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WEL COME
2LOW LIGHT, BAD FLIGHT
VISION AND VISUAL NAVIGATION IN NOCTURNAL INSECTS
PrashantPAL 0013
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Compound eyes: Insects recognize and react to conspecifics Distinguish and avoid predators Locate food sources and intercept prey Navigate Walk, swim or fly
Nocturnal insects:
Introduction
Light levels can be up to 11 orders of magnitude lower
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Behavioral modifications
Visual system itself
How?
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Apposition compound eyes
Example: Nocturnal bees and wasps
Nocturnal compound eyes
High optical sensitivity- Superposition compound eyes
Example: Nocturnal moths and beetles
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Ommatidia
Hexagonal Circular Dome
Three basic models of the compound eye
Difference
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Visual processing in nocturnal insects
Vision Eyes with an enhanced optical sensitivity to light
Visual neurons that sacrifice spatial and temporal resolution to improve visual reliability for the slower and coarser features of the world
EYES AND VISION IN NOCTURNAL INSECTS
Optics Retina of the compound eye
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A superposition eye can have optical sensitivity 100–1000 times higher than that of an apposition
compound eye
The Optical Designs of Nocturnal Compound Eyes
A
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The ratio of the number of photons absorbed by a photoreceptor to the number emitted per steradian of solid angle from a unit area of an extended source
Where,A-Diameter of eye operturel - length of the rhabdomK -peak absorption coefficient of the visual pigment f -focal length of the ommatidium d -diameter of the rhabdom.
Optical sensitivity
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Good sensitivity to a spatially extended scene results from a pupil of large area (π A2/4)
Photoreceptors that each view a large solid angle of visual space (πd2/4 f 2 steradians)
Absorb a substantial fraction of the incident light (kl/2.3+kl).
This equation predicts
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M. genalisA. mellifera
2 μm 8 μmRhabdum width
Facet size 36 μm20 μm
M. genalis an optical sensitivity that is roughly 27 times greater than that of A. mellifera
Warrant et al., 2004
How nocturnal life has affected the optical structure and sensitivity?
13Warrant et al., 2006
Ocellar optics in nocturnal and diurnal bees and wasps
Nocturnal sweat bee, Megalopta genalis, Nocturnal paper wasp, Apoica pallens
Diurnal paper wasp, Polistes occidentalis
14 Megalopta genalis Augochloropsis fuscognatha
15 Apoica pallens Polistes occidentalis
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Longitudinal light microscope sections of median ocelli Apoica pallens (A), Megalopta genalis (B),
Polistes occidentalis(C)
l=lensr=retina
p=screening pigment granules
17Polistes occidentalis (C).Megalopta genalis (A)
Apoica pallens (B)
The optical properties of median ocelli
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General property of photoreceptors- Bumps
At higher intensities: the bump responses fuse to create a graded response whose duration and amplitude are proportional to the duration and amplitude of the light stimulus
Photoreception and the Reliability of Vision in Dim Light
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At very low light levels: a light stimulus of constant intensity is coded as a train of bumps
At somewhat higher light levels: the constant intensity is coded by a graded potential of particular amplitude
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The major limitation for nocturnal vision in insects
Arises from the stochastic nature of photon arrival and absorption
Sources of Visual noise
Photon shot noise Dark noise Transducer noise
Visual noise
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• Photoreceptor absorbing a number of N photons experiences an uncertainty (or photon shot noise) of √N photons
(Land, 1981; Warrant and McIntyre, 1993)
• Decreasing photon catch in dim light results in an increasing noise level
• As two visual channels need to detect sufficient photons in order to reduce this noise level
PHOTON SHOT NOISE
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Consists of spontaneous thermal responses in the absence of photons, which are indistinguishable from
membrane potentials (quantum bumps) produced by photons (Barlow, 1956)
These fluctuations are more frequent at higher temperatures and introduce uncertainty at low light
intensities.
Even though dark noise is much lower in invertebrates than in vertebrates
Dark noise
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Photoreceptors are incapable of producing identical bumps of fixed amplitude, latency and duration to each (identical)
photon of absorbed light.
This source of noise, originating in the biochemical processes leading to signal amplification
To maximise the photon catch or signal-to-noise ratio to enhance sensitivity
Transducer noise
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Photoreceptor responses to single photons (i.e bumps)
are much larger in nocturnal insects
Retinal adaptations for nocturnal vision
Large bumps have been demonstrated
Nocturnal crane flies CockroachesBees Spiders
25Quantum bumps of nocturnal M. genalis and diurnal L.
leucozonium
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Contrast gain of the bees M. genalis and L. leucozoniumFredriksen et al., 2008
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A large number of animals are known to use colour to detect, discriminate and recognise objects
Food sources Mating partners Landmarks or their homes
Nocturnal Color Vision
An animal needs to possess and use at least two types of photoreceptors, with different spectral sensitivities, to look at an object
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Simple 4-stage model of colour discrimination with two spectral types of receptors.
