Introduction
This chapter will look more into the development of behavior, particularly the role genes play as proximate factors underlying behavior. Genes are involved in the development of may complex behaviors, including WC sparrow song. But development is dependent on many environmental factors, such as components of egg yolk, hormones provided by parents, and sensory signals like bird song. We need to first deal with the mistaken view that some traits are "genetically determined" and some are "environmentally determined". Nature vs. Nurture Misconception We can't properly analyze behavioral development from an evolutionary perspective if we believe some behaviors are 100% genetically determined or others are 100% environmentally determined (learned). This would imply natural selection wasn't involved in the later case, and that behaviors could not be modified in the former case. Part of this bias is that many of human behaviors are learned, and that nurture can always trump nature. It may be good to think of behaviors as lying somewhere on a continuum, between genetic and environmental influence. Genes ⇐―――――――――――――――――――――⇒ Environment. Interactive Theory of Development Both genes and environment play a role on the development of behaviors. Honeybee workers, shift roles during their lives. Post metamorphosis, she cleans comb cells. Next, she nurses larvae with honey. Next, she takes food to fellow workers.
Lastly, she forages for pollen and nectar. What causes a worker to pass through these phases?
If behavioral development reflects interaction between genetic and environmental inputs, genetic info has to respond to the environment. Her behavioral phenotype has to respond, and there will be changes in how genes/environment interact. Microarray analyses of mRNAs produced when genes are being transcribed have been done on various stages of worker bee lives. Whitfield et al compared the activity of ~5500 genes (out of 14000 total) of nurses and foragers. 40% of the surveyed genes showed different levels of output between the two bee types. These changes can be experimentally induced to occur earlier When colonies were created with fewer old forager role much earlier then they normally would. The gene activity also varies according to what an individual bee was doing at the time it was collected and sacrifice. Gene activity can be influenced by how far a bee has flown during foraging - or how for it was perceived it has flown. In one experiment, one group of bees flew through a striped tunnel, while the other group flew through a tunnel with no pattern. Genes expressed in the two groups differed strongly, showing that different perceptions of distance flown were based upon a difference in genetic activity in certain parts of the brain, which differed b/c of flight-experience. - Genes expressed in two different group of bees perceived distance of their flight bc the affects by the two variables (spiral tunnel and blank tunnel). The differences are based on the genetic activity in certain parts of the brain. The environment is relevant to behavioral development and brain function. Environment provides molecular building blocks needed for transcription and translation. - the surrounding environment helps with transcription and translation for DNA. This impacts gene regulation and production of specific proteins. - Cells must have the proper amino acids for translation. Example: - Chemicals that influence a honeybee come from substances eaten by a queen bee before she makes eggs, the honey and pollen eaten by larvae and adults that develop from those eggs. This initiates a cascade of developmental changes, that eventually alters the development of the brain and the behavior of the bee. One potent developmental product in bees is called "juvenile hormone" or JH. JH is found in low concentrations in young nurse workers but much higher concentrations in older foragers. If you treat young bees with JH, they become precocious foragers. If you remove the glands that makes JH, the bee delays the transition to forager. If you then give these bees JH, they will to…
Similar patterns are seen with sex hormones and their impact on sexual behavior. - Interestingly, in honey bees, if you experimentally create colonies that are the same age, a division of labor will still appear. hence social environment affects hormone production in this case. - What enable bees to make developmental adjustments? Perhaps deficits in encounters with older foragers stimulated early transition to foragers. This was tested by adding groups of older foragers to experimental colonies made up of only young workers. The higher the proportion of older bees added, the lower the proportion of young nurse bees that undergo early transformation to foragers. Apparently, behavioral interactions between older and young bees, inhibits the development of foraging behavior. Young bee transplants have no effect on young residents bees. The inhibition agent has been traced to a fatty acid called "ethyl oleate", which only foragers make and store in their crop. When foragers pass nectar in their crops to nurses in the hive, they probably transfer this inhibitor as well. More foragers means more nurses receiving the inhibitor, which slows their transition to forager status. This bee research shows the fallacy of labeling behavior phenotypes as being purely genetic, because they are the products of thousands of chemical interactions between genes and the environment. Genes are only expressed in the appropriate environment. "DNA is both inherited and environmentally responsive" - Gene Robinson