The nocturnally-active freshwater Neotropical gymnotiform electric fish generate weak electric organ discharges (EODs) that are detected by electroreceptors to facilitate active electroreception (object detection and communication - including species recognition). The EOD rate of 'pulse-type' species varies among individuals as a function of activity rate and during sexual or agonistic interactions. The extent to which EOD rate varies between and within species in natural conditions, and the ecological and evolutionary factors that influence such variation are poorly known. EOD rate is presumed to represent a measure of sensory sampling rate, and therefore we hypothesized that water flow velocity may correlate positively to EOD rate variation (both between and within species). To test this hypothesis, we made nocturnal EOD-rate recordings of 862 non-breeding individuals of nine common species in rainforest streams of the upper Amazon. These recordings were accompanied by measurements of additional parameters hypothesized to influence intraspecific (but not interspecific) variation in pulse rate by influencing activity rate. These parameters included conductivity and turbidity (proxies for recent rainfall), temperature and dissolved oxygen (a possible metabolic constraint on signaling), body size (representing ontogeny), and moonlight intensity (a metric of predation risk). Using multiple regression in the form of linear mixed effect models, and model selection, we determined that none of these variables explain interspecific variation in EOD rate – suggesting that other factors such as species recognition or non-adaptive drift represent more important ultimate drivers of interspecific variation in pulse rate. However, at the intraspecific level, we reported a substantial reduction in mean pulse rate on nights with strong moonlight in two species, Brachyhypopomus sullivani and Gymnorhamphichthys rondoni. In two other species, Brachyhypopomus beebei and Brachyhypopomus verdii, we reported elevated pulse rate during periods of increased conductivity and/or turbidity that followed rainfall and consequent flooding of ephemeral swamps adjacent to terra-firme streams.
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Master of Science (M.S.)
College of Sciences
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Correa Roldan, Ericka Vanessa, "Environmental Correlates of Sensory Sampling Rate in the Electrosensory System of Neotropical Electric Fishes" (2019). Electronic Theses and Dissertations, 2004-2019. 6470.