Call Transmission Efficiency in Native and Invasive Anurans: Competing Hypotheses of Divergence in Acoustic Signals

Abstract

Invasive species are a leading cause of the current biodiversity decline, and hence examining the major traits favouring invasion is a key and long-standing goal of invasion biology. Despite the prominent role of the advertisement calls in sexual selection and reproduction, very little attention has been paid to the features of acoustic communication of invasive species in nonindigenous habitats and their potential impacts on native species. Here we compare for the first time the transmission efficiency of the advertisement calls of native and invasive species, searching for competitive advantages for acoustic communication and reproduction of introduced taxa, and providing insights into competing hypotheses in evolutionary divergence of acoustic signals: acoustic adaptation vs. morphological constraints. Using sound propagation experiments, we measured the attenuation rates of pure tones (0.2–5 kHz) and playback calls (Lithobates catesbeianus and Pelophylax perezi) across four distances (1, 2, 4, and 8 m) and over two substrates (water and soil) in seven Iberian localities. All factors considered (signal type, distance, substrate, and locality) affected transmission efficiency of acoustic signals, which was maximized with lower frequency sounds, shorter distances, and over water surface. Despite being broadcast in nonindigenous habitats, the advertisement calls of invasive L. catesbeianus were propagated more efficiently than those of the native species, in both aquatic and terrestrial substrates, and in most of the study sites. This implies absence of optimal relationship between native environments and propagation of acoustic signals in anurans, in contrast to what predicted by the acoustic adaptation hypothesis, and it might render these vertebrates particularly vulnerable to intrusion of invasive species producing low frequency signals, such as L. catesbeianus. Our findings suggest that mechanisms optimizing sound transmission in native habitat can play a less significant role than other selective forces or biological constraints in evolutionary design of anuran acoustic signals.

SENSORY DRIVE DOES NOT EXPLAIN REPRODUCTIVE CHARACTER DISPLACEMENT OF MALE ACOUSTIC SIGNALS IN THE UPLAND CHORUS FROG (PSEUDACRIS FERIARUM)

“…These studies used amplitude measurements and transmission experiments with cross-correlation and other statistical analyses to support the idea that transmission of calls was more efficient in native habitats or that different calls transmitted more efficiently in different environments. Other studies of vocalizations in anurans that used transmission experiments, as well as extensive comparative meta-analyses failed to find evidence of sensory drive (Penna and Solis 1998;Kime et al 2000;Castellano et al 2003;Bosch and De la Riva 2004;Llusia et al 2013). Here again, method cannot explain these different results because similar methods produced opposite conclusions.…”

“…; Bosch and De la Riva ; Llusia et al. ). Here again, method cannot explain these different results because similar methods produced opposite conclusions.…”

How the environment shapes animal signals: a test of the acoustic adaptation hypothesis in frogs

“…These contradictory results are, at least partially, explained by a very broad categorization of habitats, such as 'open' vs. 'closed', which oversimplifies complex habitat conditions (Bosch & De la Riva, 2004;Goutte et al, 2016). Thus, testing predictions stemming from the AAH requires examination of the acoustic constraints in a microhabitat-specific context (Goutte et al, 2013(Goutte et al, , 2016 when it is not possible to measure the transmission properties of all the habitats (Penna & Solis, 1998;Penna et al, 2005;Llusia et al, 2013). Using continuous measurements of the habitat, Maddieson & Coup e (2015) showed a correlation between habitat characteristics and the number and cluttering of consonants in 663 local human languages, which are comparable to the complexity and the importance of high-frequency components in animal vocalizations.…”

Invading the soundscape: exploring the effects of invasive species’ calls on acoustic signals of native wildlife

“…Sound properties of invasive species' calls will also likely influence their degree of impact on native species. When species invade a new soundscape, they may introduce noises that are loud (Farina et al 2013;Llusia et al 2013) or overlap in sound properties with native species' calls or other important sounds (Azar and Bell 2016). Masking could be particularly severe for native species that call alongside an invader in a similar niche, and that share call properties with the invader.…”