A chocolate cake doesn't owe more to the recipe use than the ingredients that went into it. Learning Requires Both Genes and Environment A classic example of dependence of learning on genes is provide by studies on imprinting - imprinting is when a newborn learns behavior like social interactions from parents. It is part of learning what is an appropriate behavior. Imprinting is when a young animal's social interactions (usually w/ parents), leads to the learning of things, like who is an appropriate sex partner. Hence, a group of greylag goslings, imprinted on Konrad Lorenz rather than a goose. As a result, they formed a learned attachment to Lorenz, and a preference for humans as mates. - the greylag goslings imprinted to Lorenz and the gosling had a preference for humans. Experience of following a particular individual early in life must alter regions of a goose's brain and nervous system responsible for sexual recognition and social behavior. - the gosling altered regions of their brain and nervous system for sexual recognition and social behavior. The effects of imprinting couldn't have happened w/o prepared brain, whose development (genetically controlled) enabled it to respond in special ways to info in its social environment. - the prepared brain is part of imprinting. The behavior is something that would not exist without the brain. Imprinting with Great/Blue Tits
Different species tend to exhibit different imprinting tendencies. - FOR EXAMPLE GREAT TITS AND BLUE TITS When researchers switched blue tit and great tit nestlings, some of the cross-fostered nestlings survived to court and form pair bonds with the opposite sex. - switched around the parents in nestlings. Of the surviving fostered great tits, 3 of 11 found mates. - when a blue tit fosters great tits. all of these were blue tit females that had been fostered by great tits. Of surviving fostered blue tits, all 17 found mates. - when a great tit fosters blue tits. 3 were the above females. (blue tit females). Though some individuals of both species imprinted on other species, the degree that they imprinted on their foster parents varied between the species. - the imprinting varied to their own foster parents. None of the cross fostered great tits mated with a member of their own species. - when the blue tits fostered the great tits. Most cross fostered blue tits did. - when great tits fostered the blue tits. The blue tit females w/ great tit partners had ECP with a blue tit male -all offspring were full blue tit. The hereditary basis for imprinting was different for both species. Food Stash Recall Birds can learn to recall where they hide their food. Black-capped chickadees are very good at this.
They can relocate large numbers of seeds or small insects hidden in bark cracks and moss patches in their habitat. These birds were studied by David Sherry. Sherry's experiment's used captive chicks kept in an aviary with small trees with holes drilled in them.
After chickadees had hid food in 4-5 of 72 possible storing sites, they were held in a cage for 24 hours. The holes were emptied and covered with velcro. When released, they spent more time inspecting those original holes than other holes. There were no visual/olfactory cues - had to be memory. In nature, these birds can find their caches after 28 days. Clark' Nutcrackers may have a more incredible memory.
They scatter up to 38,000 seeds in up to 5000 caches 25 km from the harvest site. They bury seeds in the ground in Autumn. Over the winter and spring, they recover up to 2/3 of what they originally hid. Balda mapped locations of caches of nutcrackers in an aviary, removed birds, and stored food, and swept the floor clean. Birds were returned in 1 week, and despite removal of cues, dug into nearly 80% of their ex-cache sites. Other experiments suggest 6-9 month retentions. - able to recall spots up to these months. Ability to store spatial info is related to the ability of certain brain mechanisms to change biochemically and structurally while responding to sensory stimuli associated with food storage. These changes require genes to construct the learning system and those that are responsive to key stimuli. Even learned behaviors, which are environment-dependent, are gene-dependent. Environmental Differences Can Cause Behavioral Differences Differences between individuals can arise as a result of developmental differences from either differences in environment of their genes. This was evident in WC Sparrow song acquisition. Paper wasps react calmly to other female workers reared on the same nest, but not to those from other nests that may try to join. This is in part bc of an odor acquired from the nest. - paper wasps react differently to other paper wasps from another nest bc the odor distinct to their nests. The ability to record odors or appearance of nest mates requires genetic information to construct a neurosensory system. - these paper wasps developed a neurosensory system which is made up of genetic information. An experiment with Beldings ground squirrels switched newborns of captive females, creating four types of individuals: Siblings reared apart Siblings reared together
Non-siblings reared apart Non-siblings reared together
After being weaned, juvenile squirrels were paired together in an arena and observed. Usually, those reared together tolerated each other, but those apart generally reacted aggressively. HOWEVER, biological sisters reared apart engaged in fewer aggressive interactions than non-sibs reared apart. Hence, they have some way of recognizing sibs, not dependent upon growing up with them.
