Geographical variation in animals’ acoustic signals has received much attention. However, few studies have compared the patterns and underlying selective forces driving geographical divergence of vocalizations with similar and different functions within the same species. Also, the social consequences of geographical divergence in acoustic signals are still rather poorly understood. Here we recorded three types of social calls of male great Himalayan leaf-nosed bats (Hipposideros armiger) across eight colonies in China. Two calls share similar functions and the third has a function distinct from the other two. We examined the patterns and causes of geographical variation of each of these calls. We found that all three calls had significant geographic variation with similar patterns of spatial variation. Only one of the two social calls with similar functions was found to be affected by genetic drift, while the other two calls were not affected by selection and drift, or morphological constraints. Furthermore, we found that bats could discriminate between vocalizations of their own colony and those of an allopatric colony. Overall, these results suggest that acoustic signals with similar functions may be shaped by different driving forces and acoustic signals with different functions may exhibit similar geographical patterns. This study expands our limited knowledge of the patterns of geographical variation of vocalizations emitted at different emotional states and highlights the importance of comparing simultaneously patterns and causes of geographical divergence of vocalizations with similar and different functions.

Sound collection

Bats’ bUFM calls were obtained from previous recordings (Sun et al. 2020). Briefly, in April–June of 2015–2016, Sun et al. (2020) captured 80 adult males from eight colonies (10 males per colony) in China on average 896 km apart from each other (270-1978 km between adjacent sties). The eight colonies are Simao (SM), Hekou (HK), Hanzhong (HZ), Jiangkou (JK), Anlong (AL), Fanchang (FC), Lengshuijiang (LSJ) and Chongyi (CY) (Figure 2a; Table 1). For each colony, bats were introduced into a cage for acoustic and behavioral recording for six days. Vocalizations were recorded with an Avisoft UltraSoundGate 116 H (Avisoft Bioacoustics, Glienicke, Germany), connected to a condenser ultrasound microphone (CM16/CMPA, Avisoft Bioacoustics) at a sampling rate of 375 kHz and 16-bit resolution. Simultaneously, an infrared camera (HDR-CX 760E; Sony Corp., Tokyo, Japan) was used to record territorial behavior. Our previous study showed that male H. armiger emitted two versions of the bent-upward frequency modulation (bUFM) syllable calls during roost territory defence, with each version indicating a different level of aggressiveness (Sun et al. 2018). H-bUFM syllables produced during high aggression intensity interactions had lower minimum frequencies and wider bandwidths, compared to the L-bUFM syllables produced during low aggression intensity interactions (Sun et al. 2018). Both bUFM syllable call types were recorded.

Bats’ sUFM calls from the above eight colonies were recorded in April–June of 2015–2016. We recorded bats’ sUFM calls in caves between 16:30 and 20:00. Our previous observations in the field and in the lab showed that the sUFM calls are produced by a roosting male resident when a free-flying male intruder approaches (Video S2; Sun et al. 2021). The sUFM calls were recorded with the same equipment and sound parameter levels used to record bUFM calls. The microphone used to record sUFM calls was placed 3-7 m away from the bat colonies. The location of the microphone was changed daily to minimize the possibility of getting a recording from the same group of bats every time. Vocalizations were recorded every 1-2 days, making a cumulative record of 8 to 10 days per colony.