Data from: The active metabolic rate predicts a male spider’s proximity to females and expected fitness

Conspicuous traits, such as weaponry and body size, are often correlated
with fitness. By contrast, we understand less about how inconspicuous
physiological traits affect fitness. Not only is linking physiology
directly to fitness a challenge, but in addition, behavioural studies most
often focus on resting or basal metabolic rates, resulting in a poor
understanding of how active metabolic rates affect fitness. Here we use
the golden orb-web spider (Nephila plumipes), a species for which
proximity to a female on the web predicts a male's paternity share,
to examine the role of resting and active metabolic rates in fitness.
Using a semi-natural experimental set-up, we show that males closer to a
female have higher active metabolic rates than males further from females.
This higher metabolic activity is paralleled by increased citrate synthase
activity, suggesting greater mitochondrial densities. Our results link
both higher active metabolic rates and increased citrate synthase activity
with fitness. Coupled with the behaviour and life history of N. plumipes,
these results provide insight into the evolution of physiological systems.