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Genetic and Environmental Effects on Behavior 1. Types of selection on behavior. 2. How do genes affect behavior? 3. How does the environment affect behavior? 4. How is the development of behavior affected by the environment? 5. Are the effects adaptive? Artificial Selection on Nesting Behavior in Mice Data from Carol Lynch, 1980 Lesson’s from Lynch’s experiment 1. Nesting behavior responded to selection in the lab. Predicted to respond to natural selection in the wild. 2. Response to selection may decrease over time. a. Additive genetic variation gets used up. Selection has less to work with. b. Could be tradeoffs of selection. Need a minimum amount of nesting material for offspring survival. 3. Average estimated heritability of high lines = .15 of low lines = .23 Testing Natural Selection 1. Observe variation in/among populations 2. Can it be acted upon by natural selection? Test if the trait is heritable. 3. Can the trait respond to selection? Test: Do an artificial selection experiment. 4. What are the selective forces in nature? Test: observe who survives and reproduces. Determine the mode of selection. Directional Selection 1. Favors individuals at one end of a distribution of variation. 2. Changes the average value of the trait in the population. 3. Example: Directional selection for lots of nesting occurred in the high line of mice in Lynch’s experiment. Directional Selection Example: Selection in Darwin’s finches during drought conditions. Stabilizing Selection 1. Favors individuals with intermediate values of a trait. 2. Does not alter the average value of the trait in the population. 3. Reduces variation at the tails of the distribution. Stabilizing Selection Example: Clutch size of the collared flycatcher a. Gustaffson and Sutherland (1988) b. Manipulated clutch size: added and subtracted eggs. Best clutch size was no manipulation! Disruptive Selection 1. Favors individuals at both extremes of a trait’s distribution. 2. Does not alter the average value of the trait in the population. 3. Reduces variation at the middle of the distribution. Disruptive Selection Example: Black-bellied seed cracker (Smith, 1993) a. Birds have distinct beak sizes: large and small b. They specialize on different sized seeds. Frequency-Dependent Selection 1. When the relative fitnesses of genotypes are not constant but vary with their frequencies in the population. 2. It can be a type of balancing selection that maintains variation in the population. 3. Example: Handedness in scale-eating fish Perissodus microlepis (From Hori (1993) Science) Frequency-dependent selection Example: Handedness in scale-eating fish Perissodus microlepis From Hori (1993) Science Correlational Selection 1. When two traits interactively affect fitness. Some combinations work together well, some do not. 2. Example: Escape behavior in Garter Snakes (Brodie, 1992) Color traits: Striped, Blotched Escape behavior: Reverse, Don’t reverse Correlational Selection Spotted, reverse Striped, don’t reverse Correlational Selection 3. Combo of Striped, Don’t reverse is fit 4. Combo of Blotched, Reverse is fit 5. Other combos are not fit. 6. Correlation is disrupted because of random mating. 7. Preferential mating could link behavior and phenotype. Genetic and Environmental Effects on Behavior 1. Types of selection on behavior. 2. How do genes affect behavior? 3. How does the environment affect behavior? 4. How is the development of behavior affected by the environment? 5. Are the effects adaptive? Genes and behavior 1. For behaviors to evolve differences must be heritable (instead of completely learned). 2. While genes may influence many behaviors, genes alone do not produce behavior (nature vs. nurture) 3. Rarely does one gene alone code for a behavioral trait. But differences in behavior between two individuals may be due to difference in one gene. • Dawkins’s cake analogy 17 Genes and behavior 1. Molecular pathways linking genes and behavior often complex. 2. Genes influence behavior through effects on brain development and physiology but behavior can also influence gene expression • Egr1 expression increases in the forebrain of songbirds after they hear the song of another male 3. Even if genes influence a behavior, doesn’t mean genes alone produce the behavior • Genotype x environment interactions • Learning component 18 Genes and behavior-single gene effects • Fruit fly (Drosophila melanogaster) feed either by ‘roving’ or ‘sitting’ • Foraging strategy differences caused by different alleles for foraging (for) gene • gene codes for enzyme cyclic guanosine monophosphate (cGMP) dependent protein kinase (PKG), which is produced in brain • Rover allele (forR) has higher PKG activity than flies homozygous for forS • Flies with forR allele have better short-term memory for olfactory cues while flies with forS perform better at long-term memory tasks using olfactory cues • Differences may be adapted to differences in foraging behavior 19 Genes and behavior-single gene effects 1. In one orchard there were 70% rovers and 30% sitters. What maintains the two different alleles? 