Sentinels of the Pantanal: Health and territory defense in giant otters

Abstract

The giant otter (Pteronura brasiliensis) is a social and territorial semiaquatic mammal that can be found in the rivers of the Pantanal. Despite of the endangered status, the information regarding the health of the species is scarce. In this thesis we (1) assessed mercury contamination level in giant otters; (2) report a case of myiasis; and (3) evaluate their territorial behavior throughout playback experiments. Our analysis indicated higher mercury levels in connected watercourses near gold mining areas, decreasing downstream. This highlights a gradient of contamination and the far-reaching impact of local polluting activities in the Pantanal. Additionally, herein, we reported the first case of myiasis caused by the fly Cochliomyia hominivorax (Calliphoridae) in a giant otter found dead in the Pantanal. The injured otter probably got the larvae after an intraspecific fight and the myiasis probably deteriorated the health of the infested giant otter, which prevented recovery and accelerated its death. For last, in order to evaluate the territorial behavior of the giant otters, we conducted playback experiments, and evaluated their responses to the type of the broadcasted sound (adult-call and snort) and the group-proximity (self, neighbors and non-neighbors), given the presence of cubs and the effective group size. Our results showed that the sociability of giant otters is associated with their defensive capabilities, and that individuals must weigh the costs of exposure and combat. The otters presented difference in responses to the sound types, which may be related to the meaning and type of information conveyed by these sounds and differences in the vocal signature. The groups presented reduced responses when with cubs, suggesting a strategy to minimize the exposition of their cubs to potential threats. Our results did not support the Dear enemy hypothesis, yet our findings support the threat level hypothesis that states that neighbors and non-neighbors can represent different threat levels according to variation in the resources and other environmental variables.