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David Yager, Ph.D.
Associate Professor Integrative Neuroscience
E-mail: ddyager@umd.edu
Laboratory |
Research and Teaching Interests:
David D. Yager (Associate Professor), received his Ph.D. in 1989 from Cornell University. His research focuses on how the central nervous system processes auditory information to trigger and control behavior, especially predator avoidance behavior in praying mantises and tiger beetles. His laboratory also studies the evolution of hearing in insects (BI).
Insects have evolved tympanate hearing many times, and the Yager lab uses the unique auditory system of the praying mantis as a model for auditory system evolution. These animals have a single ‘cyclopean’ ear in the middle of their body that is sensitive exclusively to ultrasound. Neurophysiological projects in the lab have focused on several auditory interneurons and their role in processing and/or relaying information to the brain.
The approach to questions about mantis hearing combines neurophysiological, anatomical, biomechanical, and behavioral strategies. For instance, there is evidence from laser vibrometry and neural recordings that some mantids monitor three sound frequency bands using six tympana in two ears. There are four tympana the large auditory chamber of the ultrasound ear, and two in a second ear—also in the midline, but in a different body segment—that hears only low frequencies. Extracellular and intracellular recordings are defining the basic characteristics of these systems. A key question is whether the three systems work together or if there are three independent auditory systems within the same animal.
Some studies point to at least two separate auditory systems. Long series of behavioral experiments in the lab and in the field have proven that ultrasonic hearing protects mantids from capture by echolocating bats. High-speed video shows that ultrasound triggers a complex, multi-component behavior that throws the animal into a steep power dive. Low frequency (2-5 kHz) hearing obviously doesn’t protect against bats, but the behavioral significance of this auditory ability remains a major puzzle for future research.
Through comparative studies of other insects, the Yager lab hopes to understand the transition from earless to eared. The precursor structures to the ear itself have been identified in mantids’ closest relatives, the cockroaches (earless). The nervous system must also change in several ways to accommodate the new type of information. Proprioceptive interneurons become auditory interneurons and must alter their connections. Most importantly, the new input must be linked in the CNS to behaviors very different from the precursor function(s). Do the behaviors arise de novo or are existing behavioral modules coopted for audition (most likely)? What is the nature of the behavioral modules and how do they incorporate the context dependence we see in ultrasound-triggered behavior?
In collaboration with scientists at Brigham Young University, the Yager lab is creating a mantis ear phylogeny by combining anatomical, physiological, and molecular data. This is the first auditory phylogeny derived from such a large, broadly multidisciplinary database.
Besides mantids and cockroaches, the Yager lab studies the neurophysiology and auditory behavior of tiger beetles and several other insects. This has involved fieldwork all over North America.