Applied Vision Association and Colour Group one-day meeting on Animal
Vision.
09.30 - 17.30. Thursday, 21st September
Department of Experimental Psychology. University of Bristol.
REGISTRATION: http://www.hls.dmu.ac.uk/ava/meetings/animalvision.html .
Programme
09.30 – 10.00
Coffee
10.00 – 10.45. Mike Land (Sussex). The eye movements of animals and men.
10.45 – 11.15. Rob Harris (Sussex). Visual navigation and memory recall by ants.
11.15 – 11.45. Martina Wicklein (UCL). Strategies for colour learning in bees.
11.45 – 12.15. Hannah Rowland (Liverpool). The cryptic value of countershading in lepidopteran larvae.
12.15 – 13.45.
Lunch & Posters
13.45 – 14.15. Christian Wehrhahn (Tübingen). S-cones contribute to brightness perception in primates.
14.15 – 14.45
Jules Davidoff (Goldsmiths). Cross-species differences in colour categorisation.
14.45 – 15.15. Tom Troscianko (Bristol). Bird and primate colour constancy
15.15 – 15.45
Tea
15.45 – 16.15 Olle Håstad (Uppsala). Phylogenetic distribution of colour vision systems among birds.
16.15 – 17.00. Doekele Stavenga (Groningen). Butterfly coloration and colour vision.
17.00 – 17.30. Ulrike Siebeck (Queensland). Ultraviolet communication in reef fish.
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Abstracts
PLUMAGE COLOUR VARIATION AND ASSORTATIVE
MATING IN THE CRIMSON ROSELLA (PLATYCERCUS
ELEGANS) RING SPECIES COMPLEX
Mathew Berg1, Leonie Raijmakers2, Raoul Ribot1, Leo
Joseph3, Kate Buchanan4 and Andy Bennett1
1
School of Biological Sciences, University of Bristol,; 2 Animal Ecology
Group, University of Groningen, The Netherlands; 3 Australian National
Wildlife Collection, CSIRO, ACT, 2911, Australia; 4 School of Biosciences,
Cardiff University.
Ring species are rather unusual phenomena formed by a ring-like
arrangement of intergrading populations, with distinct terminal
forms that rarely interbreed in sympatry. Such cases offer valuable
insights into the process of speciation by showing how small
differences between often sympatric populations can lead to
species-level divergence. The crimson rosella complex
(Platycercus elegans) of south eastern Australia has been
proposed as one such system. It consists of a ring of populations
that vary dramatically in plumage coloration, culminating in
terminal forms of deep crimson red or dull yellow. To date it is
unknown whether selective processes maintain this pattern, but
sexual selection leading to assortative mating is one possibility.
Here, we describe the pattern of plumage colour variation that
occurs throughout the range. Furthermore, we studied the
relationship between plumage coloration and pairing decisions in
the highly variable intermediate adelaidae form (just east of
Adelaide) and the zone of sympatry between the terminal flaveolus
and elegans forms (south west of Canberra). Our data suggests
that rosellas do not mate assortatively based on plumage
coloration in these populations. Thus, at this stage it does not
appear that assortative mating reinforces plumage colour variation,
and hence population divergence, in this system. Instead,
ecological factors or population histories may be largely
responsible for the current pattern of plumage colour diversity in
the crimson rosella complex.
CROSS-SPECIES DIFFERENCES IN COLOUR
CATEGORISATION
Jules Davidoff1 , Joël Fagot2, Julie Goldstein1, and Alan
Pickering1
1. Goldsmiths’ College, University of London, UK; 2. CNRS-INCM Marseille,
France
Berlin and Kay (1969) found systematic restrictions in the colour
terms of the world’s languages and were inclined to look to the
primate visual system for their origin. As the visual system does
not provide adequate neurophysiological discontinuities to give
natural colour category boundaries, and recent evidence points to
a linguistic origin (Davidoff, Davies & Roberson, 1999), a new
approach investigated the controversial issue of the origin of colour
categories. Baboons and humans were given the same task of
matching to sample colours that crossed the green/blue boundary.
The data and consequent modelling were remarkably clear-cut. All
human participants matched our generalisation probe stimuli as if
to a sharp boundary close to the midpoint between their training
items. Despite good colour discrimination, none of the baboons
showed any inclination to match to a single boundary but rather
responded with two ‘boundaries’ close to the training stimuli.
Furthermore, the human colour category boundary between green
and blue was shown to promote superior recognition in a crosscategory task in humans, but not in baboons. However, despite the
category advantage for humans, psychophysically determined
colour discrimination thresholds were very similar for the two
species. The data give no support to the claim that colour
categories are explicitly instantiated in the primate colour vision
system.
Berlin, B. & Kay, P. (1969) Basic color terms: Their universality
and evolution. Berkeley: University of California Press.
