Parental effects in Plantago lanceolata L. III. Measuring parental temperature effects in the field

To determine the evolutionary importance of parental environmental effects in natural populations, we must begin to measure the magnitude of these eff ects in the field. For this reason, we conducted a combined growth chamber- held experiment to measure parental temperature effects in Plantago lanceol ata. We grew in the field offspring of controlled crosses of chamber-grown parents subjected to six temperature treatments. Each treatment was charact erized by a unique combination of maternal prezygotic (prior to fertilizati on), paternal prezygotic, and postzygotic (during fertilization and seed se t) temperatures. Offspring were followed for three years to measure the eff ects of treatment on several life-history traits and population growth rate , our estimate of fitness. Parental treatment influenced germination, growth, and reproduction of newb orns, but not survival or reproduction of offspring at least one year old. High postzygotic temperature significantly increased germination and leaf a rea at 17 weeks by approximately 35% and 2%, respectively. Probability of f lowering and spike production in the newborn age class showed significant p arental genotype X parental treatment interactions. High postzygotic temper ature increased offspring fitness by approximately 50%. The strongest contr ibutors to fitness were germination and probability of flowering and spike production of newborns. A comparison of our data with previously collected data for chamber-grown offspring shows that the influence of parental envir onment on offspring phenotype is weaker but still biologically meaningful i n the field. The results provide evidence that parental environment influences offspring fitness in natural populations of P. lanceolata and does so by affecting t he life-history traits most strongly contributing to fitness. The data sugg est that from the perspective of offspring fitness, natural selection favor s parents that flower later in the flowering season in the North Carolina P iedmont when it is warmer. Genotypic specific differences in response of of fspring reproductive traits to parental environment suggest that parental e nvironmental effects can influence the rate of evolutionary change in P. la nceolata.