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• Chapter 39 Behavioral Biology Behavior • What is Behavior? • Behavior Ecology – studies how behavior develops, evolves, and contributes to survival and reproductive success • Causation? – Proximate – Ultimate Figure 51.7 A kinesis and a taxis Dry open area Moist site under leaf (a) Kinesis increases the chance that a sow bug will encounter and stay in a moist environment. Direction of river current (b) Positive rheotaxis keeps trout facing into the current, the direction from which most food comes. Figure 51.9 Minnows responding to the presence of an alarm substance (pheromone) (a) Minnows are widely dispersed in an aquarium before an alarm substance is introduced. (b) Within seconds of the alarm substance being introduced, minnows aggregate near the bottom of the aquarium and reduce their movement. Ethology • Ethology – the scientific study of animal behavior • Tinbergen, Konrad Lorenz, Karl VonFrisch (mid 1900’s) – Four Questions: • What is the mechanistic basis of the behavior? (proximate) • How does development of the animal (zygote to mature) influence behavior? (proximate) • What is the evolutionary history of the behavior? (ultimate) • How does the behavior contribute to survival and reproduction (fitness)? (ultimate) • • • Fixed action pattern (FAP)- sequence of acts; unchangeable; carried to completion Sign stimulus- external sensory stimulus Ex: 3 spined sticklebacks (Tinbergen ‘73 Nobel) Sign stimuli in a classic fixed action pattern (a) A male three-spined stickleback fish shows its red underside. (b) The realistic model at the top, without a red underside, produces no aggressive response in a male three-spined stickleback fish. The other models, with red undersides, produce strong responses. Proximate and ultimate perspectives on aggressive behavior by male sticklebacks BEHAVIOR: A male stickleback fish attacks other male sticklebacks that invade its nesting territory. PROXIMATE CAUSE: The red belly of the intruding male acts as a sign stimulus that releases aggression in a male stickleback. ULTIMATE CAUSE: By chasing away other male sticklebacks, a male decreases the chance that eggs laid in his nesting territory will be fertilized by another male. Learning? • Maturation is the situation in which a behavior may improve because of ongoing developmental changes in neuromuscular systems, for example, flight in birds. • As a bird continues to develop its muscles and nervous system, it is able to fly. • It is not true learning. • Habituation- loss of responsiveness to stimuli that convey no information; simple learning • Imprinting- limited learning within a specific time period •critical period (Lorenz, ‘73 Nobel) • Associative learning (learn to associate one stimulus with another): •classical conditioning- (arbitrary stimulus) Pavlov’s dogs •operant conditioning (trial and error)- “Skinner’s box” Proximate and ultimate perspectives on imprinting in graylag geese BEHAVIOR: Young geese follow and imprint on their mother. PROXIMATE CAUSE: During an early, critical developmental stage, the young geese observe their mother moving away from them and calling. ULTIMATE CAUSE: On average, geese that follow and imprint on their mother receive more care and learn necessary skills, and thus have a greater chance of surviving than those that do not follow their mother. •Spacial Learning •Landmarks •Niko Tinbergen Digger Wasps 1932 Fig. 51.2 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Does a digger wasp use landmarks to find her nest? EXPERIMENT A female digger wasp excavates and cares for four or five separate underground nests, flying to each nest daily with food for the single larva in the nest. To test his hypothesis that the wasp uses visual landmarks to locate the nests, Niko Tinbergen marked one nest with a ring of pinecones. Nest After the mother visited the nest and flew away, Tinbergen moved the pinecones a few feet to one side of the nest. RESULTS When the wasp returned, she flew to the center of the pinecone circle instead of to the nearby nest. Repeating the experiment with many wasps, Tinbergen obtained the same results. Nest CONCLUSION No Nest The experiment supported the hypothesis that digger wasps use landmarks to keep track of their nests. • Songbird repertoires provide us with examples. – Why has natural selection favored a multi-song behavior? Fig. 51.5 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • It may be advantageous for males attracting females. Fig. 51.6 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings OPTIMAL FORAGING • Cost-benefit (ROI) analysis of foraging behavior. – Foraging is food-obtaining behavior. • The optimal foraging theory states that natural selection will benefit animals that maximize their energy intake-to-expenditure ratio. • Whelk (mollusk)-eating behavior in crows (Reto Zach) Height of Drop (m) Average Number Of Drops Required to Break Shell Total Flight Height (Number of Drops Height per Drop) 2 3 5 7 55 13 6 5 110 39 30 35 15 4 60 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 51.7 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • • • • • • • • • THE EVOLUTIONARY LOGIC OF BEHAVIORAL ECOLOGY Fitness is a central concept in animal behavior. Since natural selection works on genetic variation caused by mutation and recombination, organisms should have features that maximize fitness over time. Animals are expected to engage in optimal behaviors: Optimal behavior = A behavior that maximizes individual fitness. Optimal behavior is a valid concept if behavior is genetically influenced and subject to natural selection. An experiment was carried out that demonstrated that genes influence behavior. Experiment Two species of lovebirds were interbred. Female Fischer's lovebirds cut long strips of nesting material, which are carried individually to the nest. Female Peach-faced