The ventral eye of the water-surface-inhabiting springtail Podura aquatica has six ommatidia with horizontal and vertical microvilli and perceives light from the ventral, frontal and frontodorsal regions, whereas the dorsal eye possesses two upward-looking ommatidia with vertical microvilli. The ventral eye may detect water by its polarization sensitivity, even if the insect is resting with its head slightly tipped down on a raised surface. The polarization sensitivity and polarotaxis in springtails (Collembola) have not been investigated. Therefore, we performed behavioural choice experiments to study them in P. aquatica. We found that the strength of phototaxis in P. aquatica depends on the polarization characteristics of stimulating light. Horizontally and vertically polarized light were the most and least attractive, respectively, while unpolarized stimulus elicited moderate attraction. We show that horizontally polarized light attracts more springtails than unpolarized, even if the polarized stimulus was 10 times dimmer. Thus, besides phototaxis, P. aquatica also performs polarotaxis with the ability to measure or at least estimate the degree of polarization. Our results indicate that the threshold d* of polarization sensitivity in P. aquatica is between 10.1 and 25.5%.
The authors declare no competing or financial interests.
Á.E., G.H., G.K. designed the experiments, Á.E., A.F. performed the experiments, Á.E. did the programming and analyzed the data. Á.E., A.F., G.H., G.K. wrote and revised the paper.
This work was supported by the Hungarian National Research, Development and Innovation Office [NKFIH PD-115451 to Á.E.]. A.F. was supported by the Hungarian Templeton Program that was made possible through the support of a grant from Templeton World Charity Foundation, Inc. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of Templeton World Charity Foundation, Inc.
- Received February 16, 2016.
- Accepted June 10, 2016.
- © 2016. Published by The Company of Biologists Ltd