Animal Behavior Study Notes 1

Why Study Animal Behavior?

• Understanding our own behavior through comparative analysis.
• Formulating models to predict behavior for management and conservation purposes.
• Gaining insight into relationships between species (evolutionary perspective).
• Gaining insight into species-environment interactions (ecological perspective). Animal behavior helps us understand how animals adapt to their environment and how different species interact with each other.
• Because it's inherently interesting.

Methods to Study Behavior

• Requires patience, especially for rare events. Some behaviors might only occur at specific times or under particular conditions.
• Observation may influence the behavior being studied. The presence of an observer can alter the natural behavior of animals.
• Animals may be cryptic, rare, hard to find, or in difficult habitats; technology can help. Using tools like camera traps, drones, and tracking devices helps in studying elusive or inaccessible animals.

I. Observation

• Need to get to know your focal animal. This involves understanding the animal's natural history, social structure, and typical behaviors.
  *Example: Mountain Gorillas

  • George Schaller spent a year watching them and found play was rare because they were shy. His initial observations were limited due to the gorillas' wariness.
  • Dian Fossey habituated gorillas to her over many years by imitating them and not disturbing them, allowing her to observe much more play. Her long-term habituation techniques allowed for detailed behavioral studies that would not have been possible otherwise.

Forms of Observation:

• Ethogram: A simple, comprehensive description of all behaviors of a species. It's a catalog of all the behaviors an animal exhibits, used to quantify and study behavior systematically. Creating an ethogram is often the first step in a detailed behavioral study.
• Scan sampling: Observing and recording the behavior of multiple individuals at set intervals. This is useful for understanding group dynamics and activity budgets.
• Focal animal sampling: Focusing on a single individual and recording all its behaviors over a period of time. This method provides detailed insights into an individual's behavior and its interactions.
• Recording for later analysis: Requires decisions regarding what to focus on in advance. It's essential to define the specific behaviors or interactions you are interested in to make the analysis focused and efficient.

II. Hypothesis Testing

1. Make a list of potential alternative hypotheses, preferably ones that are mutually exclusive. Mutually exclusive hypotheses ensure that only one can be supported by the evidence.
2. Generate predictions based on these hypotheses that lead to sequential rejection of alternatives. Predictions must be testable through data collection.
3. Collect data to test predictions. Proper data collection involves using consistent methods and appropriate sample sizes.

• Example: Manure Spreading in Burrowing Owls
  • Burrowing Owls ($Athene cunicularis$) are migratory birds that breed in desert grasslands. Their habitat and behavior make them an interesting subject for ecological and behavioral studies.
  • Male owls dig/adopt gopher burrows, and females build nests inside. Burrow selection and modification are important aspects of their nesting behavior.
  • Males line the tunnel to the nest with mammal manure and spread it around the burrow entrance. This behavior has several potential functions that have been investigated through hypothesis testing.
  • Question: What is the function of manure around the nest opening? (Smith & Conway, 2007)

Alternative Hypotheses for Manure Use

1. Mate attraction: Males spread manure to attract mates; females use it to assess male quality. This suggests that manure may serve as a signal of male health and resourcefulness.
2. Burrow occupancy: Manure indicates the burrow is occupied, helping owls avoid costly fights. This can reduce unnecessary conflicts with other owls.
3. Olfactory camouflage: Manure hides owl nests from potential predators that hunt by smell. By masking the scent of the nest, owls may reduce predation risk.
4. Prey attraction: Manure attracts arthropods, a significant part of the owl's diet. This could create a food source near the nest to feed chicks.

Predictions Based on Hypotheses

• Manure scattering should vary with the time of the breeding season:
  • Mate attraction hypothesis: Before pair bond occurs. If manure is used to attract mates, it should be most prevalent before mating.
  • Occupancy hypothesis: As soon as males return and begin setting up the burrow. If it signals occupancy, manure should be present early in the nesting season.
  • Olfactory camouflage hypothesis: Right before incubation (when eggs are present and a parent is on the nest, needing protection). Manure use should increase when the eggs are most vulnerable.
  • Prey attraction hypothesis: When the number of burrow occupants is highest (i.e., nestlings present, mouths to feed). Manure scattering should peak when the demand for food is highest.

