Asian Herpetological Research 2018, 9(4): 240–249 ORIGINAL ARTICLE DOI: 10.16373/j.cnki.ahr.180025 Call Characteristics of Two Sympatric and Morphologically Similar Tree Frogs Species, Polypedates megacephalus and Polypedates mutus (Anura: Rhacophoridae), from Hainan, China Qiucheng LIU, Tongliang WANG, Xiaofei ZHAI and Jichao WANG* Ministry of Education Key Laboratory for Tropical Island Ecology, College of Life Sciences, Hainan Normal University, Haikou 571158, China Abstract Anuran calls are usually species-specific and therefore valued as a tool for species identification. Call characteristics are a potential honest signal in sexual selection because they often reflect male body size. Polypedates megacephalus and P. mutus are two sympatric and morphologically similar tree frogs, but it remains unknown whether their calls are associated with body size. In this study, we compared call characteristics of these two species and investigated any potential relationships with body size. We found that P. megacephalus, males produced six call types which consisting of three distinct notes, while P. mutus males produced five types consisting of two types of notes. Dominant frequency, note duration, pulse duration, and call duration exhibited significant interspecific differences. In P. megacephalus, one note exhibited a dominant frequency that was negatively correlated with body mass, snout-vent length, head length, and head width. In P. mutus, the duration of one note type was positively correlated with body mass and head width. These differences in call characteristics may play an important role in interspecific recognition. Additionally, because interspecific acoustic variation reflects body size, calls may be relevant for sexual selection. Taken together, our results confirmed that calls are a valid tool for distinguishing between the two tree-frog species in the field. Keywords body size, call characteristics, Polypedates, sexual selection 1. Introduction encounters, and females often preferentially choose larger males (Wells, 1978; Given, 1988; Richardson et al., 2010; Amphibian communication is primarily dependent on Liao and Lu, 2011; Rausch et al., 2014). Previous studies vocalizations (Gerhardt and Huber, 2002; Cui et al., have shown that the spectral and temporal parameters of 2011). In most anurans, acoustic interactions are key calls could reflect frog body size (Martin, 1972; Gerhardt, to male-male competition and female choice (Narins et 1994; Wang et al., 2012; Wei et al., 2012; Zhu et al., al., 2006; Xu et al., 2011). The spectral and temporal 2016a). However, other studies suggest that acoustic parameters of acoustic calls are species-specific, and properties and morphological characteristics are unrelated hence can be used for species identification and for in some frog species (Penna, 2004; Márquez et al., 2005). determining phylogenetic relationships (Jiang et al., Polypedates megacephalus and P. mutus (family 2002; Heyer and Barrio-Amorós, 2009). Thus, acoustic Rhacophoridae) are tree frogs common throughout studies are an important tool for clarifying the taxonomy southern China and Southeast Asia (Fei et al., 2012). of sympatric and morphologically similar species. The two species have controversial taxonomic status. In Body size may affect the outcomes of sexual selection China, Hong Kong populations previously considered through male-male competition and female choice. to be P. leucomystax were named as P. megacephalus, Larger males usually defeat smaller males in aggressive a new species (Hallowell, 1861), a classification that * Corresponding author: Dr. Jichao WANG, from Hainan Normal subsequent taxonomists conferred to all P. leucomystax University, Haikou, China, with his research focusing on behavioral populations in continental China (Matsui et al., 1986; ecology of amphibians and reptiles. E-mail: [email protected] Zhao and Adler, 1993; Fei, 1999; Fei et al., 2005, 2009). Received: 4 April 2018 Accepted: 27 November 2018 Polypedates mutus was identified from Hekou Yunnan, No. 4 Qiucheng LIU et al. Comparison of Call Characteristics of Tree Frogs 241 China, based on samples with a “striped” morphology the relationship between call characteristics and male and the lack of a vocal sac (Liu et al., 1960); this species body size. Our study contributes to existing knowledge was later found throughout southern China (Inger et al., of vocal repertoires across tree frog species and provides 1999). Recent phylogenetic and taxonomic evidence comprehensive data that will help to distinguish supports the presence of P. megacephalus and P. mutus interspecific call types. in southern China, including Hainan (Kuraishi et al., 2012; Pan et al., 2013). Acoustic call characteristics 2. Materials and Methods