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Chapter 51

BIOLOGY 1M03 Chapter 51: Biology Chapter 51

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McMaster University
Ben Evans

Chapter 51: Behaviour  Proximate causation explains how actions occur in terms of neurological, hormonal and skeletal-muscular mechanisms involved  Ultimate causation explains why actions occur, based on their evolutionary consequences and history Types of Behaviour: An Overview  Learning is defined as a change in behaviour that results from a specific experience in the life on an individual  Innate Behaviour o Highly inflexible behaviour patterns are called fixed action patterns (FAPs) o FAPs are stereotyped, meaning that they are performed in the same way every time and are usually triggered by a simple stimuli called releasers or sign stimuli o Ex. When a person hears a scream ▪ A simple sign stimulus releases a FAP, a rapid, jumping movement backward, away from the direction of the stimulus o FAPs may result in survival o FAPs are examples of innate behaviour, behaviour that is inherited and shows little variation based on learning or the individual’s condition o It is common to observe innate behaviour in response to ▪ Situations that have a high impact on fitness and demand a reflex-like, unlearned response ▪ Situations where learning is not possible  Conditional Strategies and Decision Making o Although all species studied to date show some degree of innate behaviour, it is much more common for an individual’s behaviour to change in response to learning and to show flexibility in response to changing environmental conditions o Animals take in information from the environment and based on that information, make decisions about what to do o Animals appear to take in information about their environments and weigh the costs and benefits of responding o Costs and benefits are measured in terms of their impact on fitness, the ability to produce offspring o What Decisions do White-Fronted Bee-Eaters Make when Foraging ▪ Given a choice, what should an animal eat ▪ Biologists answer this question by assuming that individuals should forage in a way that maximizes the amount of usable energy they take in, given the costs of finding and ingesting their food and the risk of being eaten while they’re at it ▪ This claim, that animals should maximize their feeding efficiency, is called optimal foraging ▪ Researchers began studying feeding behaviours in a bird called the white- fronted bee-eater ▪ Mated pairs of this species dig tunnels in riverbanks and raise their young inside ▪ Appropriate riverbanks are rare, so many pairs build tunnels in the same location, forming a colony ▪ To feed their young, pairs have to fly away from the colony, capture insects and bring the prey back to the nest ▪ Each pair defend a specific area where only they find food ▪ The key observation is that some individuals forage a few metres from the colony, while others have to look for food hundreds of metres away ▪ It takes only a few seconds to make a round trip to the closest feeding territories, versus several minutes to the farthest territories ▪ Thus, the fitness cost of each feeding trip varies widely among individuals ▪ If optimal foraging occurs, how do individuals maximize their benefits, given the cost that they have to pay in time and energy ▪ Individuals that have to find food far from the colony stay away longer on each trip ▪ Individuals foraging far from the colony bring back a much larger mass of insects on each trip, on average, than do individuals that fly a short distance each time ▪ White-fronted bee-eaters appear to make decisions that maximize the energy they deliver to their offspring, given their costs of finding food ▪ This behaviour is highly flexible and condition dependent o Why do some Bluehead Wrasses Undergo a Sex Change ▪ Male defend territories that contain nesting sites and feeding areas ▪ A group of females lives inside the boundaries of the territory ▪ When these females lay eggs, the male fertilizes the eggs ▪ Thus, a single male monopolizes all the matings in that territory ▪ This male is the largest individual in the group because the male guards the territory and because fights are usually won by the biggest contestant ▪ When the territory-holding male dies, the largest female in the group changes sex ▪ Her reproductive organs change from egg production to sperm production and her colouration changes ▪ She becomes the dominant male and begins fertilizing all of the eggs laid in the territory ▪ An idea called the size-advantage hypothesis states that if a group of fish is living in a territory dominated by a single male and if that male dies, then the largest female should switch from female to male ▪ The hypothesis is based on the observation that fish have indeterminate growth, meaning they continue to grow throughout their lives ▪ The logic behind the hypothesis is that suppose a small fish can lay 10 eggs a year, but a large female of the same species can lay 20 eggs a year ▪ If six small females and two large females live in a harem, the male that owns the territory fertilizes 100 eggs a year ▪ If the male dies, the largest female can increase the number of offspring she produces each year from 20 to 80 by changing sex and taking over the role of the