Average Inbreeding Depression Research Articles

YIELD POTENTIAL AND GENETIC VARIABILITY OF SEMIEXOTIC MAIZE POPULATIONS AS A BASIS FOR SELECTION

In order to verify the genetic and agronomic value, yield potential and inbreeding depression of synthesized composites, as well as quantifying the population variability and incorporating new sources of semiexotic germplasm in maize genetic improvement programs, four populations, identified as NAP-FA x HG-71 (P1), NAP-FL x HG-49 (P2), NAP-FB x HG-49 (P3), and NAP-DB x HG-49 (P4), with two levels of inbreeding (S0 and S1), were evaluated in three locations. From the P1 and P4 populations, 100 full-sib progenies were evaluated in only one location. Plant and ear height, lodging, breakage, ear length and diameter, resistance to diseases, ears with chalky kernels and grain yield were evaluated. The grain yield of the S0 and S1 populations varied between 5.50 and 6.65 t ha-1 and 3.8 and 4.58 t ha-1, respectively, with an average inbreeding depression between 23.9% and 38.0%. Considering all the locations, the grain yields of the non-inbreeding populations varied between 64.4% and 78.0% in relation to commercial hybrids (witnesses), indicating a good yield potential for start of improvement program. In the P1 and P4 populations, sufficient genetic variability was identified in most of the characters, which accredits them for recurrent selection. Gains of 13.7% and 17.8% for grain yield and 31.64% and 29.9% for ears with chalky kernels were estimated.

Genetic inbreeding depression load for morphological traits and defects in the Pura Raza Espa\xf1ola horse

BackgroundInbreeding is caused by mating between related individuals and is associated with reduced fitness and performance (inbreeding depression). Several studies have detected heterogeneity in inbreeding depression among founder individuals. Recently, a procedure was developed to predict hidden inbreeding depression load that is associated with founders using the Mendelian sampling of non-founders. The objectives of this study were to: (1) analyse the population structure and general inbreeding, and (2) test this recent approach for predicting hidden inbreeding depression load for four morphological traits and two morphology defects in the Pura Raza Española (PRE) horse breed.ResultsThe regression coefficients that were calculated between trait performances and inbreeding coefficients demonstrated the existence of inbreeding depression. In total, 58,772,533 partial inbreeding coefficients (Fij) were estimated for the whole PRE population (328,706 horses). We selected the descendants of horses with a Fij ≥ 6.25% that contributed to at least four offspring and for which morphological traits were measured for the subsequent analysis of inbreeding depression load (639 horses). A pedigree was generated with the last five generations (5026 animals) used as the reference population (average inbreeding coefficient of 8.39% and average relatedness coefficient of 10.76%). Heritability estimates ranged from 0.08 (cresty neck) to 0.80 (height at withers), whereas inbreeding depression load ratios ranged from 0.01 (knock knee) to 0.40 (length of shoulder), for an inbreeding coefficient of 10%. Most of the correlations between additive and inbreeding depression load genetic values and correlations between inbreeding depression load genetic values for the different traits were positive or near 0.ConclusionsAlthough the average inbreeding depression loads presented negative values, a certain percentage of the animals showed neutral or even positive values. Thus, high levels of inbreeding do not always lead to a decrease in mean phenotypic value or an increase in morphological defects. Hence, individual inbreeding depression loads could be used as a tool to select the most appropriate breeding animals. The possibility of selecting horses that have a high genetic value and are more resistant to the deleterious effects of inbreeding should help improve selection outcomes.

Comparison of growth and survival among selected population, inbreeding population, and wild population in Fenneropenaeus chinensis

