Proximate causes

• Interaction among gene/environment/ development persist and change over entire lifetime of animal

• We’re simplifying by focusing the “straight line” interactions for now

Behavioral Genetics

• Single gene effect - Drosophila sp.

• VT = VG + VE + VI

• VI = VG x VE

• Inbreeding - homogeneous strain - e.g. rearing condition (VG = 0, VT = VE)

• Strain difference (VE = 0, VT = VG )

• Hybridization - love birds, hygienic vs. unhygienic bees, cricket song

• Cross-fostering - e.g. cockatoo-reared galah

– galah begging call, alarm call,

– cockatoo contact call, slow wingbeat, food

Heritability• Degree of genetic determination

ratio of genetic variation in a behavior trait

• GD = VG /( VG + VE + VI)

• Cross inbred strains and measure behavioral variation

Mouse strainMean # wheel

revolution per 24 hrs VarinceA 1,107 112B 5,680 418

F1 (A x B) 5,235 325F2 (F1 x F1) 4,745 465

• VE = (112 + 418 + 325)/3 = 285

• VG = 465-285 = 180

• GD = VG / VT = 180/465 = 0.39

• Realized heritability, hr2 : a measure of

the response of a trait to selection

• Measure differences in behavioral traits between base stock and selected breeding parents (S), and between base stock and offspring (R)

• Selection differential, S • Response to selection, R

• hr2 =R/S

TREES 6(8): 254-262, 1991

• Genetic control of migratory behavior

• When to migrate?

Migratory pop. x Resident pop. => 40% of F1 migratory

The migratory restlessness may change by selective breeding

• How far?

---Long distance x Short distance => intermediate distance

• What direction?

---Resident x Exclusive migrant =>F1 migrant w/ parent direction

---SE migrant x SW migrant =>intermediate

---Species change direction during migration. Captive ones show same behavior

• Other migratory traits:

---morphological features

---seasonal change in feeding rate, food and habit preference, activity pattern

Group size preference• Proc. Nat. Acad. Sci. USA 97:

14825-14830

• Parent – offspring regression

• Group size of individual cliff swallow (Petrochelidon pyrrhonota) ~ parents

• Foster-raring individual ~ biological parents

• Naive animal - e.g. garter snakes and slug Mutation

• Twin studies

– identical (monozygotic) twins

– fraternal (dizygotic) twins

• Mosaic

• Quantitative Trait Locus Analysis (QLT)

Towards behavioral genomics

Science 291: 1232-1233, 2001

• Single genes do not determine most human behavior

• Nearly all behaviors that have been studied showed moderate to high heritability

• Environmental factors make people different from, rather than similar to, their relatives

• Information and techniques generated by the human genome sequence will help locate and identify genes involved in behavior

• Problems

– Detect genes of a linkage with large enough effects

– Most valid diagnostic schemes for genetic research

• A greatly improved map of human genome sequence helps improve allelic association studies to locate QTLs

• To ID the effects of QTLs

– Bottom-up: functional genomics and proteomics

– Top-down: behavioral genomics

– Genome sequences of other organisms

• Future perspectives

– Understanding the neurobiological basis of individual (behavioral) differences and a better grasp of the etiology of diseases

– Discovery of new and more specific drug treatments

• Limitation

– Gene-environment interplay

– Distribution of effective sizes of QTLs

Molecular techniques

• Transgenic

• Knockout

• Gene mapping and association

• Protein electrophoresis

• DNA fingerprinting

Per gene and song pattern• Observation –

– In both D. melanogaster and D. simulans wildtypes, difference in per alleles ~ differences in male songs (pleiotropy).

– Wildtype per alleles differ in different species

• Hypothesis – Intraspecific differences in song are caused by differences in the per alleles

Building a brainier mouse (Sci. Am. 42-48, 2000)

• Molecular basis of learning and memory

• Hebb’s learning rule – a memory is produced when 2 connected neurons are active simultaneously in a way that strengthens the synapse

• LTP – Long-term potentiation vs. LTD – Long-term depression of synaptic connection in hippocampus

• NMDA receptors require 2 signals: binding of neurotransmitter glutamate, membrane depolarization

• Dumb mouse – NMDA lack NR1 subunit in CA1 region, impairment in spatial memory and other task

• Young animals produce NR2B, old animals more NR2A in NMDA, NR2B stays longer than NR2A

• Smart mouse – extra copies of NR2B

• Test 1. Recognition of objects: smart mice explore only new objects, normal mice explore both old & new, remember objects 4~5 times longer

• Test 2. Remember fear longer

• Test 3. Fear extinction learning faster

• Test 4. Morris water maze, finding submerged platform in milky water – need analytical skill, learning and memory, ability to form strategies

• Learning and memory enhance problem-solving, but intelligence has many aspects