of both species have been previously described (Xu, 2005), but limited samples allowed only a few simple 2.1. Study species Snout-vent lengths of adult P. analyses of acoustic parameters and structure. A later megacephalus males and females are 41–48 and 57–65 study identified three note types in the complex call of P. mm, respectively (Table 1). No black or brown spots are megacephalus from Hong Kong (type locality) (Kuraishi present on the sides of the body, but spots are arranged et al., 2011). However, no comprehensive comparison in reticulate patterns along the posterior (Figure 1A). of call characteristics has been made between the two Numerous small reticulate structures are present on the species thus far. It also remains unknown whether back (Figure 1C) (Liu et al., 2018). Hind legs are stout their calls reflect body size. This missing information and tibial-tarsal joints stretch between the eyes and complicates field identification of these two sympatric nostrils. Male frogs have a pair of pharyngeal subcapsular and morphologically similar species. structures. Polypedates megacephalus inhabits altitudes The objective of the present study was to compare the ranging between 80 and 2200 m (Fei et al., 2012; Wang et spectral and temporal parameters of vocalizations from al., 2014). sympatric P. megacephalus and P. mutus. We investigated Snout-vent lengths of adult males and females of P. Figure 1 Morphological characteristics of Polypedates megacephalus (left) and P. mutus (right). 242 Asian Herpetological Research Vol. 9 mutus are 52–63 and 53–77 mm, respectively (Table 1). kHz; Marantz, Kanagawa, Japan), placed approximately Large and dark brown spots are arranged continuously on 1 m away from the subject. Calls of individuals from the sides of the body, and the posterior lacks any reticulate both species were recorded on the same night as far as patterns (Figure 1B). A few large reticulate structures possible. Actual species recorded was decided based on are present on the back (Figure 1D) (Liu et al., 2018). whichever individuals were found in one night. Data were Hind legs are slender, with tibial-tarsal joints stretching saved as wav files. to the snout or nostrils, and male frogs lack a vocal sac. Call parameters were defined and illustrated based Polypedates mutus inhabits altitudes ranging between 340 on Köhler et al. (2017). Dominant frequency was sound and 1100 m (Fei et al., 2012; Wang et al., 2014). energy concentrated within the whole power spectrum, 2.2. Vocalization recording and analyses From June while fundamental frequency was the base or lowest 10 to July 9, 2015, we recorded male P. megacephalus frequency band in each note. Acoustic parameters and P. mutus vocalizations in their original habitat of measured included the following temporal and spectral Mt. Diaoluo National Nature Reserve (18°43'22.02" N, properties: note duration (ND), call duration (CD), note 109°52'6.19" E, 933 m a.s.l.), Hainan, China. Recorded number (NN), pulse number (PN), pulse duration (PD), calls were always of isolated individuals and never from a fundamental frequency (FF), and dominant frequency mixed chorus. Vocalizations were recorded from 19:30 to (DF). According to the recording quality, we selected 23:30 h (air temperature: 20.7 ± 1.4 °C, relative humidity: 6–41 and 1–10 calls used for each individual of P. 94.5% ± 5.3%). Each recording lasted 10 min per male, megacephalus and P. mutus, respectively. Oscillograms using a directional microphone (Sennheiser ME-66 with and spectrograms were prepared in PRAAT (version K6 power module; Sennheiser, Wedemark, Germany) 5.1.11; Boersma and Weenink, 2017). Body mass, snout- connected to a digital recorder (PMD-660, 16 bit, 44.1 tovent length (SVL), head length (HL), and head width Table 1 Body size and call properties of male Polypedates megacephalus and P. mutus. P. megacephalus P. mutus Parameter Mean ± SD Min–max CVb/CVw Parameter Mean ± SD Min–max CVb/CVw BM (g) 6.78 ± 1.25 4.88–8.91 BM (g) 12.20 ± 1.83 8.22–14.34 SVL (mm) 53.38 ± 3.29 47.42–56.87 SVL (mm) 63.19 ± 3.89 55.40–68.86 HL (mm) 17.79 ± 1.30 15.91–19.52 HL (mm) 20.35 ± 1.04 18.54–22.28 HW (mm) 15.66 ± 1.31 13.10–17.84 HW (mm) 18.10 ± 1.10 16.11–19.82 DFA (Hz) 1281.23± 315.23 559.80–2196.00 1.83 DFD (Hz) 1155.32 ± 123.10 602.90–1593.00 1.05 DFB (Hz) 1134.94± 353.94 645.90–2368.00 2.79 DFE (Hz) 1088.22 ± 111.69 645.90–1464.00 0.57 DFC (Hz) 1963.64 ± 110.35 1636.00–2239.00 1.24 FFA (Hz) 227.86 ± 21.03 129.10–344.50 0.51 FFD (Hz) 209.44 ± 19.36 129.10–301.40 0.56 FFB (Hz) 213.81 ± 18.94 129.10–301.40 0.47 FFE (Hz) 217.65 ± 18.14 129.10–301.40 0.41 FFC (Hz) 236.65 ± 34.14 129.10–344.50 0.98 NDA (ms) 26.08 ± 3.78 18.00–52.00 1.64 NDD (ms) 20.32 ± 1.93 13.00–28.00 1.09 NDB (ms) 124.16 ± 26.06 64.80–197.00