In this study, inbreeding population was constructed by full-sib mating of “Huang Hai No. 2” core population in Fenneropenaeus chinensis. Growth and survival of three different stages were studied in three populations, including selected population, inbreeding population, and wild population. The growth experimental results show that body weight of selected population in all the three growth stages was significantly higher than those of inbreeding population and wild population (P < 0.05). At day 90, body weight of the selected population increased by 13.1 and 19.4%, compared with those of inbreeding population and wild population and the specific growth rate (SGR) for body weight of three populations were 2.24, 2.16, and 2.11. Coefficient of variation of body weight among the three populations were different; the highest was 23.75% in the selected population and the lowest was 16.76% in the wild population, which showed that there is potentiality for further selection. The survival results indicated that the difference of survival of the three populations were significant (P < 0.05), that of the selected population increased by 10.78 and 14.20%, compared with those of inbreeding population and wild population, and the average survival rate of the three populations were 74, 66.8, and 64.8%, respectively. Full-sib matings revealed that the amount of inbreeding depression of body weight varied from −7.68 to −11.53%, and the estimated average inbreeding depression coefficient was −4.61 per 10% increase of inbreeding coefficient of F. For survival trait, the estimated average inbreeding depression coefficient ranged from −2.62–3.81%, and the inbreeding depression was −1.05 per 10% increase of inbreeding coefficient of F, lower than the estimate obtained for growth. These results suggest that selection works well in the breeding program of F. chinensis, and inbreeding especially full-sib matings should be avoided in the following breeding programs.

Inbreeding depression and drift load in small populations at demographic disequilibrium

Inbreeding depression is a major driver of mating system evolution and has critical implications for population viability. Theoretical and empirical attention has been paid to predicting how inbreeding depression varies with population size. Lower inbreeding depression is predicted in small populations at equilibrium, primarily due to higher inbreeding rates facilitating purging and/or fixation of deleterious alleles (drift load), but predictions at demographic and genetic disequilibrium are less clear. In this study, we experimentally evaluate how lifetime inbreeding depression and drift load, estimated by heterosis, vary with census (Nc ) and effective (estimated as genetic diversity, He ) population size across six populations of the biennial Sabatia angularis as well as present novel models of inbreeding depression and heterosis under varying demographic scenarios at disequilibrium (fragmentation, bottlenecks, disturbances). Our experimental study reveals high average inbreeding depression and heterosis across populations. Across our small sample, heterosis declined with He , as predicted, whereas inbreeding depression did not vary with He and actually decreased with Nc . Our theoretical results demonstrate that inbreeding depression and heterosis levels can vary widely across populations at disequilibrium despite similar He and highlight that joint demographic and genetic dynamics are key to predicting patterns of genetic load in nonequilibrium systems.

Inbreeding depression in Zebu cattle traits.

The productivity of herds may be negatively affected by inbreeding depression, and it is important to know how intense is this effect on the livestock performance. We performed a comprehensive analysis involving five Zebu breeds reared in Brazil to estimate inbreeding depression in productive and reproductive traits. Inbreeding depression was estimated for 13 traits by including the individual inbreeding rate as a linear covariate in the standard genetic evaluation models. For all breeds and for almost all traits (no effect was observed on gestation length), the performance of the animals was compromised by an increase in inbreeding. The average inbreeding depression was -0.222% and -0.859% per 1% of inbreeding for linear regression coefficients scaled on the percentage of mean (βm ) and standard deviation (βσ ), respectively. The means for βm (and βσ ) were -0.269% (-1.202%) for weight/growth traits and -0.174% (-0.546%) for reproductive traits. Hence, inbreeding depression is more pronounced in weight/growth traits than in reproductive traits. These findings highlight the need for the management of inbreeding in the respective breeding programmes of the breeds studied here.

Variation of inbreeding depression in Centaurea cyanus L., a self-incompatible species

The evolutionary trajectory of isolated or small populations of self-incompatible species depends on genetic variation in the capacity to transition to self-compatibility and the impact of inbreeding on plant fitness. Centaurea cyanus is an example of a self-incompatible, arable field-dependent weed species that is in regression in western Europe due to agricultural intensification. However, some cases of self-fertilization have been observed. Here, we investigated how inbreeding depression impacts the plants by studying two generations of self-fertilized families. As early as at the stage of the first selfing generation, we observed reduction in the number of florets per capitulum. By the second selfing generation, we observed reductions in germination rate, plant height, above-ground plant biomass, seed set and the final number and mass of seeds per plant. In particular, dramatically lower germination rate and reduced seed set contributed to a low cumulative fitness index of the generations that resulted from selfing. Nevertheless, although high average inbreeding depression was observed, large variation in cumulative fitness among families would allow some of these selfed families to persist and trigger evolution of selfing in small, isolated populations.

