Lecture 5

Mediate Relationship With Environment

GENETIC MAKEUP

NEURAL/ENDOCRINEMECHANISMS

DEVELOPMENT

OBSERVED BEHAVIORSOLVEPROBLEMS:

• Find Food• Avoid Predators• Shelter • Mate• Parental Care

If solve problems, survive and reproduce

Mediate relationship with environment

GENES

BEHAVIOR SOLVE PROBLEMS

SURVIVE &REPRODUCE

GENE POOL

BEHAVIORAL GENETICS Natural Selection: Necessary & Sufficient Conditions

• Individual Variation

• Heritable Variation

• Fitness Consequences (i.e., individual differences affect survival and reproductive success).

BEHAVIORAL GENETICS

• Concordance

• Behavior often species specific

• Behaviors breed true (i.e., reproduced in successive generations)

• Behaviors change in response to alterations in neural structures/processes

• Behavior has an evolutionary history

BEHAVIORAL GENETICS Schizophrenia: Neuro-developmental disorder

Concordance: Percent of pairs of people in which both members display trait if one displays it

Pathophysiology of schizophrenialinked to altered dopaminergicneurotransmission

BEHAVIORAL GENETICSHeritability: Definitions

• Proportion of phenotypic variance that is attributable to genetic variance1

• Amount of variation in a trait within a group of individuals that can be accounted for by genetic differences among the individuals of the group

1 Variance is statistical measure of variation

BEHAVIORAL GENETICSHeritability

Heritability: MeasurementSelection Experiment

Heritability: MeasurementOffspring Regression

Heritability of Beak size in Darwin's Finch (Geospiza)

The correlation between beak size of offspring and their midparent value (the average of parents) is 0.90 both in 1976 (open circles) and 1978 (closed circles), even though the mean beak size increases due to a drought in 1978. This correlation shows constant high heritability independent of environmental change. Note that high heritability does not mean that a trait is constant: beak size is highly variable (note range of axes), and can vary across

time (displacement of slopes).

Heritability: Measurement

Offspring Regressioncontinued

BEHAVIORAL GENETICS:Demonstrate Genetic Basis

• Genetic Mutants

• Crossing Experiment

• Artificial Selection

BEHAVIORAL GENETICS:Genetic Mutants

• Hygienic behavior in honey bees involves the ability to detect and remove diseased, larval and pupal brood from the nest before the pathogen becomes infectious. • It consists of two distinct task-components: uncapping a cells and removing its content. • Rothenbuhler (1964) suggested that these two traits were controlled in a simple Mendelian manner by two recessive loci.

Rothenbuhler WC. 1964. Behaviour genetics of nest cleaning in honey bees. IV. Responses of F1 and backcross generations to disease-killed brood. Am Zool 4:111–123

BEHAVIORAL GENETICS:Rothenbuhler WC. 1964. Behaviour genetics of nest cleaning in honey bees

BEHAVIORAL GENETICSBehavioral Traits

• Mendelian traits: How phenotypes appear to us?

• Quantitative traits: Continuous distribution. Examples?

• How are quantitative traits controlled genetically?

• How do the traits segregate during recombination?

• Discontinuously and continuously distributed traits and Darwinian evolution/natural selection?

BEHAVIORAL GENETICS:Crossing Experiment

Berthold’s work with migratory birds

• Circannual rhythm in biology of migratory birds: see handout.

• Genetic basis of migratory activity, distance and orientation. How examine?

BEHAVIORAL GENETICS:Crossing Experiment

Berthold’s work with migratory birds

BEHAVIORAL GENETICS:Selection Experiment

BEHAVIORAL GENETICSBehavioral Traits

• Evidence indicates a genetic effect, but does not tell us how genes affect behavior

• How genes exert their influence is a challenging, complex question.

BEHAVIORAL GENETICS:Heritability Caveats

• Heritability is an abstract concept: Tells us nothing about the specific genes that contribute to a trait.

• Heritability is a population concept: Tells us nothing about the individual. A heritability estimate of 0.40 means … [?]On average 40% of observed individual differences are in some way attributable to genetic individual differences.Does not mean that 40% of any person’s behavioral trait is a result of his/her genes, and other 60% environment.

• Heritability depends on range of environments to which population exposed. If same environment, … ?

• Conversely, the influence of environment depends on the range of genotypes in the population being studied.