Dung Beetles Use the Milky Way for Orientation

Department of Biology, Lund University, 223 62 Lund, Sweden
Current biology: CB (Impact Factor: 9.57). 01/2013; 23(4). DOI: 10.1016/j.cub.2012.12.034
Source: PubMed

ABSTRACT

When the moon is absent from the night sky, stars remain as celestial visual cues. Nonetheless, only birds [1, 2], seals [3], and humans [4] are known to use stars for orientation. African ball-rolling dung beetles exploit the sun, the moon, and the celestial polarization pattern to move along straight paths, away from the intense competition at the dung pile [5-9]. Even on clear moonless nights, many beetles still manage to orientate along straight paths [5]. This led us to hypothesize that dung beetles exploit the starry sky for orientation, a feat that has, to our knowledge, never been demonstrated in an insect. Here, we show that dung beetles transport their dung balls along straight paths under a starlit sky but lose this ability under overcast conditions. In a planetarium, the beetles orientate equally well when rolling under a full starlit sky as when only the Milky Way is present. The use of this bidirectional celestial cue for orientation has been proposed for vertebrates [10], spiders [11], and insects [5, 12], but never proven. This finding represents the first convincing demonstration for the use of the starry sky for orientation in insects and provides the first documented use of the Milky Way for orientation in the animal kingdom.

