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The search for speciation genes in the house mouse
Bettina Harr
University 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?
white-crowned sparrow
http://www.naturesongs.com/wcsparrow1.wav
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.naturesongs.com/wcsparrow1.wav
http://www.mbr-pwrc.usgs.gov/id/htmwav2/h5810so.mp3
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 quality
Males 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 sex
Advertises condition
Attracts a mate
Proclaims territory: establish and maintain the territory
Stimulates and synchronizes courtship behavior
Maintains pair bond.
Identify individuals.
Identify species
Flock cohesion
Warn of enemies
To 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)