Data Collection and Results

• Smith and Conway (2007) monitored 46 burrows throughout the breeding season to see which prediction(s) actual behavior matched. By observing multiple burrows, they obtained a robust dataset.
• Results: 87% of burrows observed showed males scattered manure AFTER pair formation. This timing is crucial for evaluating the hypotheses.

This observation does not support:

• Mate attraction theory (expected before breeding).
• Burrow occupancy theory (expected before breeding).

This observation supports:

• Prey attraction theory. The timing aligns with the needs of nestlings.
• Olfactory camouflage theory. Protecting the eggs from predators is a key concern.

Further Experimentation

• What experiment could distinguish between the two remaining hypotheses (prey attraction and olfactory camouflage)? Controlled experiments could manipulate manure presence or composition to test effects on prey abundance and predator behavior.

III. Experimentation

• Controlled, carefully designed studies that tease apart alternatives. This ensures that observed effects are due to the manipulated variable.

Types of Questions

• Proximate: HOW? (How does the trait work? How does it develop?) Proximate questions explore the mechanisms and development of behaviors.
• Ultimate: WHY? (Why did the trait evolve? Why is the trait adaptive?) Ultimate questions address the evolutionary history and adaptive significance of behaviors.

Examples of Proximate vs. Ultimate Questions

• Why are some male birds more colorful than females? (Ultimate)
• Why do social insects have non-reproductive castes? (Ultimate)
• Why does a ground squirrel give a warning cry (altruism)? (Ultimate)
• How do the colors of bird feathers develop? How do they use their colors in displays? (what cues are necessary?) (Proximate)
• How do a social insect’s genetics and development affect caste? (Proximate)
• How are an animal’s nervous & muscular systems integrated to respond to a threat? What is cost/benefit? (Proximate)

Infanticide in Lions

• Serengeti lions have new groups of males coming in periodically. This social structure impacts mating behavior.
• If the old group needs to be removed, all cubs are usually killed. This ensures the new males' genes are passed on instead.

Why: Brings females into estrus, likely evolved after the evolution of social/mating system.

How: Unfamiliar odor of cubs.

History of Behavior

• Evolutionary Biology. Understanding the evolutionary roots of behavior is critical.
• Ethology. Ethology provides key insights into innate behaviors.
• Comparative Psychology. Comparative psychology focuses on learning and behavior across species.

Charles Turner

• PhD & U. Chicago. His academic background provided a foundation for his research.
• Taught at AA High School with limited resources but made many discoveries. His ability to conduct research with limited resources is notable.
• Published over 70 papers. His extensive publications demonstrate his impact on the field.
  • Discoveries: Insects' hearing & behavior modification, honey bees' color vision & pattern recognition, ants' situational judgment. These discoveries highlight his wide range of contributions.
• "Turner whirling" (non-invasive habitat observation to remain hidden). This technique allowed him to observe animals without disturbing them.
• Led education initiatives, recruited local co-authors with equal payment, and recruited from underrepresented populations, HBCUs, & smaller schools to make publishing accessible. His commitment to inclusivity is commendable.

Evolutionary Biology and Ethology

• Hard to pinpoint the beginning of animal behavior study; probably started with Greeks (Aristotle, etc.). Understanding the roots of the study helps in appreciating its development.

1. Charles Darwin

   • Naturalist on the Beagle. His voyage provided the observations that led to his groundbreaking theories.
   • First scientist to describe a plausible explanation for biological change: Theory of Natural Selection. Natural selection explains how species adapt over time.
   • Published "On the Origin of Species" (1859). This book revolutionized the study of biology.
   • Contrasted with Aristotle's scala naturae, which claimed evolution was a linear, continuous process with humans as the goal. Darwin's theory presented a branching view of evolution.

Darwin's Theory of Natural Selection Tenets:

• Individual offspring vary. Variation is the raw material for natural selection.
• This variation is heritable. Heritability allows traits to be passed on to future generations.
• Heritable variations (alleles) that provide an advantage are more likely to be passed on. This is the core concept of natural selection.
• Evolution is branching, not linear. This view emphasizes the diversity of life.
• Differential reproduction is the consequence of Natural Selection. Individuals with advantageous traits leave more offspring.
• Darwin didn’t know the mechanism of heredity (genetics). His ideas were later integrated with genetics in the “modern synthesis”

