My research is focused on the physiological and evolutionary mechanisms of vocal communication, particularly in species in which males and females produce sexually distinct vocalizations. There are two research programs in the lab. The first investigates the neural mechanisms of vocal behavior in males and females using a very simple vocal behavior in frogs as a model. The second explores physiological and evolutionary mechanisms of vocal learning by focusing on song acquisition in male and female songbirds. I take wide ranging methodological approaches, including molecular, electrophysiological, anatomical, endocrinological, and behavioral techniques, in the laboratory as well as in the field, to understand how cellular and molecular events lead to expression of behavior, and how behavior might be shaped by selective pressure.
1. Neural Mechanisms of Vocal Production
in Frogs
Vocal signals produced in the context of reproduction are often sexually distinct.
To understand the functional differences underlying male and female behavioral
differences, I have been investigating the neural mechanisms of sex-specific
vocal production in African clawed frogs (Xenopus laevis). Xenopus
generate sound using a single pair of laryngeal muscles. The sex differences
in the vocalizations can be reduced to differences in muscle contraction rates,
and in turn, differences in the firing
rates of laryngeal motoneurons. Because of the
simplicity of this behavior and its effector pathway, the Xenopus vocal
system is a powerful model for understanding the neural basis of a sexually
differentiated behavior, as well as the mechanisms by which gonadal steroids
shape neural circuitry during development. A major focus of the project is
to determine how androgens modify the function and connectivity of neurons
involved in sexually distinct vocal production. To this end, a Xenopus
hindbrain slice preparation is used to investigate the physiological properties
of vocal neurons and synapses in detail.
2. Sex Differences in Vocal Learning in Songbirds
I am also interested in how more complex vocalizations are acquired during
development. In particular, I am interested in differences in the ability
of male and female birds to learn song. Songbirds develop their songs by imitating
adults, just as human infants acquire speech. Because females of most temperate
species do not sing, our understanding of song learning has been limited to
males. However, my previous work has shown that, in the Northern cardinal
(Cardinalis cardinalis), one of a few temperate species in which both
sexes sing, females learn songs with a drastically different time course than
males. The findings demonstrate the most substantial learning differences
between male and female animals found to date, and provide a unique opportunity
to investigate not only the physiological control of vocal learning, but also
evolutionary mechanisms that shape the timing of learning in the two sexes.
I am investigating the hypotheses that, at the proximate level, the timing
of song learning in the two sexes is regulated by distinct profiles of gonadal
steroids and, at the ultimate level, the sexually distinct timing of song
learning evolved as an adaptation to meet the different functional requirements
of songs in the two sexes. These hypotheses are tested through endocrinological
(hormonal assays and manipulations) and behavioral (playback technique)experiments
in the laboratory and in the field. In addition, song learning processes of
male and female cardinals are characterized in more detail to examine previous
indications that the learning process in the two sexes is modified differently
by external factors such as photoperiod.
