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Annelid Vision  

Cynthia M. Harley and Mark K. Asplen

Annelid worms are simultaneously an interesting and difficult model system for understanding the evolution of animal vision. On the one hand, a wide variety of photoreceptor cells and eye morphologies are exhibited within a single phylum; on the other, annelid phylogenetics has been substantially re-envisioned within the last decade, suggesting the possibility of considerable convergent evolution. This article reviews the comparative anatomy of annelid visual systems within the context of the specific behaviors exhibited by these animals. Each of the major classes of annelid visual systems is examined, including both simple photoreceptor cells (including leech body eyes) and photoreceptive cells with pigment (trochophore larval eyes, ocellar tubes, complex eyes); meanwhile, behaviors examined include differential mobility and feeding strategies, similarities (or differences) in larval versus adult visual behaviors within a species, visual signaling, and depth sensing. Based on our review, several major trends in the comparative morphology and ethology of annelid vision are highlighted: (1) eye complexity tends to increase with mobility and higher-order predatory behavior; (2) although they have simple sensors these can relay complex information through large numbers or multimodality; (3) polychaete larval and adult eye morphology can differ strongly in many mobile species, but not in many sedentary species; and (4) annelids exhibiting visual signaling possess even more complex visual systems than expected, suggesting the possibility that complex eyes can be simultaneously well adapted to multiple visual tasks.


Caenorhabditis elegans Feeding Behaviors  

Nicolas Dallière, Lindy Holden-Dye, James Dillon, Vincent O'Connor, and Robert J. Walker

The microscopic free-living nematode worm Caenorhabditis elegans was the first metazoan to have its genome sequenced and for many decades has served as a genetically tractable model for the investigation of neural mechanisms of behavioral plasticity. Many of its behaviors involve the detection of its food, bacteria, which are ingested and transported to the intestine by a muscular pharynx. The structure of the pharynx and the circuitry of the pharyngeal nervous system that regulates pharyngeal activity have been described in some detail. This has provided a platform for understanding how this simple organism finely tunes its feeding behavior in response to the changing availability and quality of its food, and in the context of its own nutritional status. This resonates with fundamental principles of energy homeostasis that occur throughout the animal kingdom.


Caenorhabditis elegans Learning and Memory  

James S.H. Wong and Catharine H. Rankin

The nematode, Caenorhabditis elegans (C. elegans), is an organism useful for the study of learning and memory at the molecular, cellular, neural circuitry, and behavioral levels. Its genetic tractability, transparency, connectome, and accessibility for in vivo cellular and molecular analyses are a few of the characteristics that make the organism such a powerful system for investigating mechanisms of learning and memory. It is able to learn and remember across many sensory modalities, including mechanosensation, chemosensation, thermosensation, oxygen sensing, and carbon dioxide sensing. C. elegans habituates to mechanosensory stimuli, and shows short-, intermediate-, and long-term memory, and context conditioning for mechanosensory habituation. The organism also displays chemotaxis to various chemicals, such as diacetyl and sodium chloride. This behavior is associated with several forms of learning, including state-dependent learning, classical conditioning, and aversive learning. C. elegans also shows thermotactic learning in which it learns to associate a particular temperature with the presence or absence of food. In addition, both oxygen preference and carbon dioxide avoidance in C. elegans can be altered by experience, indicating that they have memory for the oxygen or carbon dioxide environment they were reared in. Many of the genes found to underlie learning and memory in C. elegans are homologous to genes involved in learning and memory in mammals; two examples are crh-1, which is the C. elegans homolog of the cAMP response element-binding protein (CREB), and glr-1, which encodes an AMPA glutamate receptor subunit. Both of these genes are involved in long-term memory for tap habituation, context conditioning in tap habituation, and chemosensory classical conditioning. C. elegans offers the advantage of having a very small nervous system (302 neurons), thus it is possible to understand what these conserved genes are doing at the level of single identified neurons. As many mechanisms of learning and memory in C. elegans appear to be similar in more complex organisms including humans, research with C. elegans aids our ever-growing understanding of the fundamental mechanisms of learning and memory across the animal kingdom.


