Outcrossed Progeny Research Articles

Estimating within-locus nonadditive coefficient and discriminating dominance versus overdominance as the genetic cause of heterosis.

Testing (over)dominance as the genetic cause of heterosis and estimating the (over)dominance coefficient (h) are related. Using simulations, we investigate the statistical properties of Mukai's approach, which is intended to estimate the average (h) of hi across loci by regression of outcrossed progeny on the sum of the two corresponding homozygous parents. A new approach for estimating h is also developed, utilizing data on families formed by multiple selfed genotypes from each outcrossed parent, thus not requiring constructing homozygotes. Assuming constant mutation effects, h can be estimated accurately by both approaches under dominance. When rare alleles have low frequencies at any polymorphic locus, Mukai's approach can estimate h accurately under over(under)dominance. Therefore, the (over)dominance hypothesis for heterosis can be tested by estimating h, under either dominance or overdominance at all genomic loci. However, this is invalid with more plausible mixed dominance and overdominance at different loci. Estimating the variance of hi across loci is also investigated. In self-compatible outcrossing populations with mutations of variable effects and lethals, our new approach is better than Mukai's, not only because of not requiring homozygotes but also because of the better statistical performance reflected by the smaller mean square errors of the estimates.

Homology‐based control of gene expression patterns in transgenic petunia flowers

Plant transgenes may participate in two types of homology-based gene silencing. One requires transcript homology, is post-transcriptional, and is referred to as cosuppression; the other requires promoter homology, is transcriptional, and is similar to paramutation. This paper uses flower color transgenes to address the hierarchical operation of both mechanisms in plants carrying two transgene copies. It is shown that cosuppression of homologous, endogenous flower color genes by single-copy transgenes requires that the transgene be driven by a strong promoter and that the degree of cosuppression is highly sensitive to increasing transgene dosage. Together, these observations suggest that cosuppression should be a sensitive reporter of epigenetic changes in transgene transcription, such as might be caused by paramutation-like interactions between transgene loci. Intercrosses bringing together two homologous transgene loci, one a known epimutable reporter and the other a transgene inverted repeat, result in complete loss of cosuppression in some outcross progeny and a qualitative change in morphology-based patterns of cosuppression in other outcross progeny. This paramutation-like behavior suggests that the transgenes may be altered at the transcriptional level, eliminating cosuppression altogether or changing the spatial pattern of transgene transcription to produce a new pattern of cosuppression. Dev. Genet. 22:100–109, 1998. © 1998 Wiley-Liss, Inc.

Homology-based control of gene expression patterns in transgenic petunia flowers.

Plant transgenes may participate in two types of homology-based gene silencing. One requires transcript homology, is post-transcriptional, and is referred to as cosuppression; the other requires promoter homology, is transcriptional, and is similar to paramutation. This paper uses flower color transgenes to address the hierarchical operation of both mechanisms in plants carrying two transgene copies. It is shown that cosuppression of homologous, endogenous flower color genes by single-copy transgenes requires that the transgene be driven by a strong promoter and that the degree of cosuppression is highly sensitive to increasing transgene dosage. Together, these observations suggest that cosuppression should be a sensitive reporter of epigenetic changes in transgene transcription, such as might be caused by paramutation-like interactions between transgene loci. Intercrosses bringing together two homologous transgene loci, one a known epimutable reporter and the other a transgene inverted repeat, result in complete loss of cosuppression in some outcross progeny and a qualitative change in morphology-based patterns of cosuppression in other outcross progeny. This paramutation-like behavior suggests that the transgenes may be altered at the transcriptional level, eliminating cosuppression altogether or changing the spatial pattern of transgene transcription to produce a new pattern of cosuppression.

THE EFFECTS OF FIVE GENERATIONS OF ENFORCED SELFING ON POTENTIAL MALE AND FEMALE FUNCTION IN MIMULUS GUTTATUS.