This is sometimes called the "armpit effect", as there is a different way of learning that may involve learning what oneself smells like, as reference against other individuals. - reared apart siblings were less aggressive to each other bc of the armpit effect. It is bc their own smells are almost similar to each other. Compared to non-siblings when they are apart and put together; they fight. Jill Mateo examined the squirrels and found several scent-producing glands, and that they commonly sniffed oral glands of other individuals. She found that plastic cubes that had been rubbed on a close relative were sniffed less than distant relatives, which in turn were sniffed less than non-relatives. - the relatives were sniffed less and the nonrelatives were sniffed more. Two groups of black-cap warblers in Europe Those that winter in southern UK
Those that winter further south in Africa
If differences between these two groups are based upon genetic differences...
Offspring of "Winter in Britain" birds should differ in migratory behavior from those offspring whose parents winter elsewhere. Berthold et al captured some wild blackcaps, kept them indoors then later in outdoor aviaries where they bred. This gave him a crop of young birds that had never migrated.
Young birds showed signs of restlessness when Fall arrived, just like those that were about to migrate. Their flight orientation matched that expected of birds flying from different locations to come Britain. That is, they migrated the same way that their parents did. - captured blackcaps, expecting them to migrate down to Africa but matched with their parents. Another example comes from the garter snake, Thamnophis elegans.
Diets of garter snakes in dry inland western North America and west coast of coastal California differ markedly. Inland snakes eat fish and frogs.
Coastal snakes often eat banana slugs from the surrounding forests. If diet differences have a hereditary basis, snakes in these two populations should have genetic differences. - diet differences in hereditary basis. Arnold tested this by separating babies from each other and their mother.
He then offered them frozen slug bits a few days later.
Most of the young coastal snakes ate the slugs, but not so for inland snakes. - inland snake parents ate fish and frogs. except the parents of these inland snakes are not present. Slug-refusing offspring always avoided slugs. Arnold also looked at isolated newborn snakes, that never fed on anything. He presented them odors of different prey items on cotton swabs. He counted the number of tongue flicks. Snakes from both populations reacted the same to swabs dipped in tadpole juice.
But they reacted differently to swabs dipped in slug scent. Inland snakes ignored the slug odor. Hybrid of both populations showed mixed responses, as expected. - the coastal snakes reacted the same way to the tadpole juice as to the slug scent but the inland snakes did not like the slug ones.
Single Gene Effects on Development Remember the rover vs sitter Drosophila larvae? fruit flies. Rovers have at least one dominant allele, while sitters appear to have two copies of the new recessive allele. Crosses of the two five the expected mendelian ratios. Gene knockout experiments involved inactivating a single gene in an animal's genome.
That gene's impact on development can now be seen.
Scrambling the fosB gene in mice causes mothers to be indifferent to their pups, instead gathering them and keeping them warm. - the fosB gene in mice is related to care for their own babies. yet tested, scrambled the mother mice did not have interest in the babies. Removal of Oxt genes from male mice results in the lack of oxytocin - an important neurohormone. - removing the Oxt genes in male mice makes the males not able to recall which female they copulated with. Instead they stick with reintroduced females. These males cannot recall which females they have copulated with. He will spend more time inspecting females that are reintroduced to his cage - as if it's the first time. Evolution and Behavioral Development
Evolution impacts development.
