Discussion

Males of Phyllodytes luteolus presented advertisement calls with a higher dominant frequency in natural environments when compared to highway environments, and there is no evidence that chorus noise alters the acoustic parameters of this species. Therefore, P. luteolusdoes not seem to be affected by traffic noise, which may explain its presence in anthropized areas. In addition, we found a positive relationship between advertisement call intensity and male body size.
Contrary to what was expected by our hypothesis (1), males ofPhyllodytes luteolus from natural areas presented higher dominant frequencies of the advertisement call compared to individuals from environments with road noise. Although some anuran species can increase the dominant frequency of calls to avoid overlapping with the noise frequency (e.g., Scinax nasicus , Leon et al., 2019; Litoria ewingii , Parris et al., 2009; Rana clamitans and Rana pipiens , Cunnington & Fahrig 2010, and Amolops torrents , Zhao et al., 2018), others can decrease the dominant frequency (e.g.,Boana bischoffi , Caorsi et al., 2017). In an experimental study, Caorsi et al. (2017) observed that Boana leptolineata did not change the dominant frequency when exposed to different levels of anthropic noise. Like B. leptolineata , males of Phyllodytes luteolu s have calls with an average dominant frequency (3.46 kHz) above the mean energy concentration of road noise (below 1 kHz) (Cunnington & Fahrig, 2010; Warren et al., 2006). Therefore, species that have calls with higher frequencies have little or no acoustic overlap with anthropic noise. In addition, the frequency of ambient noise in highway areas was very low and may not represent sufficient noise to disruptP. luteolus vocalizations. The dominant frequency of the call is usually a static property (little intra-individual variation) as it is related to morphological characteristics of males (Gerhardt, 1991; Köhler et al., 2017), serving as an indicator of the quality of males (Bastos et al., 2011; Gingras et al., 2013), being an important parameter for the sexual selection system of a population (specific recognition and mate selection by females). Thus, dominant frequency values may be stabilized across populations (Friedl, 2006, Andreani et al., 2020). Future studies should investigate possible causes for the difference in call frequency of different anuran populations, especially those exposed to anthropic noise.
The advertisement call of P. luteolus has a narrow bandwidth in which the energy distributions around the dominant frequency are short. Some studies suggest that acoustic signals with higher bandwidths may be less detectable against noise since the signal energy is spread over a wide range of frequencies (Parris et al., 2009; Warren et al., 2006), therefore P. luteolus would have an advantage in noisier environments. Many altered habitats present a constant noise pattern in certain frequency bands and for a long period of time, acting as a selection pressure (Warren et al., 2006). In this sense, more studies need to be carried out to assess how different types of noise, and/or even anthropogenic vibrations (e.g., Caorsi et al., 2020) can influence the reproductive behavior of anuran amphibians.
There was no influence of road noise or situation (with or without chorus) on the temporal parameters of the advertisement call of P. luteolus , also not corroborating our hypothesis (II). The advertisement call of P. luteolus has a long duration (around 5 sec.) and a series of identical notes without frequency modulation. The temporal structure of the call can influence the active space of the signal when propagated in the environment, increasing the fidelity of the transmitted information, and, therefore, decreasing the probability of acoustic overlap (Ey & Fischer, 2009; Warren et al., 2006), an attribute that is advantageous in environments with high noise levels. In general, the social context in which males are inserted in the reproductive site influences the change in call parameters (Bosch & De La Riva, 2004; Toledo et al., 2015). Furthermore, males of P. luteolus begin to vocalize after the period of greatest road traffic (between 5 and 7 pm), and therefore, the lower flow of vehicles at night may not represent a source of noise that modifies the acoustic parameters of the species. It is necessary to investigate whether other factors are more important to determine changes in the acoustic parameters of P. luteolus , such as the density of conspecific individuals in the choirs. Experimental studies on the immediate response of males are important for a better understanding of the behavioral strategies adopted by P. luteolus on the balance of costs and benefits determined by changes in acoustic parameters when they are subjected to different noise levels.
We found a positive relationship between advertisement call intensity and male body size. In general, morphological characteristics of males can determine the temporal parameters of the call (Kohler et al., 2017; Wells, 2007). For example, larger males have larger lungs and, therefore, greater energy reserves, being able to emit calls with greater intensity (Wells, 2007; Wells & Schwartz, 2006). Possibly, even in noisy scenarios, larger males are able to increase the intensities of their calls to avoid signal masking and promote greater signal detection, localization and discrimination (Halfwerk et al., 2016; Yi & Sheridan, 2019). Therefore, the intensity of the call is an important parameter for sexual selection (Gerhardt & Huber, 2002; Wells, 2007) since the sounds with higher intensities can propagate over long distances, potentially attracting a greater number of females and thus obtaining greater reproductive success (Bastos et al., 2011; Kime, 2000; Penna & Solís, 1998).
The Yellow Heart-tongued Frog (Phyllodytes luteolus ) has advantageous acoustic characteristics in conditions where anthropogenic noise is present. Therefore, even in noisy environments, individuals of this species manage to recognize and discriminate in the conspecific chorus. This fact may explain the successful occupation of areas outside its original range, having already been reported as an invasive species (Forti et al., 2017). Invasive species may impose limits on reproductive success and survival of other frog species that live in the same habitat. For example, males of P. luteolus calling in the same frequency range as the species Ischnocnema sp. The acoustic noise caused by the vocalization of an invasive species can harm the acoustic communication system in native species as it can influence the ability of females to locate males in the reproductive environment (Forti et al., 2017). This is the first study evaluating the influence of sound noise on a bromeliad anuran. Future studies may increase our knowledge on the effects of anthropogenic sound and serve as a subsidy for conservation actions, especially those aimed at acoustic monitoring in noisy environments.