AUTOGAMY AND INBREEDING DEPRESSION IN MOUNTAIN LAUREL,KALMIA LATIFOLIA (ERICACEAE)

We compared breeding systems, inbreeding depression, and pollination limitation between two populations of Kalmia latifolia in Virginia and Rhode Island. Plants were autogamous in Virginia but not Rhode Island. Although autogamy with selling is hypothesized to reduce levels of inbreeding depression, both populations showed similarly high inbreeding depression manifested as reduced fruit set. Autogamy may be uncorrelated with selling rate because autogamy is not obligate and because geitonogamy is likely. Autogamy in the Virginia population seems most likely to have evolved for reproductive assurance under competition for pollinator service. Fruit set was pollination limited in the Virginia population apparently because bumblebee pollinators were more attracted to a coflowering species, Vaccinium erythrocarpum.     

Taxonomic complexity and breeding system transitions: conservation genetics of the Epipactis leptochila complex (Orchidaceae)

The genus Epipactis contains a problematical complex of autogamous taxa among which species limits are difficult to define. Different authors have treated these plants in different ways, some recognizing the different taxa as distinct species, others considering them as minor intraspecific variants. These contrasting treatments have a direct impact on the conservation resources and status such plants command; 'endemic orchid species' are perceived as having high conservation value, 'localized minor variants' are not. We used allozyme and chloroplast restriction fragment length polymorphism (RFLP) and sequencing analyses to investigate patterns of population genetic structure underlying the taxonomic complexity in this group. Populations of E. dunensis, E. leptochila and E. muelleri were homozygous and uniform for all loci studied here. There were, however, fixed genetic differences among these taxa. Comparisons with published data from the putative progenitor species for the autogamous taxa (the widespread, allogamous E. helleborine) suggest iterative origins of autogamy, rather than the self-pollinating taxa all being merely mutational variants of a single autogamous lineage.     

RESPONSE TO SELECTION ON AUTOGAMY IN PHLOX

Two cycles of artificial selection were performed to increase autogamous fruiting in two wild populations of the self-incompatible Phlox drummondii, to decrease autogamous fruiting in two wild populations of the self-compatible Phlox cuspidata, and to both increase and decrease autogamous fruiting in a cultivar of P. drummondii which is pseudo-self-compatible. The breeding systems were determined to be genetically quite flexible, independent of inbreeding depression and other genetic phenomena which could hinder a breeding system shift. This is especially true for increasing autogamy. Self-pollen-pistil compatibility seems to be the single character affected by selection. Based on the continuous variation in both autogamy and self-compatibility, we suggest that the change has been due to genes which modify the self-incompatibility reaction rather than to the simple segregation of alleles at the S-locus.     

Association between inbreeding depression and floral traits in a generalist‐pollinated plant

Individual variation in the magnitude of inbreeding depression (ID) in plants and its association with phenotypic traits may have important consequences for mating system evolution. This association has been investigated only scarcely, and always considering traits functionally related to autogamy. Here, we explore the association between individual variation in ID and plant traits associated with pollinator attractiveness (related to plant size, corolla size and corolla shape) in two populations of Erysimum mediohispanicum (Brassicaceae). ID was calculated along the entire life cycle of the plants. In addition, we also explored the relationship between phenotypic traits and the individual levels of heterozygosity. We found significant associations between ID and corolla diameter and stalk height, being taller plants with larger corollas those undergoing a lower intensity of ID. Furthermore, we found a negative relationship between corolla diameter and heterozygosity, suggesting that plants with large flowers have purged their genetic load. Finally, we found a significant effect of corolla diameter on the intrapopulation genetic structure. All these findings suggest that plants with large flowers have secularly suffered frequent inbreeding in the study populations. Because corolla diameter is a trait frequently selected by pollinators in E. mediohispanicum, we believe that the observed relationship between this trait and ID could be mediated by pollinators, probably throughout an increasing in biparental inbreeding, geitonogamy or autogamy.     

