Territoriality has been observed in many animal species and implies the defence of a relatively fixed site (Kaufmann, 1983). The defence of a territory enables access to potential mates, reproduction areas, calling sites, hiding places, food, water, among others. Although obtaining these resources is energetically costly, they might be necessary for the survival and reproductive success of individuals (Howard, 1978; Dhondt and Schillermans, 1983; Whitham, 1986). One way of defending territories is through social interactions, such as advertisement behaviour and contests, widely observed in animals (Wells, 1977; Kluge, 1981; Dhondt and Schillermans, 1983; Whitham, 1986).

In Dendrobatidae frogs, aggressive interactions are common and consist of visual displays, chases, calls and wrestling (Crump, 1972; Bunnell, 1973; McVey et al., 1981; Sullivan et al., 1995; Pröhl, 2005; Méndez-Narváez and Amézquita, 2014). Indeed, aggressive interactions have been reported in males of the genus Oophaga (Galeano and Harms, 2015; Yang et al., 2018), Colostethus (Duellman, 1966), Dendrobates (Summers, 1992; Rojas and Pašukonis, 2019), Silverstoneia (Summers, 2000), and Phyllobates (Summers, 2000; Zimmerman and Zimmerman, 1985).

The yellow-striped poison frog, Dendrobates truncatus (Cope, 1861), is a diurnal species, endemic of Colombia and presumably aposematic. It is found in the lowest stratum of humid and dry forests (Castro and Lynch, 2004), along the Magdalena Valley, western Gulf of

Urabá, Caribbean region, and lowlands of the piedmont of central and western cordilleras (Frost, 2020; Páez et al., 2002), between 10 and 1800 m a.s.l. Currently, there is few information about the aggressive behaviour and vocalisation in this species. Although there are some descriptive approximations of the advertisement call, this is an onomatopoetic presumption (like a “buzz call”), and the authors argue that advertisement call is infrequent because this is not easy to detect (Myers and Daly, 1976). However, vocally active males were observed in a population of Tolima in the Mariquita humid forest (B. Rojas, pers. comm.). Gualdrón-Duarte et al. (2016) provides a short description of the advertisement call, composed of a dominant frequency between 1.8-2.5 kHz and note rate of 59 notes/ second. Erdtmann and Amézquita (2009) described its advertisement call with a duration of 2.35 s, a dominant frequency of 3.1 kHz and a note rate of 57.9 notes/s. Herein I describe for the first time aggressive behaviours in D. truncatus, involving two communication channels, the acoustic and the visual.

On 16 November 2016, I registered one aggressive encounter between two males of Dendrobates truncatus in the locality “Reserva Natural El Neme”, municipality of Coello, Department of Tolima, Colombia (4.2868° N; 74.9225° W, 379 m a.s.l.), between 16:00h and 17:00h. The full record of the aggressive encounter was filmed with a Canon PowerShot SX60HS digital camera and housed in YouTube (https://youtu.be/y0XIhXrTx28). The aggressive behaviours were categorised, with modifications, according to Baugh and Foster (1994) (Table 1).

Spectral and temporal parameters of the aggressive call of D. truncatus were described following Köhler et al. (2017). I considered the aggressive call of D. truncatus as a distinctive sound produced in an exhalation of air, during an encounter between at least two males (Toledo et al., 2014). A call is separated from other calls by a

Herpetology Notes, volume 13: 925-929 (2020) (published online on 16 November 2020)

First record of male-male aggressive behaviour in the yellow-striped poison frog, Dendrobates truncatus Cope, 1861 (Anura:

Dendrobatidae), with description of the aggressive call

Yeison Tolosa1,*

1 La Cumbre, Proyecto de divulgación en Biología & Astronomía, Vereda Asociadas Km 20, Santa Isabel, Tolima, 730560, Colombia.

* Corresponding author. E-mail: ytolosa@outlook.com

Yeison Tolosa926

period of silence, typically much larger than the call (Köhler et al., 2017). For the analysis of the calls, I extracted the audio file from the video in WAV format, which was visualised in Raven Pro 1.3 (Cornell Lab of Ornithology) using the Blackman Algorithm with a window size of 256, and in R Studio using the seewave and tuneR packages (Sueur and Simonis, 2008; R Studio Team, 2015; Uwe et al., 2018).

