Vocalizations of female frogs contain nonlinear characteristics and individual signatures

Abstract

Anuran vocalization is sexually dimorphic, with males doing the bulk of vocalizing. Female vocalization is rare and has been observed in a handful of species, including the concave-eared torrent frog (Odorrana tormota). Females O. tormota have been reported to emit moderate-level calls to attract males. In contrast to males, female’s vocal signals show no evidence of nonlinear phenomena (NLP). However, with females emitting calls so infrequently that this conclusion must be considered tentative in light of the limited supporting data. The present study was undertaken to test the hypotheses that their vocalizations: 1. may not be purely linear, 2. may contain individual signatures, similar to their male counterparts. We recorded 671 calls from six captive gravid females and found that their vocalizations are as complex as male calls, with numerous calls exhibiting complex upward/downward frequency modulations, and 39% of female calls containing at least one component of the NLP, i.e., subharmonics, deterministic chaos, frequency jump, or biphonation. Furthermore, females in captivity tend to call in bouts throughout the day and night, and the call rate varies hourly with a maximum of >10 calls per minute matching the maximum call rate in males. Similar to males, female vocalizations carry individual signatures, and all sound parameters analyzed differ significantly between individuals. This represents the first report ever showing that vocalizations of female anurans: 1. contain NLP, 2. carry individual signatures. Presence of signatures in both the male and female vocalizations opens up the possibility for males (and females) to distinguish individual frogs in both sexes acoustically, and thus their sound communication ability may be more advanced than previously thought.

Female concave‐eared torrent frogs prefer smaller males

“…Amplexus formation in O. tortoma has not been elucidated in full and appears more complex relative to other anuran species due in part to the fact that females in the gravid stage also emit loud vocal signals (Shen et al . , 2008; Zhang, Zhao & Feng, 2017). Playback of female’s call has been shown to elicit phonotaxis in males (Shen et al .…”

Female vocalization in the Oriente Streamside Frog, Eleutherodactylus cuneatus (Eleutherodactylidae), from Cuba

“…Vocalizations of anuran males involve five recognized types of calls (Duellman and Trueb 1994) and female vocalizations have been reported for more than 20 species from around the world (Emerson and Boyd 1999;Zhang et al 2017). The most common female vocalization consists of "reciprocal calls," in which a female responds vocally to the advertisement call of a male (Duellman and Trueb 1994).…”

“…Supporting this hypothesis is the fact that this female laid unfertilized eggs after calling, similar to the report of E. guanahacabibes females by Díaz and Estrada (2000). Among the six functions suggested for female vocalizations by Zhang et al (2017), the hypotheses of advertising receptivity and attracting, finding, or localizing a mate seem the most plausible, as these would increase the likelihood of mating while minimizing costs (Judge et al 2000).…”

Female large odorous frogs (Odorrana graminea) prefer males with higher nonlinear vocal components

“…Two asymmetrical vocal folds, with unequal masses or lengths, induce nonlinear phenomena (NLP), which include four acoustic characteristics, that is, frequency jumps, subharmonics, deterministic chaos, and biphonations (Fitch et al, 2002 ). NLP, as distinctive structural features of acoustic signals, are ubiquitous among the acoustic signals of vertebrates (Digby et al, 2014 ; Feng, Riede, et al, 2009 ; Fitch et al, 2002 ; Rice et al, 2011 ; Zhang et al, 2017 ). The occurrence and strength of NLP in calls not only increase individual vocal distinctiveness but also attract more attention from receivers in individual interactions, which was widely confirmed in fish and mammals (Fitch et al, 2002 ; Volodina et al, 2006 ; Wilden et al, 1998 ).…”