Animal Behaviour 2721 genetics (till lecture 9)

How do we know whether genes influence behaviour? Logical Argument

• genes code for proteins used in structure and regulation

• proteins influence behaviour therefore, genes produce behaviour

• but can intricate behaviour be programmed by the underlying genetic code? Yes!

genes, environment, and behaviour connections

4 Evidence for Genetic Basis of Behaviour

1. Inbreeding 2. Artificial selection 3. Hybridization 4. Molecular genetics

Inbreeding

• selective mating of closely related individuals

• reduces heterozygosity –25% lost from each generation of sibling matings–after 20 generations individuals are 98% identical

• individuals within inbred lines are virtually genetically identical

• different alleles (i.e., forms of a gene) become fixed in different inbred lines

• to explore the effect of one variable, we hold all others constant

• inbred lines provide a unique opportunity to do this

• comparison of individuals from different lines reared in a common environment reveals the effect of genetic differences on behaviour

•holding environment constant allows assessment of genetic contributions to behaviour

•inbred strains also provide a convenient source of genetically similar individuals with which to examine environmental effects

•identical twins also are commonly used to look at environmental effects– inbred strains provide a larger sample size

Adam Miklosi and colleagues (1997):

• antipredator behaviour of paradise fish larvae

• 2 strains of paradise fish (strains P & S) have been inbred for more than 30 generations

• all fish have had an identical environment

• paradise fish larvae recognize predators by their eyes

• predators evoke antipredator behaviour

p strain attacked models with eyes, s strain didnt

Fleeing – larvae darts by slapping caudal fin

Ø behavioural difference between strains must reflect genetics

Heritability

• a statistical measure of the extent to which a trait is influenced by genes

• ranges between 0 and 1– 0.5 indicates that 50% of the observed variation is attributed to genetic variation

• by holding the environment constant, observed variation must be the result of genetic variability and error

“adaptive traits

variation among individuals ensures that some individuals possess traits that enhance their survival and reproductive success

selected

if such traits are heritable, they should increase in prevalence within the population

natural selection

natural elements of the organism’s biotic and abiotic environment determine success

Artificial Selection

• humans decide which animals will reproduce

• choice based on desirable traits

• such selective breeding can result in structural change e.g., Darwin (1859) chapter on utility of artificial selection

• humans also decide which animals to breed based upon desired behavioural traits e.g., dogs

• alleles (different forms of the same gene) responsible for the behaviour of interest will increase in the population because only individuals possessing those alleles are permitted to breed

• if the frequency of a trait can be altered by selecting which individuals are permitted to breed, then that trait must have a genetic basis

Tolman (1924)

- “bright” versus “dull” rats

• examined maze navigation in rats

• counted total errors made over 14 trials in maze

• experiment to determine whether “brightness” was genetically controlled

• mated bright-bright and dull-dull

f1 gen of bright rats errors decreased over time, f1 gen of dull rats did not and fluctuated

• artificial selection for multiple generations: got more extreme as gens went on, by the 7th gen f7 bright rapidly ddecreased errors but f7 dull increased in errors over time

• because rearing conditions were held constant throughout, and selection resulted in discrete groups, maze navigation behaviour is under genetic control

• originally called two strains “bright” versus “dull” rats– found that “brightness” in maze was not transferable to other tasks (only spatial navigation)

• therefore referred to as “maze bright” versus “maze dull” rats

Lynch (1980)

– nest building in house mice

• gene(s) for nest size may also be subject to natural selection

• pup survival is reduced at low temperatures

• pup survival is higher in larger nests

• mice at northern latitudes build larger nests

Hybridization

• Cross individuals with different expressions of the same underlying behavioural trait e.g., aggressive x submissive e.g., nomadic x sedentary

• F1 behaviour – depends on pattern of dominance among alleles complete dominance - the phenotype of the heterozygote is indistinguishable from that of the dominant homozygote incomplete dominance - the phenotype of the heterozygote is intermediate to the two homozygotes

• just as Mendel came to understand the genetic basis of traits in garden peas, controlled crosses can provide insight into the genetics of behaviour

e.g., Foraging behaviour in fruit fly larvae (marla Solkolowski)

Foraging behaviour in fruit fly larvae

• 2 foraging strategies observed in nature

• Rovers explore multiple patches

• Sitters remain on one patch

• Rovers move more than Sitters within a patch

• Rovers move more than sitters within a patch

effect is specific to foraging

if u put them on just all food, they move, if you put them all on no food,, they move

• created homozygous parental strains by crossing rovers with rovers and sitters with sitters

• predicted that foraging strategy is determined by a single complete dominance gene

Hypothesis: F-rover is dominant —— f-sitter is recessive

• F1 generation were all rovers prediction: f f F Ff Ff F Ff Ff

• consistent with hypothesis that rover is dominant allele

• F2 larvae were 25% sitter and 75% rover

• consistent with hypothesis that rover is dominant allele

• single complete dominance gene determines foraging strategy

Ø gene affects production of cyclic GMP-dependent kinase Ø alters transfer of information between sensory and motor systems Ø affects foraging behaviour

the gene doesn't make the behaviour, it codes for proteins that effect behavior

calling behaviour in crickets

• males produce calls that attract females

• calls are species-specific

• in lab, hybrids can be produced

• hybrid males produce calls that are intermediate to parentals in both frequency and duration

• hybrid females preferentially orient to intermediate calls genetic control with incomplete dominance