Sexual dimorphism, behaviour and evolution

Exaggerated weaponry may evolve as a result of sexual selection and provide a reproductive advantage in contests for mates. Weapons such as the huge mandibles seen in male tree wētā (Hemideina spp.) and used for fighting can attain enormous size. However, developing and bearing large weaponry can include tradeoffs such as increased predation risk, impaired locomotion or reduced immune responses. I and colleagues have investigated sexually-skewed predation by introduced mammals (Wehi et al. 2011). We are also examining ecological costs of this evolution, including on foraging and nutrition.

Body size and male weaponry are morphological traits that have also been linked to environmental change. Body size strongly relates to individual fitness, and has profound physiological and ecological consequences. Sexual size dimorphism in a species may be affected by environmental conditions such as temperature or food availability, but effect of temperature in ectotherms still requires rigorous investigation. Males and females may also respond differentially to environmental conditions. Adult size in many species is modified along latitudinal and altitudinal gradients. I have built a large dataset of morphological and isotopic measurements for the sexually dimorphic tree wētā genus from localities and collections throughout New Zealand to explore the effects of environmental conditions on population phenotype, including diet-induced plasticity.