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The role of echolocation in communication in a high duty cycle echolocating bat, Rhinolophus clivosus (Chiroptera: Rhinolophidae): an experimental approach
Acoustic communication plays a pivotal role in species recognition across a number of taxa. Species must therefore maintain discrete acoustic signatures to facilitate communication and avoid misidentification. The Acoustic Communication Hypothesis (ACH) thus proposes that in multispecies assemblages...
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| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2017
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| Summary: | Acoustic communication plays a pivotal role in species recognition across a number of taxa. Species must therefore maintain discrete acoustic signatures to facilitate communication and avoid misidentification. The Acoustic Communication Hypothesis (ACH) thus proposes that in multispecies assemblages, multidimensional acoustic space is partitioned so that each species occupies a discrete acoustic space despite overlap in single parameters (e.g. frequency). Horseshoe bats use echolocation for the purpose of orientation and foraging. However, given the presence of individual and species specific cues in echolocation, it is likely that echolocation also functions to some degree in acoustic communication. This dual function makes echolocation a good model system to investigate the evolution of communication. In support of the ACH recent studies have shown that horseshoe bats are able to discriminate between conspecifics and heterospecifics based on echolocation calls alone even when call frequencies overlap. This suggests that multiple components of echolocation are influential in a bats ability to discriminate between species and indicates a dual function of echolocation in orientation and communication. These multiple components have not until now been identified. Studies have also suggested that preference for echolocation calls in the context of mate choice may influence the evolution of echolocation through sexual selection. Using classical habituation – dishabituation playback experiments, I tested the ability of Geoffroy's horseshoe bat, Rhinolophus clivosus, to discriminate between echolocation calls of heterospecifics with either discrete or overlapping resting frequencies. I subsequently used synthesised calls in which I manipulated individual acoustic parameters, to investigate which call components are involved in discrimination amongst species. Finally, I used a two-alternative choice experiment to investigate preference by R. clivosus to calls of individuals of opposite gender as well as between individuals with high or low body condition during the mating season. Rhinolophus clivosus was able to discriminate readily between echolocation calls with discrete frequencies from different species. When frequencies overlapped, however, the ability of bats to discriminate between species was dependant on additional spectral and temporal components of calls that defined the entire acoustic space occupied by the calls. Consequently, calls that were similar in this multi-parametric acoustic space yielded low levels of discrimination, whereas calls separated in acoustic space yielded high levels of discrimination. This study provides the first experimental evidence of call components, other than frequency, that may play a role in species discrimination and questions earlier reports that bats use echolocation in mate choice. In support of the communicative role of echolocation, bats were also able to discriminate between calls from bats that differed in their body condition, indicating echolocation might represent an honest signal of mate quality and thus a function in mate choice. However, despite this, R. clivosus showed no preference or association based on gender or body condition. The results of this study suggest that despite having the ability to use echolocation to discriminate amongst conspecifics, these bats do not base mate choice on echolocation call components. |
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