Prior to the initiation of the agonistic encounter, the males were far away from each other (roughly 5 m), calling from their locations with no apparent visual contact. The aggressive encounter began with the arrival of an intruder male within the calling site of a resident male, accompanied by a series of aggressive calls, and lasted ca. 712 seconds. The interaction took place close to a brook, on trunks, branches and leaf litter. When the intruder emitted an aggressive call, the resident displayed a behaviour called “tracking-static” (Baugh and Foster, 1994), in which one male orients his body in the direction of the other male without locomotion (Table 1; Fig. 1C), probably tuning and locating the origin of the signal. After this behaviour, the resident male usually emitted an aggressive call, as an antagonistic response to the call of the intruder. The vocal dispute among contestants generated a behaviour of approaching towards the opponent, called “advance tracking” (Table 1). This proximity caused a series of chases and escapes (Table 1; Fig. 1D and 1E), followed by a vocal dispute with some tracking-static behaviours, in which acoustic and visual contact remained despite not moving towards each other. In general, the chases and escapes ended in physical contact or wrestling. Wrestling is composed

of fast strokes with forehead movements, here called “snout blows” (Table 1; Fig. 1F and 1I). At times, a contestant stood on top of the other with movements pushing him toward the ground, which lasted almost 120 seconds. This behaviour, denominated “crush behaviour”, may prevent movement from the opponent and was reported in Oophaga pumilio (Table 1; Fig. 1G, 1H, 1J; Baugh and Foster, 1994). The contestant that was underneath continued to jump until it was released, after which the chases and escapes continued and ended in wrestling. Finally, the contestants decreased both the escapes and chases, and the aggressive encounters. Once males stopped wrestling, each one vocalised from their new locations (ca. five meters distant from each other), indicating the end of the agonistic interactions.

I quantified the budget time as the percentage of the behaviours exhibited between the two males during the whole aggressive encounter, based on the video recording. The most prominent was wrestling (30.25% of the total duration) followed by chases (21.07%), showing that the aggressive behaviour between them involved mostly physical contact. Also, statue behaviour was observed 19.88% of the time, and is considered a passive behaviour resulting from a chase or escape (Fig. 1A). Escapes (12.40%) were displayed after wrestling or calling. Likewise, males performed calling (11.44%) as an antagonistic response to an acoustic or visual behaviour. The advance tracking behaviour occurred less frequently (3.05%), because this behaviour is displayed before the chases. When males moved towards or to avoid the opponent, I considered this as chase or escape, respectively. Finally, locomotion (Table 1) was the less

Table 1. Description of the aggressive behaviours in Dendrobates truncatus in the municipality of Coello, Tolima, Colombia, according to Baugh and Foster (1994).

Behaviour Description

Calling Vocalisation is a common outcome of male-male encounters. The calling male orients toward his opponent, inflates his vocal sac and emits an aggressive call.

Locomotion Spontaneous displacement from one place to another without any aggressive stimulus.

Tracking It can be either static, when a frog orients its body towards other frog without locomotion, or with an advance, when the male orients towards its conspecific while moving forward.

Chase One male retreats following an encounter (visual, acoustic or both), and the other one pursues him.

Escape In response to aggressive behaviour, one frog attempts to hide beneath the substrate or escape.

Statue behaviour In response to aggressive behaviour, the submissive frog freezes in one position.

Wrestling Physical contact that results from the chase. This behaviour can be divided into snout blows (Fig. 1F and 1I), and crush behaviour (Fig. 1G, 1H and 1J), in which one frog presses the other to the ground by sitting on him (see Baugh and Foster, 1994).

Table 1. Description of the aggressive behaviours in Dendrobates truncatus in the municipality of Coello, Tolima, Colombia, according to Baugh and Foster (1994).

represented behaviour (1.86%), since it was considered spontaneous without any relation with acoustic, visual or aggressive behaviour. Locomotion occurred in the first seconds of the aggressive encounter and in some final moments when the intensity decreased.