Development mechanisms have an evolutionary history that might be described as a series of modifications of an ancestral pattern and its reconfiguration into a modern attribute. - development mechanisms are for modifications and its reconfigurations for modern changes. This is essentially the heart of "evolutionary development" research or "evo-devo". Most evo-devo research has focused on morphology, but this approach can also be used with behavioral development. - evo-devo focus on morphology and behavioral development. One big finding in evo-devo studies is the presence of "homeobox" (hox) genes. Hox genes are shared by a variety of organism, including humans and fruit flies. These are critical for the proper developmental organization of bodies. The base of Hox genes vary a bit from species to species, and they vary in how they influence development. However, the presence of this shared toolkit speaks to the evolutionary imprint on development. The for gene affects the behavior of Drosophila, and also occurs in honey bees. For encodes a protein that affects the operation of other genes, which impact the operation of the brain in both larva and adults. - For encodes a protein that affects the operation of certain genes. These genes are associated with the brain in larva and adults of Drosophila. Recall the sitters and rovers, and the link to differences in long/short term memory. In honey bees, a modified for gene has taken on a different but related function. It helps regulate the transition of young adult bees from sedentary to long distance foraging outside the colony. This transition is linked to increased expression of the gene in the brains of older workers. Vasopressin is neuropeptide that plays a role in mate-guarding behavior of prairie voles. All mammals carry this gene, relatively unchanged. - Vasopressin It's also seen in some invertebrates. - some carry vasopressin Despite the similarities, vasopressin is involved in many different developmental processes. Plays a role in social attachments in prairie voles, but affects the montane vole differently - which is never monogamous. The major conclusion of Evo-Devo may be that changes in base sequences of enzyme-coding genes are clearly important in the evolution of differences among species. However, changes in the mechanisms of regulating the expression of other genes may be even more important. One small change can have a cascade of effects down the line. So, rather than evolve new genes for new purposes, evolution may be teaching "old genes new tricks". Adaptive Developmental Homeostasis Developmental mechanisms can also be examined for their possible adaptive value. Organisms can often develop relatively normally, even when endowed genetic mutations that could be injurious. Often gene knockout experiments result in no perceptible changes. Could this ability to get along without (and compensate) be adaptive? Although some birds require the presence of their parents to develop normally, this isn't true for all species. Australian brush turkey eggs hatch out from deep within a compost pile. They dig their way out and walk away, without ever meeting a parent or sibling. Yet they manage to recognize their own species and interact normally. An experiment by Goth and Evans exposed newly hatched brush turkeys to feathered robots. The only thing needed to get a naive turkey to approach is a peck or two at the ground by the robot. These birds don't require extensive social experience to develop normal social behaviors towards each other. Several studies have employed genuinely weird rearing environments, but found that various forms of deprivation have little or no impact on the development of normal behavior. Beldings ground squirrels reared without their mother still respond to alarm calls of their species. Isolated male crickets sing normal songs.
Captive hand-reared female cowbirds will respond with a precopulatory pose when they hear a male cowbird song for the first time and are capable of normal sexual behavior. This phenomenon has been attributed to a process called "developmental homeostasis". It reduces the variation around a mean value for a phenotype, and reflects the ability of a developmental process to produce an adaptive phenotype very reliably. A classic example comes from an experiment by Margaret and Harry Harlow. Conducted 40 years ago, before animal rights were an issue. They looked at the development of social behavior in rhesus monkeys deprived of contact with others of their species.
In one set of experiments, young rhesus monkeys were separated from mothers shortly after birth. They were placed in cages with artificial surrogate mothers
E.g., wire cylinders or a terry cloth figure with a nursing bottle. The baby rhesus would gain weight and develop physically in a normal way. However, they soon spend their days crouched in a corner, rocking themselves and biting themselves. If confronted with a strange object or another monkey, they recoil in apparent terror. This demonstrated the need for social experience to develop normal social behavior. But what type and how much social experience is needed? Infants only reared with their mothers fail to develop truly normal sexual, play, and aggressive behaviors. To test the hypothesis that young rhesus need to interact with each other for normal social development, the Harlows isolated some infants from their mothers, but allowed them to interact with three other such infants for 15 minutes each day. At first, they only clung to each other, but later began to play. Ultimately, they developed nearly normal social behavior. In their natural habitat, they start to play at one month, and spend nearly all their time with the peers by six months. At such studies relevant to the human experience? Out intellectual development is often said to be dependent on early experience with parents and peers. Is this true? We cannot conduct comparable social isolation experiments on humans, but we can look at these things in historical contexts. A study was conducted of young Dutch men who were born or conceived during the Nazi transport embargo during the 1944-1945 winter. For most of the winter, the average caloric intake of city people was 750 calories per day.
Urban women produced babies of very low birth weights, yet rural women were better off and the babies had fairly normal birth weights.
Brain development was surprisingly unaffected by this malnutrition. Famine boys did not experience higher than normal mental retardation at age 19. They scored about the same on a standard Dutch intelligence test. Adaptive Developmental Switch Mechanisms
Selectionist approach to development brought out the adaptive value of developmental homeostasis. However, in many species, alternative phenotypes coexist that are due primarily to environmental differences between individuals. They are called "polyphenisms" "Polyphenisms" are challenging, as it is difficult to identify proximate environmental cues that activate development of the distinct phenotypes. For example: Solitary and gregarious forms occur in African migratory locusts. They develop into swarming gregarious forms when nymphs see/smell other locusts, and when they occur densely such that their hindlegs touch repeatedly. Mechanoreceptors on the hind legs signal the CNS, which triggers changes in target cells. This produces more serotonin, which signals the development from a green solitary locust to a black and yellow migratory form. What is this value of this flexibility? Migratory locusts can move to places with more food, and overwhelm non-migratory solitary ones with their swarms.
