Chapter 4: Behavioral Genetics
Lecture 4: Behavioral Genetics
Trovell Crith
Chapter 4: Key Concepts
4.1 Behaviors vary in their heritability
4.2 Behavioral variation is associated with genetic variation
4.3 The environment influences behavior via gene expression
4.4 Genomic approaches correlate gene expression with behavioral phenotypes
4.5 Genes can limit behavioral flexibility
4.1 Behaviors Vary in Their Heritability
Key Definitions
Observed Traits (Phenotype, P): The physical or behavioral characteristics of an individual.
Genotype (G): The genetic makeup of an individual, encompassing all its genetic material.
Behavioral Genetics: The study of how genes and the environment contribute to individual differences in behavior.
Behavioral Equation
Behavior (P) is influenced by:
Genotype (G)
Environment (E)
Gene-environment Interactions (GXE)
Contributions:
Phenotypic Variation (VP) = Genetic Variation (VG) + Environmental Variation (VE)
Heritability
Heritability (h^2): The proportion of phenotypic variation within a trait that is attributable to genetic influences.
Broad-sense heritability: Includes all genetic effects that influence phenotype.
Genetic Effects of Alleles
Additive Effects (A): Average effect of alleles on the phenotype.
Dominance Effects (D): Interactions between alleles at a single locus.
Epistasis (I): Interactions between genes at different loci.
Genetic Variation Equation:
VG = VA + VD + VI
Narrow-Sense Heritability
Higher narrow-sense heritability increases the likelihood that parent and offspring will share traits.
This concept is assessed through the similarity of behavior between parents and offspring, often visualized through a Parent/Offspring Regression plot.
Greater slope: Indicates strong resemblance between offspring and parents.
Lower slope: Suggests that phenotypic variance is not due to genetic variance.
Research Example in Dog Behavior
Research Question: Are key behaviors for service and hunting dogs heritable? (Ruefenacht et al. 2002)
Methods: Analyzed 25 years of behavioral field test results for German shepherds of known pedigree.
Results
Heritability scores for traits like gunshot reaction ranged from 0.09 to 0.24.
Conclusion: Behavioral traits in dogs have genetic and environmental components.
4.2 Behavioral Variation and Genetic Variation
Instinctual Behaviors
Search for genetic basis of behaviors:
Behaviors that are instinctive are performed the same way each time, expressed the first time, and observed even in isolated individuals (e.g., blinking).
Types of Instinctual Behavior
Reflexes: Automatic movement in response to stimuli.
Fixed Action Patterns: Behaviors with minimal variation that occur in sequence and conclude without interruption (Lorenz and Tinbergen, 1957).
Research on Fruit Fly Behavior
Observation by Bastock (1956): Yellow mutants of fruit flies are less common in nature than in lab settings.
Research Question: Why are yellow forms of fruit flies rarer in nature?
Hypothesis: The mutation leads to behavioral changes that result in low reproductive success in natural populations.
Methods
Subjects: Fruit flies (Drosophila melanogaster).
Process: Interbred wild-type and mutant yellow flies to create inbred flies and conducted mating trials.
Results
Wild-type males showed higher mating success than yellow mutants.
Yellow flies engaged in less courtship behavior.
Conclusion: Genotype variations lead to variations in phenotypic traits impacting reproductive success.
Major and Minor Genes
Major Gene: Responsible for a significant portion of phenotypic variation.
Minor Gene: Contributes small amounts to variation in phenotype.
Genetic Interactions
Epistasis: Interaction of genes at distinct loci.
Pleiotropy: A single gene affects multiple traits (e.g., "yellow" gene influencing color and courtship traits).
Fire Ant Research
Observation: Variance in social structures of fire ant colonies (monogyne vs polygyne).
Research Question: Do genes influence social organization in fire ants? (Ross, 1997)
Methods
Study Type: Collected samples from monogyne and polygyne colonies.
Techniques: Conducted starch gel electrophoresis to compare gene frequencies.
Results
Notable allelic frequency changes at the Gp-9 locus.
Conclusion: Specific alleles regulate social structures in fire ants.
4.3 Environmental Influence on Gene Expression
Gene Expression Processes
Genes encode for molecules though they do not produce actions directly; they influence brain functionality.
Environmental factors notably affect gene expression.
Gene Expression: The process of forming gene products influenced by environmental inputs.
Research on Zebrafish Aggression
Research Question: How does varying environments impact aggression in zebrafish?
Hypothesis
Both developmental environment (DE) and behavior environment (BE) affect aggression.
Predictions
If DE affects behavior only, aggression is highest in normoxic (high-oxygen) water.
If DE and BE interact, aggression will be highest where matched.
Methods
Process: Collected eggs from full-sibling clutches, raised them in normoxic and hypoxic conditions, and tested adult aggression levels.
Results
Fish showed aggression levels akin to their developmental environment.
Conclusion: Significant interaction exists between DE and BE affecting aggression levels.
Social Environment and Birdsong Development
Bird calls (like songs) are innate among all birds in the order Passeriformes.
Sensitive Learners: Must experience tutor songs shortly after hatching; otherwise learning is impaired.
Open-ended Learners: Can acquire new song features throughout life.
Research on FoxP2 Gene
Research Question: What role does the FoxP2 gene play in song development? (Haesler et al. 2007)
Methods: Used viral techniques to knockdown FoxP2 expression in zebra finches and monitored song recordings.
Results
Knockdown birds had reduced expression of FoxP2 compared to controls.
Omitted specific song elements, implicating FoxP2’s essential role in song learning.
4.4 Genomic Approaches Correlate Gene Expression with Behavior
Observation in Fish Mating Tactics
Dominant males defend territories, while sneaker males display differing tactics.
Research Question: Do the behavioral and morphological differences correlate with gene expression?
Featured Research: Black-faced blennies (Tripterygion delaisi).
Methods
Examined gene expression during mating season differing across reproductive roles.
Results
Territorial males showed increased expression of certain genes than sneaker males/females.
Conclusion: Male phenotype plasticity is more strongly linked with gene expression than morphological features.
4.5 Genes Can Limit Behavioral Flexibility
Concept of Animal Personalities
Animal Personalities: Consistent variations in behaviors within a population over time or across circumstances (e.g., bold vs shy; aggressive vs docile).
Research on Great Tits Behavior
Research Question: Is exploratory behavior in great tits genetic?
Hypothesis: Believed exploratory behavior has heritable components.
Methods
Recorded movements in controlled settings with multiple layers and treatments.
Results
Found significant correlation between parental and offspring exploratory behaviors.
Concluded exploratory behavior in great tits has heritable traits.
Salamander Personalities
Research Question: How do salamander larvae react to predation risk?
Hypothesis: Activity levels will vary based on perceived threat.
Results
Larvae displayed consistent behaviors across predation risk treatments, illustrating distinct personalities and heritable behavior components.
Environmental Impact on Jumping Spider Personalities
Research Question: How does rearing environment affect exploratory behavior?
Methods: Varied rearing conditions for jumping spiders and assessed exploratory behavior in open-field tests.
Results: Environment significantly affected exploratory latency and behavior, suggesting substantial influences on personality.