Replacing qualitative life-history traits by quantitative indices in parasitoid evolutionary ecology

Life-history traits, which describe the various aspects of the life cycle of a species, can be either quantitative or qualitative. Quantitative traits are likely to adapt to gradual changes in the environment of a species, whereas qualitative traits, which refer to traits that are discontinuous in their variation, pose constraints on the evolution of a species. Traits that are described as qualitative may indeed represent discontinuous characteristics or they can be the result of an oversimplification in the description of the life history of a species. The ovigeny index, which describes the temporal distribution of egg production for a species, has replaced a qualitative life-history trait and has been an important contribution in our understanding of the reproductive ecology of insect parasitoids. We propose here that several other qualitative life-history traits, currently used to describe the evolutionary ecology of insect parasitoids, could advantageously be replaced by quantitative life-history traits. Although replacing these qualitative life-history traits will require devising indices that are biologically and ecologically meaningful, the potential gain in our understanding of the evolutionary forces that have shaped the diversity of life-history strategies of insect parasitoids is important and would fully warrant this effort.