Homing trajectories and initial orientation in a Neotropical territorial frog, Allobates femoralis (Dendrobatidae)

Abstract

Introduction: The ability to relocate home or breeding sites after experimental removal has been observed in several amphibians and the sensory basis of this behavior has been studied in some temperate-region species. However, the actual return trajectories have rarely been quantified in these studies and it remains unknown how different cues guide the homing behavior. Dendrobatidae (dart-poison frogs) exhibit some of the most complex spatial behaviors among amphibians, such as territoriality and tadpole transport. Recent data showed that Allobates femoralis, a frog with paternal tadpole transport, successfully returns to the home territories after experimental translocations of up to 400 m. In the present study, we used harmonic direction finding to obtain homing trajectories. Additionally, we quantified the initial orientation of individuals, translocated 10 m to 105 m, in an arena assay.

Results: Tracking experiments revealed that homing trajectories are characterized by long periods of immobility (up to several days) and short periods (several hours) of rapid movement, closely fitting a straight line towards the home territory. In the arena assay, the frogs showed significant homeward orientation for translocation distances of 35 m to 70 m but not for longer and shorter distances.

Conclusions: Our results describe a very accurate homing behavior in male A. femoralis. The straightness of trajectories and initial homeward orientation suggest integration of learned landmarks providing a map position for translocated individuals. Future research should focus on the role of learning in homing behavior and the exact nature of cues being used.

Figure 1

Homing trajectories circular. Circular plot showing the homing trajectories of ten territorial males that were translocated over 50 m in the telemetry trials. For better visualization, all trajectories were normalized to a single starting point and axis. Each line represents a different individual. Points mark en route locations connected by linear interpolation.

Figure 2

Arena orientation. Circular vector plots representing initial orientation over one meter of territorial individuals translocated from close-range, < 35 m (a), mid-range, 35 – 70 m (b), or far-range, 70 – 105 m (c). Each vector represents an individual. Vector length represents the path straightness in the arena. Vector direction represents the bearing from the arena center to the crossing point of a one-meter radius circle. Reported significance levels were obtained by second order Hotelling’s circlular test for unimodal distribution and by a Hotelling’s two-sample test for the comparisons between distributions.

Figure 3

Trajectory map. Map of the study area showing homing trajectories and temporal distribution of ten territorial males, each individual represented by a different color. Square frog symbols indicate the home territories; x-symbols show release points; circles show en route locations connected with linear interpolation lines. The size of each circle is proportional to the time spent at each location. Contour lines (1 m) are in light gray, creeks and Arataye River in dark gray.

Figure 4

Arena trajectory. Example of a single coded trajectory from the arena experiment, using a graphical arena representation as an interface. Solid outer circle represents the arena wall, small filled gray circle represents the release device, black dots connected by an interpolation line represent each hop of the frog in the arena. The orientation bearing was measured at the outer dashed circle (100 cm) and the straightness coefficient (SC) was calculated for the path between inner (30 cm) and outer (100 cm) dashed circles.