Genetic and Environmental Variation in Floral Traits Affecting Outcrossing Rate in Clarkia tembloriensis (Onagraceae)

Abstract

Clarkia tembloriensis exhibits a wide range of variation among its natural populations in outcrossing rate and in separation ofmale and female function in space (anther-stigma separation or herkogamy) and in time (protandry). Here we show that outcrossing rate is highly correlated with protandry and anther-stigma separation. Both genetic and environmental variation contribute to inter-and intrapopulation variation in protandry and anther-stigma separation. Interpopulation differentiation for protandry and anther-stigma separation was found to be polygenic. Genetic variation for protandry and anther-stigma separation within populations was demonstrated by a significant among-family variance in two populations with contrasting breeding systems. Environmental effects on the expression of mating system traits were manifested in two ways. First, significant variation among lathhouse benches suggests that small-scale environmental heterogeneity may affect the development of floral traits. Second, protandry was shortened under hot summer conditions. Hence, hotter and drier habitats, typical of the more self-pollinating populations of C. tembloriensis, can promote self-pollination purely through environmental effects.

Outcrossing rates of individual Mimulus ringens genets are correlated with anther–stigma separation

“…Outcrossing rate of subpopulations was strongly correlated (r = 0.94), with mean anther-stigma separation (calculated from data summarized in table 3 of Dole, 1991). Holtsford & Ellstrand (1992) found a similar relationship in their study of seven populations of Clarkia tembloriensis; population outcrossing rate was strongly correlated (r = 0.85) with herkogamy.…”

“…Several studies of species with mixed-mating systems have shown a positive correlation between population outcrossing rate and mean anther-stigma separation (Rick et a!., 1977;Dole, 1991;Holtsford & Ellstrand, 1992;Belaoussoff & Shore, 1995). Despite considerable theoretical interest concerning the evolution of self-fertilization in natural populations (Holsinger, 1992;Jarne & Charlesworth, 1993;WaIler, 1993), much less is known about the relationship between herkogamy and outcrossing within populations.…”

The genetics of floral development differentiating two species of Mimulus (Scrophulariaceae)

“…However, differentiation among the domesticated lines of Curcurbita, Capsicum and maize may represent the action of strong artificial selection or selection of single gene mutants resulting in the fixation of genes of major effect (Lande, 1983). Although Gottlieb (1984) cited a number of examples of morphological differences among species that are controlled by one or two genetic factors, differences in floral morphology associated with mating-system variation are frequently due to genetic differences at many loci (e.g., Shore & Barrett, 1990;Holtsford & Ellstrand, 1992; but see Marshall & Abbott, 1982). We observed incomplete dominance for the alleles contributed by the small-flowered, autogamous M. micranthus.…”

The influence of population density on outcrossing rates in Mimulus ringens

“…However, in nature, population density is often confounded with other demographic variables such as plant size, population shape and population size (Barrett & Eckert, 1990;Kunin, 1993;Karron, 1995). In addition, differences among populations in genetically determined floral traits influencing *Correspondence the mating system (Campbell & Abbott, 1976;Schoen, 1982;Marshall & Abbott, 1984;Wyatt, 1984a,b; Holtsford & Ellstrand, 1989& Ellstrand, , 1992Barrett & Husband, 1990;Clegg & Epperson, 1988;Morgan & Barrett, 1990) may further limit the utility of descriptive studies correlating population density with outcrossing rate.…”