The aggressive call of D. truncatus was a pulsed call composed of several notes distributed in pulse groups (Buzz call) (Fig. 2). The following results are shown as average ± standard deviation (range; number of observations). Aggressive call duration was 1.60 ± 0.56 s (0.81 - 2.81 s, N = 19 calls from two males). Calls were composed by 105.57 ± 32.89 notes (56 - 180 notes, N = 19 calls from two males). Notes had a duration of 0.006 ± 0.0018s (0.0038 - 0.0101 s, N = 2006 notes from 19 calls from two males) and inter-note duration of 0.0090 ± 0.0013 s (0.0062 - 0.0115 s, N = 1968 intervals from 19 calls from two males). The note repetition rate was 68.73 ± 8.84 notes/s (56-99 notes/s, N = 2006 notes from 19 calls from two males). The dominant frequency

was 3.78 ± 0.17 kHz (3.45-4.06 kHz, N = 19 calls from two males).

The aggressive encounter of D. truncatus included mostly a combination of wrestling and chases (approximately half of the time). Chases, escapes, acoustic and visual exhibitions can be considered as behaviours that increase the probability of physical contact between intruder and resident. These intrasexual physical aggressions are arguably costly in terms of energy, and can increase the risks of both contestants to be seriously injured (Maynard-Smith and Price, 1973; Maynard-Smith and Harper, 2003). To avoid these costs, intraspecific conflicts may occur as a “limited war” type, involving inefficient weapons or “ritualised behaviours” that seldom cause serious injury to either contestant, so that the contestant that fights the longest wins the contest (Maynard-Smith and Price, 1973). To that sense, if most members of a population adopt a specific strategy (without a “mutant” strategy that would give higher

First record of male-male aggressive behaviour in the yellow-striped poison frog 927

Figure 1. Aggressive behaviours observed between two males of Dendrobates truncatus (Coello, Tolima, Colombia). (A) Statue behaviour; (B) Vocalisation, (C) Tracking-static; (D) Chase; (E) A male performs a chase while the other escapes; (F, I) Snout blows; (G, H, J) Crush behaviour. Photographs and illustrations by the author.

reproductive fitness), then it will be transmitted to future generations with higher frequencies compared to other strategies (the Evolutionary Stable Strategy - ESS; Maynard-Smith and Price, 1973). Hence, all behaviours observed in D. truncatus can be considered as “ritualised behaviours”, so visual and acoustic displays might be selected over physical aggression. The aggressive encounters documented in other dendrobatids and also in D. truncatus often include physical aggression, when visual and acoustic displays are recalcitrant in the contest (Duellman, 1966; Goodman, 1971; Crump, 1972; Silverstone, 1973; Summers, 1992; Summers and Amos, 1996; Summers, 2000; Pröhl, 2005; this study). The type of wrestling observed in D. truncatus rarely injures the contestants, and thus we hypothesise that visual, acoustic and physical aggression can be selected as ESS, and the winner will be the one that fights the longest using these ritualised behaviours.

Acknowledgments. I am very grateful to the museum team of biological collections of Villa de Leyva of the Instituto Humboldt (Boyacá, Colombia) for giving me the opportunity to share the academic and learning environment. This work was made possible by the project “Diseño de dos corredores de conectividad ecológica en fragmentos de bosque seco tropical en el departamento del Tolima”, convenio 026, Universidad del Tolima-Cortolima. I thank Sandra V. Flechas, Ana María Ospina-Larrea, Estefanía Guzmán, and referees for their comments. I am immensely grateful to Zuania Colón for her advice in R Studio and finally Bibiana Rojas for her advice on both the manuscript and the English version.

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Figure 2. Spectrogram (top), oscillogram (middle) and power spectrum (bottom) of an aggressive call in Dendrobates truncatus, municipality of Coello, Colombia. Figures (A), (B) and (C) depict the aggressive call, and figures (D), (E) and (F) represent notes with pulse groups.

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Accepted by Renato Nali