Both metabolic rate and respiratory gas exchange patterns vary considerably not only among but also within species. The variation in metabolism remains even once several biotic (e.g. size, age, sex) and abiotic (e.g. temperature, humidity) influences are taken into account. Despite a growing body of literature, there is no consensus on the life history consequences of metabolic variation, with positive, negative and non-significant correlations between metabolic rate and various life history traits revealed for a range of species. The implications of differences in discontinuous gas exchange cycle (DGC) exhibition are even less apparent. This thesis presents the findings from a body of research that broadly encompassed the examination of the life history consequences of variation in metabolism and DGCs with respect to a suite of life history and fitness traits in an ectotherm, Nauphoeta cinerea (speckled cockroach). The thesis focuses on the phenotypic association between standard metabolic rate (SMR), DGCs and survival during food and water restriction, the association between SMR, DGCs and reproductive performance (number of offspring and gestation duration) for both males and females, and the association between SMR and dominance in males. The thesis also uses quantitative genetic analyses to examine the genetic correlations among SMR, locomotor performance and chill coma recovery. To consolidate the conclusions made regarding these associations, quantitative genetic analyses are also used to estimate the narrow-sense heritability of both SMR and DGC exhibition. Repeatability of these traits is also calculated.
The results for SMR are strongly context-dependent and SMR is often only associated with the fitness traits through interactions with age and mass (although male SMR is negatively associated with the average number of offspring he sired, and SMR is also negatively associated with female gestation duration). Standard metabolic rate is not independently phenotypically associated with dominance for males, but is part of a three way interaction with mass and age. There is no genetic correlation between locomotor performance and metabolic rate, but chill coma recovery time is positively correlated with metabolic rate. For the first time, a fitness benefit for discontinuous gas exchange has been demonstrated, as this thesis reveals a positive correlation between DGC exhibition and survival during food and water restriction. The phenotypic associations between DGCs and other fitness measures (reproductive performance), however, are less clear-cut, especially for males. Quantitative genetic analyses reveal that both SMR and DGCs show significant additive genetic variance, and can be considered heritable traits. Finally, DGCs are demonstrated to be a repeatable trait, but repeatability of SMR declines with time.