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

SIMPLE SUMMARY: Vocalization is important for the survival of underwater animals. Pelodiscus sinensis spends most of its life in water, and its wild population is highly vulnerable. However, its underwater vocalization, which can serve as the basis for ecological and evolutionary research, has not been explored. We identified 10 call types of the species from underwater recordings and found differences in vocalizations between individuals of different ages and sexes. The Chinese soft-shelled turtle has a high diversity of vocalizations and shows a tendency for vocalization to become more diverse with age. These features help them to adapt to complex and dark underwater environments. 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.