Caenorhabditis elegans Olfaction  

Douglas K. Reilly and Jagan Srinivasan

To survive, animals must properly sense their surrounding environment. The types of sensation that allow for detecting these changes can be categorized as tactile, thermal, aural, or olfactory. Olfaction is one of the most primitive senses, involving the detection of environmental chemical cues. Organisms must sense and discriminate between abiotic and biogenic cues, necessitating a system that can react and respond to changes quickly. The nematode, Caenorhabditis elegans, offers a unique set of tools for studying the biology of olfactory sensation. The olfactory system in C. elegans is comprised of 14 pairs of amphid neurons in the head and two pairs of phasmid neurons in the tail. The male nervous system contains an additional 89 neurons, many of which are exposed to the environment and contribute to olfaction. The cues sensed by these olfactory neurons initiate a multitude of responses, ranging from developmental changes to behavioral responses. Environmental cues might initiate entry into or exit from a long-lived alternative larval developmental stage (dauer), or pheromonal stimuli may attract sexually mature mates, or repel conspecifics in crowded environments. C. elegans are also capable of sensing abiotic stimuli, exhibiting attraction and repulsion to diverse classes of chemicals. Unlike canonical mammalian olfactory neurons, C. elegans chemosensory neurons express more than one receptor per cell. This enables detection of hundreds of chemical structures and concentrations by a chemosensory nervous system with few cells. However, each neuron detects certain classes of olfactory cues, and, combined with their synaptic pathways, elicit similar responses (i.e., aversive behaviors). The functional architecture of this chemosensory system is capable of supporting the development and behavior of nematodes in a manner efficient enough to allow for the genus to have a cosmopolitan distribution.


Cephalochordate Nervous System  

Simona Candiani and Mario Pestarino

The central and peripheral nervous systems of amphioxus adults and larvae are characterized by morphofunctional features relevant to understanding the origins and evolutionary history of the vertebrate CNS. Classical neuroanatomical studies are mainly on adult amphioxus, but there has been a recent focus, both by TEM and molecular methods, on the larval CNS. The latter is small and remarkably simple, and new data on the localization of glutamatergic, GABAergic/glycinergic, cholinergic, dopaminergic, and serotonergic neurons within the larval CNS are now available. In consequence, it has been possible begin the process of identifying specific neuronal circuits, including those involved in controlling larval locomotion. This is especially useful for the insights it provides into the organization of comparable circuits in the midbrain and hindbrain of vertebrates. A much better understanding of basic chordate CNS organization will eventually be possible when further experimental data will emerge.


Cephalopod Nervous System Organization  

Z. Yan Wang and Clifton W. Ragsdale

Over 700 species of cephalopods live in the Earth’s waters, occupying almost every marine zone, from the benthic deep to the open ocean to tidal waters. The greatly varied forms and charismatic behaviors of these animals have long fascinated humans. Cephalopods are short-lived, highly mobile predators with sophisticated brains that are the largest among the invertebrates. While cephalopod brains share a similar anatomical organization, the nervous systems of coleoids (octopus, squid, cuttlefish) and nautiloids all display important lineage-specific neural adaptations. The octopus brain, for example, has for its arms a well-developed tactile learning and memory system that is vestigial in, or absent from, that of other cephalopods. The unique anatomy of the squid giant fiber system enables rapid escape in the event of capture. The brain of the nautilus comprises fewer lobes than its coleoid counterparts, but contains olfactory system structures and circuits not yet identified in other cephalopods.


Cephalopod Olfaction  

Anna Di Cosmo and Gianluca Polese

Within the Phylum Mollusca, cephalopods encompass a small and complex group of exclusively marine animals that live in all the oceans of the world with the exception of the Black and Caspian seas. They are distributed from shallow waters down into the deep sea, occupying a wide range of ecological niches. They are dominant predators and themselves prey with high visual capability and well-developed vestibular, auditory, and tactile systems. Nevertheless, their perceptions are chemically facilitated, so that water-soluble and volatile odorants are the key mediators of many physiological and behavioral events. For cephalopods as well as the other aquatic animals, chemical cues convey a remarkable amount of information critical to social interaction, habitat selection, defense, prey localization, courtship and mating, affecting not only individual behavior and population-level processes, but also community organization and ecosystem function. Cephalopods possess chemosensory systems that have anatomical similarities to the olfactory systems of land-based animals, but the molecules perceived from distance are different because their water solubility is of importance. Many insoluble molecules that are detected from distance on land must, in an aquatic system, be perceived by direct contact with the odour source. Most of the studies regarding olfaction in cephalopods have been performed considering only waterborne molecules detected by the “olfactory organs.” However cephalopods are also equipped with “gustatory systems” consisting of receptors distributed on the arm suckers in octopods, buccal lips in decapods, and tentacles in nautiluses. To date, what is known about the olfactory organ in cephalopods comes from studies on nautiloids and coleoids (decapods and octopods). In the nautiloid’s olfactory system, there is a pair of rhinophores located below each eye and open to the environment with a tiny pore, whereas in coleoids a small pit of ciliated cells is present on either side of the head below the eyes close to the mantle edge.


