Individual, unit and vocal clan level identity cues in sperm whale codas.

Shane Gero,Luke Rendell,Hal Whitehead

doi:10.1098/rsos.150372

Shane Gero, Luke Rendell + Show 1 more

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https://doi.org/10.1098/rsos.150372

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Abstract

The ‘social complexity hypothesis’ suggests that complex social structure is a driver of diversity in animal communication systems. Sperm whales have a hierarchically structured society in which the largest affiliative structures, the vocal clans, are marked on ocean-basin scales by culturally transmitted dialects of acoustic signals known as ‘codas’. We examined variation in coda repertoires among both individual whales and social units—the basic element of sperm whale society—using data from nine Caribbean social units across six years. Codas were assigned to individuals using photo-identification and acoustic size measurement, and we calculated similarity between repertoires using both continuous and categorical methods. We identified 21 coda types. Two of those (‘1+1+3’ and ‘5R1’) made up 65% of the codas recorded, were shared across all units and have dominated repertoires in this population for at least 30 years. Individuals appear to differ in the way they produce ‘5R1’ but not ‘1+1+3’ coda. Units use distinct 4-click coda types which contribute to making unit repertoires distinctive. Our results support the social complexity hypothesis in a marine species as different patterns of variation between coda types suggest divergent functions, perhaps representing selection for identity signals at several levels of social structure.

Highlights

Complex social structure may be an evolutionary driver of communication systems according to the ‘social complexity hypothesis’ [1]
While previous work has demonstrated the broad patterns expected under the social complexity hypothesis [7,8,9,10,11], here we demonstrate that the expected functional diversity needed to mediate the specific complexities of multiple social tiers in sperm whales society is addressed by the according variability or stereotypy in the social identity cues found in their communication system
This study has demonstrated the presence of identity cues in sperm whale codas and that the required variation in specificity and multiplicity exists with which to discriminate among several tiers of their social structure (evidence of (1) above)

Summary

Introduction

Complex social structure may be an evolutionary driver of communication systems according to the ‘social complexity hypothesis’ [1]. While communication complexity reaches a peak in primates with human language, the correlation between social complexity and greater variation in communicative signals has been demonstrated in several different taxa, including bats [7], The Authors. Non-human primates [8,9], mustelids [10] and birds [11] These patterns could result from an individual’s 2 need to navigate a wide range of social interactions by identifying themselves to conspecifics as members of broader social groups, in order to interact effectively and efficiently. Should this be the case, social complexity would drive selection for social signals which function in mediating social recognition

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