Darwin – Sexual Selection

• The Descent of Man, and Selection in Relation to Sex (1871) and Expression of the Emotions in Man and Animals (1873). These works explored the role of sexual selection and the expression of emotions.
• Recorded behavioral observations but often attributed human emotions/intellect to behaviors (anthropomorphism). Anthropomorphism can lead to misinterpretations of animal behavior.
• Differential reproduction (in addition to differential survival) also may be the result of sexual selection:
  • Male/male competition. Competition for mates can drive the evolution of certain traits.
  • Female choice. Female preferences can influence the evolution of male traits.
• May result in the evolution of complex traits at odds with natural selection; therefore, there may be a tradeoff between natural and sexual selection. This can lead to traits that are beneficial for mating but detrimental for survival.

Tungara Frog Example

• Females are attracted to males that produce more chucks. The number of chucks influences mating success.
• Sexual selection (increased mating) selects for more chucks. The pressure of sexual selection favors this trait.
• Natural selection (reduced survival due to bat predation) selects against chucks. Predation risk creates a counter-pressure against the trait.
• If bat predation increased to the point that frogs who sang multiple chucks are generally consumed BEFORE they can mate, this would impact the songs of future generations. This demonstrates how environmental factors can influence evolutionary trajectories.

1. V. C. Wynne-Edwards:

   • Published "Animal Dispersion in Relation to Social Behavior" (1964). This work explored the role of social behavior in population regulation.
   • Proponent of GROUP SELECTION (“For the good of the species” argument). Group selection suggests that behaviors evolve for the benefit of the group.

Examples:

• Species behave in ways to keep their population down (ex: reproductive output). This behavior would help prevent overpopulation.
• Self-sacrifice/altruism (ex: alarm calls). Alarm calls can warn others of danger, even at a cost to the caller.
• Now generally discredited, but important because it generated thought and discussion about how complex social behaviors could evolve. Despite being discredited, it stimulated research and discussion.
• Now accepted theory is that selection acts at the level of the individual (and its genes). Individual selection is the prevailing explanation for the evolution of behavior.

Initially Two Approaches:

1. Ethology. Ethology focuses on innate behaviors in natural settings.
2. Comparative Psychology. Comparative psychology studies learning and behavior in controlled environments.

Ethology:

• Evolutionary, comparative, descriptive, field-oriented. These characteristics define the ethological approach.
• Focus on innate behavior; studied birds, fish, and insects in natural habitats to understand behavior in context. Studying animals in their natural environment is a key aspect of ethology.
• Studied both proximate and ultimate levels of behavior. Ethologists address both the how and why of behavior.
• Emphasis on INNATE behavior (instincts). Understanding instincts is a central goal.
• Emphasis also on evolutionary basis of behavior, especially COMPARATIVE behavior (species differences). Comparing behaviors across species provides evolutionary insights.
• Ethos (Greek) – ‘character’ or ‘habit’

Early Ethologists:

• Whitman, Heinroth, von Uexküll. These early ethologists laid the foundation for the field.

von Uexküll (1905):

• Worked with ‘simple’ organisms; asked questions about the “Umwelt” of ticks (what is the mind/perception of a tick like?). He explored the sensory world of different species.
• Adult female ticks are only responsive to a sequence of simple stimuli:
  • Light: Uses light to crawl to the top of the blade of grass. Light guides their movement to a suitable location.
  • Odor (butyric acid): Smell given off by mammals. This helps them locate a potential host.
  • Heat (warmth): To orient to the skin of the host. Heat guides them to a warm-blooded host.
• ~These are the only requirements to stimulate a complex sequence of behavior~
• ~ These simple stimuli termed SIGN stimuli - Important concept in early ethology~

Later Ethologists:

• Lorenz, Tinbergen, von Frisch. These ethologists received the Nobel Prize for their work.
• Nobel Prize in Medicine or Psychology (1973) (Recognition for animal behavior as a rigorous science). This award recognized the importance of animal behavior as a scientific discipline.

Tinbergen's Four Questions:

• Proximate (HOW).
  • Causation/Mechanism. What causes the behavior?
  • Dev/Ontogeny. How does the behavior develop?
• Ultimate (WHY).
  • Function (adaptivity/current utility). What is the behavior's adaptive function?
  • Evolutionary History (phylogenetic history of trait). How did the behavior evolve over time?