Crayfish Escape  

Donald Edwards

Crayfish are decapod crustaceans that use different forms of escape to flee from different types of predatory attacks. Lateral and Medial Giant escapes are released by giant interneurons of the same name in response to sudden, sharp attacks from the rear and front of the animal, respectively. A Lateral Giant (LG) escape uses a fast rostral abdominal flexion to pitch the animal up and forward at very short latency. It is succeeded by guided swimming movements powered by a series of rapid abdominal flexions and extensions. A Medial Giant (MG) escape uses a fast, full abdominal flexion to thrust the animal directly backward, and is also followed by swimming that moves the animal rapidly away from the attacker. More slowly developing attacks evoke Non-Giant (NG) escapes, which have a longer latency, are varied in the form of abdominal flexion, and are directed initially away from the attacker. They, too, are followed by swimming away from the attacker. The neural circuitry for LG escape has been extensively studied and has provided insights into the neural control of behavior, synaptic integration, coincidence detection, electrical synapses, behavioral and synaptic plasticity, neuroeconomical decision-making, and the modulatory effects of monoamines and of changes in the animal’s social status.


Crustacean Olfaction  

Charles Derby and Manfred Schmidt

Olfaction is a chemical sense present not only in mammals, insects, and other terrestrial animals, but also in crustaceans, most of which are aquatic. Crustaceans use olfaction for detecting and responding in appropriate ways to chemicals relevant to most ecological contexts, including: environmental cues indicating quality of food, habitat, and location; interspecies cues indicating presence of predators and competitors; and intraspecific signals indicating social status of conspecifics and presence of possible mating partners. Olfaction is only one of the chemical senses of crustaceans, being distinguished based on anatomical and functional features of the sensory neurons detecting the chemicals and the pathways within the central nervous system that processes this information.


Crustacean Visual Circuits Underlying Behavior  

Daniel Tomsic and Julieta Sztarker

Decapod crustaceans, in particular semiterrestrial crabs, are highly visual animals that greatly rely on visual information. Their responsiveness to visual moving stimuli, with behavioral displays that can be easily and reliably elicited in the laboratory, together with their sturdiness for experimental manipulation and the accessibility of their nervous system for intracellular electrophysiological recordings in the intact animal, make decapod crustaceans excellent experimental subjects for investigating the neurobiology of visually guided behaviors. Investigations of crustaceans have elucidated the general structure of their eyes and some of their specializations, the anatomical organization of the main brain areas involved in visual processing and their retinotopic mapping of visual space, and the morphology, physiology, and stimulus feature preferences of a number of well-identified classes of neurons, with emphasis on motion-sensitive elements. This anatomical and physiological knowledge, in connection with results of behavioral experiments in the laboratory and the field, are revealing the neural circuits and computations involved in important visual behaviors, as well as the substrate and mechanisms underlying visual memories in decapod crustaceans.


Drosophila Olfaction  

Quentin Gaudry and Jonathan Schenk

Olfactory systems are tasked with converting the chemical environment into electrical signals that the brain can use to optimize behaviors such as navigating towards resources, finding mates, or avoiding danger. Drosophila melanogaster has long served as a model system for several attributes of olfaction. Such features include sensory coding, development, and the attempt to link sensory perception to behavior. The strength of Drosophila as a model system for neurobiology lies in the myriad of genetic tools made available to the experimentalist, and equally importantly, the numerical reduction in cell numbers within the olfactory circuit. Modern techniques have recently made it possible to target nearly all cell types in the antennal lobe to directly monitor their physiological activity or to alter their expression of endogenous proteins or transgenes.


