Alternative mating strategies in the Wellington tree weta expressed via genetic polymorphism for precocial male maturation

Abstract

The expression of alternative mating strategies is generally hypothesized to be a plastic response of the genome to the environment or a genetic polymorphism. The Wellington tree weta ( Hemideina crassidens ) is an orthopteran insect in which males express three alternative mating morphotypes related to the size of mandibular weaponry. My common garden experiment in the laboratory shows that male weapon size at maturity in this species is nether condition- nor environment-dependent; therefore, supporting the hypothesis that it is genetically polymorphic. Males that matured at the 8th instar had the shortest development time and the smallest weaponry, males that matured at the 10th instar had the longest development time and the largest weaponry, and males that matured at the 9th instar were intermediate to the other two morphs. These morph-related differences in development time suggest that male alternative mating strategies in this species are expressed via precocial male maturation, a rare mode of strategy expression in insects. Additionally, adult lifespans differed significantly among morphs with 8th instar males having the shortest, and 9th instar males having the longest lifespans. I discuss how these differences in lifespan align with morph-specific investment in pre- and post-copulatory processes to equalize fitnesses among morphs.