Announcements

The search for speciation genes in the house mouse

Bettina HarrUniversity of Cologne, Germany

(candidate for position in Vertebrate Evolutionary Genomics)

4:00 P.M.Wednesday, January 31, 2007

B102 Chem Life Science (Auditorium)

Tinbergen’s 4 questions

1. Proximate causation: sensory motor mechanisms

2. Ontogeny: interaction between genes and environment to shape behavior (development)

3. Ultimate Causation: selective processes that shape behavior (function)

4. Phylogeny: historical processes that shape behavior (constraints)

Why do birds sing?

Why does each individual have its own variant of the species song?

Why do males sing but females do not?

Why do different species of birds have different songs?

http://www.naturesongs.com/wcsparrow1.wav

white-crowned sparrow

Different regions have different dialects:

Two potential proximate explanations for variation:

1. Different dialects caused by genetic variation among the populations.

2. Variation in dialects due to environmental differences (songs learned from resident males).

Tests: raise baby males (from each area) by hand in sound-proof chambers, let some hear no song, some dialect from “home”, some other dialect

Predictions:

If genetic basis, regardless of which treatment experienced, males from each region would sing their own song.

If environmental basis, no-sound males would not have either dialect, and the other males would sing the dialect they heard, regardless of the area they came from.

Results: no-sound males did sing, but not full song; other males always had the dialect they heard while growing up.

Conclusions: results suggest that auditory environment causes differences in dialects

Moreover, the ability to sing does not require auditory inputs, suggesting that there are genes & neural processes for singing! (at least some components of song are innate)

http://www.mbr-pwrc.usgs.gov/id/htmwav2/h5810so.mp3

http://www.naturesongs.com/wcsparrow1.wav

Song learning in white-crowned sparrows:

10-50 days old is critical period

(neural capacity to record and store)

Only learn species-specific song heard(neural capacity to recognize species song)

Need to practice & hear song types (memory not enough, must compare)

Only important stimulus is auditory?What about visual/social experience?

Test: allow w.c. sparrow baby to hear w.c.sparrow song, but also to see and hear a. finch sing.

Result: sing finch song

So, what is the proximate basis for different dialects in white-crowned sparrows?

At the developmental level, differences in dialect among areas caused by:

Environmental differences (what males hear)

Social experience

So, what is the proximate basis for different dialects in white-crowned sparrows?

At the physiological level, behavioral differences arise because networks of nerve cells (neurons) that record information from social interactions (usually members of their own species).

Neural control of song learning

The neural mechanisms underlying song development:

Distinctive fore-brain circuitry for song learning.

Distinctive brain circuitry for song production.

Sexually dimorphic brain circuitry.

Presence of song, the size of the repertoire, and volume of brain nuclei are correlated between sexes, spp, subspp, & individuals.

Song is a product of stereotyped motor programs controlled by pre-motor and motor nuclei

http://www.life.uiuc.edu/clayton/

Other examples of social effects on song learning:

Why does each individual have its own variant of the species song?

Why do males sing but females do not?

Why do different species of birds have different songs?

Why do males sing but females so not?

Are there differences between male and female brain structure?

Yes, some brain regions (e.g. the RA) are larger in males than females in songbirds.

There are also many genetic differences between male (WW) and female (ZW) birds

but actual mechanism is hormonal differences in the developing brain.

What are some ultimate (evolutionary) reasons why males sing and females do not?

Non adaptive by-product of sexual development (very unlikely).

Adaptive reasons:Males need to attract mates

- song can be an indicator of qualityMales need to hold territories

Why does each individual have its own variant of the species song?

Why do males sing but females so not?

Why do different species of birds have different songs?

(or any song at all for that matter)

Differences in brain structure among species

Ultimate questions about song learning:When did song learning evolve?

How many evolutionary origins were there?

Probably 3

Ultimate questions:

Why sing a song?

Why has a behavior been maintained?

Adaptationist hypothesis: because it has a reproductive benefit (fitness)

Why do birds sing?

Advertises sexAdvertises conditionAttracts a mateProclaims territory: establish and maintain the territoryStimulates and synchronizes courtship behaviorMaintains pair bond. Identify individuals.Identify speciesFlock cohesionWarn of enemiesTo perfect song through practice "Because they enjoy it" (probably not)

Why sing a particular song?Adaptationist hypothesis:

The ecological environment requires it

Great Tit(Parus major)