Allometry and Fighting Behaviour of a Dimorphic Stag Beetle Cyclommatus mniszechi (Coleoptera: Lucanidae).

Zhen-Yi Chen,Chung-Ping Lin,Yuying Hsu

doi:10.3390/insects11020081

Abstract

Male stag beetles (Coleoptera: Lucanidae) use their mandibles as weapons to compete for resources and reproduction. Mandible size in stag beetles can be associated with different behaviours and the outcome of male contests. We investigated the allometric relationship between mandible and body size in males of the stag beetle Cyclommatus mniszechi to uncover distinct morphs. The results divided male C. mniszechi into majors and minors with the switch point of mandible length at 14.01 mm. The allometric slope of mandibles was positive for both morphs but was steeper for the minors. We also characterised the fighting behaviour of the different morphs in size-matched contests using sequential analyses. Males matched each other’s behaviour in contests with many physical contacts, no injury and a progression from low towards high aggression and rare de-escalation. Major and minor males employed the same behavioural elements in contests, but major males were more likely to escalate directly into more aggressive phases and minor males tended to stay within phases. This finding suggests that major males may compete more aggressively than minor males in contests.

Highlights

Males of many insects use weapons to compete for resources essential for their survival and reproduction [1]
“push” of phase 2; between “tussle” and “clamp2”, and repetitive “clamp1” of phase 3, Figure 3). These results suggest that minor males tend to stay within these phases more than major males, whereas major males were more likely to escalate directly into more aggressive phases
Our results suggest that the major and minor males of C. mniszechi employ the same behavioural elements in the fighting contests, but they differ in the extent to which they stay within phases in the contests and the likelihood of escalating into more aggressive tussle behaviour

Summary

Introduction

Males of many insects use weapons to compete for resources essential for their survival and reproduction [1]. Selected traits, such as ornaments and weapons, often evolve to reach extremes of size and elaboration [1,2,3,4]. Stag beetles exhibit a high diversity in the sizes and shapes of mandibles both within and across species [1,9,10,11] which might cause the behaviour they display in fighting contests to be highly variable [1]

Methods

Results

Discussion

Conclusion