Sex-specific performance, trade-offs and trait repeatability across the lifetime of the world's largest semelparous mammal (Dasyurus hallucatus)

The activities that define survival and reproductive success in animals depend on their physical performance. However, performance is a complex trait, and organisms must balance competing demands of multiple underlying factors every time they undertake an activity. For example, the morphology that increases bite force (i.e. increased head size) – improving fighting ability – should constrain sprinting performance by adding mass to the body. Consequently, trade-offs between fighting and escape performance might be sex specific where sexual dimorphism is present, or pronounced in animals with extreme breeding strategies. Northern quolls (Dasyurus hallucatus) are a sexually dimorphic marsupial, with sex-specific life history strategies; males die after a single synchronous breeding season, while females can live and breed for 2–3 years. We investigated the effects of sex and life history on whole-animal performance and assessed whether sprint speed and bite force trade off among or within individual male and female quolls. We used a repeated measures dataset spanning 3 years. We identified significant sex differences in morphology and performance, notably after breeding, where male sprint speed decreases but female bite force increases. Both body size and body condition were strong predictors of performance. However, we found no trade-off between sprint speed and bite force, suggesting that ecologically relevant tasks for survival and reproduction – fighting capacity and escape ability – may evolve independently in both male and female northern quolls. Finally, we assessed the repeatability of morphological and performance traits and demonstrated the importance of study design when quantifying variance in animal performance, especially for animals with complex life histories.