Effect of inbreeding on survival, WSSV tolerance and growth at the postlarval stage of experimental full-sibling inbred populations of the Chinese shrimp Fenneropenaeus chinensis

Inbreeding effects on growth, survival and anti-WSSV (White Spot Syndrome Virus) traits were studied in experimental full-sibling inbred populations of Chinese shrimp Fenneropenaeus chinensis at three levels of inbreeding coefficient (F=0.25, F=0.375, F=0.50) from a Chinese shrimp selection program. The body weight of the control group (F≈0.00) was significantly different from those of the three levels of inbreeding groups at three postlarval stages (PL80, PL100 and PL140). At PL140, an increasing inbreeding depression of growth was observed with increasing inbreeding coefficient. The inbreeding depression was found to be −10.4% at F=0.25, −16.61% at F=0.375 and −23.68% at F=0.50. There was also a tendency for inbreeding depression for body weight to increase with age. The estimated coefficient of body weight of PL140 were −4.16%, −4.43% and −4.74% per 10% increase of inbreeding coefficient of F=0.25, F=0.375, F=0.50, respectively. During growout, inbreeding depression of survival ranged from −0.98% to −12.44%, although the effects were not significant. Over all levels of inbreeding the average inbreeding depression was found to be −5.95% for survival of PL80, −5.51% for PL100 and −6.71% for PL140. The estimated average inbreeding depression coefficient of survival ranged from −1.27% to −1.77% per 10% increase of inbreeding coefficient of F, lower than the estimate obtained for growth. The effects of inbreeding on survival time after challenge with White Spot Syndrome Virus (WSSV) were not significant, as there was no significant difference in survivorship among the control and the three levels of inbreeding coefficient groups. The inbreeding depression of the three levels ranged from −0.68% to −2.22%, and the estimated inbreeding depression coefficient of survival time ranged from −0.27% to −0.44% per 10% increase of inbreeding coefficient of F. This study demonstrates that inbreeding has a negative effect on the economic traits, especially on growth, thus highlighting the need to maximize the genetic diversity in selective breeding programs.

Effects of a single event of close inbreeding on growth and survival in steelhead

For two populations of Alaskan steelhead (Oncorhynchus mykiss) of common ancestry we evaluated effects of inbreeding in second-generation descendants of wild fish by comparing progeny of full-sibling matings to those of non-inbred controls to determine if a single event of close inbreeding has significant effects on survival and growth in captivity or the wild. In captivity, both survival and size were highly variable between inbred and control types within each line and among the five broods during five periods of freshwater culture. However, no consistent patterns of inbreeding enhancement or depression between types within lines across years were evident. In contrast, in the wild marine environment, 34 of 34 pairwise comparisons between inbred and control types in body size of returning adults after 2 or 3 years at liberty in the ocean were consistent with inbreeding depression with significant inbreeding depression varying from 2.9% for female length to 20.0% for female weight. Survival of marked juveniles (smolts) to adults in the wild marine environment was consistently and significantly lower in inbred types for both lines, for an average inbreeding depression of 78.8%. The results underscore the potential problems that can arise from using protective culture technologies, including captive broodstocks, to supplement endangered populations, and they highlight the genetic hazards that can be faced by small wild populations. This study demonstrates that high natural mortality or selection increases the amount of inbreeding depression detected in survival. Inbreeding effects on survival and growth in captivity can be poor indicators of survival and growth in a wild marine environment.

Mating system instability in Schiedea menziesii (Caryophyllaceae).

We investigated inbreeding depression and selfing in hermaphroditic Schiedea menziesii to assess the stability of the breeding system. A combination of high selfing rates and strong inbreeding depression suggests that the mating system is unstable. The population-level selfing rate measured in three years ranged considerably from 0.425 (SE = 0.138) to 0.704 (0.048); family measures of selfing rate varied from zero to one in all three years. Inbreeding coefficients did not differ from zero, suggesting that inbred plants do not survive to reproduction in the field. Average inbreeding depression measured in two greenhouse experiments was 0.608-0.870, with values for individual plants ranging from -0.170 to 0.940. The magnitude of inbreeding depression expressed at different life-history stages depended on experimental conditions. When plants were grown during the winter, inbreeding depression was expressed at early and late life-history stages. When plants were grown during the summer, inbreeding depression was detected for germination but not for later life-history stages. Inbreeding depression for vegetative and inflorescence biomass was also measured using field-collected seeds where cross status was assigned using genotypes determined electrophoretically. We did not detect a relation between inbreeding depression and the selfing rate at the level of the individual plant. We saw no evidence for intrafloral selfing, suggesting that the evolution of increased selfing through autogamy is unlikely, despite high selfing rates. A more likely outcome of breeding system instability is the evolution of gynodioecy, which occurs in species of Schiedea closely related to S. menziesii. Females have been detected in progeny of S. menziesii that have been raised in the greenhouse. In the absence of biotic pollen vectors, the failure of these females to establish in the natural population may result from the absence of adaptations for wind pollination.

