Hd. Bradshaw et al., QUANTITATIVE TRAIT LOCI AFFECTING DIFFERENCES IN FLORAL MORPHOLOGY BETWEEN 2 SPECIES OF MONKEYFLOWER (MIMULUS), Genetics, 149(1), 1998, pp. 367-382
Conspicuous differences in floral morphology are partly responsible fo
r reproductive isolation between two sympatric species of monkeyflower
because of their effect on visitation of the flowers by different pol
linators. Mimulus lewisii flowers are visited primarily by bumblebees,
whereas M. cardinalis flowers are visited mostly by hummingbirds. The
genetic control of 12 morphological differences between the flowers o
f M. lewisii and M. cardinalis was explored in a large linkage mapping
population of F-2 plants (n = 465) to provide an accurate estimate of
the number and magnitude of effect of quantitative trait loci (QTLs)
governing each character. Between one and six QTLs were identified for
each trait. Most (9/12) traits appear to be controlled in part by at
least one major QTL explaining greater than or equal to 25% of the tot
al phenotypic variance. This implies that either single genes of indiv
idually large effect or linked clusters of genes with a large cumulati
ve effect can play a role in the evolution of reproductive isolation a
nd speciation.