Plant phenotypes as trajectories: 38-yr monitoring reveals that shape of lifetime fecundity schedule is under selection in a long-lived shrub

Abstract

Defining a phenotype is sometimes problematic in the case of modularly-built, nonunitary organisms with indeterminate growth dependent on environmental conditions, such as plants. This paper presents a proof of concept of the evolutionary significance of considering lifetime trajectories of individual plants as a component of their phenotypes. Plant size and inflorescence production were monitored for the whole reproductive lifespans of N = 128 individuals of the Mediterranean woody shrub Lavandula latifolia (Lamiaceae) over a 38-year period to address the following questions: Did individuals vary in lifetime trajectories of size and fecundity?, and were parameters describing individual trajectories significant predictors of cumulative lifetime reproduction? Individuals differed widely in lifetime fecundity and in every parameter describing lifetime fecundity schedule (age at first and last reproduction, longevity, and mean, variance, skewness and kurtosis of lifetime temporal distribution of inflorescence production). Phenotypic selection analysis revealed significant relationships between parameters of individual lifetime schedules and a surrogate of relative fitness of individuals (cumulative lifetime production of inflorescences divided by the average for all individuals). Significant selection gradients involved positive and negative directional selection, as well as instances of nonlinear selection, which showed that plants with certain shapes of lifetime fecundity schedules had fitness advantage over others. The notion of plant phenotypes as trajectories was strongly supported by the combined findings that individuals differed greatly in their "appearances" regarding the way in which size and fecundity unfolded over lifetime, and that selection efficaciously "saw" such variation.