The evolution and ecology of weapon polymorphic New Zealand harvestmen (Arachnida, Opiliones, Neopilionidae)

Abstract

Driven by sexual selection, elaborate morphological structures have arisen in males across animal taxa. Trade-offs between various traits that influence total fitness likely explain the evolution and maintenance of extreme variation among conspecifics, yet these patterns are not fully resolved and require further study. Endemic New Zealand harvestmen (Opiliones, Neopilionidae) represent a group of taxa where males have among the most exaggerated weaponry in the animal kingdom. Here I increase our body of knowledge of this group with attention to both the basic ecology of the Neopilionidae and the species, Forsteropsalis pureora, which I put forward as a model system for broader questions about the evolution of intraspecific polymorphisms. In this thesis, I first defined the male weapon polymorphism in F. pureora using both traditional morphometrics and geometric morphometric shape analysis to describe three male morphs. I went on to describe the use of the chelicerae weapons in this species during escalated contests. Next, I investigated leg autotomy in F. pureora to test for differential predation pressures on male morphs as a result of morphological and behavioural variation. While male morphs did not experience different rates of leg autotomy during adulthood, small minor males with reduced chelicerae had experienced significantly more leg autotomy as juveniles. Thus, leg loss during development affects final adult male morph. I then explored whether morphological and behavioural variation among male morphs and females may be accompanied by underlying physiological variation by measuring resting metabolic rate. Minor males had higher mass-specific resting metabolic rates than the major male morphs or females. Intraspecific variation in energetics may correspond to alternative reproductive tactics, where minor males are aerobically poised to scramble for unguarded females rather than defending territories. Finally, I described prey and predators of the Neopilionidae with notes on cannibalism, mite associations, and interactions with other heterospecifics. In sum, this thesis lays the groundwork of ecological knowledge for this group of unique harvestmen and provides a critical appraisal of a complex weapon polymorphism with investigation of rarely explored traits (leg autotomy and metabolic rate) underlying male variation.