2. Rovers do best under patchy food and high larval densities while sitters do best when food is uniformly distributed and at low larval densities • Different ecological conditions can maintain polymorphisms 3. When food is scarce competition is most intense between individuals of the same morph • Rarer type has an advantage (negative-frequency dependent selection) 20 Genes and behavior-single gene effects • Same gene regulates age changes in foraging worker honeybees (Apis mellifera) • When young, adult worker bees perform tasks inside the hive. When about 3 weeks old, expression of the for gene changes and production of PKG increases. Bees begin to forage outside the hive. • When older workers removed, younger bees begin upregulating for sooner. Also, experimental elevation of PKG in workers leads to a switch in foraging behavior. • In Drosophila, different foraging behaviors are caused by differences of the for gene. • In honeybees, differences in for gene expression within an individual are responsible for switch in behavior. 21 Genes and behavior-single gene effects 1. MC1R gene encodes a receptor expressed in melanocytes, which produce melanin. 2. Point mutations associated with color variation in fish, reptiles, birds and mammals. 3. Lesser snow geese (Anser chen caerulescens) have two color morphs-white (homozygous for one variant of MC1R) and blue (either heterozygous or homozygous for other variant of MC1R). • No known selective advantage of being white or blue • Color influences choice of mate; goslings imprint on parents’ color and choose mates of the same color 4. Rock pocket mice (Chaetodipus intermedius) are either dark or tan colored. • Dark mice live on black lava flows and tan mice live in sandy, desert habitat • Selective predation by owls against conspicuous mice 22 Genes and behavior: multiple gene effects Burrow building in Peromyscus mice is determined by multiple genes doi:10.1038/nature11816 Genes and behavior-multiple gene effects Tunnel Length Sp 1 Sp 2 Escape Tunnel Sp 1 Sp 2 doi:10.1038/nature11816 Genes and behavior-multiple gene effects doi:10.1038/nature11816 Found 3 genetic regions for tunnel length and one for making an escape tunnel. Changes in behavioral genes in the wild 1. Migratory behavior in birds is correlated with “migratory restlessness” of birds in cages. a. Duration of restlessness correlates with migration distance. b. Direction of fluttering correlates with migration direction. 2. Blackcaps (Sylvia atricapilla) from Canary Islands do not migrate while those from Germany do. 3. When birds from populations cross-bred offspring show intermediate migratory restlessness, indicating genetic control 26 Changes in behavioral genes in the wild 1. In France, 75% of blackcaps show migratory restlessness and 25% do not. 2. Selective breeding or migratory or non-migratory individuals produced lines that were either 100% migratory or 100% resident. 3. Selective breeding of migratory individuals could also affect migratory behavior (Figures below). 27 Changes in behavioral genes in the wild 1. Number of blackcaps wintering in Britain and Ireland (1500 km north of traditional wintering grounds) has increased 2. These are not British birds, but birds that originate from central Europe, that have changed their migration behavior. 3. Offspring of birds that use new migration route also overwinter in Britain (panel d). 4. Why the change? a. New migration route probably due to milder winters and more winter food in Britain b. New migrants have shorter route and arrive back at breeding grounds earlier. c. Obtain the best breeding territories and produce more offspring by arriving earlier. Genetic and Environmental Effects on Behavior 1. How do genes affect behavior? 2. How does the environment affect behavior? 3. How is the development of behavior affected by the environment? 4. Are the effects adaptive? Phenotypic Plasticity 1. Phenotypic plasticity: the ability of a genotype to produce different phenotypes in different environments. 2. There is a range in plasticity. a. Canalized: Traits do not vary much in different environments. b. Plastic: The trait can vary greatly in different environments. 