No abstract

Numerous studies have suggested a general relationship between the degree of host specialization and body size in herbivorous animals. In insects, smaller species are usually shown to be more specialized than larger-bodied ones. Various hypotheses have attempted to explain this pattern but rigorous proof of the body size-diet breadth relationship has been lacking, primarily because the scarceness of reliable phylogenetic information has precluded formal comparative analyses. Explicitly using phylogenetic information for a group of herbivores (geometrid moths) and their host plant range, we perform a comparative analysis to study the body size-diet breadth relationship. Considering several alternative measures of body size and diet breadth, our results convincingly demonstrate without previous methodological issues-a first for any taxon-a positive association between these traits, which has implications for evaluating various central aspects of the evolutionary ecology of herbivorous insects. We additionally demonstrate how the methods used in this study can be applied in assessing hypotheses to explain the body size-diet breadth relationship. By analyzing the relationship in tree-feeders alone and finding that the positive relationship remains, the result suggests that the body size-diet breadth relationship is not solely driven by the type of host plant that species feed on.

Predictive classifications of life histories are essential for evolutionary ecology. While attempts to apply a single approach to all organisms may be overambitious, recent advances suggest that more narrow ordination schemes can be useful. However, these schemes mostly lack easily observable proxies of the position of a species on respective axes. It has been proposed that, in insects, the degree of capital (vs. income) breeding, reflecting the importance of adult feeding for reproduction, correlates with various ecological traits at the level of among-species comparison. We sought to prove these ideas via rigorous phylogenetic comparative analyses. We used experimentally derived life-history data for 57 species of European Geometridae (Lepidoptera), and an original phylogenetic reconstruction. The degree of capital breeding was estimated based on morphological proxies, including relative abdomen size of females. Applying Brownian-motion-based comparative analyses (with an original update to include error estimates), we demonstrated the associations between the degree of capital breeding and larval diet breadth, sexual size dimorphism, and reproductive season. Ornstein-Uhlenbeck model based phylogenetic analysis suggested a causal relationship between the degree of capital breeding and diet breadth. Our study indicates that the gradation from capital to income breeding is an informative axis to ordinate life-history strategies in flying insects which are affected by the fecundity vs. mobility trade off, with the availability of easy to record proxies contributing to its predictive power in practical contexts.

We present a phylogenetic comparative study assessing the evolutionary determinants of egg size in the moth family Geometridae. These moths were found to show a strong negative allometric relationship between egg size and maternal body size. Using recently developed comparative methods based on an Ornstein‐Uhlenbeck process, we show that maternal body size explains over half the variation in egg size. However, other determinants are less clear: ecological factors, previously hypothesized to affect egg size, were not found to have a considerable influence in the Geometridae. The limited role of such third factors suggests a direct causal link between egg size and body size rather than an indirect correlation mediated by some ecological factors. Notably, no large geometrid species lay small eggs. This pattern suggests that maternal body size poses a physical constraint on egg size, but within these limits, there appears to be a rather invariable selection for larger eggs.

Both physiologically and ecologically based explanations have been proposed to account for among-species differences in lifespan, but they remain poorly tested. Phylogenetically explicit comparative analyses are still scarce and those that exist are biased towards homoeothermic vertebrates. Insect studies can significantly contribute as lifespan can feasibly be measured in a high number of species, and the selective forces that have shaped it may differ largely between species and from those acting on larger animals. We recorded adult lifespan in 98 species of geometrid moths. Phylogenetic comparative analyses were applied to study variation in species-specific values of lifespan and to reveal its ecological and life-history correlates. Among-species and between-gender differences in lifespan were found to be notably limited; there was also no evidence of phylogenetic signal in this trait. Larger moth species were found to live longer, with this result supporting a physiological rather than ecological explanation of this relationship. Species-specific lifespan values could not be explained by traits such as reproductive season and larval diet breadth, strengthening the evidence for the dominance of physiological determinants of longevity over ecological ones.