Factors affecting the phenologies of life history traits in two summer annual plant species

The purpose of this study was to determine the potential for natural selection to effect evolutionary change in the phenologies of life history events. Three studies were undertaken to document the amount of phenotypic variation in the phenologies of life history traits, the degree to which selection is acting on these phenologies, and the heritable basis of and genetic correlations among life history and morphological traits.First, results of a greenhouse experiment for Lobelia inflata showed that individuals watered more frequently attained greater size and flowered earlier than those in all other treatments. Offspring of one maternal parent flowered earlier than offspring of five other maternal parents tested. In the field, as in the greenhouse, plant size was negatively correlated with number of flowers produced. In turn, plants which flowered early, relative to other individuals, matured their fruit early.Second, for Chamaecrista fasciculata, another summer annual, field observations of two populations during two years showed that selection on any one trait varied both spatially, between populations, and temporally, between years. In addition, phenologies of life history events, i.e. time of emergence, flowering and fruit maturation, were correlated among themselves. Indirect effects of selection caused changes in means and variances of life history traits such as time of emergence, flowering and fruit maturation, not under direct selection, but which were correlated with morphological traits under direct selection.Third, for C. fasciculata, a partial diallel breeding design showed that paternal half-sib estimates of heritabilities and genetic correlations were low or non-significant for plant size, phenologies of life history events and fitness components. In contrast, maternal hal-sib estimates of heritabilities and genetic correlations were high and significant for phenologies of life history events, but not for plant size or fitness components.The overall conclusion of this work is that although phenotypic selection can act on the phenologies of life history events in the field, there is little or no additive variance at the genetic level for response to this selection. Thus, life history and morphological traits are plastic for these two summer annuals and can be influenced by resource levels and maternal effects.U of I OnlyETDs are only available to UIUC Users without author permissio