Classical Phenomena of Ethology: Fixed Action Pattern (FAP)

• Motor response that is initiated by an environmental stimulus. Once started, it runs to completion.
• Once initiated, behavior goes to completion. It cannot be stopped mid-way.
• First described by Konrad Lorenz. He made key contributions to understanding FAPs.

Characteristics:

1. Sequence of events unalterable. The pattern is rigid and predictable.
2. Innate (not learned). It is genetically programmed.
3. Can be triggered under inappropriate circumstances. It can be elicited even if the context is not ideal.
4. Remarkably similar among members of a species (i.e., is highly stereotyped). The behavior is consistent across individuals.

Sign Stimulus and (Social) Releasers

• The trigger of a fixed action pattern is called the SIGN STIMULUS (this stimulus triggers the FAP). This is the cue that initiates the behavior.
• When the behavior is triggered by a member of the same species, that member is called the ‘social releaser’ or ‘releaser’ (for short). This facilitates social interactions.
• If you can isolate the effective characteristic of the sign stimulus and exaggerate it -> supernormal stimulus. This can elicit an even stronger response.

Innate Releasing Mechanism (IRM)

• Internal ‘mechanism’ for initiating behavior (actual ‘mechanism’ theorized but not known). It is a theoretical construct.
• Releaser elicits the FAP via the IRM. The releaser activates the IRM, which triggers the FAP.

Example: Male-male aggression in European robin ($Erithacus rubecula$)

• Male robins defend territories from other male robins. Territorial defense is a common behavior.
• Experiments have shown that isolated clumps of red feathers will elicit the same response. The red feathers act as a releaser.
• Behavior elicited by red breast of male - what is this called when on the male?

Comparative Psychology:

• Physiological, developmental, quantitative, laboratory-oriented. These characteristics define the comparative psychology approach.
• Studied model organisms (largely mammals like rats) in lab settings because of the belief that good experimental science could not be conducted if uncontrolled variables existed. Controlled conditions are essential for experimental rigor.
• Primarily focused on proximate questions about behavior (general principles rather than species differences). Understanding general principles is a primary goal.
• Early emphasis on learning and physiological basis of behavior. Learning and physiology are key areas of focus.

Early Ethologists:

• E.L. Thorndike (early 1900s):
  • Developed trial and error learning. He explored how animals learn through experience.
  • ‘Puzzle boxes’: Cages used to test animal learning ability (measured time taken to escape box on subsequent trials). These boxes quantified learning.
  • The Law of Effect: Behaviors that are rewarded tend to be repeated --> later developed into OPERANT CONDITIONING. Reinforcement shapes behavior.

OPERANT CONDITIONING:

• Animals learn to associate voluntary behavior (operant) with a response (food reward). This is also called instrumental conditioning.

B.F. Skinner (early 1900s):

• OPERANT CONDITIONING: Conditioned behavior.
• "Skinner boxes": Hungry animal can manipulate a mechanism (lever, key) inside the cage for a reward. These boxes allowed for controlled experiments.
• Interested in what was externally observable (not internal mechanism), i.e., stimulus --> response. Focus on observable behavior is a key aspect.
• Still used to evaluate what animals perceive and are capable of. Skinner boxes are still used today in research.

Ivan Pavlov (early 1900s):

• CLASSICAL CONDITIONING: Conditioned ‘reflex’.
• Pavlov’s dog experiments. These experiments demonstrated classical conditioning.

Contrasting Classical and Operant Conditioning:

• Classical Conditioning: Associate an involuntary response and a stimulus. The animal learns to associate stimuli.
• Operant Conditioning: Associate a voluntary behavior and a consequence. The animal learns to associate actions with outcomes.

Contrast Between Ethology and Comparative Psychology:

• Led to the Nature vs. Nurture debate. This debate explores the roles of genetics and environment.
• Mid 1950s – critics of this dichotomy began to fuse ideas from both ethology and comparative psychology. Integration of ideas led to a more comprehensive understanding.
• Eventually à Realization that behavior is neither entirely learned nor entirely innate (contains aspects of BOTH). Behavior is influenced by both nature and nurture.

