The Neuroethology of Predation and Escape by unknow

Author:unknow
Language: eng
Format: epub
ISBN: 9781118527238
Publisher: John Wiley & Sons, Inc.
Published: 2016-05-16T00:00:00+00:00

6.4.4 Avoiding detection, mostly

The most primitive form of weak EOD is thought to have been asymmetrical, like the EOD of the strongly electric fish described previously. However, most pulse- and wave-type electric fish now generate EODs which oscillate symmetrically about the zero potential. In these fish, both faces of the electrocytes are excitable, and action potentials are generated in sequence – first on the innervated side, and then on the non-innervated side – thus generating a bi-phasic potential. Why has this change come about?

An asymmetric half-wave EOD has a substantial amount of energy in the low-frequency part of the spectrum (including DC), but this is much reduced in the symmetrical full-wave EOD (Figure 6.15).

Figure 6.15 Evolutionary changes in the EOD waveform have reduced low-frequency spectral power. A: The presumed ancestral EOD waveform is monophasic and asymmetrical, and this shape has been maintained in most extant strongly electric fish (solid black line). In contrast, most extant weakly electric fish have modified the EOD into a biphasic symmetrical form (dashed red line). B: The monophasic waveform has maximal power in the low-frequency spectral region (solid black line), but the biphasic waveform has maximal power between 1–2 kHz (red dashed line).

Adapted from Stoddard (1999).

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