INFERENCES ABOUT QUANTITATIVE INHERITANCE BASED ON NATURAL-POPULATIONSTRUCTURE IN THE YELLOW MONKEYFLOWER, MIMULUS-GUTTATUS

We used a nonmanipulative, marker-based method to study quantitative g enetic inheritance in two habitats of a common monkeyflower population . The method involved regressing quantitative trait similarity on mark er-estimated relatedness between individuals sampled in the field. We sampled 300 adult plants from each of two transects, one along a strea m habitat and another through a meadow habitat. For each plant we meas ured 10 quantitative characters and assayed 10 polymorphic isozyme loc i. In the meadow habitat, relatedness of plants within 1 m was moderat e (r = 0.125, corresponding to half-sibs) as was actual variance of re latedness (V-r = 0.044). Significant heritabilities of 50-70% were fou nd for corolla width and the fitness characters of flower number and p lant weight. Genetic correlations were strongly positive, but sharing of environmental effects within 1 m was weak. In the stream habitat, l evels of relatedness were lower and similar heritabilities were indica ted. To detect dominance variance and the correlation of phenotypes du e to shared inbreeding, we also estimated higher-order coefficients of relationship and inbreeding, but these did not significantly differ f rom zero. Laboratory-based estimated of heritability in the field were lower than the marker-based estimated, indicating that natural herita bilities and genetic correlations may be stronger than indicated by co ntrolled studies.