Sequential analysis reveals use of mutual assessment in contests between wild New Zealand giraffe weevils

ABSTRACT

When resources such as mates or mating sites are limited, selection drives the evolution of complex and frequently violent fighting behaviour. Contest outcome is determined by an individual’s resource holding potential (RHP) in comparison to that of their opponent. During contests individuals may assess only their own RHP, or they may mutually assess both their own and their opponent’s RHP to determine the effort they allocate to a contest. Male giraffe weevils (Lasiorhynchus barbicornis) bear an elongated rostrum used as a weapon during intense fights over access to females. We used sequential analysis to target the fine-scale structure of contests and phases of contest escalation to determine the assessment strategy used by rival male giraffe weevils in the wild. We found significant non-random temporal structure in behavioural transitions in all transition matrices, and winner and loser transition matrices were significantly different. Contest de-escalation was extremely rare compared to escalation and winners and losers used very different behaviours during contests overall. This study provides support for the sequential assessment model of mutual assessment by male giraffe weevils during competitive interactions. It also demonstrates the utility of sequential analysis in making sense of the often complex interactions occurring in wild insect populations.

KEYWORDS:

• Competitive assessment strategy
• exaggerated traits
• resource holding potential
• field observation
• mutual assessment
• sequential assessment model

Acknowledgements

We would like to thank John Staniland and Forest and Bird Waitakere branch for allowing us to conduct our research at Matuku Reserve. We also thank all of the field assistants involved in this project; J. Le Grice, R. Le Grice, I. Le Grice, S. Wallace, A. Wallace, L. Powell, E. Edney-Brown, V. Lee, L. Zellner, K. Paler, P. Mill, A. Hildreth, P. Parmar, J. Brock, A. Zank, and F. Jacomb. We also thank Emma Scheltema for her wonderful illustrations.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability

Data associated with this study is deposited at 10.6084/m9.figshare.22207954

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Ethical approval

All applicable international, national and/or institutional guidelines for the care and use of animals were followed.

Additional information

Funding

This work was supported by a University of Auckland Masters Scholarship.