High selfing and high inbreeding depression in peripheral populations of Juncus atratus

The mating system of a plant is the prime determinant of its population genetic structure. However, mating system effects may be modified by postzygotic mechanisms like inbreeding depression. Furthermore, historical as well as contemporary ecological factors and population characteristics, like the location within the species range can contribute to genetic variability. Using microsatellite markers we assessed the population genetic structure of the wind-pollinated Juncus atratus in 16 populations from peripheral and nearly central areas of the distribution range and studied the mating system of the species. In three peripheral populations, outcrossing rates at seeds stage were low (mean t(m) = 5.6%), suggesting a highly autogamous mating system. Despite this fact, on adult stage both individual heterozygosity (mean H(O) = 0.48) and gene diversity (mean H(E) = 0.58) were high even in small populations. Inbreeding coefficients were consistently low among all populations (mean F(IS) = 0.15). Within the three peripheral populations indirect estimates of lifetime inbreeding depression were surprisingly high (delta(eq) = 0.96) and inbreeding depression could be shown to act mostly on early seedling establishment. Similar conditions of autogamy combined with high inbreeding depression are typical for plants with a large lifetime genomic mutation rate that cannot avoid selfing by geitonogamy. However, the results presented here are unexpected for small-statured, herbaceous plants. Substantial genetic differentiation among all populations was found (mean F(ST) = 0.24). An isolation-by-distance pattern was apparent on large scale but not on local scale suggesting that the overall pattern was largely influenced by historical factors, e.g. colonization, whereas locally genetic drift was of greater importance than gene flow. Peripheral populations exhibited lower genetic diversity and higher inbreeding coefficients when compared with subcentral populations.     

MIXED MATING SYSTEMS IN HAWAIIAN BIDENS (ASTERACEAE)

Floral features related to the breeding system were studied for 11 species of Hawaiian Bidens. Protandry and male sterility promote outcrossing, while self-compatibility and geitonogamy contribute to inbreeding. The combination of these floral mechanisms results in a mixed mating system in all species studied. Outcrossing rates of 15 populations of these species ranged from 0.43 to 0.88, averaging 0.65. Apparent selling rates of females ranged from 0 to 0.25 in seven gynodioecious populations surveyed, suggesting that there is variation in the level of biparental inbreeding among populations. The presence of females increased the level of outcrossing by an average of 9% in gynodioecious populations. This study indicates that the efficiency of gynodioecy as an outcrossing mechanism largely depends on the current outcrossing rate of hermaphrodites, the frequency of females, and the extent of genetic substructuring in populations. On average, autogamy contributed 4%, geitonogamy contributed 24%, and consanguineous mating contributed 15% to the realized selfing rate (43%) in the hermaphrodites of these species.     

Experimental dissection of inbreeding and its adaptive significance in a flowering plant, Aquilegia canadensis (Ranunculaceae)

Inbreeding is a major component of the mating system in populations of many plants and animals, particularly hermaphroditic species. In flowering plants, inbreeding can occur through self-pollination within flowers (autogamy), self-pollination between flowers on the same plant (geitonogamy), or cross-pollination between closely related individuals (biparental inbreeding). We performed a floral emasculation experiment in 10 populations of Aquilegia canadensis (Ranunculaceae) and used allozyme markers to estimate the relative contribution of each mode of inbreeding to the mating system. We also examined how these modes of inbreeding were influenced by aspects of population structure and floral morphology and display predicted to affect the mating system. All populations engaged in substantial inbreeding. On average, only 25% of seed was produced by outcrossing (range among populations = 9-37%), which correlated positively with both population size (r = +0.61) and density (r = +0.64). Inbreeding occurred through autogamy and biparental inbreeding, and the relative contribution of each was highly variable among populations. Estimates of geitonogamy were not significantly greater than zero in any population. We detected substantial biparental inbreeding (mean = 14% of seeds, range = 4-24%) by estimating apparent selfing in emasculated plants with no opportunity for true selfing. This mode of inbreeding correlated negatively with population size (r = -0.87) and positively with canopy cover (r = +0.90), suggesting that population characteristics that increase outcross pollen transfer reduce biparental inbreeding. Autogamy was the largest component of the mating system in all populations (mean = 58%, range = 37-84%) and, as expected, was lowest in populations with the most herkogamous flowers (r = -0.59). Although autogamy provides reproductive assurance in natural populations of A. canadensis, it discounts ovules from making superior outcrossed seed. Hence, high autogamy in these populations seems disadvantageous, and therefore it is difficult to explain the extensive variation in herkogamy observed both among and especially within populations.     