In prior work we detected no significant inbreeding depression for pollen and ovule production in the highly selfing Mimulus micranthus, but both characters showed high inbreeding depression in the mixed-mating M. guttatus. The goal of this study was to determine if the genetic load for these traits in M. guttatus could be purged in a program of enforced selfing. These characters should have been under much stronger selection in our artificial breeding program than previously reported characters such as biomass and total flower production because, for example, plants unable to produce viable pollen could not contribute to future generations. Purging of genetic load was investigated at the level of both the population and the individual maternal line within two populations of M. guttatus. Mean ovule number, pollen number, and pollen viability declined significantly as plants became more inbred. The mean performance of outcross progeny generated from crosses between pairs of maternal inbred lines always exceeded that of self progeny and was fairly constant for each trait through all five generations. The consistent performance of outcross progeny and the universally negative relationships between performance and degree of inbreeding are interpreted as evidence for the weakness of selection relative to the quick fixation of deleterious alleles due to drift during the inbreeding process. The selective removal (purging) of deleterious alleles from our population would have been revealed by an increase in performance of outcross progeny or an attenuation of the effects of increasing homozygosity. The relationships between the mean of each of these traits and the expected inbreeding coefficient were linear, but one population displayed a significant negative curvilinear relationship between the log of male fertility (a function of pollen number and viability) and the inbreeding coefficient. The generally linear form of the responses to inbreeding were taken as evidence consistent with an additive model of gene action, but the negative curvilinear relationship between male fertility and the inbreeding coefficient suggested reinforcing epistasis. Within both populations there was significant genetic variation among maternal lineages for the response to inbreeding in all traits. Although all inbred lineages declined at least somewhat in performance, several maternal lines maintained levels of performance just below outcross means even after four or five generations of selfing. We suggest that selection among maternal lines will have a greater effect than selecting within lines in lowering the genetic load of populations.

Outcrossing Rate, Yield, and Selective Fruit Abscission in `Ettinger' and `Ardith' Avocado Plots

The reciprocal effect of two avocado (Persea americana Mill.) cultivars—Ardith and Ettinger—on outcrossing rate and yield was studied in several orchards in Israel. Multilocus estimates of outcrossing rates were made using the isozyme loci Mdh-1 (malate dehydrogenase) and Aat-1 (aspartate aminotransferase) for `Ettinger' progeny and Lap-2 (leucine aminopeptidase), Pgm-1 (phosphoglucomutase) and Tpi-1 (triosephosphate isomerase) for `Ardith' progeny. When the two cultivars were in close proximity, estimated yields ranged from 10 to 20 t·ha-1 and outcrossing rates ranged from 0.71 to 0.89 and from 0.87 to 0.90 for `Ettinger' and `Ardith', respectively. The effect of `Ettinger' as a pollenizer was not restricted to adjacent `Ardith' trees; it also reached more distant `Ardith' trees. Thus, outcrossing rate in `Ardith' was 0.82 at a distance of 30 m from `Ettinger' in one orchard and 0.91 at a distance of 36 m in another orchard. These results confirm previous observations that `Ettinger' is a highly potent pollenizer. Outcrossing rates in `Ardith' and `Ettinger' were found to increase from the young fruitlet stage to that of mature fruit. These findings provide evidence for selective abscission of selfed fruitlets. In addition, parentage analysis of abscised versus retained `Ardith' fruit showed that `Ardith' selfed fruit abscised at a much higher rate than outcrossed ones. The survival advantage of outcrossed fruit is probably related to the fact that selfed progeny have less-vigorous embryos than outcrossed progeny due to inbreeding depression.

Dap (Defective aleurone pigmentation) mutations affect maize aleurone development.

