Complex acoustic signals in Crossodactylodes (Leptodactylidae, Paratelmatobiinae): a frog genus historically regarded as voiceless

ABSTRACT

Vocal sounds occur in most anurans and are often emitted as simple and stereotyped acoustic signals. Some frog groups, however, have complex signals and others can produce distinctive acoustic structures, such as purely ultrasonic calls. Crossodactylodes is a genus of bromeligenous frogs that is understudied in many aspects. This genus has been historically regarded as voiceless, but recent studies reported briefly on vocal sounds in two species. Here, we provide the first quantitative description of vocalisations of Crossodactylodes frogs and describe the vocal repertoires of three species. Vocalisations are formed of up to three call types, reported herein as creaking, chirp and squeak calls. We discuss the major call patterns and the repertoire of Crossodactylodes. We also discuss the evolutionary and functional implications of the low-intensity calls produced at the water–air interface inside bromeliads. The absence of some morphological structures normally involved in sound reception (elements of the middle ear) in Crossodactylodes frogs indicates that extratympanic pathways might be the main auditory route in these highly specialised leptodactylids.

KEYWORDS:

• Acoustic signalling
• animal communication
• bromeligenous frogs
• compound signal
• rarely vocal frogs
• underwater communication

Acknowledgements

We are grateful to S. V. Martins and E. P. Silva for their assistance in the field, and the park managers S. J. Duarte at Pico do Itambé and W. P. Lopes at Serra Negra for logistical support, P. H. Teixeira for his help with video editing, P. P. G. Taucce for making available recording equipment. We thank two anonymous reviewers for their insightful comments.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethical statement

Field data collection was conducted following the national guidelines of the permits issued by the following Brazil’s federal and state agencies: Instituto Chico Mendes de Conservação da Biodiversidade (SISBIO #59179-1 and #59366-2), Instituto Estadual de Florestas (IEF-MG #098/2017), and according to the institutional guidelines for scientific research regulated by the Ethics Committee on Animal Use of São Paulo State University (CEUA-IB #24/2017).

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

Financial support was received through research grants from São Paulo Research Foundation [FAPESP #2013/50741-7], Conselho Nacional de Desenvolvimento Científico e Tecnológico [CNPq #441497/2020-9], and Rufford Foundation [#21264-2]. TRC was granted a postdoctoral fellowship and a BEPE visiting programme by FAPESP [#2017/08489-0 and #2018/17118-8, respectively], MTTS received a doctoral fellowship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior [CAPES #88881.189822/2018-01 and 88882.434124/2019-01] and a postdoctoral fellowship from CNPq [#151193/2021-5], IMB received a doctoral scholarship from CAPES [BEX 13153-13-7]. CFBH thanks CNPq for a research fellowship.