Davidoff, J., Davies, I. & Roberson, D. (1999) Colour categories of
a stone-age tribe. Nature 398, 203-204
SENSORY ECOLOGY AND ANIMAL WELFARE - THE
EFFECT OF FLICKER FROM FLUORESCENT LIGHTS
ON THE WELFARE OF EUROPEAN STARLINGS
Jennifer E Evans1, Innes C Cuthill1, Andrew T D Bennett1 &
Katherine L Buchanan2
1
School of Biological Sciences, University of Bristol, Bristol. BS8 1UG.;
Cardiff School of Biosciences, University of Cardiff, Cardiff. CF10 3TL.
2
Animals’ sensory capabilities are frequently tuned to the
characteristics of the habitats in which they evolved. However, if
animals are brought into captivity, the environmental parameters
that surround them are changed, often negatively impacting on
their welfare. As a case study, we present a series of experiments
examining how the flicker emitted from conventional, lowfrequency (LF; which flicker at 100Hz) fluorescent lights affects the
welfare of captive European starlings. We found that starlings
show a significant preference for high frequency (HF; which flicker
at 100kHz, a level imperceptible to any animal) over LF fluorescent
lights, indicating they can detect a difference between these two
lights and find HF light the least aversive condition. Starlings also
experience higher incidence of myoclonus (mild muscular spasms)
when viewing LF lights. In addition, long and short-term exposure
to LF light affects both behavioural and physiological indicators of
stress. Further experiments studied the effect of flicker rate on
visually mediated tasks. During mate choice, females ranked
males consistently under HF, but not under LF conditions. In
foraging experiments, birds differed in their foraging habits under
the two lighting types. Together, these experiments indicate that
starlings can detect a difference between HF and LF lights, with LF
lights negatively impacting not only on their welfare, but also on
visually mediated behaviours.
PHYLOGENETIC DISTRIBUTION OF COLOUR VISION
SYSTEMS AMONG BIRDS
Olle Håstad, University of Uppsala.
We have no idea of what birds looks like to other birds. Still much
research within the fields of animal ecology and evolution has
been based on observations of bird plumage colouration and the
effects of colour manipulations on bird behaviour. The
interpretation of these studies are entirely dependent on our
understanding of avian colour perception. To make matters even
more interesting, microspectrophotometry studies on bird retinas
has revealed that two distinct colour vision systems are present in
birds, one with a short-wavelength sensitivity biased toward violet
(VS) and the other biased toward ultraviolet (UVS). In the last
years information from molecular studies has given us a more
detailed picture of the basic patterns of vision system distribution
among birds, in turn enabling us to infer some effects this variation
has on the sexual signalling and prey detection of birds.
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UNUSUAL FEATURES IN THE SEQUENCES OF THE
RH1 AND RH2 OPSINS IN THE ROSELLA PARROT
PLATYCERCUS ELEGANS
Ben Knott*, Wayne L. Davies**, Mathew Berg*, James K.
Bowmaker**, Andrew T.D. Bennett*, David M. Hunt**
*Ecology of Vision Lab, School of Biological Sciences, University of Bristol.
Woodland Road. Bristol BS8 1UG; **Institute of Ophthalmology,
11-43
Bath Street, London, EC1V 9EL
Rosella parrots Platycercus elegans form a ring species with three
main intraspecific colour morphs: a crimson form, yellow form, and
a highly variable adelaide form intermediate between the previous
two. Sensory drive theories of sexual selection predict that the
extreme colour variation within the species make the rosella an
ideal potential candidate for intraspecific variation in visual
pigments, hitherto never reported in birds. Previous work shows
birds possess five visual pigments: LWS, RH1, RH2, SWS1 and
SWS2, and these basic sequences were needed from the rosella
before making comparisons between morphs. Eyes were obtained
from three wild intermediate morphs and retinal RNA extracted.
The RH1 opsin showed considerable extension at the 5` end, 25
amino acids beyond the expected position of the stop codon when
compared to birds and other vertebrates. Sequencing of the RH2
opsin produced an expected sequence, plus a sequence with an
unrecognised final exon. The change in sequence occurring at the
known exon boundary suggests and alternative splicing event has
occurred, in which the normal exon 5 has been missed and an
exon from further down the DNA strand has been spliced in its
place in messenger RNA. This is the first known case of alternative
splicing in an opsin. Since all spectral tuning sites are located in
exons 1 to 4, the above anomalies may not affect opsin function to
any significant degree. However, further work is needed to test this
hypothesis explicitly.
