Adaptive ontogeny in response to ambiguous cues

As animals develop, their capacities to sense cues, assess threats, and
perform actions change, as do the relative costs and benefits that
underlie behavioural decisions. We presented ambiguous cues to test if
hatching decisions of red-eyed treefrogs, Agalychnis callidryas, change
developmentally following adaptive predictions based on changing costs of
decision errors. These arboreal embryos hatch prematurely to escape from
egg predators, cued by vibrations in attacks. Young embryos modulate
hatching based on frequency and temporal properties of cues, reducing
false alarms that unnecessarily expose them to risk in the water. Since
the cost of false alarms decreases developmentally, we hypothesized that
hatching responses to ambiguous cues would increase. We tested this using
vibration playbacks at two ages, with two sets of 3 stimuli. We matched
sampling costs and varied ambiguity in either temporal or frequency
properties, so one stimulus elicited high hatching (positive control) and
two elicited low hatching but differed in ambiguity, based on prior
results with younger embryos. Older embryos hatched faster, indicating
reduced cue sampling. They responded strongly to both clear threat cues
and ambiguous stimuli but little when either property clearly indicated
low risk. In both experiments, we saw the greatest ontogenetic change in
response to the more ambiguous stimulus. These playback experiments
improve our understanding of how embryos facing risk trade-offs make
adaptive decisions based on incidental cues from predators. Ambiguity in
incidental cues is ubiquitous and developmental changes in behaviour due
to ontogenetic adaptation of decision processes are likely to be
widespread.