The significance of direct sunlight and polarized skylight in the ant’s celestial system of navigation

Abstract

As textbook knowledge has it, bees and ants use polarized skylight as a backup cue whenever the main compass cue, the sun, is obscured by clouds. Here we show, by employing a unique experimental paradigm, that the celestial compass system of desert ants, Cataglyphis, relies predominantly on polarized skylight. If ants experience only parts of the polarization pattern during training but the full pattern in a subsequent test situation, they systematically deviate from their true homeward courses, with the systematics depending on what parts of the skylight patterns have been presented during training. This ''signature'' of the polarization compass remains unaltered, even if the ants can simultaneously experience the sun, which, if presented alone, enables the ants to select their true homeward courses. Information provided by direct sunlight and polarized skylight is picked up by different parts of the ant's compound eyes and is channeled into two rather separate systems of navigation.insect vision ͉ polarization compass ͉ sun compass ͉ Cataglyphis B y performing his famous mirror experiment in 1911, Santschi (1) was the first to show that animals (ants, in his case) could use the sun as a compass cue. Moreover, he observed that the apparent position of the sun did not always deflect the ants from their homeward courses. In species of some genera of ants (e.g., in Messor and Monomorium), the mirror experiment worked almost always, but in others (e.g., in Cataglyphis), it worked only under certain conditions (for instance, if the remainder of the sky was experimentally obscured). Santschi (2) concluded from these experiments that at least some species of ants had to be able to derive compass information from some optical property of the sun-free sky. We now know that this property is the polarization of scattered skylight (ref. 3; for reviews, see refs. 4 and 5).A substantial amount of research has been done on the behavioral neurobiology of the insect's polarization compass (6, 7), but very few data are available about the relative significance and differential processing of compass information derived from either polarized skylight or direct sunlight. This question was addressed by Frisch (8) in his early work on honey bees, but the results he obtained from bees, which performed their recruitment dances with mirrored positions of the sun, remained ambiguous. Because more recent work tells us that (i) bees and ants process information about direct sunlight and polarized skylight by employing different sensory channels [the latter by using the dorsal rim area (DRA) of the eye (9-14)] and (ii) under particular experimental conditions, bees and ants exhibit systematic navigational errors if presented with restricted parts of the polarization patterns in the sky (10,13,15,16), unique experimental paradigms can be designed that allow us to approach the problem of the relative importance of the two compass cues more directly and in more detail. In the present account, we let desert ants, Cataglyphis fortis, experience ...

Three spectrally distinct photoreceptors in diurnal and nocturnal Australian ants

“…The difference between Myrmecia and other ants may reflect differences in the visual ecology of different species, in particular in the context of navigation. For instance, Cataglyphis ants rely predominantly on path integration and, as part of this, on the pattern of polarized skylight as a compass reference [21], for which colour vision would not seem to be required. Ants in landmark-rich habitats however, including the two species studied here, are guided by the visual panorama, often in preference to path integration information (e.g.…”

“…Ants such as C. bicolor and Cataglyphis fortis, which live in landmark-poor deserts and salt pans, for instance, use the pattern of polarized skylight as a compass reference for their path integration system [18,21,26,27]. Ants such as the Australian desert ant Melophorus bagoti that inhabit landmark-rich environments containing grass tussocks, shrubs and trees, rely more heavily on information provided by the visual landmark panorama to find home [22,23].…”

“…Some ants are highly visual animals, especially individually foraging ants that do not use pheromone trails during foraging excursions, but rely on visual cues for path integration and landmark-based navigation [15][16][17][18][19][20][21][22][23][24][25]. Ants such as C. bicolor and Cataglyphis fortis, which live in landmark-poor deserts and salt pans, for instance, use the pattern of polarized skylight as a compass reference for their path integration system [18,21,26,27].…”

Navigation by light polarization in clear and turbid waters

“…in clear skies. It was shown that in the field, desert ants choose the sky polarization pattern or even part of it as a primary compass for navigation even when the Sun disc is visible [2]. Other insects, such as spiders [3] and field crickets [4], have also been shown to use sky polarization for navigation.…”

Underwater linear polarization: physical limitations to biological functions

“…It is unlikely that squid perform such calculations in each case, but it can be expected that a distance estimation system is hard-wired in their nervous system or acquired over time and experience. Such a neurological approach for polarization calculations can be found in compact nervous systems such as those of insects [39,40].…”