Modern Fields:

• Ultimate:
  • Sociobiology: Integrated effects of genetics and ecology on social interactions (e.g., helps explain altruism). Sociobiology examines the evolutionary basis of social behavior.
  • W.D. Hamilton, E.O. Wilson, others.
  • Behavioral ecology: Social and non-social interactions (interactions with environment). Behavioral ecology explores the ecological and evolutionary context of behavior.
  • Emphasis on functional questions. Functional questions explore the adaptive significance of behavior.
  • John Krebs, Nick Davies, Richard Dawkins, many others.
• Proximate:
  • Neuroethology / behavioral neuroscience: Emphasis on questions of mechanism. Neuroethology investigates the neural mechanisms underlying behavior.
• Recently:
  • Resurgence of interest in integrating ultimate and proximate areas à especially in light of Tinbergen’s questions. Integrating evolutionary and mechanistic perspectives leads to a deeper understanding.

Behavioral Genetics

• Genetic Effects on Behavior. Genes play a significant role in shaping behavior.
• Heritability. Heritability is a measure of how much variation in behavior is due to genetics.

For a behavior to evolve:

• Genetic differences must influence behavioral differences. Genetic variation is essential for evolution.

Key Terms:

• Genotype: Genetic makeup. The genotype is the set of genes an individual carries.
• Phenotype: Observed trait (behavior), can be influenced by both genotype AND environment. The phenotype is the observable expression of the genotype.

How Much of a Behavior is Genetic vs. Environmental?

Richard Dawkins – The Selfish Gene.

Cake Analogy:

• Bake a cake using a recipe from a friend.
• Once done, the cake tastes terrible.
• Double-check recipe: Find an error in copying it (you turned ‘1 tsp of salt’ into ‘1 tbsp. of salt’).
• Q: Does this mean that a single ingredient (salt) controls the production of a terrible-tasting cake?
• A: Of course not! The entire recipe, how the ingredients were combined, oven temperature, etc., all also play a role (and affect cake taste).
• HOWEVER, small differences in the recipe (the DNA) can produce important differences in the EXPRESSION of the recipe (or behavior, in this case).
• Changing 1 base pair (point mutation) can change the protein. Point mutations can alter protein function.
• For most traits, variation exists because underlying DNA sequences are DIFFERENT. Genetic variation is a major source of behavioral differences.
• However, remember that the ENVIRONMENT can also lead to trait variation even when individuals have the same DNA sequence. Environmental factors can also lead to behavioral differences.

Genes Versus Environment

How do we determine which is influencing behavior?

1. Two general approaches:
   1. Hold environment constant, explore effects of genetics. This approach isolates the effects of genetics.
   2. Hold genotype constant, explore effects of environment. This approach isolates the effects of environment.
   3. Fix the Environment and Vary the Genotype

Susan Reichert and Ann Herick – Funnel Spiders:

• Interested in understanding variation in ‘attack speed’ when the web vibrates. Attack speed is a key behavioral trait.
• Funnel spiders found near streams respond significantly more slowly to vibrations than grassland spiders. Different environments select for different behaviors.
• Brought spiders into the lab and raised offspring in identical conditions → then tested response to web vibrations. This controlled environment eliminated environmental variation.

1. Fix the Genotype and Allow the Environment to Vary

• Twin studies: Focus on identical twins raised in different environments. Identical twins share the same genes.
• Inbreeding: Creating lines of identical ‘clones’. Inbreeding reduces genetic variation.
• Requires: >20 generations of brother/sister mating >8 generations of selfing.

Genetics Influence Behavior - Can Behavior Influence Genetics?

Songbird Brains:

• Zenk – an immediate early gene; codes for proteins that control the expression of other genes. Zenk is involved in gene regulation.
• In birds, Zenk is stimulated when a bird hears its own species song, activates genes that regulate neuronal growth (LEARNING). The gene is activated during learning.

Experiments to test for the effects of genotype on behavior:

1. Inbreeding. Inbreeding reduces genetic variation.
2. Hybridization. Hybridization combines genes from different strains.
3. Artificial selection. Artificial selection allows for targeted breeding.
4. Genetic transformation (mosaics, knockouts, etc.). Genetic transformation allows for direct manipulation of genes.
5. Inbreeding

• Minimizes genetic diversity within strains and maintains/enhances genetic diversity between strains. This allows for a focus on environmental effects.
• Any differences in behavior in different environments are due to ENVIRONMENTAL effects (and not genetic effects). Environmental effects can then be studied in isolation.

Examples: Paradise Fish, Norwegian Lab Rat.

