Reproductive bulk in capital-breeding Lepidoptera

"Reproductive bulk is the weight of the individual egg load, also the mathematical product of individual fecundity ×. mean egg weight. Somatic bulk is its complement. Interrelations among nonindependent maternal weight, reproductive bulk, somatic bulk, fecundity, egg weight and related variables were explored with eight sets of data; three original, and five previously published, all representing four capital-breeder species in three families. In traditional fecundity–maternal weight regressions, response and explanatory variables are not statistically independent because maternal weight includes reproductive bulk. Comparative regressions where nonindependent maternal weight was the explanatory variable yielded median coefficients of determination of 0.62 for fecundity and 0.76–0.14 higher—for reproductive bulk among the data sets. When maternal weight was rendered independent by subtracting reproductive bulk, the median coefficient of determination for reproductive bulk plummeted from 0.76 to 0.12, which exposes the extent to which nonindependence inflates regression test statistics. Reproductive bulk nevertheless increased with both independent and nonindependent maternal weight. Nonindependence does not necessarily invalidate the practical use of traditional fecundity–maternal weight regression models. Reproductive bulk is potentially useful as a response variable in regression models of reproductive potential where trade-offs between fecundity and egg weight occur, and where independent maternal weight is desired as an explanatory variable, as in basic research."