A guild classification system proposed for anuran advertisement calls

Abstract

Zoologists have widely acknowledged the utility of classification systems for characterising variation in anuran egg and clutch types, tadpole morphotypes, embryonic and tadpole development, amplexus types and reproductive modes. These classification systems have facilitated unambiguous communication between researchers, often working in completely different fields (e.g. taxonomy, ecology, behaviour), as well as comparisons among studies. A syntactic system, classifying anuran call guilds, is so far lacking. Based on examination of the calls of 1253 anuran species we present a simple, easy to use dichotomous key and guild system for classifying anuran advertisement calls – the call type most frequently emitted by anurans and studied by researchers. The use of only three call elements, namely clearly-defined calls, notes, and pulses, plus presence or absence of frequency modulation, allows assigning all currently known anuran advertisement calls to one of eight distinct call guilds defined here. This novel toolkit will facilitate comparative studies across the many thousand anuran species, and may help to unravel drivers of anuran call evolution, and to identify ecological patterns at the level of acoustic communities.

Behavioral context shapes vocal sequences in two anuran species with different repertoire sizes

“…Specifically, N. humayuni produced vocal sequences comprising two note types (Figure 2A). According to existing classification systems (Emmrich et al 2020), N. humayuni falls within call guild F (“frequency modulated call with uniform notes”). Henceforth, the first note type is referred to as an ‘Ascending Note’ (AN; note emission rate = 5.425 ± 2.360 notes/minute; note duration = 370 ± 66 ms, range = 228 - 619 ms; dominant frequency = 1575.2 ± 237.58 Hz, range = 1033.6 - 2153.3 Hz; N = 489 notes from 19 males).…”

Description of six new species of Xenorhina Peters, 1863 from southern Papua New Guinea (Amphibia, Anura, Microhylidae)

“…Anuran advertisement calls are useful for taxonomic studies because they are mate recognition signals that are generally species-specific, exhibit limited variation amongst individuals and populations (although some features can be influenced in partially predictable ways by environmental factors, such as temperature) and likely have a genetic basis (Hoskin 2005, Köhler et al 2017, Emmrich et al 2020. We, therefore, consider the unique bioacoustics traits of each new species described here to be a strong indicator of species level divergence.…”

“…The six new species described here each produce advertisement calls of this type, but each is distinct from the known calls of congeners and these differences are concordant with the patterns of morphological variation documented. These calls meet the criteria for Call Guild A: "non-frequency modulated, non-pulsed simple call," or Call Guild B: "frequency modulated, non-pulsed simple call" of Emmrich et al (2020), depending on the extent of modulation exhibited amongst species (defined as "with significant change" vs. "without significant change" by Emmrich et al (2020).…”

A New Limnonectes (Anura: Dicroglossidae) from Southern Thailand

“…Temporal and spectral parameters measured were modified from Cocroft and Ryan [ 48 ] and Thomas et al [ 49 ] as follows: Dominant call frequency (the frequency of maximum amplitude measured from a power spectrum generated using Raven’s selection spectrum function over the duration of the entire call); call duration (the time from beginning to end of one call); intercall interval (duration of the interval between consecutive calls); call rate (the total number of calls-1 divided by the time from beginning of first call to beginning of last call); note (the number of notes in a call); note duration (time between the onset and the offset of the middle note in a call); and internote interval (the time interval of the middle notes in a call); note rate (the number of note per second, the total number of notes-1 divided by the time from beginning of first note to beginning of last note). We used call structure description and the terminology of pulses, notes, and calls as defined by Köhler et al [ 50 ] and Emmrich et al [ 51 ]. Comparative advertisement call characters for L. dabanus , L. lauhachindai, and L. savan were taken from the literature [ 7 , 8 , 17 ].…”