Example: Paradise Fish ($Macropodos opercularis$)

• Two strains of larval fish (P, S).

Treatments:

• Predator model with eyes.
• Predator model with no eyes.

Measured frequency of ‘fleeing’.

Example: Norwegian Lab Rat ($Rattus norvegicus$)

• Two strains:
  • Bright.
  • Dull.

Raised in three environments:

• Restricted.
• Normal.
• Enriched.

Tested the number of errors when running a maze (‘learning’).

2. Hybridization

• Behavior of hybrids depends on the # of genes involved:
  • Small # genes – behavior intermediate or like one parent. The number of genes influences the behavioral outcome.
  • Large # genes – behavior likely to be intermediate between parental strains. Complex traits are more likely to show intermediate phenotypes.

Examples: Blackcap Warblers, Fruit Fly Larvae.

Example: Blackcap Warbler ($Sylvia atricapilla$)

• Migration: Which direction to go?
• Berthold hybridized SW and SE migratory birds. Hybridization can reveal the genetic basis of migratory behavior.
• Used a funnel cage to measure ‘Zugenruhe’

Zugenruhe = migratory restlessness.

Example: Fruit Fly Larvae ($Drosophila$)

• Foraging: ‘Sitter’ vs ‘Rover’ phenotypes. These phenotypes relate to foraging behavior.
• Sokolowski crossed two parental strains (R vs S)

1. Artificial Selection

• Selective breeding can demonstrate effects of genes on behavior. This can show how genes influence behavior.
• Alleles favoring direction of selection will increase in subsequent generations of the population. This is the process of artificial selection.

Examples: Fox domestication, mice nesting, Belgian Waterslager Canary.

Example: Fox Domestication

• Belyaev – silver fox domestication.
• Selected for traits similar to those of dogs (social behavior). Selection can result in rapid changes in behavior.
• Within 40 years, produced foxes that were highly social and interact with humans in a playful, friendly manner. This demonstrates the power of artificial selection.

Example: Nesting behavior in mice

• Lynch selected for ‘high’ and ‘low’ nest-building lines in mice (also had a control line with random mating).
• After 15 generations, created an 8-fold difference in nest size. This illustrates the heritability of nest-building behavior.

Example: Belgian Waterslager canary song

• Selective breeding ‘target’ not always obvious.
• Bred canaries with ‘best’ songs → selected for DEAFNESS (canaries that sang songs we could hear). This surprising result illustrates unintended consequences of selective breeding.

1. Genetic Transformation

• Modern genetic technologies allow us to manipulate the genome directly to assess its effect on behavior and often allow us to locate the genes responsible. Modern techniques allow for precise genetic manipulation.
• Knockout genes: Produce mutants that are homozygous for inactive gene. Knockout genes inactivate specific genes.
• Gene transfer: Use molecular techniques to insert a gene into the DNA of another species. Gene transfer allows genes to be moved between species.
• Genetic mosaics: Organisms that possess more than one genome. Genetic mosaics have cells with different genotypes.

Example: Fruit fly gynandromorphs, mosaic mice, etc.

• These organisms can be used to identify not only the GENE involved in a behavior, but the part of the body affected by that gene. Mosaics can help localize gene function.

Knockout Genes Example: fosB gene in Mice

• Normally, cues (odor, tactile, auditory) stimulate retrieving, huddling response (pup retrieval). These cues elicit maternal care.
• fosB is an immediate early gene (it creates proteins that activate other genes) involved in the development of neural circuits in the POA of the hypothalamus.
• These neural circuits are responsible for nurturing in mice!
• Knockouts for fosB (both alleles are inactive) neglect their offspring. Knocking out this gene eliminates maternal care.

Gene Transfer Example: Per gene in fruit flies

• Per codes for IPI (inter-pulse interval) in the courtship display of male fruit flies (Per also codes for circadian rhythms). This gene influences courtship behavior and circadian rhythms.
• Many genes have more than two alleles (in the population). Alleles can vary in their effects.
• The per gene has several forms (alleles):
  • Per +: normal diurnal activity cycles (24 hours).
  • Per S: shorter than normal activity cycles (19 hours).
  • Per L: longer than activity cycles (29 hours).
  • Per 0: arrhythmic (no set period).

Polygenic - Several Genes, One Effect

• E.g., multiple genes code for a biochemical sequence that produces a behavior. Many behaviors are influenced by multiple genes.