MATING SYSTEM INSTABILITY IN SCHIEDEA MENZIESII (CARYOPHYLLACEAE)

We investigated inbreeding depression and selfing in hermaphroditic Schiedea menziesii to assess the stability of the breeding system. A combination of high selfing rates and strong inbreeding depression suggests that the mating system is unstable. The population-level selfing rate measured in three years ranged considerably from 0.425 (SE = 0.138) to 0.704 (0.048); family measures of selfing rate varied from zero to one in all three years. Inbreeding coefficients did not differ from zero, suggesting that inbred plants do not survive to reproduction in the field. Average inbreeding depression measured in two greenhouse experiments was 0.608–0.870, with values for individual plants ranging from −0.170 to 0.940. The magnitude of inbreeding depression expressed at different life-history stages depended on experimental conditions. When plants were grown during the winter, inbreeding depression was expressed at early and late life-history stages. When plants were grown during the summer, inbreeding depression was detected for germination but not for later life-history stages. Inbreeding depression for vegetative and inflorescence biomass was also measured using field-collected seeds where cross status was assigned using genotypes determined electrophoretically. We did not detect a relation between inbreeding depression and the selfing rate at the level of the individual plant. We saw no evidence for intrafloral selfing, suggesting that the evolution of increased selfing through autogamy is unlikely, despite high selfing rates. A more likely outcome of breeding system instability is the evolution of gynodioecy, which occurs in species of Schiedea closely related to S. menziesii. Females have been detected in progeny of S. menziesii that have been raised in the greenhouse. In the absence of biotic pollen vectors, the failure of these females to establish in the natural population may result from the absence of adaptations for wind pollination.

Inbreeding and outbreeding depression in male courtship song characters in Drosophila montana.

In Drosophila montana, male courtship song frequency is closely associated with male courtship success and offspring survival. Other pulse characters (pulse length and cycle number) may also affect female mate choice, whereas pulse train characters (interpulse interval, pulse number and pulse train length) are not associated with these male fitness components. Inbreeding depression in these song characters was investigated by comparing the songs of inbred and outbred fly strains. The average change in most song characters as a result of inbreeding was only a few percent. However, in male song frequency the average inbreeding depression was about 14%, suggesting that this song character is associated with fitness. Outbreeding depression and the genetic architecture of song characters were investigated with interpopulation crosses and joint scaling tests. For pulse train characters the generation means show only evidence of additivity, and the existence of dominance or epistasis in these characters was strongly rejected in each case. In pulse characters the means of the F1 males were lower than the average of the parental generations. In pulse length and cycle number this difference was attributable to dominance alone. In frequency there was outbreeding depression also in the F2 generation, suggesting a break-up of favourable epistatic gene combinations. The outbreeding depression in this character in the F1 generation was caused by dominance, and in the F2 also by duplicate epistasis between dominant decreasers. The possible role of outbreeding depression and epistasis in speciation is discussed.

Genetic load, nutrient limitation, and seed production in Lupinus texensis (Fabaceae)

The interaction of mating system and nutrient limitation in determining seed production was investigated in the annual, self‐compatible plant Lupinus texensis (Fabaceae). Abortion of developing seeds is a major factor limiting seed production in natural populations (17‐28%). Selfing rates are generally low (0.02‐0.21), suggesting that deleterious recessive genes may be maintained at significant levels in natural populations. The average inbreeding depression associated with seed development is δ = 0.24. Nutrient limitation reduced seed output across experimental treatments by a factor of 0.22 through decreased production of inflorescences, flowers, and ovules, and by a factor of 0.29 through increased abortion of fruits and of seeds within fruits. Competition for resources among fruits increased the frequency of seed abortion. Moreover, a greater proportion of selfed seeds were aborted as the overall abortion rate increased. Estimates of genetic load may therefore only be appropriate if undertaken in the field, and inbreeding depression may vary from year to year simply due to changes in environmental conditions rather than to underlying genetic changes in populations. The existence of inbreeding depression and the high frequency of abortions suggest that selective abortion favoring outcrossed progeny occurs in natural populations of L. texensis.

