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Polarisation-dependent colour vision in Papilio butterflies

Almut Kelber^1,*, Christel Thunell¹ and Kentaro Arikawa²

¹ Department of Zoology, Lund University, Helgonavägen 3, S-22362 Lund, Sweden and
² Graduate School of Integrated Science, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027, Japan

View larger version (18K): [in a new window]   Fig. 1. (A) Diagram of an ommatidium of Papilio spp. (modified from Kitamoto et al., 1998). The ommatidium contains nine photoreceptor cells R1–R9. Photoreceptors R1–R4 are distal photoreceptors that contribute the rhabdomeral microvilli to the distal two-thirds of the rhabdom. Photoreceptors R5–R8 are proximal photoreceptors forming the rhabdom in the proximal one-third of the ommatidium. The basal photoreceptor, R9, contributes to the rhabdom at the region immediately distal to the basement membrane. UV, ultraviolet receptor; V, violet receptor: B, blue receptor; G, green receptors (two subtypes: SG, single-peaked green receptor; DG, double-peaked green receptor); R, red receptor; A, abnormally broadband receptor sensitive in the red and green ranges of the spectrum. (B) Relative sensitivities of five spectral types of photoreceptor.

View larger version (21K): [in a new window]   Fig. 2. The spectral distribution of the stimuli used in oviposition experiments (A) and in feeding experiments (B). Y, Gr, YG1 and YG2, BG1–BG3 are the abbreviations used for the colours in all further figures and the text.

View larger version (20K): [in a new window]   Fig. 3. Results of oviposition tests. (A) Choice distributions of the drumming reactions for different pairs of stimuli. Both stimuli of a pair had the same colour and intensity; YG2 was used in most tests, but BG1 was used in the left-hand test. Symbols on the abscissa show the polarisation angle of stimuli; from left to right: both stimuli horizontally polarised (=90°), =90° versus =45° (obliquely polarised light), =90° versus =0° (vertically polarised light) and so on. n is the number of choices in each test. Asterisks mark choice distributions that differ significantly from chance (G-tests, P<0.001); the remaining choice distributions do not differ from chance (P>0.1). (B) Choice distributions of curling reactions (open columns) and egg-laying (coloured columns) during the same tests as in A. Bold values of n above the columns give the total number of eggs, values of n in normal type give the total number of curling reactions in each experiment. Asterisks for the respective behavioural reactions are as in A; double daggers mark choice distributions where n was too small to obtain a significant result (P<0.1, binomial test); unmarked choice distributions to not differ from chance (G-tests, P>0.5). (C) Choice frequencies of drumming reactions for the brighter of two unpolarised stimuli with equal spectral distribution. The colour Gr was used for the spectral distribution (see Fig.1A). Asterisks are as in A.

View larger version (19K): [in a new window]   Fig. 4. Results of oviposition tests. (A) Choice frequencies for seven colours versus the reference colour BG1 (see Fig.2A); 200 choices for each colour. The abscissa gives the attractiveness of a colour, and the equation for the underlying receptor interaction is given; QB, blue receptor quantum catch; QG, green receptor quantum catch; QR, red receptor quantum catch. The red line is the fitted model curve. For further explanation, see text and Appendix. (B) Choices for horizontally polarised light versus vertically polarised light of the same colour and intensity as a function of colour attractiveness. n is the number of choices in each experiment, all choice distributions differ significantly from chance (G-tests, P<0.001).

View larger version (26K): [in a new window]   Fig. 5. Results of oviposition tests. (A) In three different tests, the same two colours were presented with the same or differing polarisation angles (). (B) In three tests, stimuli with 45° and 90° polarisation angles were presented, either both of the same colour or of different colours. In both sets of tests, choices depend on both colour and polarisation. n is the number of choices in each test; asterisks mark choice distributions that differ significantly from chance (G-test, P<0.001).

View larger version (17K): [in a new window]   Fig. 6. Results of feeding experiments. Three groups of animals were trained to discriminate stimuli differing only in the polarisation angle. Asterisks mark choice frequencies differing significantly from chance or from each other (G-tests; *P<0.0001; P<0.005). N gives the number of animals in each test, n gives the number of choices. (A) Tests with the training stimuli (see symbols above and below the diagram, + marks the rewarded pattern, - marks the unrewarded pattern). (B) Choice frequencies for the vertical polarisation angle as function of the intensity ratio between the vertically and horizontally polarised lights. Hatched circles give the polarisation angle and the colour of the training stimulus. (C) Choice frequencies for vertically and horizontally polarised lights of a colour different from the training colour (as in Fig.6A, see symbols above and below the diagram for training and testing stimuli).

View larger version (12K): [in a new window]   Fig. 7. Colour triangles for the blue, green and red receptor colour space of Papilio spp. on the basis of different assumptions about the receptors involved and their polarisation preference angles . The anatomical receptor types assumed to be involved are listed on the right, and assumed values of are given at the corners of the triangles with the respective receptor names. For receptor nomenclature, see Fig.1 and Table1. Coloured circles show the colour loci of the stimuli used in oviposition and feeding tests (B, blue used in feeding tests; R, red used in feeding test; for the other colours and for the spectral curves, see Fig.2). Two connected circles show the position of stimuli with the same spectral distribution (hence the same colour of the circle) but different polarisation angle (vertical, v; horizontal, h). PS, polarisation sensitivity (see Table 1).