Rival assessment among northern elephant seals: evidence of associative learning during male-male contests.

Caroline Casey,Isabelle Charrier,Nicolas Mathevon,Colleen Reichmuth

doi:10.1098/rsos.150228

Abstract

Specialized signals emitted by competing males often convey honest information about fighting ability. It is generally believed that receivers use these signals to directly assess their opponents. Here, we demonstrate an alternative communication strategy used by males in a breeding system where the costs of conflict are extreme. We evaluated the acoustic displays of breeding male northern elephant seals (Mirounga angustirostris), and found that social knowledge gained through prior experience with signallers was sufficient to maintain structured dominance relationships. Using sound analysis and playback experiments with both natural and modified signals, we determined that males do not rely on encoded information about size or dominance status, but rather learn to recognize individual acoustic signatures produced by their rivals. Further, we show that behavioural responses to competitors' calls are modulated by relative position in the hierarchy: the highest ranking (alpha) males defend their harems from all opponents, whereas mid-ranking (beta) males respond differentially to familiar challengers based on the outcome of previous competitive interactions. Our findings demonstrate that social knowledge of rivals alone can regulate dominance relationships among competing males within large, spatially dynamic social groups, and illustrate the importance of combining descriptive and experimental methods when deciphering the biological relevance of animal signals.

Highlights

Specialized signals emitted by competing males often convey honest information about fighting ability
We evaluated the acoustic displays of breeding male northern elephant seals (Mirounga angustirostris), and found that social knowledge gained through prior experience with signallers was sufficient to maintain structured dominance relationships
Our findings demonstrate that social knowledge of rivals alone can regulate dominance relationships among competing males within large, spatially dynamic social groups, and illustrate the importance of combining descriptive and experimental methods when deciphering the biological relevance of animal signals

Summary

Introduction

Specialized signals emitted by competing males often convey honest information about fighting ability. An individual may remember the outcome of previous competitive interactions with an opponent, and learn to associate these consequences with a signal emitted by the individual with whom he previously fought This information can be used to influence decision-making during later encounters. Owing to extreme selection pressures for rival assessment, the northern elephant seal (Mirounga angustirostris) provides an optimal social model to explore how signals can be used to mediate competitive behaviour among breeding males. Reproduction in this species is annually synchronous, and mature females congregate by the hundreds or thousands on beaches to give birth and breed [11]. While behavioural exchanges between competing males are common, physical battles are relatively rare [14] and extremely costly [16]

Methods

Results

Discussion

Conclusion