Astyanax mexicanus, or the Mexican tetra, inhabits both surface streams and cave systems, and has subsequently developed two unique morphologies: a cave morph and a surface morph. Cave morphs of the species have evolved several troglomorphic phenotypes, including vestigial eyes, reduced pigmentation, and increased olfactory and lateral line sensitivity. Interestingly, several satellite populations of surface fish were introduced to a Texas aquifer approximately 100 years ago and, following cave colonization, rapid evolution of various sensory adaptations between the cave and surface populations have been observed. Auditory evoked potential (AEP) data was collected to compare hearing sensitivities between cave and surface satellite populations, and both populations responded to sound presentation up to 4 kHz. However, because AEPs measure action potential summation to screen for frequency sensitivities, behavioral data is needed to determine absolute hearing sensitivity. The current study examines behavioral differences in sound detection between these two populations using reflexive startle behaviors to sound, namely the “C-start” escape response, which has been shown to be a reliable means of determining neurological responses to acoustic stimuli. Based on behavioral audiograms collected on satellite three populations, San Pedro Springs (cave) and Honey Creek (surface) appear to respond more readily to acoustic stimuli and habituate at a similar rate when compared to San Antonio Zoo (surface), which appear to respond less readily and habituate faster. Differences in sound pressure thresholds, as well as stimulus-response latencies between these populations, will be determined through finer volume control and modeling sub-thresholds.
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Kistner, Amanda R; Enriquez, Maya S; Michels, Noland O; Mensinger, Allen F.
Behavioral differences in sound detection in recently diverged cave and surface forms of Astyanax mexicanus.
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