Flexible alternative mating tactics by New Zealand giraffe weevils

Abstract

Alternative reproductive tactics (ARTs) occur in many species where there is intense competition for mates and substantial variation in reproductive success between males of different size, age, or condition. Males of the giraffe weevil Lasiorhynchus barbicornis display an elongated rostrum used as a weapon during contests with other males. In addition, both sexes are extremely variable in body size. We determined the presence of ARTs in this species using extensive field observations. Larger males were found to rely only on aggressive behavior to secure females, but smaller males exhibited greater plasticity in their reproductive tactics. Males less than 30mm in body length frequently employed sneaking strategies but would also readily fight with smaller or equally matched opponents. Surprisingly, using mating success as a proxy for fitness, we found no evidence for directional or stabilizing selection on rostrum length, indicating that rostrum length has no detectable influence on the number of copulations that each male performed. Giraffe weevils are a rare example of a species that has evolved ARTs characterized by highly context-dependent behavior in which sneaking and aggressive behaviors are both used by small males in relation to opponent body size.