| Most bats use echolocation to orient in space, and also to detect, classify and localize preys. Similar to other animals such as insects, amphibians and birds, bats can also use their vocalizations for communication, mutual recognition, mate attraction, threat warning and territorial defense. Variation in echolocation signal structure can be observed between populations or among individuals within a certain population, bats also show plasticity in echolocation calls for given individuals. Bats may show adaptive phenotypic plasticity so as to function efficiently under different environmental conditions, and change in echolocation behavior may account for increased success of foraging. Researching on distinctions of bats echolocation calls in different conditions and focusing on impact factors and its relevant functions to bats ecological behavior have a great role in revealing the essence of vital activities of bats. In present study, we investigated and analyzed the plasticity in echolocation calls of great leaf-nosed bat (Hipposideros armiger), intermediate leaf-nosed bats (H. larvatus), and large myotis (Myotis chinensis), in response to different environments and conditions. And we deduced the reasons and meanings of these varieties in echolocation calls.1. From July to August2013,8adult great leaf-nosed bats captured from field were kept in a novel enclosed environment. Variations of echolocation calls when bats lived in and adapt to the indoor environment were observed. H. armiger exhibited significant plastic in response to a novel enclosed environment. This plasticity was indicated by significant variation in call parameters including call duration, peak frequency (PF) and pulse rate (PR). PF showed no significant difference when bats were exposed in the novel enclosed environment at first time (t54=-0.55, P=0.588); however, there was a strong positive correlation in PF with time across indoor trials (Pearson correlation:r8=0.92, P=0.001). Inversely, call duration showed significant difference at the first time when bats were flying in indoor environment (t54=-3.30, P=0.002), but it did not show any significant correlations with the time across indoor trials (Pearson correlation:r8=0.31, P=0.425). There was also a mean negative genetic relationship between PR and the time across indoor trials (Pearson correlation:r8=-0.74, P=0.022), although we did not compare it with the sound of the field for we could not confirm flight time of bats. Moreover, a paired t-test showed that the PF of the11th,14th,16th, and19th d (t7=-5.69, P=0.029; t7=-21.17, P=0.002; t7=-10.63, P=0.009; t7=-8.88, P=0.012, respectively) and the pulse rate of the16th d (t7=6.15, P=0.025) were different from those from the1st d. Both the PF and the pulse rate represented a peak or floor level on the16th d, and no continuous increment in the next few days. We concluded that bats may adjust their echolocation structures slowly in adapting to changes of the external environment.2. The PF of echolocation calls in H. larvatus show significant differences in different geographical populations. From September2012to November2013,12intermediate leaf-nosed bats from two populations captured from Guangdong province (A:PF,87.22±0.29kHz, n=6) and Guangxi autonomous region(B:PF,83.05±0.27kHz, n=6) were kept together, the results showed that the PF of them all presented significant changes (A,(A,t5=15.59, P<0.001;B,t5=-13.43, P<0.001, respectively) when they were mixed in paired for a month, the PF of A colony decreased to86.32±0.26kHz, and the PF of B colony increased to85.35±0.45kHz; However, they basically return initial state after separated for a while(A:PF,87.18±0.41kHz; B:PF,83.13±0.41kHz, respectively). Moreover, the PF of B colony increased to86.45±0.36from86.32±0.26kHz (f5=-16.13, P<0.001) when they were mixed with A colony one by one, but the PF of A colony showed no significant changes in this period. And they also almost return initial state after separated for a while (83.10±0.32kHz). This means that echolocation calls play an important role in Social communication, and social vocal communication inversely impact on the echolocation calls structures. However, the changes arose by these factors is temporary and reversible.3. From June to August2013, we observed the effect of light on echolocation calls of M. chinensis in hunting period. We found that bats dropped pulse rate in light environment (t5=3.63, P=0.015), and the interpulse interval would be shorter in light environment than that in dark environment (t5=2.65, P=0.045). They would also decrease their PF to a certain extent in light environment, but it did not reached the significant level (t5=2.35, P=0.063). So light plays a supporting role in hunting behavior of bats, and they produce different echolocation calls under different light intensities.In conclusion, bats exhibit a remarkable flexibility in using acoustic signals to meet the sensory demand, and they would change their echolocation calls characteristics, include frequency, duration, interval, pulse rate, etcetera, in respond to different environment and activities. |
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