Diversity of Underwater Vocalizations in Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

Abstract

Sound communication is important for underwater species. The wild population of the Chinese soft-shelled turtle (Pelodiscus sinensis) is listed as vulnerable. However, its vocalization, which can serve as the basis for ecological and evolutionary research, has not been studied. Here, we performed underwater recordings of 23 Chinese soft-shelled turtles of different ages and sexes and identified 720 underwater calls. The turtle calls were manually divided into 10 call types according to visual and aural inspection properties. The similarity test indicated that the manual division was reliable. We described the acoustic properties of the calls and the statistical analysis showed that the peak frequency of calls was significantly different between adult females and males, and also between subadults and adults. Similar to other aquatic turtles that prefer to live in deep water, Chinese soft-shelled turtles have a high vocal diversity and many harmonic calls, indicating that this highly aquatic species developed a variety of vocalizations to enhance their underwater communication, which helped them adapt to the complex and dim underwater environment. Furthermore, the turtles showed a tendency for vocalization to become more diverse with age.

Keywords: Pelodiscus sinensis; age-sex difference; call types; underwater recordings; vocalization diversity.

Figure 1

Spectrogram and waveform views of underwater sounds produced by Pelodiscus sinensis. All spectrograms were obtained with Raven Pro 1.5 using Hamming windows with 1024 pt fast Fourier transform. The waveforms were drawn in MATLAB R2021a. Capital letters A–J represent call types A–J.

Figure 2

Differences analysis in peak frequencies between five groups. Capital letters A–J represent call types A–J. Boxplots with different lowercase letters indicate significant results (p < 0.05). Boxplots with the same lowercase letters indicate no significant difference (p > 0.05). When boxplots are marked with only one letter, the boxplot marked “a” is significantly higher than the boxplot marked “b” in a call type (p < 0.05). Call types without letters on the boxplots means no significant differences between groups. Groups: 1 represents subadult males, 2 represents subadult females, 3 represents adult males, 4 represents adult females and 5 represents mixed-sex adults.

Figure 3

Differences analysis of call durations between five groups. Capital letters A–J represent call types A–J. Boxplots with different lowercase letters indicate significant results (p < 0.05). Boxplots with the same lowercase letters indicate no significant difference (p > 0.05). When boxplots are marked with only one letter, the boxplot marked “a” is significantly higher than the boxplot marked “b” in a call type (p < 0.05). Call types without letters on the boxplots means no significant differences between groups. Groups: 1 represents subadult males, 2 represents subadult females, 3 represents adult males, 4 represents adult females and 5 represents mixed-sex adults.