Exploring the Mind of Songbirds: Connecting gene
sequence with the evolution of behavior
Kev Chapman
Perhaps the smartest bird that we know is the flamboyant Big Bird from Sesame
Street, who entertained our youths with a wide array of talents. He can roller
skate, dance, draw, write poetry and even ride a unicycle. In reality, songbirds
display complex cognitive and social behaviors. Therefore, they are excellent
biological model for neurological research. Received her PhD in Neurobiology &
Behavior from the University of Washington in 1997 and has been at Emory
since 2002, Dr. Donna Maney, the principle investigator of the Birdbrain Lab at
the Emory Department of Psychology, is currently conducting research to
evaluate the effects of hormones on brain structure and function in songbirds.
What was your concentration in graduate school? Why did you pick it?
Neurobiology and Behavior. I am interested in brain plasticity, in other
words how the brain changes to respond to stimuli in adaptive ways.
Why songbirds?
Songbirds exhibit remarkable brain plasticity. Songbirds are famous for
the large and obvious changes that occur in their brains in response to
hormone fluctuations. You don’t even need a microscope to see
differences in brain morphology between a bird with high vs. low
testosterone, or between a male and a female. The magnitude of these
changes, like the giant squid neurons, makes songbirds obvious models
for studying plasticity, seasonality, and the neuroendocrine control of
behavior. They exhibit vocal learning. Songbirds and parrots are able to
learn vocalization patterns from other members of their species, making
their vocal development more similar to humans than any mammal. There
is huge variation in social behavior across species. Researchers in the
field of ornithology have been amassing an impressive body of literature
pertaining to the social behavior of thousands of species of wild birds. As
a result, we know for over 4,000 species whether they defend territories or
live in social groups, whether they form pair bonds, how they
communicate and how they care for their offspring. This database on
behavior is unparalleled in any vertebrate group, and can be used to guide
research into the neural mechanisms underlying pair bonding, aggression,
sociality, parenting, and many other social behaviors. They are easily
studied in their natural habitat. To be valuable and informative, research in
neuroscience should be conducted using ethologically relevant tasks and
contexts close the animals’ natural state. Few neuroscientists, however,
are developing techniques to study wild populations. We are developing
tools to study comparative behavioral neuroendocrinology in animals’
natural habitats. My research is not limited to songbirds. Over the course
of my career, I have studied rats, mice, chickens, frogs, spiders and
humans. Today, I am collaborating with other labs that work with humans,
non-human primates, mice, and social insects.
Why conducting these studies?
Very little research, except possibly that conducted directly on humans, is
aimed toward understanding the biology of only one type of organism.
Because the basic biology of every animal is the same, results obtained in
one species are applicable on a broad level to others and to real life. Most
biological research makes use of model organisms, or species that are
well-suited for studying a particular question or system. For example,
Hodgkin and Huxley, scientists who studied how nerves conduct impulses,
worked with squid because of their large neurons that were easy to study.
As a result, most of what we know about the conduction of nerve impulses
in humans came from research on squid. Similarly, much of what we know
about genes and pattern development in humans came from work on fruit
flies. Songbirds are excellent models for our research questions.
What is the focus of your current research?
We have three projects that are ongoing. They focus on (1) the hormonal
basis of sensory plasticity and how hormones alter motivation (2) how
small changes in genetic sequence can have large effects on behaviors
and (3) how seasonally breeding songbirds “know” it is time to breed each
year.
What is the real life application of these projects?
The evolution of behavior relies on changes at the level of the genome;
yet the ability to attribute a behavioral change to a specific, naturally
occurring genetic change is rare in vertebrates. In white-throated
sparrows, a genetic polymorphism segregates with a behavioral
phenotype. Males and females of the white-striped (WS) morph are
heterozygous for a rearranged chromosome 2, called ZAL2m, and
respond to a simulated territorial intrusion with high levels of aggressive
singing. Birds of the tan-striped (TS) morph are homozygous for the
standard arrangement (ZAL2) and respond with relatively little or no
singing. In addition to the difference in aggression, TS males engage in
more parental behavior than WS males. Because of its association with
aggressive and parental phenotypes, the ZAL2m chromosome represents
a powerful target for studying the genes involved in these behaviors. We
are using complementary approaches to identify genes that contribute to
the behavioral phenotypes.
