Artificial SelectionChapter 2 The Evolution of Behavior

Natural SelectionWhen nature is the selective agent, traits, including behavioral traits, increase or decrease as a function of how well they suit

organisms to their environment.

If an animal’s trait variation allows for better survival and reproduction that trait is bound to be passed on. Small

differences in fitness can accumulate into large changes in gene frequencies.

The process of natural selection requires three prerequisites to operate:

1. Variation

Can be caused by genetics, i.e. genetic variation

- Mutation

- Genetic recombination

Or can be caused by environment

- Migration

2. Fitness Consequences

The trait must affect reproduction success

3. Mode of InheritanceTruncation selection experiment

Xo = mean value

Truncation line-only birds above this speed allowed to breed

X1 = mean of Truncation line

S = selection differential

X2 = mean value of 2nd generation

Behavioral GeneticsBehavioral geneticists are involved in many activities linked to ethology:

1. Mendel’s Laws

Used to better understand the underlying genetics of

behavioral traits.

Satellite males vs. Independent male ruff birds (Philomachus pugnax)

2. Mapping Genes for Behavioral (Polygenic) TraitsBehavioral geneticists often search for a set of genes responsible for the expression of polygenic traits. QTLs are quantitative trait loci.

Jonathan Flint and his colleagues’ work found evidence of QTLs associated with fear on 14 different chromosomes of mice.

3. Determining What Variation of a Trait is due to Genetics & What is Due to Environment

Cliff swallows (Petrochelidon pyrrhonota)

Cross-fostering experiment

Modern Theoretical Framework for Animal Behavior

The Selfish Gene

Any gene that codes for a trait that increases the fitness of its bearer

above and beyond that of others in the population will increase in

frequency.

Antipredator Behavior in Guppies

Most guppy studies are conducted in the Northern Mountains of Trinidad and Tobago.

Upstream from waterfalls – low predation pressure

Downstream from waterfalls - severe predation pressure

Differences in the two populations include antipredator behavior, color, number of offspring in a clutch, offspring size, aging patters, & age at reproduction.

Antipredator behavior

- Shoaling- Predator inspection

1957 Transfer of guppies demonstrated evolution via natural selection

Demonstrates that Natural Selection can act fairly quickly