Variability in escape trajectory in the Trinidadian stream frog and two treefrogs at different life-history stages

Abstract

Most studies investigating anuran jumping behaviour have examined the relationship between body size and parameters such as jump distance, velocity, and force; however, few have investigated jump trajectory. We constructed an arena to determine escape trajectories in relation to the direction of an artificial stimulus in the aromobatid Mannophryne trinitatis (Garman, 1888) and two treefrogs, Trachycephalus venulosus (Laurenti, 1768) and Hypsiboas geographicus (Spix, 1824). Three categories of M. trinitatis (i.e., tadpole-transporting males, nontransporting males, and females) and three ontogenetic stages of the treefrogs were compared. Mannophryne trinitatis escaped in a broadly predictable trajectory away from the stimulus, although jump trajectories were highly variable, suggesting a degree of unpredictability. No systematic differences were found between categories of M. trinitatis, adding to the findings of previous studies that larval transport incurs no measurable locomotor costs on antipredatory jumping behaviour with regards to jump angle and distance. The treefrogs showed similar patterns of escape trajectory and unpredictability. There were no consistent differences between life-history stages and no relationship between distance jumped and angular deviation. In M. trinitatis and H. geographicus, there was some evidence of bimodality in escape trajectory. The results are discussed in the context of other work on escape trajectories and the concept of “protean” defence strategies.