Who is Calling? Intraspecific Call Variation in the Aromobatid Frog Allobates femoralis

Abstract

Many territorial species respond less aggressively to familiar neighbours than to unfamiliar floating strangers based on individual differences in acoustic signals. This form of social recognition, termed neighbour–stranger discrimination (NSD) or dear‐enemy phenomenon has been reported so far from three anuran species. To investigate the potential of auditory signal features to convey information on sender’s identity, we determined patterns of within‐male and between‐male variability in the advertisement call of the aromobatid frog Allobates femoralis. We examined 285 calls from 19 males to assess those call properties showing sufficient and reliable inter‐individual differences to function as possible recognition cues. Beside calls per call bout and call rate, all other examined call properties were more variable among males than within males. Generally, temporal call features showed higher between‐ and within‐male variability ratios than spectral properties and contributed mostly to distinguish individual males in the discriminant‐function analysis. Mean classification success of 64.9% correctly assigned calls to individual males is mainly attributable to three temporal call properties (duration of note 1 and 4, note repetition rate). Altogether, our results suggest that there is sufficient variation in the advertisement call to discriminate statistically among individual males. However, assessed call differences between A. femoralis males were rather small, suggesting that potential NSD might be based either on a combination of call features or even on the whole pattern of individual call variation instead on single call properties. Habituation–discrimination experiments in the field using modified playback signals to test for differential behavioural responses are required to confirm this hypothesis.

Individual variation in the advertisement calls of a Neotropical treefrog (Scinax constrictus)

“…Because many of the call properties were correlated, we per formed a principal components analysis (PCA) to create a set of five orthogonal predictor variables. The correspond ing principal component scores were used as input variables for the DFA, which is a multivariate statistical method used to distinguish between the acoustic parameters of differ ent individuals (Bee et al, 2001;Bee, 2004;Gasser et al, 2009). We measured classification success using a 'leaveone-out' cross-validation procedure.…”

The use of bioacoustics in anuran taxonomy: theory, terminology, methods and recommendations for best practice

“…In many species, environmental temperature regulates the vocal activity period (Wells 2007;Steelman & Dorcas 2010) as well as characteristics of the acoustic signals emitted. Temperature effects are more evident in those temporal features directly linked to muscular contractions like call rate, pulse rate and call duration, while it tends to be subtle or inexistent on spectral traits (Gayou 1984;Gerhardt 1994a;Pröhl et al 2007;Gasser et al 2009;Lemmon 2009;Bee et al 2013a, b;Ziegler et al 2015).…”

“…Although some studies provided statistical evidence for the individual distinctiveness of frog calls ('individual signature': Shy 1985; Bee et al , 2010Gasser et al 2009;Feng et al 2009b;Pettitt et al 2013), only a few tested individual recognition experimentally. The so called 'neighbor stranger discrimination' (NSD) or 'dear enemy-effect' (Table 6) TABLE 6.…”

“…It is mostly used on the within-individual level (CV wi ; Gerhardt 1991) and has become a standard method . CVs may be used on other levels as well, such as the comparisons among / between individual males (CV a or CV b ), and very often the relation of within-and between-individual variation (CV wi / CV a ) is used, for example, to test if individuals differ from each other by their calls (i.e., CV a > CV wi ; Bee et al , 2010Bee et al , 2016Bee 2004a;Pröhl 2003;Gasser et al 2009;Feng et al 2009a;Forti et al 2016).…”

How do males of Hypsiboas goianus (Hylidae: Anura) respond to conspecific acoustic stimuli?

“…Overall, the spectral parameters (e.g., dominant frequency) of the calls are under morphological constraints (RYAN 1986); therefore, they have been frequently classified as static proprieties, since they present low intra-individual coefficient (GERHARDT 1991, BEE et al 2001, GASSER et al 2009, MORAIS et al 2012. However, as observed in H. goianus, some anuran species also reduce the frequency of their calls in response to conspecific individuals (WELLS 1988, WAGNER 1989b, BEE et al 2000, BEE & BOWLING 2002, NALI & PRADO 2014.…”