3. Plasticity measured by exposing particular genotypes to different environments and observing if there are different phenotypes. Innate Behaviors (Instinct) 1. NO learning involved with innate behaviors 2. Environmental cue required, but there is no change in the behavioral phenotype (canalized). 3. Two ways to recognize: a. Performed perfectly the first time that the appropriate stimulus is encountered. b. Performed to completion even if the stimulus is removed. Innate Behaviors (Instinct) Three components 1. Sign stimulus – stimulus that releases innate behavior. A particularly relevant stimulus that is innately recognized 2. Innate releasing mechanism – neural path involved in responding to the stimulus (very vague, not well understood) 3. Fixed action pattern – pre-programmed behavior or set of behaviors in response to the stimulus (the behavioral outcome) Examples of Innate Behaviors 1. Gull Begging Behavior (Tinbergen). a. Red dot on gulls bill = Sign stimulus b. Chick’s nervous system = Innate releasing mechanism. c. Begging behavior (peck the red dot to get food) = Fixed action pattern Tests a. b. c. d. Cardboard cutout of gull head with red dot = 100% response Cutout with just bill and red dot = 92% Full head, no red dot = 35% Red pencil with white stripes = 126% response Examples of Innate Behaviors (Instinct) 2. Egg retrieval behavior in geese (Tinbergen and Lorenz) a. Remove egg from nest, put .5 meters away, goose stretches neck, tucks egg under bill, rolls egg back into nest. b. Replace egg with egg sized object, goose does egg retrieval response. c. Remove object as it is being retrieved, goose continues pulling its head back as if it had an egg. Yawning as a releaser Phenotypic Plasticity 1. Phenotypic plasticity: the ability of a genotype to produce different phenotypes in different environments. 2. There is a range in plasticity. a. Canalized: Traits do not vary much in different environments. b. Plastic: The trait can vary greatly in different environments. 3. Plasticity measured by exposing particular genotypes to different environments and observing if there are different phenotypes. The Development of Worker Behavior in Honey Bees Colony consists of three types of bees: Queen (2N), Workers (sterile females, 2N), Males (N). 2. Worker bees divide up labor in the colony. a. Cleaning nursery cells b. Feeding juveniles c. Cache and distribute honey to workers d. Foragers e. Scout (new sources of food) 3. Workers go through all 5 tasks sequentially. Hormonal Causes of Worker Behavior 1. Age related transitions are regulated, in part, by juvenile hormone (JH). 2. Young workers have low concentrations of JH, older foragers have higher concentrations. 3. Young bees treated with JH become precocious foragers. 4. Foraging behavior is delayed if the glands that produce JH are removed from a worker. Social Causes of Worker Behavior 1. Is worker behavior only determined by age? Experiment: Colonies made with workers of all the same age. Result: There is still division of labor. Some become foragers sooner, some stay nurses longer. 2. Do social encounters influence transitions in worker behavior? Experiment: Added older foragers to colonies of only young workers. Result: As more older bees are added, fewer young workers undergo an early transformation. 3. Conclusion: Worker behavior is plastic. It changes depending on the social environment Genetic and Environmental Effects on Behavior 1. How do genes affect behavior? 2. How does the environment affect behavior? 3. How is the development of behavior affected by the environment? 4. Are the effects adaptive? Developmental Plasticity 1. Developmental phenotypic plasticity – permanent changes to morphology and/or physiology • Polyphenism: a single genome produces two or more alternative phenotypes in response to an environmental cue. Alternative forms are markedly distinct. • Polymorphism: genetic variation results in different forms. Examples of Polyphenism Foraging behavior and development interact Genetic and Environmental Effects on Behavior 1. How do genes affect behavior? 2. How does the environment affect behavior? 3. How is the development of behavior affected by the environment? 4. Are the effects adaptive? Cannibalism in Tiger Salamanders Two forms of Tiger Salamanders 1. Small form eats pond invertebrates. 2. Large form feeds on other tiger salamander larvae. 3. Cannibals only develop when many salamanders live together. Presence of Kin affects Cannibal Development from Pfennig and Collins, 1993 Composition of population Cannibals Develop No Cannibals Experiments Develop Siblings only 31 (40%) 46 (60%) 77 Non-siblings present 67 (84%) 12 (16%) 79 Presence of kin reduces change of cannibals developing. This is adaptive. Natural selection favors those that do not eat their relatives.