Partial self-fertilization and inbreeding depression in two populations of Mimulus guttatus

Abstract

Inbreeding depression is likely to be a common selective force opposing the automatic selective advantage of self-fertilization in self-compatible plants and animals, yet relatively few studies have measured both the breeding system and inbreeding depression in natural populations. In this study, I estimated the frequency of selfing, using data obtained by gel electrophoresis, in two annual populations of the monkeyflower Mimulus guuatus for 2 years, and measured the relative performance of selfed and outcrossed progeny over several stages of the life cycle in both the field and the greenhouse. Rates of outcrossing were not significantly different from 1.0 in either population in 1989, but both populations exhibited significant and moderate amounts of selfing in 1990. Outcrossing rates were significantly different between years for the Cone Peak population but not for the Iron Mountain population. Significant inbreeding depression was detected for almost every component of fitness measured, including germination success, survival to flowering, and flower, fruit and seed production in the native field enviromnents for both populations. The final cumulative value of inbreeding depression, calculated as one minus the relative total seed production of selfed to outcrossed progeny, was 0.69 for Iron Mountain and 0.64 for Cone Peak.Inbreeding depression was also severe in the greenhouse experiments, even though fitness components only up to flower production were measured: 0.52 for Iron Mountain and 0.48 for Cone Peak. These results are consistent with theoretical predictions of the magnitude of inbreeding depression in primarily outcrossing populations, and indicate that inbreeding depression is an important factor in the maintenance of outcrossing in these populations.

Inbreeding depression under a competitive regime in Mimulus guttatus: consequences for potential male and female function

“…However, Willis (1993a) observed little difference in inbreeding depression between greenhouse and field-grown M guttatus. Dole & Ritland (1993) have reported an 81 per cent reduction in fitness of self M guttatus progeny based on multigenerational changes in population inbreeding coefficients estimated from allozyme data.…”

“…The 'elbow-room' hypothesis suggests that greater phenotypic variation among sibs could reduce competition and therefore increase mean progeny fitness (Young, 1981). This could lead to a selective advantage of mixed-mating systems because phenotypic variation may be maximized at intermediate levels of outcrossing (McCall et al, 1989 common phenomenon in M guttatus because of its mixed-mating system (Ritland & Ritland, 1989;Ritland, 1990;Dudash & Ritland, 1991;Willis, 1993a), but the data from our competition study and those presented by others (Schmitt & Ehrhardt, 1990;Argyres & Schmitt, 1992) do not support this application of the elbow-room hypothesis. We found that the difference in performance between self and outcross progeny was greatest when self and outcross progeny were grown together, although the differences among competitive regimes fell short of significance.…”

“…The showy flowers are produced in pairs at each stem node. It is fully selfcompatible, and outcrossing rates measured for M. guttatus populations vary from 0.25 to 1.00, averaging about 0.60 (Ritland & Ritland, 1989;Ritland, 1990;Dudash & Ritland, 1991;Willis, 1993a).…”

CORRELATED EVOLUTION OF SELF-FERTILIZATION AND INBREEDING DEPRESSION: AN EXPERIMENTAL STUDY OF NINE POPULATIONS OFAMSINCKIA(BORAGINACEAE)

“…There was consequently more opportunity for progeny from selfing and outcrossing to differ, and inbreeding depression was therefore higher in the greenhouse. Nevertheless, other studies conducted in both environments have found higher inbreeding depression in the field (Dudash 1990) or no difference (Willis 1993a). The variety of results further highlights the dependence of inbreeding depression on environmental conditions (Griffing and Langridge 1963;Griffing 1990).…”

An experimental method for evaluating the contribution of deleterious mutations to quantitative trait variation

“…If the interactions among loci are neither additive nor multiplicative (e.g. Sved & Wilton, 1989 ;Willis, 1993 ;Charlesworth, 1998), then a more complicated transformation may be required.…”