Ocellar structure of African and Australian desert ants
Few walking insects possess simple eyes known as the ocelli. The role of the ocelli in walking insects such as ants has been less explored. Physiological and behavioural evidence in the desert ant, Cataglyphis bicolor, indicates that ocellar receptors are polarisation sensitive and are used to derive compass information from the pattern of polarised skylight. The ability to detect polarised skylight can also be inferred from the structure and the organisation of the ocellar retina. However, the functional anatomy of the desert ant ocelli has not been investigated. Here we characterised the anatomical organisation of the ocelli in three species of desert ants. The two congeneric species of Cataglyphis we studied had a fused rhabdom, but differed in their organisation of the retina. In Cataglyphis bicolor, each retinula cell contributed microvilli in one orientation enabling them to compare e-vector intensities. In Cataglyphis fortis, some retinula cells contributed microvilli in more than one orientation, indicating that not all cells are polarisation sensitive. The desert ant Melophorus bagoti had an unusual ocellar retina with a hexagonal or pentagonal rhabdomere arrangement forming an open rhabdom. Each retinula cell contributed microvilli in more than one orientation, making them unlikely to be polarisation detectors.
KeywordsVisual system Ants Cataglyphis Melophorus Polarisation sensitivity
We are grateful to Wolfgang Rössler for loaning us samples of Cataglyphis ants and to Sebastian Schwarz for providing us samples of Melophorus bagoti. We acknowledge the microscopy facilities at Macquarie University, The Australian National University, and at the MPI of Tübingen. Working with these ants requires no ethics approval in Australia, but we treated them with care. We thank financial support from the ANU endowment fund to Willi Ribi, the Australian Research Council (FT140100221, DP150101172) and the Hermon Slade Foundation (HSF17/08).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted.
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