THE EYE MOVEMENTS OF ANIMALS AND MEN
Michael Land. University of Sussex
Most of our dealings with the visual world are mediated by brief
fixations, with gaze being shifted up to four times a second by
saccadic eye movements during which we are blind. This 'saccade
and fixate' strategy is not limited to primates that need to move
their high resolution foveas around the scene, but also occurs in
most vertebrates, many insects, crustaceans and even cephalopod
molluscs. The underlying reason for this ubiquitous behaviour
seems to be the avoidance of motion blur, although there may be
other benefits as well. A few animals - sea snails, mantis shrimps,
and jumping spiders - do break the general rule, and move their
eyes continuously across the surroundings. These exceptions all
have in common that their retinas are linear strips, a few receptors
wide. Rather than having a two-dimensional retina, they use time
to provide the missing image dimension.
RELATIVE EYE SIZE AND ECOLOGY IN
ELASMOBRANCH FISHES
Thomas J. Lisney* and Shaun P. Collin
be coastal, often benthic, rays and sharks. Active benthopelagic
and pelagic species, which prey on active, mobile prey also have
relatively larger eyes than more sluggish, benthic elasmobranchs
that feed on more sedentary prey such as benthic invertebrates.
THE CRYPTIC VALUE OF COUNTERSHADING IN
LEPIDOPTERAN LARVAE
Hannah Rowland. University of Liverpool
Of the many traits seen in cryptic prey animals, countershading
(darker pigmentation on those surfaces exposed to the most
lighting) is one of the common, and paradoxically one of the least
well understood. Countershading has been hypothesised to
enhance crypsis by shadow-obliteration, in which lighter
colouration on the undersides compensates for increased shadow
in these regions, thus reducing detection by visually hunting
predators. We tested the hypothesis that there is an optimal level
of contrast between upper and lower surfaces which facilitates
self-shadow concealment and therefore enhances crypsis. We
report two experiments with artificial prey presented to individual
free living birds. In the first experiment, artificial prey with different
levels of contrast were presented on green boards to individual
blackbirds (Turdus merula) and robins (Erithacus rubecula) In the
second experiment a second set of lighter prey with the same level
of contrast were presented on lighter green boards. In the first
experiments an intermediate level of contrast in countershaded
prey provided significantly more protection from predation than
other levels of contrast and controls.
ULTRAVIOLET COMMUNICATION IN REEF FISH
Ulrike E. Siebeck. Vision Touch and Hearing Research
Centre, School of Biomedical Sciences, University of
Queensland, Australia
In contrast to their freshwater and deep-sea counterparts, coral
reef fish are extremely colourful. Many possess ultraviolet (UV)
colour patterns invisible to humans and many predatory fish. This
study set out to study the behavioural significance of these
patterns. In the first experiment, the response of Pomacentrus
amboinensis males towards a choice of two conspecific intruders
was tested. One intruder was presented in a UV-transmitting (UV+)
container and the other in a UV-absorbing (UV-) container.
Territory owners attacked intruders viewed though UV+ filters
significantly more vigorously than those seen through UV- filters,
revealing that the males are sensitive to UV light and that they
modified their behaviour based on the visibility of UV patterning. In
the second experiment, the response of Pomacentrus amboinensis
males was tested towards a conspecific intruder and a
heterospecific intruder possessing similar general appearance but
a markedly different UV facial pattern. Conspecifics were
preferentially attacked in UV+ conditions but not under UVconditions. Taken as a whole, the two experiments strongly
support the hypothesis that UV light has an important impact on
behaviour. Communication in the UV may represent an effective
solution to the age-old evolutionary conflict between being
conspicuous to conspecifics and inconspicuous to predators.
Vision Touch and Hearing Research Centre, School of Biomedical Sciences,
University of Queensland, Australia. email: tom_lisney@hotmail.com
Variation in relative eye size was investigated in a sample of 46
species of elasmobranchs (sharks and rays). To get a measure of
eye size relative to body size, eye axial diameter was scaled with
body mass using least-squares linear regression, using both raw
species data, where species are treated as independent data
points, and phylogenetically independent contrasts. Residual
values calculated for each species calculated using the regression
equations describing these scaling relationships, were then used
as a measure of relative eye size. Relative eye size varies
considerably in elasmobranchs, although sharks have significantly
larger eyes than rays. The sharks with the relatively largest eyes
are oceanic species; either pelagic sharks that move between the
epipelagic (0-200m) and ‘upper’ mesopelagic (200-600m) zones,
or benthic and benthopelagic species that live in the mesopelagic
(200-1000m) and, to a lesser extent, bathypelagic (1000-4000m)
zones. The elasmobranchs with the relatively smallest eyes tend to
BUTTERFLY COLORATION AND COLOUR VISION.
D.G. Stavenga. Department of Neurobiophysics, University
of Groningen, the Netherlands
A comparative survey of wing coloration of pierid butterflies, using
UV photography and reflectance spectrophotometry, reveals that
two quite different methods of sexual dichroism have been
developed among pierid butterflies. The colourful wing patterns are
presumably tuned to the color vision properties of the butterflies.
