genetics iii: examples mutation analyses- strengths: implicate roles for specific genes in animal...

Genetics III: Examples

• Mutation Analyses-• Strengths: Implicate roles for specific genes

in animal behaviors

• Weakness: Lead to misconception that those genes alone cause the behavior…

• Weakness: Confined to Lab model systems (e.g. mice, Drosophila)


• Mutation Analyses-

• Concept: Knock-out expression of focal gene, and measure changes to behavior


• Mutation Analyses-

• Concept: Knock-out expression of focal gene, and measure changes to behavior

• Classic Example: "Periodicity" gene in flies

(Bayles, Bargiello, Jackson & Young 1987)

Standard Method to confirm functional role of gene:• Look at mutant, then insert a functional copy of that gene to

test whether normal phenotype is restored…

• E.g. "Met" gene and allometry: (Thomas Flatt, Douglas Emlen, Quenna Szafran & Olga Helmy)

Standard Method to confirm functional role of gene:• E.g. Larval foraging behavior in Drosophila (Marla

Sokolowski)

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• Hybridization Studies-

• 'Common Garden' Experiments: Rear animals from two populations (that differ) in a common (laboratory) environment. Do the differences persist? Are hybrids intermediate in phenotype?





• Example:

• Migration in Blackcap Warblers:

• (Peter Berthold & colleagues)

• Recent Twist (2005):• Female preferences for males

with different migration routes contributes to speciation…



• Heritability Studies-

• Strengths: Measure the heritability, which is directly relevant to the potential for that behavior to evolve…. (R = h2 * s)

• Weakness: A LOT of work

• Weakness: Tells us nothing about the actual genes or physiological/ developmental pathways involved

• Example Methods:

• Parent/Offspring Regression and Sibling Analyses (1/2 Sib and Full Sib): Measure the resemblance among relatives to quantify heritability

• Example:

• Heritability of cricket song (Anne Hedrick)







Male song is heritable, and differs across populations & species…


• Artificial Selection: Extremely powerful because the population actually does evolve

• But very labor-intensive!

R = h2 * s




R = h2 * sYou know the strength of selection (s) and you measure the response (R)




R = h2 * s

So you can calculate the heritability…

Example: Nesting behavior of mice (Carol Lynch)





Example: Migratory behavior in milkweed bugs (Hugh Dingle & James Palmer)





Polyphenism: A special type of ‘reaction norm’

Household Thermostat

The phenotype exhibits discrete variation,

and low heritability

But the threshold varies continuously,

and heritably

1. Artificial Selection can shiftthe threshold….

1. Artificial Selection can shiftthe threshold….

2. Populations differ in theirThreshold...

3. Species differ in their threshold

• Many behaviors are 'threshold' traits: • Animals often do one thing at a time….

– Feed or run– Guard or sneak

• Individuals switch between alternative states,and they may differ heritably in their switchpoints….

• (e.g. boldness, aggressiveness)

• Example: Diapause in green lacewings (Catherine & Maurice Tauber)





• Example: Sex ratio in snapping turtles (Frederick Jansen)







Genomic Approaches:

-Measure levels of expression of thousands of genes simultaneously (i.e. genomes)

Can be used on non-model taxa!



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Castes differ in the expression of many genes….


Queens


larvae


Workers

Larval genes:

Worker genes:

Queen genes:


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Different behaviors of bees are associated with the expression of different genes…

"age polyethism"

Young Nurse Bees

Old Forager Bees

Genomics is transforming studies of the inheritance

of animal behavior

Compare gene expression in animals involved with all sorts of behaviors….

e.g. female sticklebacks choosing

and not choosing among male

mates (Molly Cummings, UT Austin)



genetics iii: examples mutation analyses- strengths: implicate roles for specific genes in animal...

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