Seasonal, hormonally controlled, phase-specific sex differences in electric organ discharges of the weakly electric fish, Gnathonemus petersii (Mormyridae), and the effects of captivity on these discharges.
Item
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Title
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Seasonal, hormonally controlled, phase-specific sex differences in electric organ discharges of the weakly electric fish, Gnathonemus petersii (Mormyridae), and the effects of captivity on these discharges.
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Identifier
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AAI9020775
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identifier
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9020775
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Creator
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Landsman, Robert Eric.
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Contributor
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Adviser: Cheryl F. Harding | Peter Moller
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Date
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1990
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Neuroscience | Psychology, Psychobiology | Biology, Zoology | Biology, General | Agriculture, Fisheries and Aquaculture
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Abstract
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Little is known about the effects of captivity on physiology and behavior in wild-caught vertebrates. Studying the effects of captivity on reproduction is hampered because most wild animals fail to exhibit sexual behavior under captive conditions. The present studies were designed to describe the electric organ discharge (EOD) in Gnathonemus petersii with emphases on plasticity of the EOD as a potential signal for sexual identity and the effects of captivity. Initially, males at rest were found to exhibit higher peak power spectral frequencies (PPSFs) of the Fourier transformation of EODs than females. When these subjects were confined or restrained, the sex difference was abolished due to increased individual variability in PPSFs. Subsequently, seasonal sex differences were found in two of the four EOD phases, in the PPSF, and in external morphology in newly imported fish during 1988. During the rainy breeding season, but not during the pre- or post-rainy seasons, males exhibited longer durations in phases 2 and 3 and lower PPSFs than females. Further, only males had an indentation in the dorsal margin of the anal fin. These sex differences were demonstrated to be controlled by androgens. Testosterone (T) induced the male-like indentation and exerted more profound increases in the durations of phases 2 and 3 and decreases in PPSF than dihydrotestosterone in both juveniles and adults. In juveniles, low-dose T decreased the durations of phases 1 and 4, while high-dose T increased the durations of both phases. Estradiol had no effects on EODs or external morphology in juveniles, but caused a slight increase in adult PPSFs. The seasonal hormonally-controlled phase-specific sex differences in EODs in just imported fish were abolished or even reversed, depending on housing conditions, by 37 days in captivity. Within 5 days in captivity, plasma levels of T and 11-keto T in males dropped to near non-detectable levels. These endogenous hormone changes were closely followed by a decrease in the duration of phase 3 by day 10, and an increase in PPSF by day 15 in captivity. Together, these studies demonstrate the link between captivity, hormones, and behavior.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
