Eric Warrant

Lund University, Biology, Faculty Member

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6 Ommatidial Adaptations for Spatial, Spectral, and Polarization Vision in Arthropods

Cold Spring Harbor Monograph Archive, 2007

The arthropods constitute the largest single phylum of the animal kingdom and, with almost a mill... more The arthropods constitute the largest single phylum of the animal kingdom and, with almost a million known species, more than three-quarters of all animal species. The insects and crustaceans alone account for nearly all arthropods, and their compound eyes are thus the most numerous and widespread eye design found on Earth. Not surprisingly, the great adaptability and versatility of arthropods, and their conquest of almost every conceivable habitat, have led to the evolution of a remarkable range of visual specializations, both peripherally in the eyes themselves and centrally in the brain centers responsible for the higher processing of visual information. The compound eyes of insects, crustaceans, and the horseshoe crab Limulus (a xiphosurid chelicerate) are composed of individual optical units known as ommatidia (Fig. 1A). Each of these generally contains one or more lenses (the dioptric apparatus) that capture and focus the incoming light and a number of photoreceptors that toge...

Author response: A unified platform to manage, share, and archive morphological and functional data in insect neuroscience

Built-in polarizers form part of a compass organ in spiders

Nature, 1999

2. Vision Group, Research School of Biological Sciences, Australian National University, GPO Box ... more

Insect motion detectors matched to visual ecology

Nature, 1996

Video: Dung beetle climbing its ball and preening on hot soil

Ommatidial adaptations for spatial, spectral and polarisation vision in arthropods

Invertebrate Neurobiology, 2007

Video: Thermal video of a dung beetle rolling its ball on hot soil

Infrared thermography shows that during each rolling phase, the surface temperature of the beetle... more

Sensitivity to motion and higher-order visual processing in nocturnal and diurnal hawk moths

Frontiers in Physiology, 2013

Light scattering by selected zooplankton from the Gulf of Aqaba

Journal of Experimental Biology, 2007

Light scattering by zooplankton was investigated as a major factor undermining transparency camou... more Light scattering by zooplankton was investigated as a major factor undermining transparency camouflage in these pelagic animals. Zooplankton of differing transparencies-including the hyperiid amphipod Anchylomera blossevillei, an unknown gammarid amphipod species, the brine shrimp Artemia salina, the euphausiid shrimp Euphausia diomedeae, the isopod Gnathia sp., the copepods Pontella karachiensis, Rhincalanus sp. and Sapphirina sp., the chaetognath Sagitta elegans and an enteropneust tornaria larva-were illuminated dorsally with white light (400-700•nm). Spectral measurements of direct transmittance as well as relative scattered radiances at angles of 30°, 90°, 150° and 180° from the light source were taken. The animals sampled had transparencies between 1.5% and 75%. For all species, the highest recorded relative scattered radiance was at 30°, with radiances reaching 38% of the incident radiance for the amphipod A. blossevillei. Scattering patterns were also found to be species-specific for most animals. Relative scattered radiances were used to estimate sighting distances at different depths. These calculations predict that all of the examined zooplankton are brighter than the background radiance when viewed horizontally, or from diagonally above or below at shallow depths. Thus, in contrast to greater depths, the best strategy for detecting transparent zooplankton in the epipelagic environment may be to search for them from above while looking diagonally downwards, looking horizontally or looking from below diagonally upwards. Looking directly upwards proved to be more beneficial than the other viewing angles only when the viewed animal was at depths greater than 40•m.

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Visual training improves underwater vision in children

Vision Research, 2006

Children in a tribe of sea-gypsies from SouthEast Asia have been found to have superior underwate... more Children in a tribe of sea-gypsies from SouthEast Asia have been found to have superior underwater vision compared to European children. In this study, we show that the improved underwater vision of these Moken children is not due to better contrast sensitivity in general. We also show that European children can achieve the same underwater acuity as the Moken children. After 1 month of underwater training (11 sessions) followed by 4 months with no underwater activities, European children showed improved underwater vision and distinct bursts of pupil constriction. When tested 8 months after the last training session in an outdoor pool in bright sunlight-comparable to light environments in SouthEast Asia-the children had attained the same underwater acuity as the sea-gypsy children. The achieved performance can be explained by the combined effect of pupil constriction and strong accommodation.

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Insect orientation to polarized moonlight

Nature, 2003

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A novel method for comparative analysis of retinal specialization traits from topographic maps

Journal of Vision, 2012

Are harbour seals (Phoca vitulina) able to perceive and use polarised light?

