Compound Eye Adaptations for Diurnal and Nocturnal Lifestyle in the Intertidal Ant, Polyrhachis sokolova

Abstract

The Australian intertidal ant, Polyrhachis sokolova lives in mudflat habitats and nests at the base of mangroves. They are solitary foraging ants that rely on visual cues. The ants are active during low tides at both day and night and thus experience a wide range of light intensities. We here ask the extent to which the compound eyes of P. sokolova reflect the fact that they operate during both day and night. The ants have typical apposition compound eyes with 596 ommatidia per eye and an interommatidial angle of 6.0°. We find the ants have developed large lenses (33 µm in diameter) and wide rhabdoms (5 µm in diameter) to make their eyes highly sensitive to low light conditions. To be active at bright light conditions, the ants have developed an extreme pupillary mechanism during which the primary pigment cells constrict the crystalline cone to form a narrow tract of 0.5 µm wide and 16 µm long. This pupillary mechanism protects the photoreceptors from bright light, making the eyes less sensitive during the day. The dorsal rim area of their compound eye has specialised photoreceptors that could aid in detecting the orientation of the pattern of polarised skylight, which would assist the animals to determine compass directions required while navigating between nest and food sources.

Light and dark adaptation mechanisms in the compound eyes of Myrmecia ants that occupy discrete temporal niches

“…2). Variable primary pigment cell pupils have also been found in other ants capable of being active in dim light such as Camponotus ligniperda, Camponotus irritans (Menzi, 1987) and Polyrhachis sokolova (Narendra et al, 2013a). Similar to our findings in the strictly day-active M. croslandi, such a primary pigment pupil mechanism is absent in other day-active ants such as Cataglyphis bicolor (Brunnert and Wehner, 1973) and Formica polyctena (Menzel and Knaut, 1973).…”

“…Home, 1976;Kolb and Autrum, 1972;Lüdtke, 1953;Mclean and Horridge, 1977;MeyerRochow, 1972MeyerRochow, , 1999Schneider, 1967, 1968;Walcott, 1971;Williams, 1980). In the light-adapted eyes of ants active in dim light, such a constriction forms a narrow aperture of 0.5-1.0 µm, which opens up to nearly 5 µm in the dark-adapted state (Menzi, 1987;Narendra et al, 2013a). In the strictly day-active ants, the only light adaptation mechanism that has been observed is the radial migration of retinular cell screening pigment granules wherein the pigments tightly ensheath the rhabdom in the lightadapted state and move away from the rhabdom in the dark-adapted state (Brunnert and Wehner, 1973;Menzel and Knaut, 1973;Menzi, 1987).…”

The giant butterfly-moth Paysandisia archon has spectrally rich apposition eyes with unique light-dependent photoreceptor dynamics

“…Changes in rhabdom composition have been observed during diurnal cycles in other arthropods (e.g. locusts: Williams 1982; grapsid crabs: Arikawa et al 1987; desert ants: Narendra et al 2013). Reshaping of the photoreceptors and their rhabdoms upon light and dark adaptation has been reported in some lepidopteran superposition eyes (Yagi and Koyama 1963; Horridge and Giddings 1971; Satoh et al 2017), but to our knowledge not in the afocal apposition eyes of butterflies.…”

Homing abilities of the Australian intertidal ant, Polyrhachis sokolova

“…The stationary base station electronics and antenna were mounted on a tripod and set to integrate antenna position readings over 30min. The rover receiver electronics were carried on a backpack and connected to the rover antenna that was mounted at the end of a long, hand-held stick, so that it could be moved close to the ground along a flag-marked path (Narendra et al, 2013a;Narendra et al, 2013b). The base station and rover communicate through a radio link, allowing the exchange of corrections that provide position accuracy of the rover antennae of 1-2cm.…”

“…These ants navigate to specific trees during the evening twilight and return to their nest in the morning twilight (Narendra et al, 2010), the periods of the day when the pattern of polarised skylight is most simple because the sun is at the horizon (Cronin et al, 2006). These ants derive compass information from both the pattern of polarised skylight and visual landmarks even in the dim light conditions under which they operate (Narendra et al, 2013b;Reid et al, 2011). It is becoming increasingly evident that the information content available in the environment strongly influences the navigation strategies used by ants and the navigational decisions they make (Zeil, 2012).…”