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The Rhinella granulosa group currently includes 12 species distributed eastern to the Andes, from Panama to central Argentina. We studied bioacoustic features of the advertisement calls in seven of these species: Rhinella azarai, R. bergi, R. centralis, R. dorbignyi, R. fernandezae, R. major, and R. merianae. In addition, we analyzed the release calls of R. azarai, R. bergi, R. dorbignyi, and R. fernandezae. The advertisement calls consisted of long trills, composed by notes with a variable pulse number (2–8) that was characteristic of each species. The release calls consisted of a single note, pulsed or not. Both advertisement and release calls clearly varied between species, except for R. dorbignyi and R. fernandezae. The study of specimens sharing exosomatic characters with R. bergi and R. major from a syntopy area, which presented intermediate spectral and temporal call parameters, confirmed natural hybridization between these two species.

The role of the vagus nerve in determining heart rate (f(H)) and cardiorespiratory interactions was investigated in a neotropical fish, Piaractus mesopotamicus. During progressive hypoxia f(H) initially increased, establishing a 1:1 ratio with ventilation rate (f(R)). Subsequently there was a hypoxic bradycardia. Injection of atropine abolished a normoxic inhibitory tonus on the heart and the f(H) adjustments during progressive hypoxia, confirming that they are imposed by efferent parasympathetic inputs via the vagus nerve. Efferent activity recorded from the cardiac vagus in lightly anesthetized normoxic fish included occasional bursts of activity related to spontaneous changes in ventilation amplitude, which increased the cardiac interval. Restricting the flow of aerated water irrigating the gills resulted in increased respiratory effort and bursts of respiration-related activity in the cardiac vagus that seemed to cause f(H) to couple with f(R). Cell bodies of cardiac vagal pre-ganglionic neurons were located in two distinct groups within the dorsal vagal motor column having an overlapping distribution with respiratory motor-neurons. A small proportion of cardiac vagal pre-ganglionic neurons (2%) was in scattered positions in the ventrolateral medulla. This division of cardiac vagal pre-ganglionic neurons into distinct motor groups may relate to their functional roles in determining cardiorespiratory interactions.

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