Genetics, Development, and Behaviour

BIOL 3100

Variation in behaviour is a constant

shy

skeptical

bold

Behaviour is influenced by both genetics and the

environment

G X E

Evolutionary change in behaviour will only occur if variation in the trait has a heritable genetic component….

Tricks to studying GxE

• Behaviour often involves complex traits with many underlying genes, resulting in continuous variation of the trait

• Environmental variability influences behavioural variability (and GxE)

“There’s a gene for that”

How do we test for heritable variation in behaviour?

video

Behavioural variation in personality

“active”“passive”

BoldnessShyness

- Rapid decisions- Manipulating stressful

events- Relatively insensitive

to external stimuli- Ready to form

routines- High aggressiveness,

boldness- High testosterone and

high reactivity of sympathetic nerve system

- Caution in decisions- High sensitivity,

readily adjustable to new situation

- Low aggressiveness, high shyness

- High reactivity of nervous system and adrenal system

- Adaptable to environment

Great tits have shown variation in:- Ways they explore new environements

(fast/slow)- Behaviour towards novel objects

Significant differences among sibling-groups, suggest there may be a heritable component

Personality behaviours predict aggressiveness, foraging, stress reactions, etc., all of which affect fitness

Experimental setup• Raised wild-caught birds in the

laboratory• Tested exploration behaviour and

reactions to novel objects to score personality 40 days post-hatch

• Individuals with high and low scores were mated assortitively to be parents of the next generation

• Used cross-fostering and split broods to separate genetic effects from environmental effects

Exploratory behaviour

Approaching novel objects

implications

• Strong response to bi-directional artificial selection

• Variation in personality is highly heritable in great-tits

• However, a lack of environmental variation can overestimate natural heritability

• Supports previous work by Dingemanse et al. (2002) showing ~30% heritability in wild birds

Quantifying the genetic component

H2 = VG/(VG + VE)

Studying heritability does not tell us that a trait is “genetic” or “environmental”, simply how strong or weak the effect of environment is on the GxE landscape

- When h2 is low, the environment has a strong effect

- When h2 is high, the environment has a relatively weak effect

High h2 Low h2

So, clearly it is critical to study the influence of both genetics and the environment…

How?

Examining Heritability1) Common garden experiments: what

is the phenotype if raised in a new environment

2) Artificial selection experiments: can phenotype be changed if we bias breeding from one generation to the next?

3) Hybridization and other breeding studies4) Mutations: “knockouts”5) Relatedness and “twin studies”: how strong is correlation between genes and phenotype?6) Behavioral genomics

Example 1: common-garden experiment

Observation: Some blackcaps (Sylvia atricapilla) over-winter in Southern Great Britain while most over-winter in Africa

Question: Are those birds non-migratory? Do genetic differences explain this pattern?

Test: Compare behaviour of offspring to parents

• Capture wild black-caps in Great Britain during the winter, kept them in a lab over the winter

• During spring, released birds into an outdoor aviary where they bred – offspring had never migrated

• Hypothesis: If migratory, offspring should exhibit zugunruhe (migratory restlessness) in the fall

Where do they breed?

Are these behaviours heritable?

NorthNorth

Adults from Britain F1 offspring from British adults

Orientation suggests they’re coming from Central Germany or Belgium (confirmed by banding data)

Common-garden

Perdeck, A. C. 1958. Two types of orientation in migrating Starlings, Sturnus vulgaris L., and chaffinches, Fringilla coelebs L., as revealed by displacement experiments. Ardea 46: 1-37.

Wanted to test the theory that migratory orientation was genetically determined

…in an incredibly ambitious and awesome way

Kinda like this but there were birds involved

What happened?

• Young birds behaved as though their migratory route was innate (programed) and ended up south of their normal wintering grounds

• Adult birds ended up in their normal wintering area, apparently being able to compensate for the displacement.

• So…. migration relies on both an innate program (G) and experience (E)

What happened?

• After wintering 600 km south of where they should have wintered, the young birds flew north and ended up….exactly where they were reared the year before!

• Next year, where did they go on fall migration?

• So…migratory behaviour is both heritable and involves learning and imprinting.

Testing for hereditary differences

1) Take pregnant females fro the two populations into the laboratory and hold under identical conditions

2) Place each baby snake in a separate cage, away from littermates and mother (remove environmental influences)

3) Days later, offer banana slug to eat (coastal snakes at them, inland ones didn’t)

4) Present swabs from multiple prey items to snakes, measure tongue-flick response

Eat lots of slugs

Eat very few slugs

Artificial selection experiments

Example: