Biology Reference
In-Depth Information
due to neurite growth, increased synapse formation, and neurogenesis
(
Nottebohm, 2005; Tramontin & Brenowitz, 2000
).
Several parameters have an effect both on song behavior and the underlying
neural mechanisms. Testosterone triggers singing behavior and an increase in
song nuclei volume in female canaries, which do not usually sing or exhibit
seasonal plasticity (
Nottebohm, 1980
). House sparrows (
Passer domesticus
)
housed in constant conditions and administered melatonin mimicking long
days comparable to their natural breeding season exhibited large song control
nuclei. Conversely, sparrows administered short day melatonin durations
exhibited small song nuclei (
Cassone, Bartell, Earnest, & Kumar, 2008
). Mel-
atonin receptors are found in the song control system of house sparrows,
including HVC, RA, and Area X (
Whitfield-Rucker & Cassone, 1996
),
suggesting that melatonin signaling could influence seasonal song production.
On the molecular level, a recent study examined seasonal gene expression
changes in HVC and RA in Gambel's white-crowned sparrows (
Zonotrichia
leucophrys gambelii
)(
Thompson et al., 2012
). They identified over 300 differ-
entially expressed genes, including cerebellin precursor protein 2 (CBLN2),
which is important for synaptic plasticity and is upregulated during long days
when the song nuclei are increased in volume, but downregulated during
short days. Similarly, brain-specific angiogenesis inhibitor 1-associated protein
2 (BAIAP2), important for positive neurite extension and axonogenesis, is
upregulated at the beginning of exposure to long days, but is downregulated
after several weeks in long days and in short days. In addition to plasticity-
related genes, there was also differential expression of genes associated with
apoptosis, angiogenesis, and proliferation, along with transcripts for growth
factors and hormones.
Mukai et al. (2009)
used the same microarray methods
in song sparrows to examine seasonal changes in gene expression in the hypo-
thalamus in relation to territorial aggression behavior, which included both
singing and aggressive displays. They found differential expression of genes
associated with thyroid hormone signaling, including glycoprotein hormones
alpha chain precursor (
CGA
), mu-crystallin homolog (
CRYM
), and trans-
thyretin precursor (
TTR
).
CGA
and
CRYM
were increased in spring, while
TTR
was increased in autumn. These changes occurred even in control ani-
mals and were therefore associated with season and not territorial behavior.
3. MIGRATION
While seasonal courtship behavior specifically promotes successful
reproductive behavior by attracting mates and defending resources, there
are also several examples of circannually timed events that are important
