purcc 2012 - University of the Pacific

Poster Session Abstracts
pressures, with increased sound intensity and
reduced airflow. This indicates that the
reinforced medial edges lead to increased
concavity of the membranes, producing a lateral
force that compresses the medial edges against
each other. This lateral force should be the key
that allows the vocal folds of frogs to produce
intense sound over a wide range of pressures
without requiring muscular positioning of the
vocal folds.
The Effect of Cell Size on Auditory
Morphology and Tuning in Gray
Treefrogs
Erica Chean and Heidi Huh
Faculty Mentor: Marcos Gridi-Papp
For the brain to perceive sound, signals have to
be transmitted across the eardrum, ossicles, inner
ear fluid, hair cells and nerves. The hearing
properties of frogs are affected by the
mechanical properties of tissues in the auditory
chain. If the sizes of the cells vary, the tuning of
the auditory structures formed by them might be
affected. Two gray treefrogs: Hyla versicolor
and Hyla chrysoscelis, are identical, but the
former has twice the number of chromosomes
than the later, and chromosomal duplication
always results in increased cell size. We
hypothesized that the larger cells of auditory
elements in the tetraploid H. versicolor make it
more sensitive to lower frequencies than diploid
H. chrysoscelis. We are characterizing the
auditory morphology of both
frogs to relate it to their hearing performance. In
order to obtain quantitative results, we have been
dissecting out the inner ear, middle ear, and
auditory ossicles. These tissues are then
decalcified and embedded in paraffin, sectioned
in the microtome and stained with
hematoxylineosin. These methods have been
initially tested in Rana pipiens, to establish
decalcification procedures involving acids,
EDTA, and microwaving. We are currently
obtaining the sections for gray treefrogs and
these results should allow us to determine
relationships between polyploidy, cell size,
auditory morphology and hearing performance.
These data should advance our understanding of
ear design and explain how morphological
differences in the ears result in the hearing
sensitivities of various species.
Hearing Sensitivity in the Golden
Treefrog Polypedates leucomystax from
Vietnam
Emilio Cortes Elviña
Faculty Mentor: Marcos Gridi-Papp
For sound stimuli to be perceived by the brain,
they have to transmitted across several structures
in the ears. In order to unveil general principles
of auditory design, our lab is conducting
comparative studies of natural variation in
auditory morphology and hearing sensitivity.
This study is focused on hearing performance in
the South Asian common treefrog (Polypedates
leucomystax), as a representative of the family
Rachophoridae for which auditory information is
very scarce. Auditory responses to pure tones at
various frequencies are being quantified with
two methods: 1) The vibration of the eardrum is
measured with a laser vibrometer, in order to
assess the function of the mechanical portions of
the ear; and 2) Since frogs cannot be trained to
press a button when they hear a sound, we
employ neurophysiological recordings to
determine which sounds elicit neural responses
at the brain. A tungsten electrode is positioned
among neurons in the torus semicircularis, an
auditory center located in the optic lobe. Sound
tones are then played at various intensities and
frequencies to stimulate neural response. The
data are currently being collected and the
preliminary results indicate that the hearing
sensitivity of this frog matches closely those of
similar-sized treefrogs in the New World, despite
their significant geographic and phylogenetic
distance.
Variations in Sound Production
Frequency Among North American Gray
Tree Frogs
Joanna Mari Concha Guhit
Faculty Mentor: Marcos Gridi-Papp
Studies of mammalian vocal structures have
demonstrated the relationship between laryngeal
size and sound production frequency. This
relationship is also present in anurans. Hyla
chrysoscelis and Hyla versicolor, two North
American gray tree frog sister species, share
their physical aspect, size, ecology and behavior,
but differ in chromosome numbers as H.
chrysoscelis is diploid and H. versciolor is
tetraploid. It has been hypothesized that H.
versicolor should produce lower frequency calls
46