EVOLUTION OF THE MAGNITUDE AND TIMING OF INBREEDING DEPRESSION IN PLANTS.

Estimates of inbreeding depression obtained from the literature were used to evaluate the association between inbreeding depression and the degree of self-fertilization in natural plant populations. Theoretical models predict that the magnitude of inbreeding depression will decrease with inbreeding as deleterious recessive alleles are expressed and purged through selection. If selection acts differentially among life history stages and deleterious effects are uncorrelated among stages, then the timing of inbreeding depression may also evolve with inbreeding. Estimates of cumulative inbreeding depression and stage-specific inbreeding depression (four stages: seed production of parent, germination, juvenile survival, and growth/reproduction) were compiled for 79 populations (using means of replicates, N = 62) comprising 54 species from 23 families of vascular plants. Where available, data on the mating system also were collected and used as a measure of inbreeding history. A significant negative correlation was found between cumulative inbreeding depression and the primary selfing rate for the combined sample of angiosperms (N = 35) and gymnosperms (N = 9); the correlation was significant for angiosperms but not gymnosperms examined separately. The average inbreeding depression in predominantly selfing species (δ = 0.23) was significantly less (43%) than that in predominantly outcrossing species (δ = 0.53). These results support the theoretical prediction that selfing reduces the magnitude of inbreeding depression. Most self-fertilizing species expressed the majority of their inbreeding depression late in the life cycle, at the stage of growth/reproduction (14 of 18 species), whereas outcrossing species expressed much of their inbreeding depression either early, at seed production (17 of 40 species), or late (19 species). For species with four life stages examined, selfing and outcrossing species differed in the magnitude of inbreeding depression at the stage of seed production (selfing δ = 0.05, N = 11; outcrossing δ = 0.32, N = 31), germination (selfing δ = 0.02, outcrossing δ = 0.12), and survival to reproduction (selfing δ = 0.04, outcrossing δ = 0.15), but not at growth and reproduction (selfing δ = 0.21, outcrossing δ = 0.27); inbreeding depression in selfers relative to outcrossers increased from early to late life stages. These results support the hypothesis that most early acting inbreeding depression is due to recessive lethals and can be purged through inbreeding, whereas much of the late-acting inbreeding depression is due to weakly deleterious mutations and is very difficult to purge, even under extreme inbreeding.

Models for the evolution of selfing under alternative modes of inheritance

In an approach that explicitly incorporates genetic changes over consecutive generations of self-fertilization, we contrast the effect of different modes of inheritance for selfing rate upon the evolutionary equilibrium selfing rate. A monotonic decline of fitness with consecutive generations of selfing was assumed. We found the range of conditions permitting evolutionarily stable mixed-mating systems to increase with the number of genes controlling the selfing rate. When the mating system is controlled by a single locus with alternative alleles for complete selfing or outcrossing, alleles for selfing concentrate in inbred individuals and are exposed to stronger selection than the average inbreeding depression. By contrast, when alleles of small effect control the selfing rate, selfing rates do not vary as much between inbred vs. outcrossed individuals; this results in the broader stability of mixed mating. We also find that, provided selfing is not caused by recessive alleles, low levels of outcrossing can be maintained when the average relative fitness of selfed progeny is above 0.5. This is postulated to be due to a long-term advantage for occasional outcrossing in terms of the restoration of low inbreeding coefficients. The assumption of a mono-tonic decline in fitness with consecutive generations of selfing is also discussed.

Inbreeding depression in two field trials of young pinus sylvestris (L.)

Inbreeding depression after selfing was estimated in two field trials of Pinus sylvestris, age 11 and 14 years, respectively, by comparing stem volume and height after selfing and outcrossing. For the majority of trees, inbreeding caused a statistically significant reduction in stem volume. The average inbreeding depression for stem volume was 46% and 66% for the two trials, respectively, with a large variation among trees. For one of the trials, the inbreeding depression for height remained at a constant level between age 6 to 14 years, while the inbreeding depression increased between age 6 to 11 years for the other trial. Inbreeding depression was not found to be correlated with the GCA for stem volume of the individual trees. The relative phenotypic within‐family variance was found to be higher in progenies after selfing as compared to outcrossing.

