Data from: Food-limited mothers favor offspring quality over offspring number: a principal components approach

Mothers are expected to balance the tradeoff between the number and
quality of offspring, and many theoretical studies describe how the
maternal environment might influence the evolution of the number-quality
tradeoff. However, few empirical studies attempt to test these theories
(and their assumptions) by measuring the fitness consequences of variation
in investment per offspring. Part of the problem is that measuring
offspring fitness is difficult, which frequently leads experimenters to
measure several proxies of offspring fitness in place of a comprehensive
fitness assay. This strategy tends to result in multiple univariate
analyses that involve different offspring fitness proxies, and these tests
can have low power and may produce conflicting conclusions. Here, we
demonstrate the benefits of integrating maternal fecundity and proxies of
offspring size and fitness into multivariate analyses to elucidate
variation in reproductive allocation strategies. In a 2×2 factorial
experiment, we manipulated the quality of maternal environment (food
availability) throughout early and late adulthood (acute and chronic
exposure to the maternal environment) in a field cricket. We developed a
multivariate index of reproductive allocation by incorporating maternal
fecundity and the performance of offspring in low- and high-food
environments into a principle components analysis. This index of
reproductive allocation indicated that females decreased fecundity and
increased offspring quality after chronic exposure to low-food
environments, thereby providing evidence of adaptive plasticity in
investment per offspring. In contrast, few treatment effects were observed
using univariate analyses. The present study demonstrates that
multivariate analysis can increase our ability to assess the adaptive
significance of reproductive strategies, particularly in situations when
offspring size and fitness are difficult to measure with accuracy. Such an
approach might ultimately help assess the adaptive significance of
reproductive allocation across a wider range of taxa, thereby providing
broader insight into the evolution of reproductive strategies.