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Askypolarizationcompassinlizards:which
wavelengthsoflightareinvolved?
CONFERENCEPAPER·APRIL2011
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AntonioParretta
FerruccioPetrucci
UniversityofFerrara
UniversityofFerrara
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AugustoFoa
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A SKY POLARIZATION COMPASS IN LIZARDS: ONLY SOME WAVELENGTHS ARE INVOLVED
G. Beltrami1; P. Buttini1, C. Bertolucci1; A. Parretta2,3; F. Petrucci2,4; and A. Foà1
1Dipartimento di Biologia ed Evoluzione; 2Dipartimento di Fisica, Università di Ferrara, Ferrara, Italy;
3ENEA, Centro Ricerche “E. Clementel”, Bologna, Italy; 4INFN, sezione di Ferrara, Italy
Purpose
We demonstrated that ruin lizard Podarcis sicula uses the e-vector direction of polarized light in compass orientation.
To perform this task, does P. sicula use a preferential region of the light spectrum?
Results
Ruin lizards were trained under white plane polarized light with a single e-vector and then were tested under 4 different chromatic
polarized lights (blue:
blue: 460nm;
460nm red: 611nm;
611nm green: 544nm;
544nm turquoise).
turquoise
WHITE LIGHT
LAST TRAINING TRIAL
WHITE LIGHT
90°ROTATED E-VECTOR
Legend: each symbol indicates the directional choice of a single lizard identified by its
number. In each hexagon the inner arrow represents the mean vector of the group calculated
after doubling the angles. In each hexagon the mean vector length (r) and the mean direction
(α) of the group are reported. Solid line mean vector: the bearings distribution deviated from
uniform; dotted line mean vector: the bearings distribution did not deviate from uniform. For
each hexagon, the two outer solid arrows mark the expected axis of orientation.
r = 0.9
α= 001°
r = 0.4
α= 087°
N = 30
N = 43
V TEST: P < 0.001
V TEST: P < 0.0005
TURQUOISE LIGHT
E-VECTOR PARALLEL TO THE
TRAINING AXIS
BLUE LIGHT
90°ROTATED E-VECTOR
BLUE LIGHT
E-VECTOR PARALLEL TO THE
TRAINING AXIS
r = 0.4
α= 017°
r = 0.5
α= 111°
N = 10
N = 13
V TEST:
P < 0.025
RED LIGHT
E-VECTOR PARALLEL TO THE
TRAINING AXIS
r = 0.1
α= 155°
N = 13
V TEST: P < 0.05
V TEST: P < 0.05
V TEST: P < 0.05
r = 0.3
α= 320°
r = 0.4
α= 345°
N = 10
N = 10
P < 0.005
GREEN LIGHT
90°ROTATED E-VECTOR
GREENLIGHT
E-VECTOR PARALLEL TO THE
TRAINING AXIS
TURQUOISE LIGHT
90°ROTATED E-VECTOR
r = 0.4
α= 356°
r = 0.6
α= 113°
V TEST:
White Polarized Light: lizards (N= 43) meeting learning criteria (left panel), were subjected to 90°
rotation of the e-vector direction (right panel). Lizards directional choices rotated
correspondingly, producing a bimodal distribution which was perpendicular to the training axis.
N = 10
N = 16
V TEST: P > 0.05
V TEST : P > 0.25
Under both blue light and turquoise light
lizards were able to orientate in both e-vector’s
conditions, whereas under red light lizards
resulted completely disorientated (so we
tested lizards only under e-vector parallel to
the training axis). Under green light lizards
were able to orientated themselves only when
the direction of the e-vector was the same as
in training, whereas after 90° rotation of the evector lizards were disorientated.
Conclusions: present data showed that both the blue and the turquoise wavelengths are crucial for perceiving e-vector,
whereas the red wavelength did not mediate the perception of the e-vector. The green wavelength’s results were borderline.
Furthermore, the present experiment confirmed that in the ruin lizard the UV is not necessary to perceive polarized light.
LCD
Methods: we trained and tested lizards inside an hexagonal
Morris water maze, filled with obscured water and positioned
under an LCD screen producing by itself plane polarized light.
Lizards were subjected to axial training by positioning two
identical goals in contact with the centre of two opposite side
walls along the axis 0–180° (the training axis) of t he maze.
After reaching learning criteria, lizards could be tested under
different chromatic polarized lights, both with e-vector parallel
to the training axis and after 90° e-vector rotation.
ACKNOWLEDGEMENTS
This work was supported by University of Ferrara research grants. We are grateful to Federico Evangelisti and Stefano Squerzanti (Istituto Nazionale di Fisica Nucleare–Sezione di Ferrara), Luca Landi
(Dipartimento di Fisica, Università di Ferrara) for technical assistance. We are also grateful to Edoardo Chiodelli and Vincenzo Ricci (Photo Analytical S.r.l ) for the spectral measurements.