suppinfo/401470a0.html).
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Fig. 8. Fields of view of the left set of secondary eyes of Drassodes cupreus. The fields are plotted onto a globe with the spider at the centre. The pole of the grid is straight up, and the one-ended arrow marks the longitudinal axis of the spider. The two-ended arrows indicate the direction of polarization to which each of the three eyes is most sensitive. Note the large and almost circular field of view of the posterio-median eye. AL, anterio-lateral; PL, posterio-lateral; PM, posterio-median.
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© The Company of Biologists Ltd 2001
