Bad vibrations: Mechanosensory risk assessment by red-eyed treefrog embryos

Abstract

Red-eyed treefrogs, Agalychnis callidryas, lay gelatinous egg masses on vegetation overhanging ponds; tadpoles fall into the water upon hatching. Embryos hatch up to 30% prematurely in attacks by egg-eating snakes, but not in other intense but benign disturbances, such as storms. We used modal analysis and vibration recordings from clutches in natural disturbances to characterize the vibrational environment of embryos, and playbacks to assess if vibrations cue hatching, and how vibration characteristics affect hatching behavior. Escape hatching can be induced by snake vibrations, without actual snakes, and embryos distinguish between the vibrational patterns of snake attacks and rainstorms. Benign and dangerous disturbances overlap in individual temporal and frequency characteristics, but can be distinguished using combinations of features. Both frequency and temporal characteristics of vibrations affect the hatching response. Embryos use at least two temporal pattern elements—disturbance duration and interdisturbance interval—and respond to a limited range of low frequencies. These are all necessary elements of a composite cue. Moreover, higher frequencies, found in rainstorms but not attacks, reduce hatching. This is the most detailed examination of mechanisms underlying embryo decision making to date, and a demonstration of the importance of vibrational information in predator-prey interactions. [Work supported by NSF IBN-0234439.]