Ocellar structure is driven by the mode of locomotion and activity time in Myrmecia ants

Abstract

Insects have exquisitely adapted their compound eyes to suit the ambient light intensity in the different temporal niches they occupy. In addition to the compound eye, most flying insects have simple eyes known as ocelli, which assist in flight stabilisation, horizon detection and orientation. Among ants, typically the flying alates have ocelli while the pedestrian workers lack this structure. The Australian ant genus is one of the few ant genera in which both workers and alates have three ocellar lenses. Here, we studied the variation in the ocellar structure in four sympatric species of that are active at different times of the day. In addition, we took advantage of the walking and flying modes of locomotion in workers and males, respectively, to ask whether the type of movement influences the ocellar structure. We found that ants active in dim light had larger ocellar lenses and wider rhabdoms compared with those in bright-light conditions. In the ocellar rhabdoms of workers active in dim-light habitats, typically each retinula cell contributed microvilli in more than one direction, probably destroying polarisation sensitivity. The organisation of the ocellar retina in the day-active workers and the males suggests that in these animals some cells are sensitive to the pattern of polarised skylight. We found that the night-flying males had a tapetum that reflects light back to the rhabdom, increasing their optical sensitivity. We discuss the possible functions of ocelli to suit the different modes of locomotion and the discrete temporal niches that animals occupy.

Differential investment in brain regions for a diurnal and nocturnal lifestyle in Australian Myrmecia ants

“…Accessing visual information in dim‐light conditions is difficult due to low visual signal‐to‐noise ratio. Thus, nocturnal ants have evolved distinct visual adaptations to improve optical sensitivity (Greiner et al, ; Narendra et al, ; Narendra, Greiner, Ribi, & Zeil, ; Narendra & Ribi, ). It is evident from our results that dim‐light conditions have driven changes in sensory neuropils as well.…”

“…We studied a set of closely related species of the Australian ant genus Myrmecia (i.e., bull ants, jack jumpers, or inch ants) that almost exclusively depend on visual information for above‐ground activity irrespective of their time of activity (Eriksson, ; Freas, Narendra, Lemesle, & Cheng, ; Freas, Wystrach, Narendra, & Cheng, ; Narendra, Gourmaud, & Zeil, ; Narendra & Ramirez‐Esquivel, ; Narendra, Reid, & Hemmi, ; Narendra, Reid, & Raderschall, ). Closely related species of this genus have evolved distinct visual adaptations to occupy their respective light environments (Greiner et al, ; Narendra et al, ; Narendra & Ribi, ). However, although ant brains have been well‐characterized and functionally distinct brain regions are known to change with size, morphologically distinct subcaste, age and experience (Bressan et al, ; Ehmer & Gronenberg, ; Gronenberg, Heeren, & Hölldobler, ; Kamhi, Sandridge‐Gresko, Walker, Robson, & Traniello, ; Muscedere, Gronenberg, Moreau, & Traniello, ; Muscedere & Traniello, ; Stieb, Muenz, Wehner, & Rössler, ), how brains of nocturnal ants adapt to dim‐light conditions has never been investigated.…”

The impact of artificial light at night on nocturnal insects: A review and synthesis

“…Among dung beetles, larger eye size, smoother facets, and absence of screening pigment correlate to nocturnal activity (McIntyre & Caveney, ). Nocturnal bees, wasps, and ants have dorsal ocelli—simple eyes used to detect ambient light, movement, and/or orientation—that are significantly larger than those of their diurnal relatives (Narendra & Ribi, ; Somanathan, Kelber, Borges, Wallén, & Warrant, ; Warrant, Kelber, Wallén, & Wcislo, ). The ocelli of nocturnal bees and cockroaches are sensitive, but poor at perceiving fast movements; they also lack UV‐sensitive opsins, perhaps as an adaptation to their UV‐poor light environments (Berry, Wcislo, & Warrant, ); similarly, the ocelli of nocturnal ants may have lost polarization sensitivity in response to the loss of polarized skylight signals (Narendra & Ribi, ).…”

Principles of Insect Path Integration

“…Specialized sets of ommatidia located in the dorsal rim area of the insect’s compound eyes detect changes in the angle of polarization (E-vector) [10,11]. Many insects in addition possess simple eyes ( ocelli ) on the dorsal surface of the head that are often also sensitive to polarized light [12–15], but their contribution to path integration behavior is unclear. Similarly, compass information derived from other global cues such as the position of the Sun [16], the Moon [17] spectral and intensity cues [18,19], magnetic cues [20–22], and the Milky Way [23,24], are also used for insect navigation, yet whether they contribute to path integration is still unclear.…”