Adaptive Developmental Switch Mechanisms: Tiger Salamanders There are two tiger salamander phenotypes: ) typical immature aquatic form (eats small inverts, like aquatic insects). ) cannibal morph, which grows larger, with more powerful teeth (eats other tiger salamander larvae). Development of cannibals depends proximately on their social environment. i.e., cannibals develop only when many salamander larvae live together. They are more likely to occur when there is already a big differences in sizes. AND if the population members are mostly unrelated. What selective advantage is there for these two phenotypes?
Individuals with some developmental flexibility may be able to better exploit a resource niche, than with an inflexible system. These salamanders can exploit two sources of protein, potentially.
They don't know in advance that their situation is, so this gives them the ability to shift under the right circumstances. Selection seems to favor this flexibility - and a relatively rare number of large cannibals when the time is right. Adaptive Developmental Switch Mechanisms: Astatotilapia burtoni Males of this cichlid are either competitively superior OR socially inferior to others. They have the capacity to switch between these phenotypes. Males compete for a territory to attract females- winners hold sites until they are kicked out by stronger intruders. In this situation it pays to be either aggressively territorial (with bright colors) or nonaggressive (dull colors). Fish that are intermediate in behavior will fail to hold territories and not conserve energy, since they won't always opt of fighting. Fish respond to changes in social status with changes in gene activity within particular brain cells. If a male has the chance to secure a territory when its resident is removed, the gonadotrophin-releasing (GnRH1) cells in the brain ramp up activity of the egr-1 gene, which codes GNRH, a protein that regulates another gene. In males that are "socially ascendant", egr1 is expressed 2x as in subordinates or long-time territory holders. After a week, these males were not only larger and more aggressive, but had larger GNRH1 neurons and testes. These changes help an ascendant subordinate to take advantage of a situation and become reproductively active, while suppressing reproduction of neighboring males. Adaptive Developmental Switch Mechanisms: Red Back Spiders
Polyphenisms may be common, but aren't universal. This may be because many environmental conditions vary continuously, rather than discontinuously. Under continuous variation, it doesn't pay to develop something that works for a narrow range of circumstances. Selection instead may favor the ability to shift phenotype by degrees - making for a broad range of phenotypes - each one an adaptive response to variable factors. For example, the final size of a male redback spider varies in response to variation in available food and cues associated with virgin females (mates) and male redbacks (rivals). Males reared with virgin females develop more quickly and reach adulthood at smaller sizes than males reared with the same diet, with no odor cues from females. Males reared in the presence of other males are opposite - larger and more slowly maturing. Hence you have a wide range of male phenotypes caused by developmental plasticity. Adaptive Value of Learning
Let's now focus on development and learning. Animals that learn alter their behavior based on experiences. - altered behaviors are based on their own experiences in their life. Learning then can be a polyphenism - when two or more phenotypes are produced by the same genotype. It confers a highly focused flexibility in behavior that arises from developmental modifications in the nervous system. It does not produces change for the sake of change. There still should be a cost-benefit argument. For example, long-billed marsh wrens from the W US learn nearly 100 songs, while their counterparts from the east coast only learn 40. We might predict that the brains of males from the west coast should be larger, and data show that they have 25% larger mass for song control nuclei. If learning mechanisms are expensive, then we should expect learning to evolve only when there is some clear benefit. Example: Male thynine wasps derive a considerable benefit by learning to avoid sites where they have encountered sexually deceptive orchids. Once they have been fooled by particular flower, they generally learn to avoid the place where that flower occurs. But if these orchids are moved to a new location, they get fooled again and will have to learn over time.
