THE RELATIONSHIP BETWEEN INBREEDING DEPRESSION AND PRIOR INBREEDING AMONG POPULATIONS OF FOUR MIMULUS TAXA

Abstract.-If inbreeding depression is caused by deleterious recessive alleles, as suggested by the partial dominance hypothesis, a negative correlation between inbreeding and inbreeding depression is predicted. This hypothesis has been tested several times by comparisons of closely related species or comparisons of populations of the same species with different histories of inbreeding. However, if one is interested in whether this relationship contributes to matingsystem evolution, which occurs within populations, comparisons among families within a population are needed; that is, inbreeding depression among individuals with genetically based differences in their rate of selfing should be compared. In gynodioecious species with self-compatible hermaphrodites, hermaphrodites will have a greater history of potential inbreeding via both selfing and biparental inbreeding as compared to females and may therefore express a lower level of inbreeding depression. We estimated the inbreeding depression of female and hermaphrodite lineages in gynodioecious Lobelia siphilitica in a greenhouse experiment by comparing the performance of selfed and outcrossed progeny, as well as sibling crosses and crosses among subpopulations. We did not find support for lower inbreeding depression in hermaphrodite lineages. Multiplicative inbreeding depression (based on seed germination, juvenile survival, survival to flowering, and flower production in the first growing season) was not significantly different between hermaphrodite lineages (8 = 0.30 ± 0.08) and female lineages (8 = 0.15 ± 0.18), although the trend was for higher inbreeding depression in the hermaphrodite lineages. The population-level estimate of inbreeding depression was relatively low for a gynodioecious species (8 = 0.25) and there was no significant inbreeding depression following biparental inbreeding (8 = 0.01). All measured traits showed significant variation among families, and there was a significant interaction between family and pollination treatment for four traits (germination date, date of first flowering, number of flowers, and aboveground biomass). Our results suggest that the families responded differently to selfing and outcrossing: Some families exhibited lower fitness following selfing whereas others seemed to benefit from selfing as compared to outcrossing. Our results support recent simulation results in that prior inbreeding of the lineages did not determine the level of inbreeding depression. These results also emphasize the importance of determining familylevel estimates of inbreeding depression, relative to population-level estimates, for studies of mating-system evolution.Key words.-Biparental inbreeding, gynodioecy, inbreeding depression, Lobelia siphilitica. Received October 8, 1997. Accepted June 25, 1998 Inbreeding depression, the reduced fitness of progeny derived from inbreeding relative to outcrossing, has received much attention in recent decades. According to the "partial dominance" hypothesis, inbreeding depression is a consequence of in...

Section: Comparisons With Other Studiesmentioning

confidence: 99%

INBREEDING DEPRESSION IN GYNODIOECIOUSLOBELIA SIPHILITICA: AMONG-FAMILY DIFFERENCES OVERRIDE BETWEEN-MORPH DIFFERENCES

Mutikäinen

Delph

1998

“…In a study of three populations of Clarkia tembloriensis with selfing rates ranging from 42% to 97%, Holtsford and Ellstrand (1990) found some evidence for a negative relationship in some reproductive characters. Latta and Ritland (1994) investigated the relationship between inbreeding depression and the inbreeding coefficient (rather than the selfing rate) in Mimulus taxa. The relationship was negative for all five traits related to fitness, but significantly so for only one trait.…”

Section: Relation Of Data To Theory Based On Mutation-selection Balancementioning