Butterfly compound eyes are composed of numerous ommatidia.
All ommatidia contain 9 photoreceptor cells. The basic groundplan
of butterfly eyes, encountered in the nymphalids, exists of three
types of randomly arranged ommatidia, with either 1 UV and 1 blue
receptor, or 2 UV, or 2 blue receptors. In Pieridae, the green
receptors have greatly diversified by spectrally selective filters,
resulting in two different types of red receptors, which greatly
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improves red discriminability. The set of short-wavelength
receptors is expanded by multiplication of the short-wavelength
rhodopsins, presumably for sexual discrimination of the wing
colors. In Papilionidae a similar diversification occurred, with
multiplication of the long-wavelength rhodopsins, as well as
application of different spectral filters; presumably all to the benefit
of colour vision.
COLOUR VISION AND ILLUMINATION NOISE IN
PRIMATES AND BIRDS
Tom Troscianko, P George Lovell, C Alejandro Párraga,
Roland Baddeley, Michelle To, David Tolhurst. Universities
of Bristol & Cambridge.
There is considerable evidence that the properties of primate
colour vision are optimised to allow foraging for food. The data on
which these conclusions are based are the reflectance spectra of
fruit and leaves, and measures of the spectral composition of the
illumination. However, the 3D structure of natural scenes
containing leaves results in considerable variation in the intensity
and chromatic content of light reflected from different elements of
each scene. We present data which show that the absorption
spectra of cones in primates and passerine birds have an effect on
the degree to which this illumination noise is encoded by the visual
system. In particular, the close spacing of primate L and M cones
results in a greater degree of invariance to shadows and
illumination than the equivalent spacing of these cones in
passerine birds. The results point to a trade-off between (a)
achieving greater chromatic resolution, and (b) immunity from
illumination noise.
INDIVIDUAL STRATEGIES FOR COLOUR LEARNING IN
BUMBLE BEES
Martina Wicklein, Institute of Ophthalmology, UCL, London
It is well known that bumblebees have a labour division in the hive
and that foragers can be mainly foraging for pollen, water or nectar
and therefore be divided into distinct task groups. Here we explore
if bumblebees could also become specialists for foraging under
different illumination conditions. We trained bumblebees to forage
in an artificial flower meadow consisting of 64 flowers (8 different
flower colours) presented under two different illuminants. Only one
flower colour was rewarded (target) and the task of the bees was
to learn to find the targets under both illuminants. In the first
condition the bees encountered a situation akin to a dappled
illumination, both illuminants were present simultaneously. In the
second condition the illuminants were presented sequentially. Over
the course of training we preformed regular tests to assess how
well the bees were able to find the correct targets under the two
training illuminants and what strategies they used to find the
targets. We found that under the first, simultaneous, illumination
condition the forager population split up into two groups, each
forager group specializing for one of the illuminants, using a
different strategy to find the target. Interestingly the split into two
specialized forager groups only happens under the simultaneous
training regime, not when the bees were trained to both illuminants
sequentially. The main implication of this is that whether bees spilt
into two specialized forager groups does not depend on the
identity of the illuminants, but the temporal and spatial
arrangement of the illumination.
Given that primate vision has a particularly enhanced ability to
ignore shadows and changes in the colour of the illumination, we
present data to show that human observers are able to ignore
such changes when making judgments about the degree of
similarity of natural scenes.
S CONES CONTRIBUTE TO BRIGHTNESS
PERCEPTION IN PRIMATES
Christian Wehrhahn. Max-Planck-Institut, Tubingen,
Germany
The perception of brightness in animals or humans is currently not
well understood, as demonstrated by our inability to explain
illusions that rely on mid and/or high level mechanisms. Although
animal studies have shown the activation of neurons in the early
visual pathways whose functional properties correlate with the
perception of brightness, the components of a “brightness
pathway” (in analogy to the motion pathway) have not yet been
described.
Perception of brightness has been explored in psychophysical
experiments in monkeys. Rhesus monkeys, trained to discriminate
the brightness of two test fields, also succeeded in performing the
tasks of brightness induction and White's effect (Huang et al.
2002). In all three tasks, the performance of monkey observers
was similar to that of human observers. This indicates that
monkeys perceive surface brightness in a way comparable to
humans.
So far, only retinal contributions to the perception of brightness
have been successfully investigated. Results related to the
contribution of S cones to brightness perception have been
reported. In physiological experiments in anaesthetized monkeys,
responses of V1 neurons to S cone isolating stimuli showed that S
cones account for about 10% of the total amplitude of modulation
(Chatterjee & Callaway 2003). For human observers, flicker fusion
experiments in 73 color normal human observers indicated that on
average S-cone input accounts for about 5% of the total brightness
signal.
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