Randy D. Zelick - US grants

There are three general classes of behavioral responses to a novel stimulus: startle, arousal and orientation. The startle response is a short latency set of muscular contractions induced by a brief stimulus, typically visual or acoustic. It is characteristic for the startle threshold to be much greater than the animal's detection threshold. Arousal behavior is characterized by a suite of physical responses. Although more subtle than startle behavior, both the effective stimuli and the responses are quite general with arousal, making investigation of the individual neural elements involved in novelty detection problematic. Although orienting responses have not been well defined in fish, the novelty response of pulse-type weakly electric fish fits best into this category as defined for mammals. The novelty response is a transient acceleration of the pacemaker which drives the fish's electric organ. Elicited by small stimulus changes near detection threshold, it is a subtle but reliable behavior which is not explosive, has a short refractory period, and involves a single effector pathway. The novelty response of pulse-type weakly electric fish is well suited to neurophysiological analysis and permits simultaneous measurement of behavioral and neural responses. Dr. Randy Zelick will continue his work on novelty detection in electric fish. This work is significant since it will give us a better understanding of the means by which the nervous system distinguishes novel from background sensory input. //

Description:(taken from the abstract) The objective of this study is to understand how the auditory periphery maintains function under conditions of ionic and osmotic stress. The auditory subsystem comprised of the hair cell end organs, afferent synapses and VIIIn will be examined in two species of anuran amphibians - a toad (Bufo marinus) which is dehydration-tolerant and a frog (Rana catesbeiana) which is dehydration-sensitive. This study is specifically designed to determine if auditory function is ultimately compromised due principally to: 1) ionic or osmetic effects on the fluid spaces of the hair cells (otic capsule/endolymph) or 2) direct effects on hair cells and their ability to ion-regulate or volume-regulate. Amphibians make an excellent model for this research because they are uniquely adapted to endure dehydration; at the same time, they cannot use renal mechanisms to compensate for increased plasma salt load. This means that frogs and toads are largely dependent on inner ear regulatory mechanisms to maintain function. Species of anurans differ in their dehydration tolerance, thus the amphibian model will permit an understanding of the compensatory mechanisms and adaptations specific to this tolerance. The anatomy of the anuran inner ear permits access to the endolymphatic space of the hair cells, and this space can be directly manipulated and monitored relative to ion and osmolyte concentration. Finally, the presence of two independent auditory organs in each anuran ear, the amphibian and basilar papillae, allow for comparison of differential effects of ionic and osmotic stressors on non- identical hair cell end organs. The recording of evoked potentials (Brainstem Auditory Evoked Potential and Frequency Following Response) and single-unit recordings from the VIIIn will be performed while challenging R. catesbeiana and B. marinus with increased concentrations of ions (NaCl) and osmotic agents (sucrose, urea). Comparisons will be made of induced auditory dysfunction with both whole body and direct otic capsule challenges. How hair cell systems deal with ionic and osmotic stress is of critical importance in understanding pathological dysfunction of inner hair cell homeostatic mechanisms, as occurs with Meniere's disease, and mechanisms protecting sensory systems from extreme ionic and osmotic disequilibrium.

A major question in understanding the natural world is how each species is able to successfully identify a mate to assure persistence of the species and how changing environmental conditions might influence its reproductive success. In many species male advertisement calls are essential for attracting a female to mate with as well as being used for species recognition when more than one species co-occurs within an area. The researchers have identified a novel system to quantify how male advertisement and recognition calls are altered when the calls are performed underwater among populations of northern red-legged frogs in the Pacific North West. This research on sound transmission and mating will be complemented by an investigation of the genetic differentiation among populations of this frog species throughout its geographic range. The research will be shared via an outreach initiative at Portland State University's "Better Know a Lab" that brings together the surrounding community and research labs to jointly conduct data collection all the way through to the presentation of their findings. Furthermore, networking is planned with local teachers to help design interdisciplinary curricula highlighting the role of communication, ecology, and the science of sound to engage students in learning about mating strategies and the important role animal communication plays in species successful persistence in nature.

The sensory drive hypothesis asserts that sensory conditions (environmental biophysics) and sensory systems drive divergence in mate signaling in a particular direction, one that optimizes signal propagation ultimately through resultant reproductive success. This research is unique in testing the sensory drive hypothesis with a terrestrial anuran that (1) calls underwater and (2) calls in shallow ponds that may dramatically alter "normal" acoustic attenuation. Attenuation of acoustic signal components is generally proportional to the square of sound frequency; higher frequencies attenuate much more quickly. However it has been shown that in shallow ponds, substrate and depth can dramatically increase the attenuation of lower frequencies. Because the energetically dominant frequencies upon which female choice is based fall in the lower range of the signal, a system where low frequencies may be dramatically attenuated is far more likely to create reproductive isolation among frog populations than the previous systems studied. The project will test the acoustic and genetic differentiation of allopatric northern red-legged frog populations compared across ponds with significantly differing acoustic profiles across a large geographical scale. How well male advertisement calls are matched to the frequency profile of the breeding site should determine reproductive success and create directional selection on spectral characteristics, and provide a first test for the sensory drive hypothesis through the utilization of underwater calling.