Abstract
Animals communicating via scent often deposit composite signals that incorporate odorants from multiple sources; however, the function of mixing chemical signals remains understudied. We tested both a ‘multiple-messages’ and a ‘fixative’ hypothesis of composite olfactory signalling, which, respectively, posit that mixing scents functions to increase information content or prolong signal longevity. Our subjects—adult, male ring-tailed lemurs (Lemur catta)—have a complex scent-marking repertoire, involving volatile antebrachial (A) secretions, deposited pure or after being mixed with a squalene-rich paste exuded from brachial (B) glands. Using behavioural bioassays, we examined recipient responses to odorants collected from conspecific strangers. We concurrently presented pure A, pure B and mixed A + B secretions, in fresh or decayed conditions. Lemurs preferentially responded to mixed over pure secretions, their interest increasing and shifting over time, from sniffing and countermarking fresh mixtures, to licking and countermarking decayed mixtures. Substituting synthetic squalene (S)—a well-known fixative—for B secretions did not replicate prior results: B secretions, which contain additional chemicals that probably encode salient information, were preferred over pure S. Whereas support for the ‘multiple-messages’ hypothesis underscores the unique contribution from each of an animal's various secretions, support for the ‘fixative’ hypothesis highlights the synergistic benefits of composite signals.
Highlights
When communicating with conspecifics, animals often use composite signals that comprise elements from either multiple or single sensory modalities [1,2,3]
As predicted by the multiple-messages hypothesis, male ring-tailed lemurs responding to conspecific scent in the natural experiment generally attended to the mixed secretions more than to either of the pure secretions
In this study of conspecific response to composite olfactory signals, focused on the male ring-tailed lemur, we provide new evidence to support minimally two functions of scent mixing
Summary
Animals often use composite signals that comprise elements from either multiple or single sensory modalities (including vocal, visual, olfactory and tactile modalities) [1,2,3]. Whereas multimodal signals include elements from minimally two modalities, unimodal composite. Whether investigating multimodal 2 or unimodal signals, attributing function to composite signals presents a significant challenge [4,5], because one must deconstruct the signal to assess the contribution of its individual components and examine how those elements potentially enhance, complement or modulate one another [3]. Using the scent-marking system of a strepsirrhine primate, we test two non-mutually exclusive hypotheses about the function of composite olfactory signals
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