Drosophila Reward Circuits  

John S. Hernandez, Tariq M. Brown, and Karla R. Kaun

The ability to sense and respond to a rewarding stimulus is a key advantage for animals in their natural environment. The circuits that mediate these responses are complex, and it has been difficult to identify the fundamental principles of reward structure and function. However, the well-characterized brain anatomy and sophisticated neurogenetic tools in Drosophila melanogaster make the fly an ideal model to understand the mechanisms through which reward is encoded. Drosophila find food, water, intoxicating substances, and social acts rewarding. Basic monoaminergic neurotransmitters, including dopamine (DA), serotonin (5-HT), and octopamine (OA), play a central role in encoding these rewards. DA is central to sensing, encoding, responding, and predicting reward, whereas 5-HT and OA carry information about the environment that influences DA circuit activity. In contrast, slower-acting neuromodulators such as hormones and neuropeptides play a key role in both encoding the pleasurable stimulus and modulating how the internal environment of the fly influences reward sensation and seeking. Recurring circuit motifs for reward signaling identified in Drosophila suggest that these key principles will help elucidate understanding of how reward circuits function in all animals.


Echinoderm Nervous System  

Carlos A. Díaz-Balzac and José E. García-Arrarás

The nervous system of echinoderms has been studied for well over a century. Nonetheless, the information available is disparate, with in-depth descriptions for the nervous component of some groups or of particular organs while scant data is available for others. The best studied representatives to date are the nervous system of echinoid embryos and larva, and the adult holothurian nervous system. Although described sometimes inaccurately as a neural net, the echinoderm nervous system consists of well-defined neural structures. This is observed since early embryogenesis when activation of the anterior neuroectoderm gene regulatory networks initiate the formation of the embryonic nervous system. This system then undergoes expansion and differentiation to form the larval nervous system, which is centered on the ciliary bands. This “simpler” nervous system is then metamorphosed into the adult echinoderm nervous system. The adult echinoderm nervous system is composed of a central nervous system made up of a nerve ring connected to a series of radial nerve cords. Peripheral nerves extending from the radial nerve cords or nerve ring connect with the peripheral nervous system, located in other organs or effectors including the viscera, podia, body wall muscles, and connective tissue. Both the central and peripheral nervous systems are composed of complex and diverse subdivisions. These are mainly characterized by the expression of neurotransmitters, namely acetylcholine, catecholamines, histamine, amino acids, GABA, and neuropeptides. Other areas of interest include the amazing regenerative capabilities of echinoderms that have been shown to be able to regenerate their nervous system components; and the analysis of the echinoderm genome that has provided essential insights into the molecular basis of how echinoderms develop an adult pentaradial symmetry from bilaterally symmetric larvae and the role of the nervous system in this process.


Electrophysiology and Behavior of Cnidarian Nervous Systems  

Robert W. Meech

Although the Cnidaria have evolved a wide range of body forms matched with an equally varied neural anatomy, individual species exhibit common patterns of behavior. For example, in all species a key challenge for the nervous system is to transfer food from the peripherally mounted tentacles to the centrally located stomach. Foraging movements, necessary to maintain the food supply, must be accomplished in such a way as to avoid interference with the primary objective of getting prey into the mouth. Furthermore, the hunt for prey must be balanced by a measured response to “threat.” Different species respond to threat in markedly different ways, but in each case foraging is inhibited, just as it is during transmission of food. One hundred years ago, G. H. Parker questioned whether a centralized or a locally organized nervous system could best account for sea anemone behavior. Anatomical and electrophysiological studies now suggest that in most Cnidaria there is a degree of hierarchical control, with local reflexes coordinated by more condensed systems of neurons. This organization is highly developed in the nerve rings of hydrozoan medusae and takes the form of ganglion-like rhopalia in the Cubozoa. Even in hydrozoan polyps such as Hydra there are at least four separate neuronal systems. It is likely that the underlying mechanisms (containing both homologous and analogous elements) will be best revealed by a comparative approach that directly relates behavior with its molecular basis. Useful examples include comparisons between sea anemones with and without through-conducting systems; between hydra with and without oral rings; between medusae with and without coordinated escape swimming. Recent advances in transgenomic labeling have shown the way forward.


