Relationship between male head size and mating opportunity in the harem-defence, polygynous tree weta Hemideina maori (Orthoptera: Anostostomatidae)

The most distinguishing feature of the tree weta genus Hemideina (Orthoptera: Anostostomatidae) is their cephalic weaponry, which is thought to be the result of sexual selection on males to aggressively defend groups of reproductive females. Mountain stone weta H. maori is a tree weta that shelters in cavities under flat rocks on rocky outcrops in the alpine region of the South Island. The main objectives of this study were to determine whether males with larger heads have access to greater numbers of females, and whether head size has an effect on male survival and longevity. Males with larger heads associated with larger groups of females than males with smaller heads. Male head size only accounted for 11% of the variation in mating opportunity when all rocks with females were considered, but explained 36% of the variation when only a few specific rocks that had large numbers of females were taken into account. The lower recapture rates of males in general and of smallheaded males in particular, further suggested that small males intermittently retreat to small cracks or cavities within tor columns, where there are unlikely to be large female groups. Thus, larger males had access to more females than smaller males. Moreover, larger males had no detectable disadvantage in terms of daily survival and longevity. This study provides strong evidence that larger male tree weta do associate with larger harems in the wild, however, questions relating to male weaponry size and mating success will become clearer only through paternity testing of weta under natural conditions.