Journal of Comparative Physiology A, 2012

Harbour seals are active at night and during the day and see well in both air and water. Polarise... more Harbour seals are active at night and during the day and see well in both air and water. Polarised light, which is a well-known visual cue for orientation, navigation and foraging, is richly available in harbour seal habitats, both above and below the water surface. We hypothesised that an ability to detect and use polarised light could be valuable for seals, and thus tested if they are able to see this property of light. We performed two behavioural experiments, one involving object discrimination and the other involving object detection. These objects were presented to the seals as two-dimensional stimuli on a specially modified liquid crystal display that generated objects whose contrast was purely defined in terms of polarisation (i.e. objects lacked luminance contrast). In both experiments, the seals' performance did not deviate significantly from chance. In contrast, the seals showed a high baseline performance when presented with objects on a non-modified display (whose contrast was purely defined in terms of luminance). We conclude that harbour seals are unable to use polarised light in our experimental context. It remains for future work to elucidate if they are polarisation insensitive per se.

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Visual cues used by ball-rolling dung beetles for orientation

Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 2003

Ball rolling by dung beetles is considered to be a derived behaviour that evolved under pressure ... more Ball rolling by dung beetles is considered to be a derived behaviour that evolved under pressure for space, and from competitors at the dung pat. Straight-line orientation away from the pat using a celestial cue should be the most successful rolling strategy to move dung to an unknown burial site. We tested this hypothesis in the field and the laboratory by presenting five species of ball-rolling beetles with different orientation tasks, involving reaction to obstacles as well as to reflected sunlight and artificial light sources. Beetles were found to consistently orientate along a chosen route, usually in the direction of the sun. Beetles rolling dung balls successfully negotiated barriers and returned to the original path as did beetles falling from ramps, or rotated about a fixed point while rolling a ball. The sun was found to be the main orientation cue, which could be substituted by reflected or artificial light. However, beetles reoriented themselves less accurately in response to lights in the laboratory, than they did to the reflected sun in the field. It is probable that phototactic orientation using the sun, which is widespread amongst arthropods, has been incorporated in the straight-line foraging behaviour that has evolved in ballrolling dung beetles.

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Dung beetles ignore landmarks for straight-line orientation

Journal of Comparative Physiology A, 2012

Upon locating a suitable dung pile, ball-rolling dung beetles shape a piece of dung into a ball a... more Upon locating a suitable dung pile, ball-rolling dung beetles shape a piece of dung into a ball and roll it away in a straight line. This guarantees that they will not return to the dung pile, where they risk having their ball stolen by other beetles. Dung beetles are known to use celestial compass cues such as the sun, the moon and the pattern of polarised light formed around these light sources to roll their balls of dung along straight paths. Here, we investigate whether terrestrial landmarks have any influence on straight-line orientation in dung beetles. We find that the removal or re-arrangement of landmarks has no effect on the beetle&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s orientation precision. Celestial compass cues dominate straight-line orientation in dung beetles so strongly that, under heavily overcast conditions or when prevented from seeing the sky, the beetles can no longer orient along straight paths. To our knowledge, this is the only animal with a visual compass system that ignores the extra orientation precision that landmarks can offer.

Lens optical properties in the eyes of large marine predatory teleosts

Journal of Comparative Physiology A, 2008

Bearing selection in ball-rolling dung beetles: is it constant?

Journal of Comparative Physiology A, 2010

Ball rolling in dung beetles is thought to have evolved as a means to escape intense inter-and in... more Ball rolling in dung beetles is thought to have evolved as a means to escape intense inter-and intraspecific competition at the dung pile. Accordingly, dung beetles typically roll along a straight-line path away from the pile, this being the most effective escape strategy for transporting dung to a suitable burial site. In this study, we investigate how individual diurnal dung beetles, Scarabaeus (Kheper) nigroaeneus, select the compass bearing of their straight-line rolls. In particular, we examine whether roll bearings are constant with respect to geographic cues, celestial cues, or other environmental cues (such as wind direction). Our results reveal that the roll bearings taken by individual beetles are not constant with respect to geographic or celestial references. Environmental cues appear to have some influence over bearing selection, although the relationship is not strong. Furthermore, the variance in roll bearing that we observe is not affected by the presence or absence of other beetles. Thus, rather than being constant for individual beetles, bearing selection varies each time a beetle makes a ball and rolls it away from the dung pile. This strategy allows beetles to make an efficient escape from the dung pile while minimizing the chance of encountering competition.

