Award details

The role of colour in insect pattern vision

Reference	BB/I009329/1
Principal Investigator / Supervisor	Professor Natalie Hempel de Ibarra
Co-Investigators / Co-Supervisors
Institution	University of Exeter
Department	Psychology
Funding type	Research
Value (£)	336,639
Status	Completed
Type	Research Grant
Start date	15/09/2011
End date	14/09/2014
Duration	36 months

Abstract

Both colour and pattern vision has been extensively studied in insects, mostly bees, but the role of colour for the perception of patterns is still poorly understood. The current widely hold view is that pattern vision is segregated from colour vision and accomplished by achromatic (brightness-coding) mechanisms. Evidence however exists that bees can distinguish patterns without the contribution from an achromatic mechanism. This study aims to scrutinise this evidence by examining the role of chromatic and pattern cues for the detectability and discriminability of coloured patterns through the colour vision system. We will determine detection differences and thresholds for two-coloured disk-shaped patterns by testing bees in Y-mazes where we can vary the angular size of stimuli. Pattern colours will only differ in hue and chromatic contrast to background, but not in achromatic contrast, and pattern elements will vary in size to identify filter mechanisms. Another set of experiments will investigate the accuracy of discrimination of these patterns through chromatic cues. Previous results indicate that bees may ignore pattern cues in such tasks, therefore chromatic and pattern cues will be systematically varied to identify perceptual constraints and pattern discrimination strategies. Finally we will measure chromatic and pattern cues in flower patterns and base their analysis on our behaviourally derived models. The aim is to identify potential trade-offs between the detectability and discriminability of coloured patterns in floral displays which may reflect pollinator-driven selection processes.

Summary

A century ago Karl von Frisch advanced our understanding of animal sensory worlds demonstrating in classic experiments that bees see colours. Many insects as most other animals have colour vision and the perception of colour does not require complex higher brain functions. Insects are small-sized and equipped with compound eyes that give blurred views of a spatially complex world. How colourful are these views and how does an insect recognise colourful objects, patterns and shapes in a visual scene? These questions can be well studied in bees, an important insect model system in ecological, behavioural and physiological research. Foraging bees, as other pollinating insects, usually look for particular flowers to efficiently collect nectar and pollen. They will dismiss many other flowers during their search and not approach or land on them. Such flower constancy requires that floral features, e.g. colours, patterns and odours are learned and recognised by bees. This learning ability can be exploited to easily train bees to artificial food sources, as done by von Frisch, where different colours or patterns signal the presence of reward. Using such experimental methods and new tools to measure and quantify colours as they are perceived by bees, I shall investigate how patterns look to a bee if they are colourful, whether and when a bee sees or learns colours independently from patterns. A crucial hypothesis that I will test is whether pattern and colour vision are segregated in the bee visual system, e.g. whether and to which extent pattern vision in insects may be colour-blind, as has been suggested in the past. I shall also look at flowers through bee eyes and brain using optical and sensory models and make predictions of how detectable and disciminable floral colours and patterns are for bees. Detection is the main visual task if a flower is at a large distance and needs to be picked out from the background. In the first set of experiments I will train bees to detect a pattern which are placed on the back wall of one of two Y-maze arms. The other arm is empty. In the maze the bee will have to decide in which arm it sees the pattern. The distance to the pattern determines the size with which it is projected onto the bee eye. As long as the bee can detect a pattern it will enter the correct arm and find a sucrose reward. Moving the pattern further away the detection limit will be reached when the bee will choose both arms randomly. Detection limits will be determined for a variety of two-coloured patterns that consist of a central disc and a surrounding ring or a disc divided in two halfs, resembling the major types of flower displays as seen through the low-resolution eyes of bees. Colours will be varied systematically to understand how colour hue and colour contrast against the background influence pattern detectability. These parameters will be used to analyse colours and patterns in displays of intact wild flowers that I will record using UV-sensitive multispectral imaging. Pattern elements will be also varied in shape and relative size for identifying possible filter mechanisms in the visual system of the bee. In a second set of experiments bees will discriminate between these patterns. Only one pattern will be rewarded. If bees can distinguish them, they will show a clear preference for the rewarded pattern. These results will tell us, how spatial and colour cues in a pattern are perceived by the bee and which ones may be more important in some patterns. Knowing how bees perform pattern detection and discrimination, I will be able to explain how bees see and memorise complex colourful flower displays. The study will provide new insights the bees' perceptual abilities may have influenced the evolution of complex and colourful displays in flowers that aim to advertise themselves effectively to bees and other insect pollinators with excellent colour vision and learning capacity.

Impact Summary

Many researchers working in the field of insect and arthropod vision, visual ecology and machine vision will be interested in our findings. The bee has been a long-standing model system, and motivated much comparative research testing models that have been established by bee vision scientists. This is also the case for this proposal as the questions related to the role of colour in insect pattern vision have rarely been addressed. Given that we use our experimental findings to determine the effectiveness of naturally evolved flower signals, pollination ecologists as well as researcher concerned with insect-plant interactions will benefit from this study, as well as researchers in the field of animal communication. We will ensure that our results are presented swiftly on international and national meetings and submitted for publication in leading international journals to effectively share them with the scientific community. The research proposed here will be of interest to this wider public because honeybees are important pollinators, both for agricultural crops, horticulture and wild flowering plants. They currently enjoy much attention from the public, governments and environmental organisations given current declines reported all over the world in numbers and diversity of pollinators. People are keener than ever to learn about bees. Bee behaviour and pollination ecology is a standard topic in national school and college curricula, therefore a general interest in the educational sector exists in new findings relevant to fundamental concepts of animal physiology and ecology. Visualising animal senses that differ strongly from our own, like bee colour vision and their perception of flower patterns, always receives much interest and offers opportunities to incorporate new research findings into environmental and curricular teaching for children and people of different ages, in schools, colleges and HEIs. I have good experience in running workshops, such as duringthe National Science Week 2008, and interacting with schools and the media. These activities and support to the media have been always well-received and I expect a large impact and knowledge transfer through the activities outlined in the Impact Plan.

Committee	Research Committee A (Animal disease, health and welfare)
Research Topics	Neuroscience and Behaviour
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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