Polarised moonlight guides nocturnal bull ants home
- School of Natural Sciences, Macquarie University, Australia
Figures
Figure 1
Diagram of the polarisation filter and changes to the overhead lunar polarisation pattern.
(A) During the inbound journey, a linear polarisation filter was placed over the forager, rotating the overhead e-vector by ±45°. Panel depicts the positional measurements recorded during testing. Initial orientation routes were measured from the foraging tree release point (a) to when the polarisation filter was placed over each forager (b). Exit orientations were measured from the filter centre (b) to the forager’s exit location at the filter edge (c). Route directions under the filter (b°) were calculated from the forager’s initial route direction zeroed. Reorientations were measured from the forager’s exit location from the polarisation filter (c) to the forager’s path 1 m after exit (d). Reorientation directions (c°) were calculated from the under-filter route direction zeroed. (B) Images of the sky and canopy cover at both nests. Photos were taken at the on-route midpoint between the foraging and nest trees. Both Nests were located on the edge of tree stands. However, Nest 1 was in a more barren area of the field site, with less vegetation both along the horizontal plane and in the overhead canopy. (C) Lunar phases denote the sunlit part of the moon’s surface and where this area is increasing (Waxing) or decreasing (Waning). The lunar phase cycle repeats every 29.5 d. Moon images are public domain art accessed through Wiki Commons (https://commons.wikimedia.org/).
Figure 2
Circular distributions of headings during the original full moon conditions.
In both conditions, testing occurs on the nights preceding the full moon (illumination >80%) with the moon waxing. Circular plot shifts show the exit orientations of individual foragers relative to initial headings while the reorientation represents the change in headings 1 m after exiting the filter. Triangles denote the ±45° e-vector rotation. The arrow denotes the length and direction of the mean vector while red arc denotes the 95% confidence interval of headings. (A) Nest 1 foragers, 5 m from the nest (6.0 m foraging route). (B) Nest 2 foragers, 2 m from the nest (3.1 m foraging route). n, number of individuals; b°, mean vector of shift; c°, mean vector of reorientation; r, length of the mean vector.
Figure 3
Circular distributions of headings during (A) Waxing Quarter Moon, (B) Waxing Crescent Moon, and (C) No Moon conditions.
Circular plot shifts show the exit orientations of individual foragers relative to initial headings while the reorientation represents the change in headings 1 m after exiting the filter. Triangles denote ±45° e-vector rotation. The arrow denotes the length/direction of the mean vector. n, number of individuals; b°, mean vector of shift; c°, mean vector of reorientation; r, length of the mea vector. The red arc denotes the 95% convedence interval of headings.
Figure 4
Circular distributions of headings during (A) Waning Full Moon, (B) Waning Quarter Moon conditions.
Circular plot shifts show the exit orientations of individual foragers relative to initial headings while the reorientation represents the change in headings 1 m after exiting the filter. Triangles denote ±45° e-vector rotation. The arrow denotes the length/direction of the mean vector while the red arc shows the 95% confidence interval of headings. n, number of individuals; b°, mean vector of shift; c°, mean vector of reorientation; r, length of the mean vector.
Figure 5
Shift magnitudes for lunar phase conditions at Nest 1.
Each circular plot shows the ±45° combined shifts for each condition. Triangles denote +45° e-vector rotation; data from –45° were mirrored and combined. The arrow denotes the length and direction of the mean vector. n, number of individuals; b°, mean vector of shift; c°, mean vector of reorientation; r, length of the mean vector. The red arc denotes the 95% confidence interval of headings.
Figure 6
Diagram of collection procedures and circular distributions of M. midas headings during Released Halfway, Collected & Released Halfway conditions.
(A) Foragers in both conditions were tested at 2 m from the nest with (B) Released Halfway foragers having a long 6.0 m vector and (C) Collected & Released Halfway foragers having a 3.1 m vector. Circular plot shifts show the exit orientations of individual foragers relative to their initial headings while the reorientation represents the change in headings 1 m after exiting the filter. Triangles denote ±45° e-vector rotation. The arrow denotes the length and direction of the mean vector. n, number of individuals; b°, mean vector of shift; c°, mean vector of reorientation; r, length of the mean vector. The red arc denotes the 95% confidence interval of headings.
Figure 7
Mean shift magnitudes, +45° and –45° combined, were reported as percentages of the 45° e-vector rotation (100%=45°).
Vector data for solar polarised light is reported by Freas et al., 2017b; Freas et al., 2017c, Royal Society Open Science. Sun and moon images are public domain art accessed through Wiki Commons (https://commons.wikimedia.org/).
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Polarised moonlight guides nocturnal bull ants home
eLife 13:RP97615.
https://doi.org/10.7554/eLife.97615.4