Dap (Defective aleurone pigmentation) is the designation for mutations in maize that give rise to a characteristic dappled endosperm phenotype, consisting of patches of purple tissue, of variable size and shape, on a yellow background. Features shared by all Dap mutants are: dominant expression when they are maternally derived, lack of expression or transmission when they originate from pollen, failure to recover homozygous Dap genotypes, reduced frequency of Dap seeds in the progeny of outcrosses of Dap/+ females, association of the dappled phenotype with reduction in seed size. The mutants so far tested, six in all, can be grouped into two classes, one including male-transmissible (MT) isolates not expressed in the endosperm if their contribution is paternal, and a second class of isolates (NMT) that are permanently lost following paternal transmission. We suggest that the NMT mutations are on a chromosome that carries an intercalary deletion. Assuming linkage between the mutant and the deletion, selection against the deficient chromosome during male gametogenesis would account for the failure to recover Dap seeds in the progeny of Dap/+ male parents. We have obtained genetic evidence supporting this hypothesis. This interpretation, however, does not apply to MT alleles. For these, other mechanisms, such as imprinting and/or dosage effects may be proposed. The mutable pattern in the endosperm to which all Dap mutants give rise is an intriguing phenotype which remains to be clarified. An unexpected finding is that aleuronic and subaleuronic cells corresponding to the colourless areas are abnormal in shape and anthocyanin biosynthesis is blocked in these cells. This finding calls for further investigation in light of a possible connection between flavonoid precursors and cell shape.

Selfing and biparental inbreeding: a mating system analysis in Lymnaea peregra (Gastropoda: Lymnaeidae)

The mating system was analysed in three populations of Lymnaea peregra, under the mixed-mating model (MMM) and the effective selfing model (ESM), using progeny array data and allozyme markers. The results revealed variation among populations for the outcrossing rate (tm ranged from 0.646 to 0.983). This finding modifies the earlier classification of L. peregra as a predominantly outcrossing species. The occurrence of biparental inbreeding and population substructure in one of three populations was suggested from positive (tm—ts) under the MMM, covariation of the effective selfing rate with parental fixation index, as well as the great difference between the effective selfing rate of inbred and outbred parents under the ESM. The within-population distribution of the outcrossing rates varied extensively and may involve different patterns of selection and levels of inbreeding depression among the populations studied. Consistently, the estimation of correlated matings showed different levels of the correlation of selfing within progenies in the three populations. Levels of multiple paternity for the outcrossed progeny were positively associated with higher population outcrossing rates, which may reflect the propensity of preferential outcrossers to copulate actively.

EVOLUTION OF A BENEFICIAL ALLELE UNDER PARTIAL SELFING AND INBREEDING DEPRESSION.

Classical population genetics has often focused on the dynamics of one or a few genes in isolation from the rest of the genome. Recently, however, there has been a recognition that the selective environment of a gene includes the entire genome (Charlesworth 1994; Peck 1994; Barton 1995). This study investigates the influence of a genomic trait, inbreeding depression, on the evolution of a beneficial allele at a single locus under partial selfing. Much of the effect of inbreeding depression is accounted for by its reduction of the selfing rate experienced in the population. In addition, however, I find evidence for a secondary consequence of a genomic background of inbreeding depression under partial selfing, namely, associations between the beneficial allele and the background. These associations, while small, may have a measurable effect on the evolution of advantageous alleles in a background of inbreeding depression. Inbreeding depression is the decrement in fitness associated with inbreeding compared to outbreeding. In selfcompatible plants, this is generally measured as 8 = 1 (wslwO), where wi is the average fitness of selfed progeny and w0 is the average fitness of outcrossed progeny. Inbreeding depression has been studied extensively as an important factor in the evolution of self-fertilization in plants, and is thought to be present in most sexual species (Charlesworth and Charlesworth 1987). Experimental evidence now generally supports the hypothesis that a substantial proportion of the inbreeding depression observed in plants is due to recurrent mutation to deleterious recessive or nearly recessive alleles at many loci (Crow 1993; Ritland 1996). An important property of this form of inbreeding depression is that it is dynamic and interacts with the breeding system, so that the input of new mutations is balanced by a purging of recessives through exposure to selection due to the increase in homozygosity that accompanies self-fertilization (Lande and Schemske 1985). Evolution in partially selfing populations has features that distinguish it from evolution in random-mating populations, both from a single-locus and a multilocus perspective. At a single locus, levels of dominance and inbreeding can interact to affect the fate of individual alleles. In a phenomenon known as Haldane's Sieve, recessive beneficial mu-

EVOLUTION OF GYNODIOECY AND MAINTENANCE OF FEMALES: THE ROLE OF INBREEDING DEPRESSION, OUTCROSSING RATES, AND RESOURCE ALLOCATION IN SCHIEDEA ADAMANTIS (CARYOPHYLLACEAE).