Gastropod Feeding Systems: Evolution of Neural Circuits that Generate Diverse Behaviors  

Paul Benjamin and Michael Crossley

It is conceptually reasonable to explore how the evolution of behavior involves changes in neural circuitry. Progress in determining this evolutionary relationship has been limited in neuroscience because of difficulties in identifying individual neurons that contribute to the evolutionary development of behaviors across species. However, the results from the feeding systems of gastropod mollusks provide evidence for this concept of co-evolution because the evolution of different types of feeding behaviors in this diverse group of mollusks is mirrored by species-specific changes in neural circuitry. The evolution of feeding behaviors involves changes in the motor actions that allow diverse food items to be acquired and ingested. The evolution in neural control accompanies this variation in food and the associated changes in flexibility of feeding behaviors. This is present in components of the feeding network that are involved in decision making, rhythm generation, and behavioral switching but is absent in background mechanisms that are conserved across species, such as those controlling arousal state. These findings show how evolutionary changes, even at the single neuron level, closely reflect the details of behavioral evolution.


Gastropod Learning and Memory (Aplysia, Hermissenda, Lymnaea, and Others)  

Alexis Bédécarrats and Romuald Nargeot

Euopisthobranchia (Aplysia), Nudipleura (Tritonia, Hermissenda, Pleurobranchaea), and Panpulmonata (Lymnaea, Helix, Limax) gastropod mollusks exhibit a variety of reflex, rhythmic, and motivated behaviors that can be modified by elementary forms of learning and memory. The relative simplicity of their nervous systems and behavioral repertoires has allowed the uncovering of processes of neuronal and synaptic plasticity underlying non-associative learning, such as habituation, sensitization, and different forms of associative learning, such as classical and operant conditioning. Decades of work on these simpler and accessible animal systems have almost uniquely yielded an understanding into the mechanistic basis of learning and memory spanning behavior, neuronal circuitry, and molecules. Given the conservative nature of evolutionary processes, the mechanisms deciphered have also provided valuable insights into the neural basis of learning and memory in other metazoans, including higher vertebrates.


Genetics of C. elegans Behavior  

Denise S. Walker, Yee Lian Chew, and William R. Schafer

The nematode Caenorhabditis elegans is among the most intensely studied animals in modern experimental biology. Its amenability to classical and molecular genetics, compact nervous system, and transparency to optogenetic recording and manipulation have led to its being widely used to investigate how individual gene products act in the context of neuronal circuits to generate behavior. C. elegans was the first animal neuronal connectome to be characterized at the level of individual neurons and synapses, and the wiring organization shows significant parallels with the micro- and macro-level structures of more complex brains. It uses a wide array of sensory cues (mechanical, gustatory, olfactory, and thermal), with impressive precision, to determine an appropriate behavioral response, in the form of changes in locomotion and other motor outputs. The small number of neurons (302) and their highly stereotyped morphology have enabled the interrogation of the precise function of individual neurons, in terms of both the genes that they express and the behaviors in which they function. Approximately one third are sensory neurons, located around the mouth and in the tail, as well as along the length of the body. A complex network of interneurons connects these to the motor neurons, the majority of which output to the body wall muscles, arranged along the body, determining the changes in direction and speed of locomotion required for behaviors such as taxiing up gradients of food-related cues or avoiding noxious cues. The ability to combine information about the precise function of individual neurons with circuit knowledge, genetics, and optogenetic approaches has been critical in advancing the molecular and circuit-level understanding of the mechanisms underlying C. elegans’s behavior. In common with that of other animals, C. elegans’s behavior is subject to change in response to prior experience, and this same complement of experimental approaches has provided significant insight into how plasticity and changes in behavioral states are achieved.


Hemichordate Nervous System  

Norio Miyamoto and Hiroshi Wada

Hemichordates are marine invertebrates consisting of two distinct groups: the solitary enteropneusts and the colonial pterobranchs. Hemichordates are phylogenetically a sister group to echinoderm composing Ambulacraria. The adult morphology of hemichordates shares some features with chordates. For that reason, hemichordates have been considered key organisms to understand the evolution of deuterostomes and the origin of the chordate body plan. The nervous system of hemichordates is also important in the discussion of the origin of centralized nervous systems. However, unlike other deuterostomes, such as echinoderms and chordates, information on the nervous system of hemichordates is limited. Recent improvements in the accessibility of embryos, development of functional tools, and genomic resources from several model organisms have provided essential information on the nervous system organization and neurogenesis in hemichordates. The comparison of the nervous system between hemichordates and other bilaterians helps to elucidate the origin of the chordate central nervous system. Extant hemichordates are divided into two groups: enteropneusts and pterobranchs. The nervous system of adult enteropneusts consists of nerve cords and the basiepidermal nerve net. The two nerve cords run along the dorsal and ventral midlines. The dorsal nerve cord forms a tubular structure in the collar region. The two nerve cords are connected through the prebranchial nerve ring. The larval nervous system of enteropneusts develops along the ciliary band and there is a ganglion at the anterior end of the body called the apical ganglion. A pair of pigmented eyespots is situated at the lateral side of the apical ganglion. The adult nervous system of pterobranchs is basiepidermal and there are several condensations of plexuses. The most prominent one is the brain, located at the base of the tentaculated arms. From the brain, small fibers radiate and enter tentaculated arms to form a tentacle nerve in each. There is a basiepidermal nerve cord in the ventral midline of the trunk.