Pleiotropic - One Gene, Several Effects

• E.g., a gene that codes for a common enzyme used in multiple pathways that affect different behaviors. A single gene can have diverse effects.

Polygenic

• Most behaviors are polygenic. Polygenic inheritance is common.

Pleiotropy

Example: ‘Yellow’ mutant in fruit flies

• Single gene on X chromosome: Codes for:
  • Yellow body color.
  • Lower frequency wing vibrations in courtship. This gene affects both color and courtship behavior.

Two Gene Traits: Example: Honeybee ‘hygiene’

• Worker bees clean the hive of dead larvae (hygienic behavior). This is an important social behavior.
• To do this, they must find cells with dead larvae, uncap cells, and remove the larvae.
• Wild Type colonies are ‘Unhygienic’, only the mutant strain of bee is ‘Hygienic.’

Behavioral Genetics

• Genetic Effects on Behavior.
• Heritability.

Estimation of Polygenic Effects (Heritability)

• Selection can be used to determine heritability for individual traits.

I. Narrow sense heritability

• Measure of ‘realized heritability’ ($h^2$)
• Measure of the response of a particular trait to selection Selection Differential (S) = difference between mean of selected parents and mean of population (base stock) Response to Selection (R) = difference between mean of offspring of selected parents and mean of overall population Realized Heritability ($h^2$) = $\\frac{R}{S}$, percent of trait that responds to selection (i.e. is heritable)

Mouse Litter Size Example:

• Realized Heritability ($h^2$) = $\frac{R}{S}$, percent of trait that responds to selection (i.e. is heritable).

Measuring The Proportion of Phenotypic Variance Due To Genes

II. Broad Sense Heritability

• Measure of the ‘degree of genetic determination’ (0GD)
• Measure is a population measure, not applied to an individual’s inheritance of a particular trait 0GD = $\frac{Vg}{VT}$, where VT = Vg + Ve Vg = genetic variance Ve = variance due to environment VT = total variance (for our purposes, = Vg + Ve )=variance Geneticenvironmental total Environmental varivariancearianceannce+

Discussion Questions

1. What do you think the Vg of an inbred population would be?
2. What do you think the Ve would be for organisms that are raised in identical laboratory conditions?
3. If you inbred a strain of mice for 30 generations, then selectively bred only the mice that built the largest nests for 30 generations, how should nest size change over time? Why? (assume no novel mutations have arisen).

Broad Sense Heritability Example

Calculating the degree of genetic determination for wheel-running activity in mice

• Two mouse strains A and B (F0) that show different behavior for wheel-running activity
• To determine the heritability of these strains, scientists crossed them to produce F1 hybrids (A x B) Then scientists crossed F2 hybrids (F1 x F1)

Mouse Strain Mean # wheel revolutions / day Variance A 1107 112 B 5680 418 F1 5235 325 F2 4745 465

How can you use these data to calculate the 0GD of this trait? (hint: Think about what forms of variation (genetic, environmental, both) exist in each mouse strain)

I. First, calculate an estimate of Ve by averaging the variance from all strains that lack genetic variation.

ii. Second, estimate Vg from the one population that has BOTH genetic and environmental variation (do this by subtracting estimated Ve from VT).

iii. Now, plug the numbers into the equation below to calculate 0GD 0GD= $\frac{Vg}{VT}$

Trait Variance A 182 B 300 F1 260 F2 715

Determinig Relatedness Rules

Raise ½ to a power equal to the number of links in a pedigree separating 2 relatives (going back through common ancestors) and Sum independent paths that connect between individuals.

Calculating the degree of relatedness – the proportion of genes shared that are identical by descent

A parent (from a diploid, sexual organism) shares half its genes with each of its progeny, so a diploid offspring gets: ½ (0.5) of its genes from one parent, ½ (0.5) from the other parent

Question

What is the degree of relatedness between Md and Ma?

$(1/2)^1$ = 1/2 or 0.5 (What is their relationship?) Father and son P Ma Fb Mc

F1 Md Fe Ff Mg

F2 Fh Mi Fj

F3 FkExample Pedigree father + son

What is the degree of relatedness between Md and Ff?

$(1/2)^2$ = 1/4 or 0.25 (What is their relationship?) Half siblings

Question: What