The Parietal Eye of Lizards (Pogona vitticeps) Needs Light at a Wavelength Lower than 580 nm to Activate Light-Dependent Magnetoreception

Simple Summary

In this study, the author sought to identify the wavelength of light that activates light-dependent magnetoreception. Pogona vitticeps lizards were randomly divided into two groups. In both groups, small round light-absorbing filters were fixed to the back of each lizard’s head, to block light of wavelengths lower than 580 nm. The electromagnetic field group received 12 h of systemic exposure per day to an electromagnetic field at an extremely low frequency (light period), whereas the control group did not. For each animal, the average number of tail lifts per day was determined. No significant difference between the two groups, neither for the average ratio of the number of tail lifts on test days to the baseline value nor the average increase in the number of tail lifts on test days minus the baseline value (p = 0.41 and p = 0.67, respectively). The results of this experiment suggest that light-dependent magnetoreception in P. vitticeps only occurs when the light hitting the parietal eye is of a wavelength lower than 580 nm.

Abstract

In a previous study, the agamid lizard Pogona vitticeps was discovered to respond to an electromagnetic field (EMF) of extremely low frequency (6 and 8 Hz; peak magnetic and electric fields of 2.6 µT and 10 V/m, respectively). Furthermore, when the third eye of a lizard was covered, using a small round aluminum cap, the reaction to the EMF disappeared. These results suggested that the parietal eye has a role in light-dependent magnetoreception. However, the wavelength of light needed to activate light-dependent magnetoreception has not been identified and was thus explored in the present study. Lizards were randomly divided into control and EMF groups. In both groups, a small round light-absorbing filter was positioned on the back of the head of each lizard and blocked light of wavelengths lower than 580 nm. The EMF group was subjected to EMF exposure for half of the day, whereas the control group was not. No significant intergroup differences were discovered in the average ratio of the number of tail lifts on test days to the baseline value or average increase in the number of test-day tail lifts minus the baseline value (p = 0.41 and p = 0.67, respectively). Lizards with light-absorption filters that cut out light with wavelengths lower than 380 nm were found to respond to the EMF. Therefore, the lizards appeared to respond to light of certain wavelengths rather than the filters themselves. The results of these experiments suggest that light of wavelengths lower than 580 nm is required to activate light-dependent magnetoreception in the parietal eye of P. vitticeps.

Correlation between the Lunar Phase and Tail-Lifting Behavior of Lizards (Pogona vitticeps) Exposed to an Extremely Low-Frequency Electromagnetic Field

Simple Summary

We examined the relationship between the number of tail lifts of lizards (Pogona vitticeps) and environmental factors, such as the calendar month, daily mean temperature, daily mean humidity, daily mean atmospheric pressure, lunar phase (full moon/new moon), and K index as a geomagnetic disturbance index using 16 months of data. We set up an extremely low-frequency electromagnetic field (ELF-EMF) group and a control group. In a multiple linear regression analysis, the independent determinants associated with the number of tail lifts were the full moon, the temperature, February, March, April, and May in the ELF-EMF group and March, April, May, and June in the control group. The P. vitticeps in the ELF-EMF group responded to the full moon whereas those in the control group did not.

Abstract

We previously showed that the agamid lizard Pogona vitticeps responded to an extremely low-frequency electromagnetic field (ELF-EMF; frequency: 6 and 8 Hz; peak magnetic field: 2.6 µT; peak electric field: 10 V/m) with tail-lifting behavior. In addition, the tail-lifting response to ELF-EMF disappeared when the parietal eyes of the lizards were covered by small round aluminum caps. This result suggests that the parietal eye contributes to light-dependent magnetoreception. In the present study, we set up an ELF-EMF group to evaluate the long-term effect of the ELF-EMF on lizards’ behavior and examine our hypothesis that exposure to ELF-EMFs increases the magnetic field sensitivity in lizards. We therefore include the lunar phase (full moon/new moon) and K index as environmental factors related to the geomagnetic field in the analysis. The number of tail lifts per individual per day was the response variable while calendar month, daily mean temperature, daily mean humidity, daily mean atmospheric pressure, full moon, new moon, and K index were the explanatory variables. We analyzed an ELF-EMF group and a control group separately. In a multiple linear regression analysis, the independent determinants associated with the number of tail lifts were the full moon, the temperature, February, March, April, and May in the ELF-EMF group and March, April, May, and June in the control group. The P. vitticeps in the ELF-EMF group responded to the full moon whereas those in the control group did not. In addition, in the ELF-EMF group, the number of tail lifts was higher on days when the K index was higher (P = 0.07) in the first period whereas there was no such tendency in either period in the control group. There is the possibility that the exposure to ELF-EMFs may increase magnetic-field sensitivity in lizards.