Levels of inbreeding depression, outcrossing rates, and phenotypic patterns of resource allocation were studied to examine their relative importance in the maintenance of high numbers of females in gynodioecious Schiedea adamantis (Caryophyllaceae), an endemic Hawaiian shrub found in a single population on Diamond Head Crater, Oahu. In studies of inbreeding depression in two greenhouse environments, families of hermaphrodites exhibited significant inbreeding depression (δ = 0.60), based on a multiplicative fitness function using seeds per capsule, germination, survival, and the inflorescence biomass of progeny. Differences between inbred and outcrossed progeny were smallest at the early stage of seeds per capsule and more pronounced at the later stages of survival and inflorescence production. These results are consistent with inbreeding depression caused by many mutations of small effect. Using allozyme analyses, the inbreeding coefficient of adult plants in the field was not significantly different from zero, implying that δ in nature may be equal to one. The single locus estimate of the outcrossing rate for hermaphrodites was 0.50 based on progeny that survived to flowering; corrected for the disproportionate loss before flowering of progeny from selfing, the adjusted outcrossing rate at the zygote stage was 0.32, suggesting that considerable selfing occurs in hermaphrodites. Females were totally outcrossed. When females and hermaphrodites were compared for reproductive output in the field, females produced over twice as many seeds per plant as hermaphrodites, primarily because females had far more capsules per inflorescence than hermaphrodites. Females had greater mass per seed than hermaphrodites in the field, either because of greater provisioning or reduced inbreeding depression. There was no significant differential mortality with respect to sex over a seven year period. The higher number of seeds per plant of females, combined with substantial inbreeding depression and relatively high selfing rates for hermaphrodites, are probably responsible for the maintenance of females in this population. The predicted frequency of females based on data for seed production, the adjusted selfing rate, and inbreeding depression is 42%, remarkably close to the observed frequency of 39%. High levels of inbreeding depression suggest that considerable quantitative genetic variation is present for traits affecting fitness in this population, despite low allozyme variability and a presumed founder effect.

Selfing, Outcrossing, and Mixed Mating in the Freshwater Snail Physa heterostropha: Lifetime Fitness and Inbreeding Depression

Selfing, Outcrossing, and Mixed Mating in the Freshwater Snail Physa heterostropha: Lifetime Fitness and Inbreeding Depression

ECOLOGICAL AND GENETIC CONSEQUENCES OF POLLINATION BY SEXUAL DECEPTION IN THE ORCHID CALADENIA TENTACTULATA.

Only orchids affect pollination by the deceptive sexual attraction of male insects, a syndrome particularly well developed in Australia. We examined the ecological and genetic consequences of exclusive pollination by sexually attracted male thynnine wasps in the orchid Caladenia tentaculata. Male wasps respond rapidly to flowers artificially presented in 1 × 1 m2 experimental patches. Sixty of 287 wasps approached within centimeters of the flower, but did not land. Of the remaining 79% who made floral contact, only 7.5% attempted copulation, the step critical for pollination. Wasps only rarely moved among patches (19% of flights) and none attempted copulation a second time, resembling observations in natural populations. We confirmed outcrossing and long distance pollen flow by monitoring how colored pollen moved in natural populations. Pollen movements approximated a linear rather than a leptokurtic distribution (mean distance: 17 m; maximum: 58 m). Pollinator visits varied independently of flower density in three of four populations with most solitary flowers being visited. Allozyme analysis revealed within-population fixation indices (F) close to zero and low levels of differentiation (FST) among populations. Despite behavioral evidence for long distance pollen flow, significant local genetic structure exists, perhaps reflecting restricted seed dispersal. Long distance pollen flow in C. tentaculata may therefore promote outbreeding by minimizing pollen transfers among related neighbors. Although this species is self-compatible, outcrossed progeny develop significantly faster than selfed progeny. Effective pollination at low flower densities could accentuate this advantage. The data are consistent with the predictions that deceptive pollination will result in long distance pollen flow, which may be of selective advantage at low density. Comparative studies of how food reward, food deceptive, and sexual deceptive pollination systems vary within a phylogenetic framework could further illuminate the evolution of sexual deception.

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.

