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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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