confidence: 99%

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

Johnston

Schoen

1996

Abstract.-The relation between inbreeding depression and rate of self-fertilization was studied in nine natural populations of the annual genus Amsinckia. The study included two clades (phylogenetic lineages) in which small-flowered, homostylous populations or species are believed to have evolved from large-flowered, heterostylous, self-compatible ones. In one lineage the small-flowered species is tetraploid with disomic inheritance. Rates of self-fertilization were 25% to 55% in the four large-flowered, heterostylous populations; 72% in a large-flowered but homostylous population; and greater than 99.5% in the four small-flowered, homostylous populations, which produce seed autonomously. When present, inbreeding depression occurred in the fertility but not the survival components of fitness. Using a cumulative fitness measure incorporating both survival and fertility (flower number), we found inbreeding depression to be lower in the four very highly self-fertilizing populations than in the five intermediate ones. The Spearman rank correlation between inbreeding depression and selfing rate for the nine populations was -0.50, but was not statistically significant (P = 0.12). Inbreeding depression was greater in the two tetraploid populations than in the very highly self-fertilizing, diploid ones. Phenotypic stability of progeny from self-fertilization tended to be higher in populations with lower inbreeding depression. We conclude that levels of self-fertilization and inbreeding depression in Amsinckia are determined more by other factors than by each other. Estimates of mutation rates and dominance coefficients of deleterious alleles, obtained from a companion study of the four highly self-fertilizing populations, suggest that a strong relationship may not be expected. We discuss the relationship of the present results to current theory of the coevolution of selffertilization and inbreeding depression.

“…Its magnitude in natural populations differs greatly among species and sometimes among populations within species. This variation, both in severity of depression and in its ontogenetic timing, has been related to differences in the mating system, particularly the degree of selfing (Charlesworth and Charlesworth 1987;Lande et al 1994;Latta and Ritland 1994;Parker et al 1995;Husband and Schemske 1996). The review by Husband and Schemske (1996) is recent and thorough, and the reader is referred to it for details.…”

mentioning

confidence: 99%

Relationship Between Self-Fertility, Allocation of Growth, and Inbreeding Depression in Three Coniferous Species

Sorensen

1999

Abstract.-Mortality and growth of self and outcross families of three wind-pollinated, mixed-mating, long-lived conifers, Douglas-fir (Pseudotsuga menziesiii, ponderosa pine (Pinus ponderosa), and noble fir (Abies procera) were followed from outplanting to age 26 (25 for noble fir) in spaced plantings at a common test site. Response to inbreeding differed greatly among species over time and in all regards. Only Douglas-fir and noble fir will be contrasted here, because ponderosa pine usually was intermediate to the other two in its response to inbreeding. In earlier reports, compared to noble fir Douglas-fir had a higher rate of primary selfing and larger inbreeding depression in seed set. Douglas-fir continued to have higher inbreeding depression in nursery and early field survival. The species differed in time courses of inbreeding depression in height and in allocation of growth due to crowding. Between ages 6 and 12, the relative elongation rate (dm . dm-1 • yr") of Douglas-fir was significantly greater in the selfs than in the outcrosses. The response was not observed in noble fir. At final measurement, inbreeding depression in diameter relative to inbreeding depression in height was greater in Douglas-fir than in noble fir. At final measurement inbreeding depression in height was inversely related to inbreeding depression in survival. Cumulative inbreeding depressions from time of fertilization to final measurement were 0.98, 0.94, and 0.83 for Douglas-fir, ponderosa pine, and noble fir, respectively, which indicates that selfs will not contribute to the mature, reproductive populations.Key words.-Abies procera, Douglas-fir, inbreeding depression, noble fir, photomorphogenic effects, Pinus ponderosa, ponderosa pine, Pseudotsuga menziesii.Received January 28, 1998. Accepted November 12, 1998 Inbreeding depression (ID) is the reduction in fitness associated with increased homozygosity. Its magnitude in natural populations differs greatly among species and sometimes among populations within species. This variation, both in severity of depression and in its ontogenetic timing, has been related to differences in the mating system, particularly the degree of selfing (Charlesworth and Charlesworth 1987;Lande et al. 1994;Latta and Ritland 1994;Parker et al. 1995;Husband and Schemske 1996). The review by Husband and Schemske (1996) is recent and thorough, and the reader is referred to it for details.The theoretical expectation is that high rates of primary selfing (selfing at the fertilization stage) will purge highly deleterious alleles (Lande and Schemske 1985;Charlesworth and Charlesworth 1987). Within-and among-species comparisons do indeed indicate that ID in embryo and neonatal survival and growth traits are negatively related with rate of primary selfing (Latta and Ritland 1994;Husband and Schemske 1996). However, the relationship also shows large variation around the regression line. This indicates that factors such as degree of dominance or complex modes of inheritance, magnitude of effect, genomic mutatio...