Fighting, survival and mating success in wild New Zealand giraffe weevils (Lasiorhynchus barbicornis)

Abstract

Exaggerated traits such as elaborate ornaments and weaponry evolve in animal populations under the influence of sexual selection. These traits are used (almost exclusively by males) to compete for and gain access to mates. Competition for reproductive opportunities can be intense, resulting in the possibility of severe injury or even fatality. Consequently, species are expected to evolve strategies to effectively assess a rival’s fighting ability and thereby reduce the cost of interactions. It is suggested that exaggerated weaponry may provide a signal to allow competitors to engage in such assessment. Reproductive success is not weighted entirely on a single mating opportunity for most species, but varies throughout an individual’s lifetime. Consequently, lifetime reproductive success is a more definitive measure of an individual’s fitness, revealing any trade-offs during their life history. The New Zealand giraffe weevil (Lasiorhynchus barbicornis) provides an ideal study subject for the investigation of competitive assessment and reproductive success in the field. Males bear an elongated rostrum used as a weapon in male-male contests over females. Furthermore, extreme variation in male body size potentially influences lifetime reproductive success. In this study I investigate competitive assessment strategies in giraffe weevils using fine-scale video analysis techniques, to determine the strategies involved. Additionally, I use mark-recapture observational studies to determine the effect of lifespan, body size, and sex on individual lifetime mating success. The relative importance of self versus mutual assessment during fights has met great debate in the scientific literature recently, making this study an important contribution to this field. Similarly, lifetime reproductive success is challenging to study, especially in wild insect populations, where information is extremely scant. This research will significantly contribute to our understanding of the reproductive ecology of wild animal populations and draw a clearer picture of the way in which sexual selection drives trait exaggeration in the giraffe weevil.