Severe outbreeding and inbreeding depression maintain mating system differentiation in Epipactis (Orchidaceae)

In hermaphroditic plants, theory for mating system evolution predicts that populations will evolve to either complete autonomous selfing (AS) or complete outcrossing, depending on the balance between automatic selection favouring self‐fertilization and costs resulting from inbreeding depression (ID). Theory also predicts that selection for selfing can occur rapidly and is driven by purging of genetic load and the loss of ID. Therefore, selfing species are predicted to have low levels of ID or even to suffer from outbreeding depression (OD), whereas predominantly outcrossing species are expected to have high levels of ID. To test these predictions, we related the capacity of AS to the magnitude of early‐acting inbreeding or OD in both allogamous and autogamous species of the orchid genus Epipactis. For each species, the level of AS was assessed under controlled greenhouse conditions, whereas hand‐pollinations were performed to quantify early costs of inbreeding or OD acting at the level of fruit and seed production. In the autogamous species, the capacity of AS was high (> 0.72), whereas in the allogamous species AS was virtually absent (< 0.10). Consistent with our hypothesis, allogamous Epipactis species had significantly higher total ID (average: 0.46) than autogamous species, which showed severe costs of OD (average: ?0.45). Overall, our findings indicate that strong early‐acting ID represents an important mechanism that contributes to allogamy in Epipactis, whereas OD may maintain selfing in species that have evolved to complete selfing.     

THE RELATIONSHIP BETWEEN MATING-SYSTEM CHARACTERS AND INBREEDING DEPRESSION IN MIMULUS GUTTATUS

Several recent theoretical considerations of mating-system evolution predict within-population covariation between levels of inbreeding depression and genetically controlled mating-system characters. If inbreeding depression is caused by deleterious recessive alleles, families with characters that promote self-pollination should show lower levels of inbreeding depression than families with characters that promote outcrossing. The converse is expected if inbreeding depression is due to overdominant allelic interactions. Whether these associations between mating-system and viability loci evolve will have important consequences for mating-system evolution. The evolution of selfing within the genus Mimulus is associated with a reduction in stigma-anther separation (i.e., a loss of herkogamy) and high autogamous seed set. In this study we compared families from two M. guttatus populations that differed genetically in their degree of stigma-anther separation. In one of these populations we also compared families that differed genetically in the degree to which they autogamously set seed in a pollinator-free greenhouse. Dams often differed significantly in levels of inbreeding depression for aboveground biomass and flower production, but variation in inbreeding depression was never explained by herkogamy class or autogamy class. Several factors might account for why families with traits associated with selfing did not show lower inbreeding depression, and these are discussed. Our study also demonstrated significant variation among self progeny from a given female likely due to differences in pollination date and position of fruit maturation. The detection of significant dam × sire interactions suggests biparental inbreeding or differences in combining ability for specific pairs of parents.     

GENETIC VARIATION AND ESTIMATES OF GENE FLOW IN CLARKIA SPECIOSA SUBSP. POLYANTHA (ONAGRACEAE)

Estimates of interpopulational gene flow and the levels and distribution of genetic variation in Clarkia speciosa subsp. polyantha were obtained using enzyme electrophoresis. Eight enzymes encoded by 17 loci were analyzed. Nei's mean genetic identity was 0.96, indicating little genetic divergence among populations. Gene diversity statistics also suggest little heterogeneity among populations. Interpopulational gene flow, estimated according to Slatkin (1985), was fairly high, Nm = 3.9, probably accounting for the lack of differentiation among populations.     

Local evolution of obligate autogamy inEpipactis helleborine subsp.neerlandica (Orchidaceae)

Isozyme analysis was used to assess the origin of the DanishEpipactis renzii, a local endemic of open coastal dunes. It seems to have evolved recently in several local populations of the more or less allogamousE. helleborine subsp.neerlandica. The obligately autogamousE. renzii is restricted to the easternmost part of the Danish range ofE. helleborine subsp.neerlandica, indicating that transition to obligate autogamy has been a selective advantage in that area. This may be explained by water stress, caused by a higher evapotranspiration (cf. the mean temperature of July which increases towards the east) — obligate autogamy shortens the time span from anthesis to fruit set due to a rapid pollination process. We propose thatE. renzii should only be recognized as a variety ofE. helleborine subsp.neerlandica.     

Quantitative genetics of autogamous F2

General quantitative genetic properties are derived for the F2 originating from self-fertilisation of hybrid (F1) individuals. These results extend and generalize previous restricted knowledge about this F2. New equations are found for all genotype frequencies, allele frequencies, inbreeding coefficient, genic (additive-genetic) and dominance variances, broadsense and narrowsense heritabilities, and selection potential. The bulk mean is generally lower, and the genotypic variance is generally higher, than those of the F1 and the allogamous F2. Genic and dominance variances for the selfed F2 are very different to the classical counterparts. Their relationships with inbreeding have been investigated, and they are more elaborate than previously considered. The level of inbreeding is constant irrespective of parental combinations, which is different to the inbreeding of an allogamous F2. Selection potential is generally high, and selection advance generally exceeds bulk inbreeding depression. If selection is assisted by dispersion, the autogamous F2 may obtain greater genetic advance than its allogamous counterpart for the same selection pressure. Under conditions of spatially separated F2, swarms, natural selection may be enhanced by selfing.     