Relatedness measured by oligonucleotide probe DNA fingerprints and an estimate of the mating system of Sea Lavender (Limonium carolinianum)

Using DNA fingerprint markers within species and populations of wild plants requires information on the relationship between fingerprint similarity and relatedness. We identified a hypervariable marker based on oliog(GATA)4-hybridization of DpnII-cut genomic DNA from Sea Lavender (Limonium carolinianum). Banding patterns were somatically stable and highly variable among unrelated individuals. Band molecular-weight sizing errors (as a percent of band molecular weight) were estimated at 0.44%±0.003 within gels and 0.76%±0.964 between gels. Band sizing errors defined a 99% confidence bin of ±0.95% (1.90% total) of molecular weight. Band-sharing estimates were based on this bin size and on variance estimates that compensate for non-independent comparisons. Band-sharing among nine unrelated individuals (θ) was 0.198±0.O11. Experimental pollinations designed to produce selfed, fulland half-sib progeny groups led to five selfed progeny groups and no outcrossed progeny (mean band-sharing, ovS=0.468±0.074). A linear regression between band-sharing (S) and relatedness (r) assuming 17% inbreeding was r=0.006+0.914*S (R(2)=0.973) and established the maximum amount of inbreeding. ovS(0.392±0.022) estimated from wild pollinated seeds from four maternal families was intermediate to unrelated individuals and experimental selfed progeny, giving evidence for mixed mating in wild plants. More extensive plant pedigrees with known levels of inbreeding will be needed to measure variation in the relationship between S and r among populations and families.

Inbreeding depression in the gynodioecious shrubHebe subalpina(Scrophulahaceae)

Abstract Inbreeding depression caused by self-fertilisation was examined in the gynodioecious shrub Hebe subalpina under two planting regimens, non-competitive and competitive. We found differences among families in the magnitude of inbreeding depression, ranging from 0.31 to 0.63. On average, outcrossed progeny grew nearly twice as large as selfed progeny, and the coefficients of variation (CVs) for dry mass were lower for outcrossed progeny than selfed progeny within the non-competitive regimen. Planting regime had a highly significant effect on dry mass, such that plants grown in the competitive regimen were an order of magnitude smaller than those in the non-competitive regimen, and they also had higher CVs. However, planting regimen did not significantly affect the magnitude of inbreeding depression. Our results suggest that intrinsic differences exist in the growth rate of selfed and outcrossed individuals, and that inbreeding depression helps to maintain females at a high frequency in the populatio...

Inbreeding Depression in Two Species of Mimulus (Scrophulariaceae) with Contrasting Mating Systems

We examined the effect of self- and cross-pollination on germination success, flowering probability, pollen and ovule production, survivorship, and adult aboveground biomass in two species of Mimulus with contrasting mating systems: the highly seifing M. micranthus and an outcrossing population of M. guttatus. Cross-pollinations were performed both within and between populations in order to examine the scale at which the genetic load is distributed. We found significant inbreeding depression in M. guttatus in four of the six traits, with the highest inbreeding depression observed in biomass (68% and 69% based on within- and between-population crosses, respectively) and lowest in ovule production (21% based on between-population crosses only). M. micranthus displayed significant inbreeding depression in only two of the six traits examined. Again, we observed the highest inbreeding depression in biomass (47–60% based on within- and between-population crosses, respectively), but both traits showing significant differences between self and outcross progeny expressed lower inbreeding depression than in M. guttatus. We detected no significant inbreeding depression for either pollen or ovule production in M. micranthus. An estimate of total inbreeding depression based on the multiplicative effects of all traits was also lower in M. micanthus than∗∗∗ in M. guttatus. Our results are consistent with the expected purging of genetic load in populations with high selfing rates. The absence of inbreeding depression in M. micranthus pollen and ovule production, two traits with strong links to fitness in a selfing annual, further suggests the important role of directional selection in determining the population's genetic load. Comparison of cross-pollinations made within and between populations revealed little evidence of divergence of genetic load among the M. micranthus and M. guttatus populations examined.