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    • "Even when neither the sun nor the moon itself is visible, dung beetles can still orient using wide-field celestial cues, such as the pattern of polarized skylight surrounding the sun or moon (Dacke, Nilsson, et al, 2003; Dacke, Nordstr€ om, et al, 2003; el Jundi et al., 2014), gradients of intensity across the sky (el Jundi et al., 2014) or the Milky Way (Dacke, Baird, et al., 2013). To test whether nocturnal beetles are better than diurnal beetles at keeping a straight line when the moon is hidden from sight, we compared the orientation performance of both species under three conditions in which no major celestial body was visible: (1) on a full moon night with the moon shaded from view by a large wooden board, (2) on a crescent moon night with the moon similarly shaded and (3) on a moonless night, illuminated only by the light of the stars. "
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    ABSTRACT: The visual systems of many animals feature energetically costly specializations to enable them to function in dim light. It is often unclear, however, how large the behavioural benefit of these specializations is, because a direct comparison in a behaviourally relevant task between closely related day- and night-active species is not usually possible. Here we compared the orientation performance of diurnal and nocturnal species of dung beetles, Scarabaeus (Kheper) lamarcki and Scarabaeus satyrus, respectively, attempting to roll dung balls along straight paths both during the day and at night. Using video tracking, we quantified the straightness of paths and the repeatability of roll bearings as beetles exited a flat arena in their natural habitat or under controlled conditions indoors. Both species oriented equally well when either the moon or an artificial point light source was available, but when the view of the moon was blocked and only wide-field cues such as the lunar polarization pattern or the stars were available for orientation, nocturnal beetles were oriented substantially better. We found no evidence that ball-rolling speed changed with light level, which suggests little or no temporal summation in the visual system. Finally, we found that both diurnal and nocturnal beetles tended to choose bearings that led them towards a bright light source, but away from a dim one. Our results show that even diurnal insects, at least those with superposition eyes, could orient by the light of the moon, but that dim-light adaptations are needed for precise orientation when the moon is not visible.
    No preview · Article · Jan 2016 · Animal Behaviour
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    • "Many organisms are sensitive to extremely low levels of light at night, well below the upper level of ANTL (Longcore and Rich, 2004; Stone et al., 2009; Gaston et al., 2013). For example, many organisms use nightscapes as cues for migration, directional movement and orientation (Wehner, 1989; A ˚ kesson et al., 2001; Dacke et al., 2003, 2013; Tuxbury and Salmon, 2005; Ugolini et al., 2005; Warrant and Dacke, 2010; Rodríguez et al., 2012), while some species are sensitive to nightscape patterns for temporal and spatial exploitation of foraging habitats (Buchanan, 1993; Stone et al., 2009; Santos et al., 2010; Polak et al., 2011; Titulaer et al., 2012; Dwyer et al., 2013), inter-specific interactions or predation (Gliwicz, 1986; Longcore and Rich, 2004; Polak et al., 2011), communication (Lloyd, 1994; Bergen and Abs, 1997), moulting, mating and reproduction (Peters and Verhoeven, 1994; Salmon et al., 1995; Rand et al., 1997; Boldogh et al., 2007; Dominoni et al., 2013a). Thus the reorganisation of the nightscape due to ANTL pollution can result in these ecological patterns being affected, altered or even completely disrupted. "
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    ABSTRACT: High-biodiversity landscapes around the globe are under immense pressure due to the expansion of human activities. To ensure effective monitoring and management of such landscapes, it is necessary to integrate landscape composition and the associated socio-economic processes in the conservation schemes. Artificial Night-Time Light (ANTL) pollution is a recent but striking environmental alteration due to human interventions. It is a major threat for species and communities which co-evolved with invariant natural light patterns over geological times. In spite of its potential key role in re-shaping natural systems, ANTL is seldom considered in macroecology. Remote sensing provides a unique set of tools to integrate ANTL in macroecological studies. In this work, we used remote sensing data of night-time lights along with Enhanced Vegetation Index (EVI) to study the effects and extent of ANTL in the night-time landscape (nightscape) of two protected areas in Italy. Our results showed that a considerable number of semi-natural vegetated patches suffer from ANTL pollution with varying magnitude. We observed a decline in highly suitable patches for biodiversity while the remaining patches were found concentrated in the innermost part of the parks. By simulating an exponential decrease in ANTL we showed that a moderate reduction in ANTL pollution would result in regaining a substantial amount of highly suitable patches for biodiversity. The decline in homogeneous dark patches in vegetated landscapes has negative impacts on biodiversity as well as on the ecosystem services it provides. Therefore, it is high time that the scientific community and the policy-makers increase their efforts to monitor and mitigate the ecological impacts of ANTL on ecosystems. The integration of light pollution in landscape ecology could combine remote sensing with other aspects of light pollution like indirect propagation and spectral composition.
    Full-text · Article · Jun 2015 · Ecological Complexity
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    • "Research over the past 15–20 yearsV particularly on fast-flying and highly aerodynamic moths and bees and on ball-rolling dung beetlesVindicates that nocturnal insects that rely on vision for the tasks of daily life invariably see extremely well (reviewed by Warrant and Dacke [81]). We now know, for instance, that nocturnal insects are able to distinguish colors [31], [66], to detect faint movements [70], to avoid obstacles during flight by analyzing optic flow patterns [3], to learn visual landmarks [57], [67], [77], to orient to the faint polarization pattern produced by the moon [12], and to navigate using the faint stripe of light provided by the Milky Way [11]. "
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    ABSTRACT: Despite their tiny eyes and brains, nocturnal insects have remarkable visual abilities. Recent work—particularly on fast-flying moths and bees and on ball-rolling dung beetles—has shown that nocturnal insects are able to distinguish colors, to detect faint movements, to learn visual landmarks, to orient to the faint pattern of polarized light produced by the moon, and to navigate using the stars. These impressive visual abilities are the result of exquisitely adapted eyes and visual systems, the product of millions of years of evolution. Even though we are only at the threshold of understanding the neural mechanisms responsible for reliable nocturnal vision, growing evidence suggests that the neural summation of photons in space and time is critically important: even though vision in dim light becomes necessarily coarser and slower, those details that are preserved are seen clearly. These benefits of spatio–temporal summation have obvious implications for dim-light video technologies. In addition to reviewing the visual adaptations of nocturnal insects, we here describe an algorithm inspired by nocturnal visual processing strategies—from amplification of primary image signals to optimized spatio–temporal summation to reduce noise—that dramatically increases the reliability of video collected in dim light, including the preservation of color.
    Full-text · Article · Oct 2014 · Proceedings of the IEEE
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