The Insect Central Complex  

Stanley Heinze

The central complex (CX) is the only unpaired brain region of the insect brain. It is located at the interface of sensory processing and motor control and plays a vital role in context dependent action selection. The CX has four main tasks. First, the encoding of the insect’s orientation in space, i.e., the generation of an internal head direction signal based on both rotational self-motion and external sensory signals. Second, the generation of goal direction representations. Third, the selection of an appropriate goal direction based on context, internal state, and previous experience. And finally, the initiation of motor steering signals based on comparing heading direction and goal directions. The highly regular, almost crystalline neuroarchitecture of repeating computational elements provide the structural basis for these computations. These tight structure function relationships have revealed that the CX performs highly efficient, vector-based computations, in which vectors are encoded as sinusoidal activity patterns across populations of neurons. The deep insight into the computational algorithms implemented in this brain area have made the CX a prime model system to study the neural basis of context-dependent action selection and behavioral decisions, as well as the mechanisms of circuit evolution.


Insect Color Vision  

Natalie Hempel de Ibarra and Misha Vorobyev

Color plays an important role in insect life—many insects forage on colorful flowers and/or have colorful bodies. Accordingly, most insects have multiple spectral types of photoreceptors in their eyes, which gives them the capability to see colors. However, insects cannot perceive colors in the same way as human beings do because their eyes and brains differ substantially. An insect was the first nonhuman animal whose ability to discriminate colors has been demonstrated - in the beginning of the 20th century, von Frisch showed that the honeybee, Apis mellifera, can discriminate blue from any shade of gray. This method, called the gray-card experiment, is an accepted “gold standard” for the proof of color vision in animals. Insect species differ in the combinations of photoreceptors in their eyes, with peak sensitivities in ultraviolet (UV) and/or blue, green, and sometimes red parts of the spectrum. The number of photoreceptor spectral types can be as little as one or two, as in the grasshopper Phlaeoba and the beetle Tribolium, and as many as 10 and more in some species of butterflies and dragonflies. However, not all spectral receptor types are necessarily used for color vison. For example, the butterfly Papilio xuthus uses only four of its eight photoreceptors for color vision. Some insects have separate channels for processing chromatic and achromatic (lightness) information. In the honeybee, the achromatic channel has high spatial resolution and is mediated only by long-wavelength sensitive, or “green,” photoreceptors alone, whereas the spatial resolution of chromatic vision is low and mediated by all three spectral types of photoreceptors. Whether other insects have a similar separation of chromatic and achromatic vision remains uncertain. In contrast to vertebrates, insects do not use distinct sets of photoreceptors for nocturnal vision, and some nocturnal insects can see color at night. Insect photoreceptors are inherently polarization sensitive because of their microvillar organization. Therefore, some insects cannot discriminate changes in polarization of light from changes in its spectral composition. However, many insects sacrifice polarization sensitivity to retain reliable color vision. For example, in the honeybee, polarization sensitivity is eliminated by twisting the rhabdom in most parts of its compound eye except for the dorsal rim area that is specialized in polarization vision. Insects experience color constancy and color-contrast phenomena. Although in humans these aspects of vision are often attributed to cortical processing of color, simple models based on photoreceptor adaptation may explain color constancy and color induction in insects. Color discriminations can be evaluated using a simple model, which assumes that it is limited by photoreceptor noise. This model can help to predict discrimination of colors that are ecologically relevant, such as flower colors for pollinating insects. However, despite the fact that many insects forage on flowers, there is no evidence that insect pollinator vision coevolved with flower colors. The diverse color vision in butterflies appears to adaptively facilitate the recognition of their wing colors.