7 Memorandum : Vibration effects on amphibians (Leiopelmatid frogs) 64524 Vibration effects_memorandum (15 June 2022)_Final Rev 0.docx physiological costs in response to sustained stimuli (e.g., noise-legacy populations of wood frogs have adapted to physiologically costly anthropogenic [traffic] noise; Tennessen et al., 2018). Similarly, Garner et al, (2018) suggested that rodent responses (e.g., startle and freeze reflexes) seemed to decrease when repeatedly exposed to vibration, though their results were largely inconclusive. Vibration impacts on animals appear to be influenced by a combination of amplitude, duration, and frequency of vibration events, as well as body size characteristics, species ecology, and individual variation in perception across species or within the same species. Consequently, it is exceedingly difficult to determine if and how a species will respond to vibration stimuli and even more difficult to determine what the short- and longer-term affects might be without designed laboratory experiments or intensive monitoring of wild populations pre- and post-stimulus. 6.1 Vibration effects: potential implications for Leiopelma species. Archey’s and Hochstetter’s frog lack middle ear structures altogether. That is, the tympanic membrane (a round patch, corresponding to an eardrum, found behind and below the eye in many frogs) and columella are absent, but the operculum and inner ear structures remain present (Stephenson 1951; Pereyra et al., 2016). Thus, while Leiopelma are incapable of hearing sound in the traditional sense they theoretically can detect vibrations in the same way as other ‘earless‘ amphibian species (e.g., bufonids; Womack et al., 2017). As mentioned previously, leiopelmatid frogs do not produce calls as a means of communication and it has been demonstrated that chemosensory cues are important in conspecific communication (Lee & Waldman, 2002; Waldman & Bishop, 2004). However, communication through other means such as vibratory modalities has largely been ignored (Waldman & Bishop, 2004), i.e., there is no published literature on vibration sensing in Leiopelma. Furthermore, I have been unable to find any literature on vibration perception in their closest relatives; two species of frogs in the genus Ascaphus. This makes it hard to determine the extent to which Leiopelma can sense vibration and how vibration from anthropogenic sources may or may not affect them. The ecology of leiopelmatids may provide some insights into to importance of vibration sensitivity. These frogs remain stationary for long periods of time, and all employ a sit-and-wait strategy to secure prey. These characteristics allow the frogs to establish strong and constant coupling of the body with the substrate. The low levels of self-generated noise obtained with the lack of body motion and/or optimised coupling might be requirements for the frog to take advantage of a highly sensitive seismic detection system. It is not unplausible to suppose that vibration could be used as a means of detecting approaching prey and/ or predators, or potentially associated with con-specific recognition, or even detecting environmental cues (e.g., rainfall) that elicit behavioural responses (e.g., emergence). Approaching predators (e.g., birds) or other frogs could cause low-frequency vibrations, which may elicit the startle and freezing responses in frogs that assist with concealing themselves from predators/ conspecifics. Detection of approaching conspecifics by their vibrations could allow frogs to prepare for subsequent behaviours, e.g., escaping or mating. These kinds of responses have been reported in studies of other anurans (Lewis & Narins, 1985; Narins, 1990).
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