Zebra Finch : The machine behind the mouth (or beak)

1. Zebra Finch : The machine behind the mouth (or beak) • General facts about Zebra Finches: • The common and widespread in Australia (particularly drier areas), Timor and the Lesser Sunda Islands. • Live year round in social flocks of up to 100 or more birds. • Feed on grass seed and insects. • One of the most common “caged birds” selectively bread for a number of traits. • Considered to be one of the best model systems for basic biomedical research of learning and memory. • Also used as a model system to study many other thing (i.e. olfaction).

2. Basic harmonic stack clay-colored thrush • The syrinx: The song machine • located at the point where the trachea branches into the two primary bronchi. • Sound is generated when: • Air from air sacs is forced through the bronchi & syrinx • the air molecules vibrate as they pass through the narrow passageways between the external labia & the tympanic membrane. • Because there are 2 separate passageways and membranes, some birds are able to generate multiple sounds (harmonics) at the same time:

3. Zebra Finch Song : Unique because of its harmonic characteristics and complexity • The song of the zebra finch as of other birds can be broken down into 3 hierarchical levels: • Syllables: Consist of the basic elements of song for a species. They develop and crystallize during song learning Some types of syllables • harmonic stacks • frequency sweeps • high-pitch notes • broadband sounds • Motifs: Consist of a number of introductory notes followed by sequences of syllables: these sequences are crystallized • Bouts: Consist of a sequence of motifs that is not necessarily stereotyped even in the adult • In adult birdsong, syllables may also be demarcated by intervals of relative silence or sharp frequency modulation changes

4. Zebra Finches female

5. Zebra finch hearing • The most sensitive hearing thresholds of zebra finches are still not quite as good as those of humans. • Zebra finches can discriminating among complex harmonic sounds such as detecting the mistuning of a single harmonic in a harmonic stack.

6. cHV: Hyperstriatum Ventrale NCM: Neostriatum Caudo-Medial nucleus HVc:High Vocal Center (Hyperstriatum Ventralis pars caudalis) NIf: interfacial nucleus of the neostriatum MMAN: Medial nucleus Magnocelularis of the Anterior Neostriatum NCM RA: Robust nucleus of the Archistriatum LMAN:Lateral Magnocellular nucleus of the Anterior Neostriatum nXII:nucleus of the 12th cranial nerve X: Area X of the paraolfactory lobe DLM: Dorso-Lateral division of the Medial thalamus AVT:Area Ventralis of Tsai VL medulla:VentroLateral medulla Uva: nucleus Uvaeformis of the thalamus DM:Dorso-Medial subdivision of the intercollicular nucleus Nuclei of the avian song learning and production pathways Red (learning pathway) Blue (production pathway) is the song output pathway

7. Hormones control brain structure size… controls acquisition/singing behavior Learning and production systems also change size, complexity or protein profiles with changing hormonal levels. There is evidence that song production and learning are hormone-dependent. • EG: • Cells in the… • LMAN • RA • nXIIts … • …accumulate testosterone or testosterone metabolites: these chemicals can directly influence cell proliferation: nuclei size Male produced estrogen and melatonin are necessary for normal development of HVC--RA pathway. • Known environmental mediatorsof hormone levels: • Social interactions: territorial battles, sex, child bearing, love • Stress, diet parasite load • Season: light/dark cycles, temperature • Weather: barometric pressure, temperature

8. Hormone levels mediate sexually related differences in song production nuclei

9. Experiment: Localized neuronal activation in the zebra finch brain is related to the strength of song learning • Rational: • It is not known where in the brain the memories of these learned sounds are stored. • Song perception in songbirds may involve neuronal activation in brain regions that have not traditionally been implicated in the control of song production or song learning. • Hypothesis: learning is mediated in the caudal part of the neostriatum (NCM) and of the hyperstriatum ventrale (cHV). • Procedures: • Zebra finch males (Taeniopygia guttata castanotis) were reared without their father/song and exposed to a tape-recorded song during the sensitive period for song learning. • Placed in sound isolation cages 76-142 days when sound production began recordings were made of the juvenile song to confirm learning from tutor. • At 250 days (when song begins crystallization) adults, they were reexposed to the tutor song but in the dark so that they would not sing. • Controls received all of the same treatment except they were not reexposed to tutor song. • Measured expression of the protein products of the immediate early genes egr-1 (ZENK) and c-fos: these are indicators of neural activity

10. Results: • The males showed increased staining for immediate early genes egr-1 (ZENK) and c-fos in the cell bodies of: • NCM • cHV • Males did not show increased ZENK or c-fos in any other region. conventional "song-control nuclei." Photomicrographs of the zebra finch brain at the level of the NCM, showing egr-1 (ZENK)-like immunostaining. The sections are from a bird in the control (a) and of a bird in the experimental group (b) that both showed a high degree of song learning. V, ventricle; Hp, hippocampus.

11. Counts of stained cells reveal relative differences in ZENK & c-fos between experimental and controls c-Fos ZENK experimental control

12. Furthermore: Strength of ZENK and c-fos staining in NCM and cHV correlates to the number of song elements that the birds had copied from the tutor song Stained nuclei per sq mm ZENK C-fos Fraction shared song elements Exp Exp Cont. Cont. Conclusion: These results show localized neural activation in response to tutor song exposure that correlates with the strength of song learning. This suggests that the memory for tutor song is stored in NCM and cHV

13. Ultimate explanation for bird song: parasite resistance • Females prefer males with higher quality song and higher quality plumage. • Healthy males in heavily parasitized species may result in extravagant trait expression (i.e. elaborate song and fancy feathers. Conclusion: parasite load influences phenotype which in turn influences mate choice decisions. Thus, song complexity could be driven by parasite resistance. Garamszegi et al. (2003)