Analysis of the genetic diversity of wild Spanish populations of the genusHordeum through the study of their endosperm proteins

A study was made of the genetic variability of 101 barley populations belonging to the four, wild, Spanish species of the genusHordeum (the autogamousH. marinum subspp.marinum andgussoneanum, andH. murinum subspp.murinum andleporinum, plus the allogamous speciesH. bulbosum andH. secalinum). Electrophoresis of endosperm proteins was performed using a large number of individuals from each population sampled, in order to determine intra- and interpopulational variation. The distribution of variability observed by population and taxonomic unit, is closely related to the breeding system.Hordeum bulbosum showed the greatest intrapopulational variability andH. marinum subsp.gussoneanum the least. In contrast to the autogamous species, the allogamous species showed low levels of interpopulational variation.     

Genetic variation in rural and urban populations of Epipactis helleborine (L.) Crantz. (Orchidaceae) in Britain

Genetic variation in Epipactis helleborine in the British Isles was assessed using starch gel electrophoresis of isozymes; 273 individuals were sampled from 13 populations and examined for genetic variation using eight enzyme systems encoded for by 13 loci. Overall, 46% of the loci examined were polymorphic, with an average of 1.69 alleles per locus. Within populations, a mean of 33% of the loci were polymorphic, with a mean number of 1.46 alleles per locus. Levels of genetic variation were compared between urban and well established rural populations to assess the genetic consequences of colonization of the urban sites. The average levels of genetic variation detected in urban populations were lower than that found in rural populations, although there was a much greater range of variation among the urban populations. Large urban populations actually have patterns of variation similar to rural populations and show evidence of multiple founders. This indicates that the high dispersibility of Epipactis seeds can in some cases overcome the predicted loss of genetic variation associated with founder effects during colonization. Small urban populations, however, show significantly lower levels of genetic variation compared with these large urban populations and the rural populations, and it seems likely that this is attributable to single founding events and/or genetic drift.     

The distribution of random amplified polymorphic DNA (RAPD) diversity amongst populations of Isotoma petraea (Lobeliaceae)

RAPDs were generated from plants of six populations of Isotoma petraea F. Muell. The species occurs on rock outcrops in southern and western Australia, with populations exhibiting different breeding systems, including complete autogamy, varying levels of outbreeding and complex hybridity. Non-metric multidimensional scaling (nMDS) analysis of the random amplified polymorphic DNA (RAPD) data set clearly resolved all populations. The Pigeon Rock population, which is home to both complex hybrid and structural homozygote plants, was divided into those two groups by the nMDS analysis. There was little diversity in highly autogamous populations, but levels were higher in the outbred Yackeyackine population. All complex hybrid populations and plants possessed numerous genetic system-specific RAPDs, some of which were shown to be held in fixed heterozygosity. Estimating G _ST using RAPDs has been problematical due to their dominance, and analytical methods usually rely on knowledge of the selfing rate or assume Hardy–Weinberg equilibrium. This assumption does not hold when populations exhibit fixed heterozygosity, and an alternative method, Shannon's Index, was used to partition genetic diversity. The distribution of genetic diversity fit expectations for an inbreeding species, with most of the variation (87.5%) occurring between populations. This compares to an average RAPD-based G _ST of 59.6% for inbreeding species generally and 15.5% for outbreeding species.     

POLLEN-OVULE RATIOS IN THE CRUCIFERAE

Several recent studies have revealed sources of variation in pollen-ovule ratios that might limit their usefulness as breeding system indicators. In this survey, pollen-ovule ratios were determined for 66 crucifer taxa (Cruciferae) with known breeding systems to establish whether a clear distinction could be made between the pollen-ovule ratios of allogamous and autogamous crucifers and whether this was sufficient to allow a standard to be set for the Cruciferae. Both the mean number of pollen grains per flower and the pollen-ovule ratio were significantly larger in the allogamous taxa than in the autogamous taxa, whereas the mean number of ovules per flower was not significantly different. However, the pollen-ovule ratio was found to be a much better indicator of the breeding system than the mean number of pollen grains by itself, based on the degree of overlap between the values for the allogamous and autogamous taxa. Variation in the amount of pollen produced by different sets of stamens and a correlation between the pollen-ovule ratio and seed size were identified as potential sources of error in calculating and interpreting the pollen-ovule ratios. This survey suggests that the pollen-ovule ratios of allogamous crucifers are typically greater than 3,500, that those of autogamous crucifers are typically less than 1,000, and that these standards can be used for indicating the breeding systems of other species in the Cruciferae.     