dominant male ▪ The switch is costly in terms of time and energy, but the benefit is large ▪ There is no fitness advantage for smaller females to switch sex because they would be defeated in fights and have 0 offspring per year instead of 10 ▪ Sex change is flexible and condition dependant ▪ If conditions don’t change, females remain female ▪ If conditions change, the same individual will stay female if she is small, but become a male if she is large o In many cases, animals have alleles that make a wide range of behaviours possible o What an individual actually does is based on decisions that change, depending on the conditions Learning  Learning occurs when behaviour changes in response to specific life experiences  Particularly important in species that have large brains and a lifestyle dominated by complex social interactions  In species such as these, FAPs and other types of inflexible, stereotyped behaviours are relatively rare  Simple Types of Learning: Classical Conditioning and Imprinting o In classical conditioning, individuals are trained by experience to give the same response to more than one stimulus, even a stimulus that has nothing to do with the normal response o Another type of simple learning takes place in newly hatched ducks, geese and other species of birds ▪ Upon hatching, ducklings and goslings adopt as their mother the first moving thing they see ▪ This type of learning is called imprinting o Konrad Lorenz incubated eggs artificially ▪ Young greylag geese would imprint on whatever boots he was wearing at the time ▪ Mallard ducklings would imprint on him only if he crawled on all fours and quacked continuously o Why does imprinting occur ▪ At the ultimate level of causation, the leading hypothesis is that offspring must quickly learn to recognize and respond to their mother in order to survive ▪ Lorenz was also able to establish that imprinting occurs only in early life of the animal, during a short interval called the critical period or sensitive period ▪ His research showed that imprinting lasts for life and may establish not only the identity of the offspring’s mother, but also its species identity o The key characteristics of imprinting, that it is fast and irreversible and occurs during a critical period, are not typical of most types of learning  More Complex Types of Learning: Birdsong o Results of experiments show that, depending on the species, song-learning behaviour falls at various locations on the learning continuum o Ex. If young chickens, birds that have simple vocalizations, are raised in isolation from other members of their species and never hear their species-specific call, they still produce the correct vocalizations as adults ▪ Song learning behaviour is innate in these species and may be highly stereotyped o In contrast, white-crowned sparrows that are raised in isolation do not sing a normal song unless they hear a tape recording of their species-specific song during the early months of life o In this species, which sings a complex song, singing is learned during a critical period o Yet, if researchers play the song of a song sparrow or other closely related species during the critical period for language acquisition, white-crowned sparrow chicks do not learn it o Instead, they learn an abnormal song differing from that of their own species and from that of the alien introduced species o In this species, the ability to learn songs is restricted to songs of their own species o The critical period for song learning in white-crowned sparrows is augmented by practice that occurs when the individual is older o White-crowned sparrows don’t begin to sing until they are almost one year old o Beginning singers produce a disorganized warbling called sub-song o With practice, sub-song becomes more and more organized and progressively closer to adult song o Eventually, an adult song develops and remains unchanged for the rest of the individual’s life o For this improvement to occur, however, the individual must hear itself sing o Individuals that are prevented from hearing their own practice never sing a normal song o Yet if the same individual is deafened after it has developed adult song, it continues to sing a perfectly normal song o These results suggest that individuals have two critical periods for song learning during their lives, one as a nestling, when they must hear the song of their own species and a second as a one-year-old, when they must hear themselves practice  Can Animals Think o Cognition is defined as recognition and manipulation of facts about the world, combined with the ability to form concepts and gain insight o Unlike the results of classical conditioning, imprinting and song learning, the results of cognition cannot be observed directly o Recent experiment on tool use by New Caledonian crows ▪ Straight or curved stick are broken off and cleaned before us ▪ Several other bird species, including Galapagos finches, are known to modify sticks or plant stems to “fish” for insects ▪ Recent experiments have shown that when these crows are presented with an array of straight sticks along with a piece of food in a clear plastic tube, the crows select a stick whose width or length is appropriate for the tube’s width and the food’s distance is from the end of the tube • The crow then inserts the stick into