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  • 1
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Flow cytometric DNA analysis was used to determine the DNA content of red blood cells from Ginglymostoma cirratum (Bonaterre) and Raja eglanteria (Bosc). The DNA content/nucleus was calculated to be 7.6 and 7.1 pg/nucleus, respectively. Peripheral red blood cells obtained both from G. cirratum and from R. eglanteria were demonstrated to be actively cell cycling. Percentages of red blood cells in the phases of the cell cycle (G0/G1, S, and G2/M) not only varied considerably between different fishes but also were quite variable in weekly samples obtained from individual animals.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1351
    Keywords: Key words Ampullae of Lorenzini ; Elasmobranch ; Electrorecptor ; Frequency response ; Communication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract This study examined the response properties of skate electrosensory primary afferent neurons of pre-hatch embryo (8–11 weeks), post-hatch juvenile (1–8 months), and adult (〉2 year) clearnose skates (Raja eglanteria) to determine whether encoding of electrosensory information changes with age, and if the electro-sense is adapted to encode natural bioelectric stimuli across life history stages. During ontogeny, electrosensory primary afferents increase resting discharge rate, spike regularity, and sensitivity at best frequency. Best frequency was at 1–2 Hz for embryos, showed an upwards shift to 5 Hz in juveniles, and a downward shift to 2–3 Hz in adults. Encapsulated embryos exhibit ventilatory movements that are interrupted by a “freeze response”” when presented with weak uniform fields at 0.5 and 1 Hz. This phasic electric stimulus contains spectral information found in potentials produced by natural fish predators, and therefore indicates that the embryo electrosense can efficiently mediate predator detection and avoidance. In contrast, reproductively active adult clearnose skates discharge their electric organs at rates near the peak frequency sensitivity of the adult electrosensory system, which; facilitates electric communication during social behavior. We suggest that life-history-dependent functions such as these may shape the evolution of the low-frequency response properties for the elasmobranch electrosensory system.
    Type of Medium: Electronic Resource
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