First record of underwater sound produced by the Balkan crested newt (Triturus ivanbureschi)

Simeon Lukanov, Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, Bulgaria

Sound production plays an important role for many taxa across the animal kingdom. For amphibians, this is mainly true for anurans — the first early attempts at more detailed studies of the functions of vocal signals in anurans date from the first half of the 20th century (Noble and Noble, 1923), and the first comprehensive work on acoustic communication in amphibians and reptiles is by Bogert (1960), which is also the first attempt to view the information of amphibian vocal signals in an evolutionary and ecological frame.

In recent decades there is a growing number of publications describing the structure of anuran calls (e.g., Ziegler et al., 2011; Guerra et al, 2018; Stanescu et al., 2018; Carvalho et al., 2019), geo-graphic variations of vocal signals in some species (e.g., Amezquita et al., 2009; Kaefer and Lima, 2012), as well as the role of the signals as phylogeographic indicators (e.g., Stöck et al., 2008; Vences et al., 2013).In contrast, caudate amphibians have received very little attention in this regard.

While they lack a tympanc middle ear, a number of studies have established that their underwater auditory abilities are sufficient for them to sense sound frequencies by other means, such as their mouths or lungs (e.g., Hetherington and Lombard, 1983; Christensen et al., 2015). Available data on their sound production is limited to just a few taxa, and even then, the information is mostly descriptive, with little effort to analyse its ecological function. In addition, most of the data is on North American species, leaving the rest of the world almost unstudied. Even though a variety of sounds made by caudate amphibians have been described as early as the mid-twentieth century (Maslin, 1950; Neil, 1952), they were assumed to be mostly non-functional and produced by unintentional expulsion of air (Bogert, 1960).

On land, some caudate species are known to produce squeaking noises when stressed (“mouse-like squeaking note”; Maslin, 1950). Although a num-ber of authors have registered underwater hisses, clicks or squeaks in various species (Maslin, 1950; Gehlbach and Walker, 1970; Wyman and Thrall, 1972; Davis and Brattstrom, 1975; Crovo et al., 2016), their exact purpose is still unknown. Maslin (1950) suggests they are unintentional, but others propose they could serve a purpose in social interactions (Gehlbach and Walker, 1970; Davis and Brattstrom, 1975; Crovo et al., 2016) or orientation (Gehlbach and Walker, 1970). A recent study by Hubáček et al. (2019) registered a high number of underwater low and mid-frequency clicks produced by Ichthyosaura alpestris and Lissotriton vulgaris, suggesting that newts are much more vocally active than demonstrated by currently available data. This study tested the hypothesis that the Balkan crested newt Triturus ivanbureschi Arntzen & Wielstra, 2013 was vocally active underwater.

The aim was to describe the registered sounds and to present possible explanations for the potential role of the produced clicks in the species orientation or interaction.


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