Is the Northern Spectacled Salamander Salamandrina perspicillata aposematic? A preliminary test with clay models

From Firenze University Press Journal: Acta Herpetologica

Giacomo Barbieri, DISTAV, University of Genova

Andrea Costa, DISTAV, University of Genova

Sebastiano Salvidio, DISTAV, University of Genova

Many animal taxa evolved conspicuous colourations associated with different mechanisms of antipredator defence such as claws, beaks, teeth, spines, stings and a variety of toxic compounds that are actively inoculated or passively delivered to predators (Stevens, 2013; Caro and Allen, 2017). This visual communication system is known as aposematism (Steven, 2013), a widespread phenomenon that independently evolved many times in different amphibians lineages (Wells, 2007). Aposematic colourations are usually associated with a variety of toxic compounds that are produced or sequestered and stored in specialised glandular skin glands (e.g., Wells, 2007; Rojas, 2017; Demori et al., 2019).

Several species of aquatic and terrestrial salamanders exhibit a variety of combinations of red, orange yellow or white marks usually displayed on brown or black backgrounds. In salamanders, conspicuous colourations are typically assumed to act as aposematic warning anti-predatory signals (e.g., Wells, 2007; Lüddecke et al., 2018). In fact, several alkaloids (e.g., tetradoxins) and other toxic com-pounds are isolated from the skin of newts and salamanders, reinforcing the assumption that these contrasted colourations are associated with unpalatability (e.g., Yotsu-Yamashita et al., 2007, 2017; Preissler et al., 2019). Usually, bright colour patterns are usually displayed on the dorsal surface of amphibians. However, some salamanders are dorsally cryptic while possessing aposematic colourations on the underside. These species dis-play their ventral bright colours by exposing the venter by coiling laterally (e.g., the Asian newt Paramesotriton deloustali) or coiling the tail above the body (e.g., the North American newt Taricha rivularis and the Alpine newt Ichthyosaura alpestris) (see Fig. 14.30 in Wells, 2007). This latter anti-predatory behaviour is known as “Unkenreflex”, first described in the fire-bellied toad Bombina bombina (Hinsche, 1926).

This peculiar behaviour, i.e. exposing bright ventral colouration by arching the body, is displayed also by the two species of Spectacled salamander belonging to the genus SalamandrinaFitzinger, 1826: S. perspicillata and S. terdigitata (Angelini et al., 2007). However, Lanza (1967) casted doubts on the aposematic function of Unkenreflex in Salamandrina, because this genus does not possess the parotoid glands typical of many toxic salamanders, while Utzeri et al. (2005) presented some anecdotal evidence for unpalatibility. Therefore, the function of the black, white and red coloured ventral side and of the red tail of Sala-mandrina remains uncertain, although no alternative explanation has been proposed.To better understand if the ventral colouration of S. perspicillata could represent an aposematic signal, we made a predation experiment by using of clay replicas representing the dorsal and ventral patterns of the focal species.

Experiments using this technique are non-invasive and easy to perform in natural habitats, but problems and limitations should be also taken into consideration (Bateman et al., 2017; Rössler et al., 2018). In the present study, clay models were exposed in the species’ natural habitat and predation rates on different model types com-pared. If the aposematic hypothesis holds true, we expected that models with a conspicuous red colouration typical of the body underside and tail would be attacked less frequently than those bearing a dark dorsal appearance.

Salamandrina perspicillata (Savi, 1821), the Northern Spectacled Salamander, is endemic to central and northern Italy (Angelini et al., 2007). This species is found from the sea level up to about 1900 m, in Mediterranean vegetation areas and in humid broadleaf wood-lands (Angelini et al., 2007; Romano et al., 2009). Adults usually range from 70 to 100 mm in total length and are fully terrestrial, with the exception of gravid females that enter water bodies for spawning (Angelini et al., 2007). The dorsal colouration is characterised by a very dark or black dorsal pattern with, during the terrestrial phase, a matt appearance.

DOI: https://doi.org/10.36253/a_h-10229

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