Purging of inbreeding depression within a population of Oxalis alpina (Oxalidaceae)

? Premise of the study: Variation among individuals in levels of inbreeding depression associated with selfing levels could influence mating system evolution by purging deleterious alleles, but empirical evidence for this association is limited. ? Methods: We investigated the association of family-level inbreeding depression and presumed inbreeding history in a tristylous population of Oxalis alpina (Oxalidaceae). ? Key results: Mid-styled individuals possessed the greatest degree of self-compatibility (SC) and produced more autogamous capsules than short- or long-styled individuals. Offspring of highly self-compatible mid-styled individuals showed reduced inbreeding depression. Mid-styled plants that produced capsules autogamously exhibited reduced stigma-anther separation compared to mid-styled plants that produced no capsules autogamously. Reduced inbreeding depression was not correlated with stigma-anther separation, suggesting that self-compatibility and autogamy evolve before morphological changes in stigma-anther separation. ? Conclusions: Purging of inbreeding depression occurred in SC mid-styled maternal families. Low inbreeding depression in SC mid-styled plants may lead to retention of the mid-styled morph in populations, despite the occurrence of higher selfing rates in mid-styled relative to short- or long-styled morphs. Variation among individuals in levels of self-fertilization within populations may lead to associations between inbreeding lineages and lower levels of inbreeding depression, influencing the evolution of mating systems.     

ENTOMOPHILOUS,INTRAFLORAL POLLINATION IN PHYLA INCISA

Experimental pollination studies indicate that probing into the corolla tube by insects is a requirement for autogamous reproduction in Phyla incisa. Insect-mediated self-fertilization combines the anthecology of allogamous reproduction with the genetic consequences of autogamy.     

The relationship between flower size, inbreeding coefficient and inferred selfing rate in British Euphrasia species

The genus Euphrasia in Britain comprises a taxonomically complex group of self-compatible, morphologically similar, hemi-parasitic, annual plant species of high conservation importance. The 19 diploid and tetraploid taxa currently recognised show striking variation in flower size. The objective of this paper is to determine whether a relationship exists between flower size and breeding system within Euphrasia. Following a survey of flower size variation among the 19 taxa, seven diploid populations, encompassing a broad range of flower sizes, were selected for detailed study. Four nuclear microsatellite loci were used to estimate the inbreeding coefficient Fis within each population. Fis values varied from to 0.17-0.77 and showed a significant, negative correlation with flower size. These results are best explained as the consequence of variation in selfing rate among the Euphrasia populations, with selfing rate increasing as flower size decreases. The potential factors influencing breeding system evolution in Euphrasia are discussed, together with the role of autogamy in generating taxonomic complexity and facilitating lineage differentiation within the genus.     

Genetic diversity in adult and seedling populations of <Emphasis Type="Italic">Primula vulgaris</Emphasis> in a fragmented agricultural landscape

Habitat fragmentation is known to generally reduce the size of plant populations and increase their isolation, leading to genetic erosion and increased between-population genetic differentiation. In Flanders (northern Belgium) Primula vulgaris is very rare and declining. Populations have incurred strong fragmentation for the last decades and are now restricted to a few highly fragmented areas in an intensively used agricultural landscape. Previous studies showed that small populations of this long-lived perennial herb still maintained high levels of genetic variation and low genetic differentiation. This pattern can either indicate recent gene flow or represent historical variation. Therefore, we used polymorphic microsatellite loci to investigate genetic variation and structure in adult (which may still reflect historical variation) and seedling (recent generation, thus affected by current processes) life stages. The recent generation (seedlings) showed a significant loss of observed heterozygosity (H _o) together with lower expected heterozygosity (H _e), a trend for higher inbreeding levels (F _IS) and higher differentiation (F _ST) between populations compared to the adult generation. This might result from (1) a reduction in effective population size, (2) higher inbreeding levels in the seedlings, (3) a higher survival of heterozygotes over time due to a higher fitness of heterozygotes (heterosis) and/or a lower fitness of homozygotes (inbreeding depression), (4) overlapping generations in the adult life stage, or (5) a lack of establishment of new (inbred) adults from seedlings due to degraded habitat conditions. Combining restoration of both habitat quality and gene flow between populations may be indispensable to ensure a sustainable conservation of fragmented populations.