Effect of inbreeding on survival and growth in rainbow trout

The effect of three levels of inbreeding ( F = 0.25, F = 0.375 and F = 0.50) on survival and growth in rainbow trout ( Salmo gairdneri) has been studied. At each level the inbreeding depression for survival of eyed eggs, alevins and fry was highly significant, but no linear relationship was found between level of inbreeding and inbreeding depression. Over all levels of inbreeding the average inbreeding depression was found to be 10.0% for survival of eyed-eggs, 5.3% for alevins and 11.1% for fry. For growth of fingerlings at an age of 160 days after first feeding, no significant inbreeding depression was found at any of the inbreeding levels studied. For growth of adults after a seawater period of about 18 months, a highly significant inbreeding depression was found at each level of inbreeding. An increasing growth depression with increasing inbreeding was also observed. Thus, per 10% of the inbreeding coefficient, the inbreeding depression was found to be 4.5% at F = 0.25, 5.3% at F = 0.375 and 6.1% at F = 0.50.

Comparison of Combined Half‐sib and S1 Family Selection with Half‐sib, S1, and Selection Index Procedures in Maize

A combined half‐sib (HS) and Sl family evaluation procedure (HS‐S1) in a maize (Zea mays L.) population was compared with HS and S1 per se evaluation and with a selection index of the form I = b1Xl + b2X2 where X1 and X2 are grain yields of the HS and S1 families, respectively. The combined HS‐S1 evaluation resulted in lower selection differentials than either HS or S1 evaluation. Combined HS‐S1 selection in the CO (original population) identified 81, 71, and 77% of the selected families in common with HS, S1 and a selection index, respectively, and 60, 58, and 85% in CI. HS‐S1 resulted in selection of genotypes better buffered to environmental differences than either HS or $1 alone. The evidence indicates that HS evaluation results in selection of genotypes with above average population heterotic response and greater than average inbreeding depression while S1 evaluation has the opposite effect. Selection on combined HS‐S1 evaluation resulted in genotypes with less than average inbreeding depression and average or better heterotic response. The selection index has a similar effect. Expected gains showed combined HS‐S1 with resynthesis using S1 progenies to be equal to or greater than other procedures.

Heterosis and Combining Ability in Barley1

Eight parental varieties of barley and the 28 possible F1 and F1 populations were evaluated in spaced plantings in two environments. The traits studied were yield, kernel weight, kernels per head, heads per plant, and height.The average heterosis values of F1's based on midparent means for yield, kernel weight, kernels per head, heads per plant, and height were 21.5, 5.9, 7.1, 7.6, and 3.2%, respectively. When the F1's were compared to the high parent, the average heterosis for yield was 9.1%. The average inbreeding depression for yield in the F2 generation was 26.1%General and specific combining ability variances were obtained from the F1 data, using Griffing's experimental method 4, model II. A substantial amount of additive and nonadditive genetic variance for yield was indicated. Most of the genetic variance for kernel weight, heads per plant, kernels per head, and height was additive.The yield of the best hybrid exceeded the highest yielding parental varieties, Liberty and Traill, by 22 and 38%, respectively. A hybrid advantage of this degree combined with evidence of considerable nonadditive genetic variance for yield indicates the desirability of additional research on hybrid barley. The results reported indicated that performance per se can be used as a basis for initial screening in evaluating potential parental varieties for use in a hybrid breeding program.

Chilling wheat blooms makes crossing easier

The evolutionary trajectory of isolated or small populations of self-incompatible species depends on genetic variation in the capacity to transition to self-compatibility and the impact of inbreeding on plant fitness. Centaurea cyanus is an example of a self-incompatible, arable field-dependent weed species that is in regression in western Europe due to agricultural intensification. However, some cases of self-fertilization have been observed. Here, we investigated how inbreeding depression impacts the plants by studying two generations of self-fertilized families. As early as at the stage of the first selfing generation, we observed reduction in the number of florets per capitulum. By the second selfing generation, we observed reductions in germination rate, plant height, above-ground plant biomass, seed set and the final number and mass of seeds per plant. In particular, dramatically lower germination rate and reduced seed set contributed to a low cumulative fitness index of the generations that resulted from selfing. Nevertheless, although high average inbreeding depression was observed, large variation in cumulative fitness among families would allow some of these selfed families to persist and trigger evolution of selfing in small, isolated populations.