The Neurobiology of Social Reward: Conspecific vocalizations are special
sounds. In some cases, animals will approach and even work to hear
them; they have incentive salience. In female songbirds, the motivation to
hear male song is dramatically altered by plasma levels of the
reproductive hormone estradiol (E2). For example, female white-throated
sparrows in non-breeding condition will press a key to hear male
song several hundred times per day if they are treated with E2, whereas
untreated females with low E2 are completely uninterested in hearing
song. Our research goal is to understand exactly what E2 does in the
brain to change the rewarding properties of social signals. A female whitecrowned sparrow responds to male song by performing a courtship
display. Attending to a stimulus and assigning value to it both depend on
monoamine neuromodulators such as dopamine and norepinephrine.
Neurons containing these catecholamines serve as dynamic filters that
integrate ascending sensory signals with environmental context and
internal state, allowing behavioral responses to change accordingly. We
have shown that E2 alters these systems; for example, E2 increases the
density of catecholaminergic and serotonergic fibers innervating auditory
areas. We are now testing whether E2 modulates the sound-induced
release of these monoamines in auditory and reward areas. Animal
models are needed in order to understand autism and other human
disorders of social reward. We are developing an assay to quantify social
reward in zebra finches learning song. During the song learning period,
juveniles are highly motivated to hear song and will peck a key to trigger
song playback from a plastic model of an adult male. This assay nicely
models social interactions between parent and offspring and will allow us
to determine the effects of pharmacological manipulations on the reward
value of those interactions. We are working closely with researchers at the
Marcus Autism Center in Atlanta to maximize the translational impact of
our assay.
Environmental Modulation of Reproductive Function: Most living things
use cues from the environment to time their reproductive efforts. For
example, many seasonally breeding animals increase the secretion of
reproductive hormones in response to lengthening days in the spring.
Other species use different kinds of cues, such as social context or food
availability. How such signals are processed by the brain, and particularly
how these signals are transduced into an endocrine response, is not well
understood. Using a marker for new protein synthesis (Egr-1), we can
map the brain’s response to cues in white-throated sparrows in the lab. By
studying a model organism that responds to light cues with increases in
hormone release, we can see that after just one long day, the mediobasal
hypothalamus, a region at the base of the brain where reproductive
hormones are released into the bloodstream, is actively producing Egr-1.
The Egr-1 indicates that this brain region is actively engaging in new gene
transcription; in other words, responding to the environmental signal.
Since reproductive development can be accelerated in females when they
hear male song, we played recordings of song to females in the lab in
order to map the brain response. We found that within minutes, hearing
song induces Egr-1 expression in the mediobasal hypothalamus and also
triggers release of reproductive hormones. Our results suggest that cells
in the mediobasal hypothalamus are part of a final common pathway for
both kinds of environmental cue (light and sound). The research helps us
to understand how the brain uses information from the external
environment to bring about adaptive changes in the organism.
Are these projects different from what your lab has been doing for the past
years?
Recent newer directions include operant conditioning tasks and RNA
transcriptome analysis.
Would you give us a short description of the GA Tech lab that you are
collaborating with?
Soojin Yi is the principle investigator at GA Tech. We were introduced by
Dr. James Thomas, formerly of Emory and now at NIH in Bethesda.
Why are you working with this lab?
Soojin is an expert in comparative genomics, which complements our
expertise in behavioral neuroendocrinology. Together, we can ask
questions about how genomic architecture can affect behavior and how
behaviors evolve.
Why is it important for different universities/ organizations to collaborate in
research?
You can’t always find exactly the right complementary expertise at your
own institution, so it’s important to branch out.
Any advice for students who are interested in doing research in the future?
PIs are always interested in hearing from undergraduates who are
interested in their research. The best way to contact a PI is by email. Be
sure to use professional English (e.g. not “hey prof!”) and explain why you
are interested in that PI’s research. I get a lot of emails from students who
don’t bother to tell me why they want to work in my lab, and it’s obvious
that they sent the email to a lot of different professors. Sometimes my
name is in a different font or not mentioned at all. Emails like that are very
unlikely to get a response. Take the time to explain yourself and show that
you have a genuine interest in the research, because the PIs are looking
for people who will get excited about the project.