Ants of the Australian genus Myrmecia partition their foraging niche temporally, allowing them to be sympatric with overlapping foraging requirements. We used histological techniques to study the light and dark adaptation mechanisms in the compound eyes of diurnal (Myrmecia croslandi), crepuscular (M. tarsata, M. nigriceps) and nocturnal ants (M. pyriformis). We found that, except in the day-active species, all ants have a variable primary pigment cell pupil that constricts the crystalline cone in bright light to control for light flux. We show for the nocturnal M. pyriformis that the constriction of the crystalline cone by the primary pigment cells is light dependent whereas the opening of the aperture is regulated by an endogenous rhythm. In addition, in the light-adapted eyes of all species, the retinular cell pigment granules radially migrate towards the rhabdom, a process that in both the day-active M. croslandi and the night-active M. pyriformis is driven by ambient light intensity. Visual system properties thus do not restrict crepuscular and night-active ants to their temporal foraging niche, while day-active ants require high light intensities to operate. We discuss the ecological significance of these adaptation mechanisms and their role in temporal niche partitioning.
The authors declare no competing or financial interests.
A.N., W.A.R. and J.Z. conceptualized the study; A.N., B.G. and W.A.R. performed the experiments; A.N. carried out data analysis and wrote the first draft of the manuscript; A.N., W.A.R. and J.Z. revised the manuscript.
This work was supported by grants from the Australian Research Council (ARC, FT140100221, DE120100019) to A.N., the Deutsche Forschungsgemeinschaft to B.G., the ARC Centre of Excellence Scheme (ARC Centre of Excellence for Vision Science, CEO561903) to A.N. and J.Z. and the Private Universität im Fürstentum Liechtenstein to W.R.
- Received April 18, 2016.
- Accepted May 31, 2016.
- © 2016. Published by The Company of Biologists Ltd