Females and males respond differently to calls impaired by noise in a tree frog

Abstract

Both human and nonhuman animals communicating acoustically face the problem of noise interference, especially anurans during mating activities. Previous studies concentrated on the effect of continuous noise on signal recognition, but it is still unknown whether different notes in advertisement calls impaired by noise affect female choice and male-male competition or not. In this study, we tested female preferences and male-evoked vocal responses in serrate-legged small tree frog (Kurixalus odontotarsus), by broadcasting the five-note advertisement call and the advertisement call with the second, third, or fourth note replaced by noise, respectively. In phonotaxis experiments, females significantly discriminated against the advertisement call with the fourth note impaired by noise, although they did not discriminate against other two calls impaired by noise, which indicates that the negative effect of noise on female preference is related to the order of impaired notes in the advertisement call. In playback experiments, males increased the total number of notes in response to noise-impaired calls compared with spontaneous calls. More interestingly, the vocal responses evoked by noise-impaired calls were generally similar to those evoked by complete advertisement calls, suggesting that males may recognize the noise-impaired calls as complete advertisement calls. Taken together, our study shows that different notes in advertisement calls replaced by noise have distinct effects on female choice and male-male competition.

Keywords: acoustic communication; female choice; male–male competition; noise interference; signal recognition.

FIGURE 1

A male serrate‐legged small tree frog (Kurixalus odontotarsus)

FIGURE 2

Spectrograms and relative amplitude of each acoustic stimulus. “AC,” five‐note advertisement call; “AN2,” advertisement call with the second note replaced by noise; “AN3,” advertisement call with the third note replaced by noise; “AN4,” advertisement call with the fourth note replaced by noise. The grayscale spectrogram indicates the frequency components of each stimulus. The purple line indicates the relative amplitude of each stimulus

FIGURE 3

Female preferences and motivations in phonotaxis experiments. (a) Proportion of females choosing noise‐impaired calls. (b) The latency to move and (c) the latency to choose under different stimulus pairs. Each stimulus pairs consists of a five‐note advertisement call (AC) and a noise‐impaired call (AN2, AN3, or AN4). The median values of the latency to move were 10, 11, and 12 s, the latency to choose were 235.5, 311 and 244 s, respectively. In (a), two‐tailed binomial test; *p < 0.05. In (b) and (c), generalized linear mixed model (GLMM)

FIGURE 4

The overall vocal responses in male playback experiments. (a) The total number of calls, (b) total number of notes during the spontaneous period (S) and playback periods (AC, AN2, AN3, and AN4). The median values of the total number of calls were 22, 19, 18, 18, and 21, total number of notes were 29, 57, 56, 51, and 59 respectively. GLMM; different superscript letters indicate significant differences among different treatments (p < 0.05)

FIGURE 5

The intensity of advertisement calls in male playback experiments. (a) The number of advertisement calls, (b) number of A notes, (c) maximum number of A notes during the spontaneous period (S) and playback periods (AC, AN2, AN3, and AN4). The median values of the number of advertisement calls were 22, 11, 13, 9, and 14, number of A notes were 28, 35, 31, 35, and 43, and maximum number of A notes were 2, 5, 4, 5, and 5 respectively. GLMM; different superscript letters indicate significant differences among different treatments (p < 0.05)

FIGURE 6

The intensity of aggressive calls in male playback experiments. (a) The number of aggressive calls, (b) number of B notes, (c) maximum number of B notes during the spontaneous period (S) and playback periods (AC, AN2, AN3, and AN4). The median values of the number of aggressive calls were 0, 4, 2, 3, and 3, and number of B notes were 0, 14, 6, 11, and 8, maximum number of B notes were 0, 5, 2, 6, and 2, respectively. GLMM; different superscript letters indicate significant differences among different treatments (p < 0.05)