The male wasps are able to store information about the locations of female-mimic orchids and learn to avoid the luring scents at those sites. The benefits of flexibility are clear - males can't be programmed to know beforehand where real females and mimic orchids are on a given day. So, they use experience to learn where the orchids are, while remaining responsive to novel sources of sex pheromone. They save time and energy, improving their chance of meeting an receptive female that has released sex pheromone. Such spatial learning is also seen in comparison of crow species that vary in their predisposition to store food - a task that tests vary in their predisposition to store food - a task that tests requires considerable spatial memory. Clark's nutcracker is a food-storing specialist, with a large pouch to transport seeds. Pinyon Jays have expandable esophagus. Scrub Jays and Mexican Jays lack these foods transfer structures, and hide less food than others. Individuals from these four species were tested on two different learning tasks to get rewards. One task had them remember the color of a circle on the screen and peck at the correct one (non-spatial task). The other task required them to remember the location of the circle on the screen (spatial task). Pinyon and Mexican Jays did much better than the other two for non-spatial learning. But in the spatial learning trials, the nutcracker was the best, followed by the Pinyon jay, Mexican jay, and scrub jay. These results show that birds have not evolved all-purpose learning abilities, but specific leaning skills to solve relevant problems. We might also expect that sex differences may evolve in learning skills. Pinyon Jays can find food up to 5 months after hiding it, but its's the males that more likely to get these caches, as they are the ones that bring food to the nest most of the time (females stay and provide care). As predicted, males have evolved better long term memory than females. Males made fewer errors than females when tested. Females' relatively poor performance suggests there is a substantial cost in the ability to learn - which requires special benefits if those traits were to evolve them. NOTES CONTINUED: The sex differences hypothesis has also been tested by Gaulin and Fitzgerald with spatial learning of three species of voles in the genus Microtus. Males of polygynous and wide-ranging meadow vole do better than females on maze-learning tests. There was little difference in males/females of the monogamous prairie vole they both share the same living space. In species where females have greater spatial challenges, we would expect them to have larger investments in the neural hardware for spatial learning. - more neural hardware for spatial learning compared to the males in a species. Brown-headed cowbirds are brood parasites - a female has to search broadly for nests to parasitize, and recall where potential victims have started nests to return several days later and her eggs to those already there. - the females need more spatial learning in this species bc they need to learn where they parasitize the nest. Males don't have such challenges. As expected, the hippocampus of females is much larger - this region thought to be important for spatial learning. Non-parasitic relatives of cowbirds have no such sex differences in the size of these regions. - no differences in the brain since they are not parasitic. Spatial learning is not the only thing affected by natural selection. Operant conditioning (trial and error learning) occurs when an animal associates a voluntary action with the consequences that follow. - it is used for learning where behavior or consequence is associated with a punishment or positive reward. The Skinner box is a classical psychology set up, where rats learn to press a bar to obtain a reward (food). Skinnerian psychologists once boasted than one could condition with equal ease almost any operant behavior. There are lots of operant conditioning examples - pigeons playing ping pong and blue jays using computers. However Garcia et al found that the ability to learn to avoid certain punishing food or liquids have limitations. - limitations of conditioning since a rat won't be able to hear a ring in the wild vs. when they hear a ring in lab where that ring is associated with their own behavior to it. The degree that rats associate the effects of irradiation with some stimulus depends on the intensity of the illness, the taste, the novelty of a substance and shortness between consumption and illness. - And rats can still associate events that are up to 7 hours apart. However, rats don't learn that a distinctive sound is a signal that always precedes and event associated with nausea. Nor can rats easily make associations between a particular taste and a shock punishment. Such failures are likely related to the fact that in nature, particular sounds are never associated with illness inducing meals any more than drinking certain fluids makes a rat's feet hurt. Understanding the natural environment of Norway rats gives us some perspective. They usually become very familiar with the area around their burrows, foraging in that are for a variety of foods. Since they cannot vomit, it pays to be cautious. Taking a small bite of new foods first. Avoiding ones with bad consequences from then on. If this is true, we might expect other dietary generalist mammals to behave much like the rats - they should quickly form taste aversions to bad-tasting, illness inducing items. - telling the difference of laced foods, bad tasting foods, testing foods etc. This seems to be the case for bats. Three species that feed on a range of foods behave in the predicted manner. They readily formed taste aversions when fed a meal laced with an unfamiliar flavor, before being injected with something that made them vomit. While dietary specialists should be unable to acquire taste aversions in this manner. Vampire bats are unable to associate an off-tasting substance with gastrointestinal distress. Hence, then changes associated with learned behavior are worth the cost only they confer a net benefit to individuals capable of modifying their behavior in a particular way.