29Natural light levels and limits of colour vision
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UV Violet Green
Kelber, 2003
Deilephila elpenorMacroglossum stellatarum
Colour Vision in Diurnal and Nocturnal Hawkmoths
Three different spectral classes of photoreceptors
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Schematic drawings of the structure of the rhabdom of Deilephila elpenor
Schlecht et al., 1978
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Color vision in D. elpenor is color-constant
This moth can not only be trained to associate a sugar reward with a blue disc at starlight
Discriminate this blue disk from other discs in various shades of gray with a choice frequency of at least 80%.
Kelber, 2003
33Colour vision in Deilephila elpenor
Kelber et al., 2002
34Colour constancy
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Many nocturnal insects have evolved sufficiently sensitive visual systems
Celestial cues
Terrestrial visual Cues
Nocturnal Navigation and Orientation
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At night, the brightest and most easily discernable cue in the sky is undoubtedly the moon
Navigation and orientation using celestial cues
Its bright disk is used for orientation and navigation in a number of different nocturnal insects
Ants Earwigs
Moths
Beetles
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A much dimmer and more subtle cue associated with the moon is its pattern of polarized light.
This circular pattern, centered around the moon, arises because of the atmospheric scattering of moonlight as it travels toward Earth
Light is most polarized around a circular celestial locus 90◦ from the moon, and the circular pattern of polarized light moves with the moon
Cont….
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On full moon nights
On four nights before and after this event
Dacke et al., 2003
Lunar orientation in a beetle
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The path taken by a ball-rolling Scarabaeus zambesianus
0 to 90 90 or 180
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Circular diagrams of turns made by Scarabaeus zambesianus rolling under the night sky.
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Visual detection of optic flow is also clearly necessary for controlling nocturnal flight
Navigation and orientation using terrestrial cues
Dim light gypsy moths Mosquitoes Locust
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Landmark orientation in sweat beeWarrant et al., 2004
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X. leucothorax is diurnal
X. tenuiscapa is largely diurnal and occasionally crepuscular
X. tranquebarica is truly nocturnal
Somanathan et al., 2008
Flight activity in three species of carpenter bees in relation to light intensities
44Somanathan et al., 2008
Flight activity in all three species as a function of light intensity
Two-dimensional reconstruction of flight paths of X. tranquebarica at a nest site 45
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X. leucothorax X. tenuiscapa
X. tranquebarica
Scanning electron micrograph of heads
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Canopy or Individual trees
As the animal moves under the tree canopy, the brighter sky in the gaps of the canopy, together with the darker area under the canopy
Ex: Nocturnal shield bug, Parastrachia japonensis
Insects living in forests
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Schematic drawing of the displacement test
A nocturnal provisioning path and the distribution of foraging and homing directions 49
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Homing path and distribution of homing directions in a nocturnal displacement test
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Nocturnal homing using canopy cues in the shield bug Parastrachia japonensis
Hironaka et al., 2008
Reid et al., 2011
Myrmecia pyriformis Smith
Landmark panorama provide night-active bull ants with compass information during route
following
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Landmark-blocking experiment
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A) initial orientation of individual ants at the nest the B) time taken to exit the 30cm circle and C) the proportion that crossed the 1.2m reference line
55Displacement experiment.
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Neural adaptations
An increase in the response gain of the photoreceptors with decreasing light intensity can further enhance sensitivity but does not improve photon capture itself
(Laughlin, 1981)
The ultimate solution to optimise sensitivity at low light intensities is to process the incoming visual signal using a strategy of neural summation in space and time
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Temporal Summation
Visual systems can also improve image reliability at night by slowing vision down
Lengthening the eye’s visual integration time at night
Signal-to-noise ratio of lower temporal frequencies is improved
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Temporal summation results in a slower but more reliable visual world
Extremely long photoreceptor integration times
Sit-and-wait predators and slowly moving animals, temporal summation is certainly a good strategy
Cont…
59Theory of spatial summation
Spatial Summation
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Photons are integrated over wider visual fields,
which is similar to a widening of the angular
sensitivity function
Only when neural summation is matched to the
extent of the visual overlap present in the eye
61Warrant, 2004
A Possible Mechanism for Spatial Summation in Megalopta’s Eye
Greiner et al., 2004 and Ribi, 1975
Comparison of the First-Order Interneurons, L-fiber types L3 and L4, of the M. genalis female (left) and the worker
honeybee A. mellifera (right)62
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Nocturnal insects have excellent night vision
With the capacity to discriminate colors
Orient themselves using faint celestial cues fly unimpeded through a complicated habitat
Navigate to and from a nest using learned visual landmarks
Conclusion
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The photoreceptors of nocturnal insects respond more slowly and have a higher contrast gain
A neural strategy of spatial and temporal summation at a higher level in the visual system is hypothesized as the necessary bridge between retinal signaling and visual behavior.
Cont…
65THANK YOU
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