SPATIAL AND TEMPORAL VARIATION IN SELECTION ON CORRELATED LIFE-HISTORY TRAITS AND PLANT SIZE IN CHAMAECRISTA FASCICULATA.

Abstract

Intraspecific studies of selection on multiple traits of a plant's life history provide insight as to how the composite life history of an organism evolves. Current understanding of selection on plant life-history traits is deficient in three important areas: 1) the effects of selection through correlated traits, 2) the effects of selection on a trait throughout the plant's lifetime, and 3) spatial and temporal variation in selection on plant life-history traits among populations and years. This study documents spatial and temporal variation in selection on three life-history and two morphological traits for two natural populations of Chamaecrista fasciculata, a native summer annual. Life-history and morphological traits (date of seedling emergence, size at establishment, size prior to reproduction, date of initial flowering, and date of initial fruit maturation) varied significantly between sites and/or years. Selection on traits varied either spatially, between sites and among transects within one site, or temporally, between years. In addition, life-history traits were phenotypically correlated among themselves and with morphological traits; correlations were generally constant over time and space. Indirect selection caused changes in means and variances in traits not under direct selection, but which were correlated with traits under selection. Selection on date of emergence varied in direction and magnitude among different life-cycle stages, while selection on other traits varied only in magnitude among life stages of the plant. This study documents the complexity of the selective process and the importance of considering multiple life stages and traits when studying the evolution of life-history traits.