GENETIC CONSTRAINTS ON LIFE-HISTORY EVOLUTION - QUANTITATIVE-TRAIT LOCI INFLUENCING GROWTH AND FLOWERING IN ARABIDOPSIS-THALIANA

We have mapped genes causing life-history trade-offs, and they behave as predicted by ecological theory. Energetic and quantitative-genetic models suggest a trade-off between age and size at first reproduction. Natural selection favored plants that flower early and attain large s ize at first reproduction. Response to selection was opposed by a gene tic trade-off between these two components of fitness. Two quantitativ e-trait loci (QTLs) influencing flowering time were mapped in a recomb inant inbred population of Arabinopsis. These QTLs also influenced siz e at first reproduction, but did not affect growth rate (resource acqu isition). Substitutions of small chromosomal segments, which may repre sent allelic differences at flowering time loci, caused genetic trade- offs between life-history components. One QTL explained 22% of the gen etic variation in flowering time. It is within a few centiMorgans (cM) of the gigantea (GI) locus, and may be allelic with GI. Sixteen perce nt of the genetic variation was explained by another QTL, FDR1, near 1 8 cM on chromosome II, which does not correspond to any previously ide ntified flowering time locus. These life-history genes regulate patter ns of resource allocation and life-history trade-offs in this populati on.