the tube to fish out the food ▪ Hooks are made by breaking complex leaves into pieces ▪ Spearing tools are constructed from a complex series of cuts and rips, made with the beak, along the edge of leaves from pandanus plants o These observations support the hypothesis that crows can think ▪ Recognize that if they choose or manipulate tools in a certain way, they can use the resulting structure to get food ▪ The idea is that natural selection has favoured the evolution of cognition in this species because crows with the ability to manufacture and manipulate tools have higher fitness than do crows that lack the ability  What is Adaptive Significance of Learning o Biologists view learning as an adaptation that allows individuals to change their behaviour in response to a changing and unpredictable environment o Under this hypothesis, the ability to learn varies among species because some species live in environments that are much more unpredictable than others o The type of learning that occurs in a given species is correlated with the type of environmental unpredictability it encounters o Ex. Norway rats ▪ Extremely adept at learning to navigate mazes and learning to avoid foods that contain poisons ▪ These animals live in sewers, the walls of homes or other locations where ability to travel routes is essential for survival ▪ In nature they feed on a wide variety of fruits, seeds and insects ▪ The availability of these foods changes with the season and many potential food items are actually toxic ▪ Rats will taste only small quantities of novel foods and they quickly learn to avoid any foods that cause illness o Ex. Scrub Jays ▪ Not particularly adept at negotiating mazes or learning to avoid foods ▪ Instead are proficient at remembering where they have cached seeds ▪ In this species, spatial learning and good memory are essential for survival ▪ Also learn how to prevent theft ▪ This species lives in social groups and it is not unusual for some members of the group to steal food that was cached by other jays in the group How Animals Act: Hormonal and Neural Control  Sexual Activity in Anolis Lizards o After spending the winter under a log or rock, males emerge in January and establish breeding territories o Females become active a month later and the breeding season begins in April o By May, females are laying an egg every 10-14 days o By the time the breeding season is complete three months later, the eggs produced by a female will total twice her body mass o The cause of these dramatic seasonal changes in behaviour is sex hormones, testosterone in males and estradiol in females o Testosterone injections induce sexual behaviours even in castrated males o Estradiol injections induce sexual activity in females whose ovaries have been removed o What environmental cues trigger the production of sex hormones in early spring and how do male and female Anolis synchronize their sexual behaviour so that they are ready to produce gametes at the same time o To answer these questions, a biologist brought a large group of sexually inactive lizards into the lab during the winter and divided them into five treatment groups o The physical environment was exactly the same in all treatments o Each individual received identical food and in all treatments, high “daytime” temperatures were followed by slightly lower “night time” settings o The biologist also continued to monitor the condition of lizards that remained in natural habitats nearby o To test the hypothesis that changes in day length signal the arrival of spring and trigger initial changes in sex hormones, the biologist exposed the five treatment groups in the lab to artificial lighting that stimulated the long days and short nights of spring o To test the hypothesis that social interactions among individuals are responsible for synchronizing sexual behaviour, the social setting was varied among treatment groups ▪ Single isolated females/groups of females only/pairs of lizards (single females each with single male)/single females each with a group of castrated males/single females, each with a group of uncastrated males o Each week, the researcher examined the ovaries of females in each group o He also monitored the ovaries of females in nearby natural habitats, since those females were not exposed to spring-like conditions o Results show that females not exposed to spring-like conditions began producing eggs, but females in the field that were not exposed to the conditions did not o In addition, females that were exposed to breeding males began producing eggs much earlier than did the females placed in other treatment groups o These results support the hypothesis that two types of stimulation are necessary to produce the hormonal changes that lead to sexual behaviour o Females need to experience spring-like light and temperature and exposure to breeding males o Another experiment showed that the visual stimulation of the male dewlap triggers changes in estradiol production Communication  Communication is defined as any process in which a signal from one individual modifies the behaviour of a recipient individual  A signal is any information-containing behaviour  Communication is a crucial component of animal behaviour because it creates stimulus that elicits a r
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