lovebirds cut short strips and carry several at a time by tucking them into her back feathers. Results Hybrid females cut intermediate length strips and tried, but failed, to transport them by tucking into back feathers. They learned to carry strips in their beaks, but never gave up all tucking behavior. Conclusions Phenotypic differences in the behavior of the two species are based on different genotypes. Innate behavior can be modified by experience. Learned behaviors are typically based upon gene created neural systems that are receptive to learning. Fig. 51.1 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Social behavior • Sociobiology- evolutionary theory applied to social behavior (Hamilton) • Agonistic behavior- contest behavior determining access to resources • Dominance hierarchy- linear “pecking order” • Territoriality- an area an individual defends excluding others • Mating systems: •promiscuous- no strong pair bonds •monogamous- one male/one female •polygamous- one with many •polygyny- one male/many females •polyandry- one female/many males Social Interactions Animal Signals and Communication Signal: Behavior that causes a change in behavior of another animal Communication: Transmission of, reception of, and response to signals - Pheromones – chemical signals (communicate by odor) Honeybees – pheromones produced by a hive’s queen and her daughters, workers, maintain social order in the colony. - Movement – Honeybee Waggle Dance (VonFrisch) Altruistic behavior • Inclusive fitness- total effect an individual has on proliferating its genes by its own offspring and aid to close relatives • Kin selection- aiding related individuals altruistically • Hamilton’s Rule – Coefficient of relatednessproportion of genes that are identical because of common ancestors • Reciprocal altruism- exchange of aid; humans? Hamilton’s Rule – Kin Selection KIN SELECTION & ALTRUISM Kin Selection: selection of a trait through helping relatives, either 1. descendant kin (offspring): direct selection - or - 2. non-descendant relatives: indirect selection inclusive fitness = direct + indirect nepotism = helping relatives other than offspring (descendant kin) Fitness Accounting A female Belding ground squirrel is dying. During her life she has successfully raised a total of 10 of her own offspring. She has helped her parents rear 8 offspring, 2 of which would not have survived without her help. Her altruistic acts (e.g., alarm calls) have resulted in her having the equivalent of 3 more offspring. In terms of numbers of offspring, what is her Direct fitness? 10 Indirect fitness? 2 + 3 = 5 Inclusive fitness? 10 + 5 = 15 Three factors are important in the spread and maintenance of an altruism gene by kin selection: 1. benefit to recipient, B 2. cost to altruist, C 3. degree of relatedness between altruist and recipient, r Coefficient of Relatedness “r” = 1. probability that a rare gene is shared by two individuals, OR 2. the proportion of genes shared by two individuals Taken From: Hamilton's Theory, by: B Brembs, 2001 Academic Press Hamilton’s Rule states the conditions under which altruism will spread. In its simplest form it is: rB > C “The Story of The Surfing Brothers” Two brothers (close in age, not fathers yet, reproductively fertile) decide to go surfing. As they are surfing, one brother (the beneficiary) is dragged under the current and is in danger of drowning. The other brother (the altruist) decides to attempt to save his brother, thus risking his own life. This decision, on its face, seems very natural and devoid of conscious thought. However, we need to find out if there are ultimate (evolutionary, even “selfish”) causes for the altruist’s decision. Let’s quantify this decision using Hamilton’s Rule! rB > C r = .5 (sibling = .5 co-efficient of relatedness B = 2 (amt. of projected offspring for beneficiary) C = 2 x .05 (amt. of proj.offspring for altruist x RISK) (the risk of the altruist dying while trying to save the brother is .05) Thus: rB = .5 x 2 = 1 C = 2 x .05 = .1 or rB > C = 1 > .1 Thus, Hamilton’s Rule would dictate that this action would be profitable in a genetic or evolutionary sense! Other Cases • Uncle saving Nephew: .25 x 2 = .5 > .1 – Profitable! • 1st Cousin saving 1st Cousin: .125 x 2 = .25 > .1 – Profitable! Kin Selection Weakens with Hereditary Distance! Other Considerations – Haplodiploidy Relationships • Haplodiploidy. The Hymenoptera (bees, ants and wasps) provide the perfect window into sociobiology as explained by Hamilton's rule. They are haplodiploid; males are produced from unfertilized eggs, having only half the normal genetic number as the females. The result of this is that sisters, who usually have the same father and all of his genes, are related by 3/4. To their mother and to their offspring they are related by only 1/2. Therefore, Hamilton's rule essentially predicts that sisters should be prone to sacrificing for each other. In a family situation (a hymenopteran colony for example) this amounts to sisters cooperating in raising more of their own generation and in risking their lives to defend the colony, which is made up mostly of sisters. • Problems with the genetic explanation. In most eusocial colonies, the primary reproductive ("queens") mates more than once, reducing the degree of relatedness between her daughters. Therefore, the effects of haplodiploidy in kin selection are reduced. Also, the termites, the only completely eusocial order, are not haplodiploid at all. A Final Word This situation is purely fictitious and not meant to suggest that a human being would actually calculate the benefit of saving another human being. This example deals with deeply engrained ultimate causes of behavior, meant to preserve a species, which have been passed on genetically over time (evolution) . Hamilton’s Rule quantifies a rationale for passing on a gene for altruistic behavior.