Inbreeding depression in two species of Mimulus (Scrophulariaceae) with contrasting mating systems

We examined the effect of self‐ and cross‐pollination on germination success, flowering probability, pollen and ovule production, survivorship, and adult aboveground biomass in two species of Mimulus with contrasting mating systems: the highly seifing M. micranthus and an outcrossing population of M. guttatus. Cross‐pollinations were performed both within and between populations in order to examine the scale at which the genetic load is distributed. We found significant inbreeding depression in M. guttatus in four of the six traits, with the highest inbreeding depression observed in biomass (68% and 69% based on within‐ and between‐population crosses, respectively) and lowest in ovule production (21% based on between‐population crosses only). M. micranthus displayed significant inbreeding depression in only two of the six traits examined. Again, we observed the highest inbreeding depression in biomass (47–60% based on within‐ and between‐population crosses, respectively), but both traits showing significant differences between self and outcross progeny expressed lower inbreeding depression than in M. guttatus. We detected no significant inbreeding depression for either pollen or ovule production in M. micranthus. An estimate of total inbreeding depression based on the multiplicative effects of all traits was also lower in M. micanthus than∗∗∗ in M. guttatus. Our results are consistent with the expected purging of genetic load in populations with high selfing rates. The absence of inbreeding depression in M. micranthus pollen and ovule production, two traits with strong links to fitness in a selfing annual, further suggests the important role of directional selection in determining the population's genetic load. Comparison of cross‐pollinations made within and between populations revealed little evidence of divergence of genetic load among the M. micranthus and M. guttatus populations examined.

EVOLUTION OF UNISEXUALITY IN THE HAWAIIAN FLORA: A TEST OF MICROEVOLUTIONARY THEORY.

The evolution of separate sexes as a means of avoiding self-fertilization requires the controversial coexistence of large inbreeding depression and high selfing rate in the ancestral hermaphrodite population. Fitness components of adult females and hermaphrodites in nature, of their open-pollinated progeny, and of experimental selfs and outcrosses onto hermaphrodites were compared in endemic Hawaiian Bidens sandvicensis, all of whose known populations are gynodioecious, consisting of a mixture of females and hermaphrodites. Multilocus selfing rates of hermaphrodites were also estimated, and sex morph ratio monitored over four seasons in three populations of B. sandvicensis and one population of gynodioecious B. cervicata. Total mean inbreeding depression in seed set (in the glasshouse), germination rate (in an open-air nursery on Kauai), and first year survivorship and fecundity in the field were estimated as 0.94 (SE 0.04), and occurred primarily in drought months. Lower survivorship and fecundity of selfs were partially explained by their consistently smaller size. Open-pollinated seed of females had significantly lower germination rate, proportion flowering, and fecundity than outcrossed progeny of hermaphrodites, suggesting moderate biparental inbreeding in females and a lack of any non-outcrossing advantage to progeny of females. In all fitness components, open-pollinated progeny of hermaphrodites were inferior to those of females and to outcrosses, and in most components were superior to selfs. Total performance of open-pollinated progeny of females relative to those of hermaphrodites was calculated as 2.3 (SE = 0.4), but since inflorescences of females also set 20% to 50% more seed than those of hermaphrodites, their total relative ovule success was estimated as 3.2 (SE = 0.5). If inheritance of male sterility is nuclear, this superiority is sufficient to maintain females in frequencies over 20% in populations, whose actual frequencies ranged from 14% to 33%. In four populations, selfing rates of hermaphrodites, assayed in seedlings, were 0.50, 0.45, 0.25, and 0.30, but since substantial inbreeding depression occurred prior to germination, the mean selfing rate of hermaphrodite ovules exceeded 0.57. Female frequencies were significantly higher in the two populations with higher hermaphrodite selfing rate. These results suggest that inbreeding depression can exert a profound influence on the mating system of self-compatible plants on Hawaii and perhaps other oceanic islands, and can be sufficiently strong to electively favor the elimination of the male function.

