Are chemical cues important to individual recognition in the territorialist frog Leptodactylus fuscus (Scheneider, 1799) (Anura, Leptodactylidae)?

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Thayllon Orzechowsky Gomes, Iuri Emmanuel de Paula Ferreira and Vinicius de Avelar São Pedro, Federal University of São Carlos, Buri, Brazil, Daniel Marques Almeida Pessoa, Department of Physiology and Behavior, Federal University of Rio Grande do Norte, Natal, Brazil

Background/Question/Methods
Chemical signaling is the most widespread and oldest type of communication between individuals. In anurans, studies on chemical communication are historically neglected to the detriment of those on acoustic communication and the extent of the use of chemical cues by frogs is still underestimated. This study aimed to determine whether the semifossorial frog Leptodactylus fuscus can use chemical cues for recognition between individuals. In this species males are territorial and usually call near the entrance of underground retreats. Forty-five specimens (40 males and 5 females) of L. fuscus were collected by nocturnal active search in four different sites at the municipality of Campina do Monte Alegre (southwest of São Paulo state, Brazil). The specimens were individually kept in small plastic containers with a clean moist sheet of filter paper, which served to maintain humidity and absorb volatile chemical compounds present in the frog’s skin. Frogs were individually submitted to two-alternative forced choices in an experimental arena with two options of shelters, each one containing a moist filter paper with a specific chemical cue, which could be from the own specimen, from a neighbor (collected in the same site), from a non-neighbor (collected in a different site) or just distilled water (control). In the end, each specimen was tested once in four experimental conditions: (I) own odor vs neutral cue; (II) neighbor's vs neutral cue; (III) non-neighbor's vs neutral cue and (IV) neighbor's vs non-neighbor's cue.
Results/Conclusions
Individuals choose one of the two possible retreats in 152 of 180 tests performed (45 repetitions of each experimental condition). Individual preference was detected in the experimental conditions II and IV. The neutral cue was preferred over the neighbor's odor, whereas the neighbor's odor was preferred over non-neighbor's. We conclude that the odors present in the shelters influenced the choices made by the frogs. Our results suggest that L. fuscus may also rely on chemical cues for individual recognition. However, because our findings were contradictory, it is not clear yet how the species uses such information in territorial behavior. Thus, it is evident the need for additional research that could contribute to understanding the role chemical compounds may play in anurans behavior and territoriality.