Sky compass orientation in diurnal and nocturnal dung beetles
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1
University of Lund, Department of Biology, Sweden
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2
University of Witwatersrand, Department of Biology, South Africa
To escape from the intense competition at the dung pile, ball-rolling dung beetles have developed a unique and simple orientation behavior in which they roll a dung ball away from the dung pile in a straight line. To keep this straight path, dung beetles use celestial compass cues such as the sun, the moon and the pattern of polarized light formed around these sources (Dacke et al., 2003, Nature, 424: 33). These sky compass cues provide all the precision these insects need to ensure a safe exit from the dung pile. However, whether the relevance of individual sky compass signals varies between diurnal and nocturnal dung beetle is still an open question. Furthermore, nothing is known concerning the neural substrate that allows nocturnal dung beetles to orientate at light levels a million times dimmer than those that allow orientation in their diurnal relatives.
To investigate these questions, we analyzed the orientation performance in a diurnal (Scarabaeus nigroaeneus) and a nocturnal (S. satyrus) beetle species to celestial compass signals, both in the laboratory and in their natural habitat in South Africa. We tested whether a change in the orientation of polarized light in the laboratory or a shift of the plane of skylight polarization in the field affects the rolling bearing of the beetles. In addition, we studied how beetles change their bearing in response to a 180° reflection of the sun. Finally, we used a combination of immunohistochemistry, confocal microscopy and 3D reconstruction of different brain areas to show how nocturnality affects the neuroanatomy of the dung beetle brain.
Our data show that both diurnal and nocturnal dung beetle species use patterns of polarized light (either artificial or from the sun/moon) and the sun/moon in a similar way for straight line orientation. While brain areas in the optic lobes are remarkably larger in the nocturnal species compared to the diurnal species, our preliminary data suggest that, in the central brain, the relative volumes of brain areas dedicated to visual processing are similar. These results indicate that sky compass signals in the brain of nocturnal beetles converge more strongly towards late processing stages and thus, could lead to a greater sensitivity in dim light conditions.
Keywords:
Anatomy,
Behavior,
dung beetle,
Insect brain,
insect navigation,
Orientation,
polarized light,
sky compass signals
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for student poster award)
Topic:
Orientation and Navigation
Citation:
El Jundi
B,
Smolka
J,
Baird
E,
Byrne
M,
Dacke
M and
Warrant
E
(2012). Sky compass orientation in diurnal and nocturnal dung beetles.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00231
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Received:
30 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Basil El Jundi, University of Lund, Department of Biology, Lund, Sweden, basil.el.jundi@ntnu.no