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

The effects of one generation of selfing and outcrossing on six life history characters were examined in the greenhouse for two populations of the mixed-mating species Mimulus guttatus. Inbreeding depression was not detected in the mass of seed produced by maternal plants, but selfing significantly reduced germination success by 13–20 per cent relative to outcross seeds. Seedlings produced by self-pollination were 26–31 per cent smaller than outcross progeny. Late life history stages were examined under varied competitive regimes in which each plant was grown with a neighbour of either an inbred or outbred individual. Progeny resulting from self-pollinations showed a 14–30 per cent reduction in ovule number per locule, and their pollen production per flower was reduced by 28–33 per cent. Adult above-ground biomass showed the greatest inbreeding depression, ranging from 24–50 per cent depending on the competitive conditions. Thus progeny resulting from selfing are smaller as adults and contribute significantly fewer potential gametes into the gene pool as pollen grains and ovules. The multiplicative effects of these characters is calculated. For all traits except ovule number, outcross progeny from parents of the same population did not differ significantly from outcross progeny produced by parents that came from populations separated by 10 km, suggesting relatively little differentiation between populations. The relative performance of self and outcross progeny in later life history stages was independent of the relative performance observed in earlier stages.

Susceptibility to platelet-activating factor-induced airway hyperreactivity and hyperpermeability: interstrain variation and genetic control.

Platelet-activating factor (PAF) is a proinflammatory mediator known to elicit changes in airway reactivity and vascular permeability, and it may also have a role in the development and progression of acute respiratory distress syndrome and asthma. We have developed a mouse model to test the hypothesis that these traits were controlled by a single gene and were mechanistically related. We further hypothesized that there was a relationship between PAF-induced hyperreactivity and baseline reactivity to acetylcholine (ACh). Among eight inbred strains of mice that exhibited significant interstrain variation in ACh reactivity, intravenous PAF induced 16 to 278% increases in reactivity to ACh (25 micrograms/kg). PAF also elicited 95 to 307% increases in lung permeability as measured by Evans blue extravasation. Both reactivity and permeability changes induced by PAF were blocked by a PAF receptor antagonist (L-659,989). Strain distribution patterns for baseline reactivity to ACh and PAF-induced hyperreactivity and lung permeability were not significantly concordant, and suggest that the variables were not interdependent. Progeny derived from AKR/J (PAF hyperresponsive) and C3H/HeJ (PAF hyporesponsive) mice were characterized for their PAF responsiveness as determined by PAF-induced hyperreactivity and hyperpermeability. The ratios of hyperresponsive and hyporesponsive phenotypes in outcross progeny were compared to those predicted for Mendelian inheritance and assessed for relatedness by chi 2 and cosegregation analyses. Results suggested that PAF-induced hyperreactivity was controlled by a single gene, but PAF-induced hyperpermeability was controlled by a more complicated interaction of factors.(ABSTRACT TRUNCATED AT 250 WORDS)

INBREEDING DEPRESSION IN MORPHOLOGICAL AND PHYSIOLOGICAL TRAITS OF SCHIEDEA LYDGATEI (CARYOPHYLLACEAE) IN TWO ENVIRONMENTS.

We compared inbreeding depression in hermaphroditic Schiedea lydgatei and its gynodioecious sister species, S. salicaria, to infer the level of inbreeding depression in their common ancestor. With measurements of selfing rates, this information can be used to assess the importance of inbreeding depression in the evolution of breeding systems in S. lydgatei and S. salicaria. Morphological and physiological characters related to fitness were compared for inbred and outcrossed S. lydgatei in high- and low-fertilizer environments in the greenhouse. Seed mass, number of seeds per capsule, germination, survival, biomass, number of flowers, and age at first flowering were compared for inbred versus outcrossed progeny. We also measured inbreeding depression in maximal rates of photosynthetic carbon assimilation and stomatal conductance to water vapor, traits that affect fitness through their influence on plant carbon balance and water-use efficiency (ratio of carbon gain to water loss). All traits except number of seeds per capsule in parents and survival showed inbreeding depression, with the magnitude depending on family and environment. High inbreeding depression is likely in the ancestor of S. lydgatei and S. salicaria, indicating that, with sufficiently high selfing rates, females could spread in populations. Hermaphroditism in S. lydgatei is probably favored by low selfing rates. In contrast, the evolution of gynodioecy in S. salicaria apparently has been favored by relatively high selfing rates in combination with high inbreeding depression.