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Stretch to See: Lateral Tension Strongly Determines Cell Survival in Long-Term Cultures of Adult Porcine Retina

Investigative Opthalmology & Visual Science, 2013

Superior Underwater Vision in a Human Population of Sea Gypsies

Current Biology, 2003

sea gypsies, a people known for their skills in swimming and diving [2]. The children do not use ... more sea gypsies, a people known for their skills in swimming and diving [2]. The children do not use visual aids when Zoology Building Lund University diving for shells, clams, and sea cucumbers. For this, good underwater vision should be essential. A particular Helgonavä gen 3 S-223 62 Lund tribe of sea gypsies, the Moken, live in the archipelago of Burma and along the West Coast of Thailand [5]. Sweden 2 Department of Ophthalmology Because these children clearly manage to see small objects underwater, we suspected that the Moken might Institute of Clinical Neuroscience SU/Mö lndal be adapted for improved underwater vision. We tested the visual acuity of six Moken children. We S-431 80 Mö lndal Sweden used 28 European children in the same age range, on holiday with their families in nearby areas, as a control group. We set up a head-stabilizing apparatus underwater with a fixed viewing distance. With this apparatus, Summary we presented the children with achromatic sinusoidal gratings of different spatial frequencies. The results Humans are poorly adapted for underwater vision. In clearly show that the Moken children have significantly air, the curved corneal surface accounts for two-thirds better underwater acuity (Mann-Whitney test: p Ͻ of the eye's refractive power, and this is lost when air 0.001); they were able to resolve gratings (100% conis replaced by water [1]. Despite this, some tribes of trast) more than twice as fine as those resolved by the sea gypsies in Southeast Asia live off the sea, and the European children (Moken children: 6.06 Ϯ 0.59 cycles/ children collect food from the sea floor without the degree (mean Ϯ SE), European children 2.95 Ϯ 0.13 use of visual aids [2]. This is a remarkable feat when cycles/degree). When further tested with gratings havone considers that the human eye is not focused uning a range of different contrasts, the Moken children derwater and small objects should remain unresolved. also had higher contrast sensitivities underwater at all We have measured the visual acuity of children in a spatial frequencies presented (Figure 1). sea gypsy population, the Moken, and found that the We next performed several experiments to explain children see much better underwater than one might this improved underwater vision. Some of the possible expect. Their underwater acuity (6.06 cycles/degree) explanations require the eye to have undergone drastic is more than twice as good as that of European chilchanges in morphology. If, for instance, the Moken have dren (2.95 cycles/degree). Our investigations show evolved a flatter cornea and a stronger lens, they would that the Moken children achieve their superior underachieve good resolution on land and improved resoluwater vision by maximally constricting the pupil (1.96 tion when diving. If, instead, they have become severely mm compared to 2.50 mm in European children) and myopic, this would improve vision underwater but result by accommodating to the known limit of human perin blurred vision when on land. And finally, if Moken formance (15-16 D) [3]. This extreme reaction-which children simply have the ability to accommodate more is routine in Moken children-is completely absent than normal, this too would improve underwater vision. in European children. Because they are completely All three of these strategies are known to exist in the dependent on the sea, the Moken are very likely to animal kingdom. We thus examined (on land) the eye's derive great benefit from this strategy. corneal curvature (keratometry), refractive state, and accommodative power in both groups of children. These Results and Discussion results show us that on land the Moken children do not differ from the European children in any of these Several animals, such as amphibious fishes, frogs, birds, respects. The keratometry values are well within the and insects, are known to have evolved special adaptanormal range [6] in both groups. The majority of the tions-such as a flattened cornea or greater accommochildren are slightly hyperopic, with refractive errors dative power-to be able to see well in both air and water ranging from ϩ2 to Ϫ0.5 D, and there is no difference [1, 4]. The human eye, however, is generally considered a in accommodative range between the two groups of typical example of a terrestrial eye because it uses both children. In conclusion, all results are well within the the curved outer cornea and an internal lens to refract normal limits for children of that age range. the incoming light. If a human eye is immersed in water, However, we did find one important difference conwhich has about the same refractive index as the cornea cerning pupil size. On land, pupil size normally has little and aqueous humor, the image becomes severely effect on resolution, and both groups of children were blurred because the eye loses about two-thirds of its found to have the same pupil size (Moken children, 2.33 Ϯ 0.06 mm, n ϭ 6; European children, 2.30 Ϯ 0.04 mm, n ϭ 15; Mann-Whitney, p ϭ 0.48). But underwater,

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Dung Beetles Use the Milky Way for Orientation

Current Biology, 2013

When the moon is absent from the night sky, stars remain as celestial visual cues. Nonetheless, o... more 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 plan

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