Different levels of inbreeding depression between outcrossing and selfing Serapias species

We quantified inbreeding depression for fruit production, embryo vitality and seed germination in three deceptive orchids, Serapias vomeracea, S. cordigera and S. parviflora, which do not provide any reward to their pollinators, and are predicted to experience high outcrossing. Of the three species examined only S. parviflora was autonomously selfing. Both S. vomeracea and S. cordigera showed highly significant differences in fitness between selfed and outcrossed progenies, resulting in high levels of inbreeding depression, which increased in magnitude from seed set to seed germination. Inbreeding depression may promote outcrossing in Serapias by acting as a post-pollination barrier to selfing. Cumulative inbreeding depression across three stages in S. parviflora was lower that in both outcrossing species. The large difference in germination between selfed and outcrossed seeds is an important issue in conservation biology.     

Sargassum boreale sp. nov. (Fucales, Phaeophyceae) from Hokkaido, Japan

A new species, Sargassum boreale Yoshida et Horiguchi is described. It belongs to the subgenus Bactrophycus section Teretia, with cylindrical receptacles and is distinct from Sargassum confusum C. Agardh, S. pallidum (Turner) C. Agardh and Sargassum microceratium (Turner) C. Agardh in having a rather elongated stem with smooth surface and distantly issuing main branches, with narrow leaves. The distinction between S. boreale and these species is also revealed by a difference in internal transcribed spacer 2 (ITS‐2) sequences. In addition to the base substitutions, the existence of a large gap in S. boreale distinguishes this species from others. Sargassum boreale is distributed around Hokkaido and Saghalien to 50°N latitude. A key to the species of section Teretia is provided.     

Relatively weak inbreeding depression in selfing but also in outcrossing populations of North American Arabidopsis lyrata

Hermaphroditic plants can potentially self‐fertilize, but most possess adaptations that promote outcrossing. However, evolutionary transitions to higher selfing rates are frequent. Selfing comes with a transmission advantage over outcrossing, but self‐progeny may suffer from inbreeding depression, which forms the main barrier to the evolution of higher selfing rates. Here, we assessed inbreeding depression in the North American herb Arabidopsis lyrata, which is normally self‐incompatible, with a low frequency of self‐compatible plants. However, a few populations have become fixed for self‐compatibility and have high selfing rates. Under greenhouse conditions, we estimated mean inbreeding depression per seed (based on cumulative vegetative performance calculated as the product of germination, survival and aboveground biomass) to be 0.34 for six outcrossing populations, and 0.26 for five selfing populations. Exposing plants to drought and inducing defences with jasmonic acid did not magnify these estimates. For outcrossing populations, however, inbreeding depression per seed may underestimate true levels of inbreeding depression, because self‐incompatible plants showed strong reductions in seed set after (enforced) selfing. Inbreeding‐depression estimates incorporating seed set averaged 0.63 for outcrossing populations (compared to 0.30 for selfing populations). However, this is likely an overestimate because exposing plants to 5% CO₂ to circumvent self‐incompatibility to produce selfed seed might leave residual effects of self‐incompatibility that contribute to reduced seed set. Nevertheless, our estimates of inbreeding depression were clearly lower than previous estimates based on the same performance traits in outcrossing European populations of A. lyrata, which may help explain why selfing could evolve in North American A. lyrata.     

Pollination ecology of Isoglossa woodii,a long‐lived,synchronously monocarpic herb from coastal forests in South Africa

Synchronous monocarpy in long‐lived plants is often associated with pollination by wind, in part because infrequent mass flowering may satiate pollinators. Selfing in synchronous monocarps may provide reproductive assurance but conflict with the benefits of outcrossing, a key evolutionary driver of synchrony. We predicted that animal‐pollinated species with synchronous flowering would have unspecialised flowers and attract abundant generalised pollinators, but predictions for selfing and outcrossing frequencies were not obvious. We examined the pollination biology of Isoglossa woodii (Acanthaceae), an insect‐pollinated, monocarpic herb that flowers synchronously at 4–7‐year intervals. The most frequent visitor to I. woodii flowers was the African honeybee, Apis mellifera adansonii. Hand‐pollination failed to enhance seed production, indicating that the pollinators were not saturated. No seed was set in the absence of pollinators. Seed set was similar among selfed and outcrossed flowers, demonstrating a geitonogamous mixed‐mating strategy with no direct evidence of preferential outcrossing. Flowers contained four ovules, but most fruits only developed one seed, raising the possibility that preferential outcrossing occurs by post‐pollination processes. We argue that a number of the theoretical concerns about geitonogamous selfing as a form of reproductive assurance do not apply to a long‐lived synchronous monocarp such as I. woodii.     

The morphometric variation of Actinomma boreale (Radiolaria) in Atlantic boreal waters

A morphometric study on the polycystine radiolarian species Actinomma boreale (Cleve) from ten trigger weight core-tops from the Norwegian-Iceland Seas, three piston cores taken offshore western Norway and three surface sediment samples from Lygrepollen, Sogndalsfjord and Høyangsfjord (western Norwegian fjords) shows a variation in morphology that groups A. boreale into three distinct clusters, interpreted to be related to different oceanographic settings. The largest specimens of A. boreale are found in the western Norwegian fjords, the smallest in the Iceland Sea, giving an apparent positive correlation with temperature.Down core studies in piston cores from the Norwegian Sea demonstrate a considerable size variation of the cortical shell of A. boreale. In the eastern Norwegian Sea, the climatically cold Younger Dryas had a population of A. boreale that was characterized by large cortical shells, while the climatically warm Holocene population was dominated by small sized cortical shells, showing a negative correlation with temperature. We suggest that the large sized conical shell population of A. boreale in the Younger Dryas is not reflecting precisely the sea-surface water temperature. Another factor must play the dominant role here, probably nutrients.     

INTERACTIONS FOR POLLINATION BETWEEN TWO SYNCHRONOUSLY BLOOMING HEDYSARUM SPECIES (FABACEAE) IN ALASKA

In interior and arctic Alaska, Hedysarum boreale and H. alpinum (Fabaceae) occur sympatrically, bloom nearly synchronously, have similar floral morphology and color, and require pollination by insects to set seed. I studied the pollination ecology of these species at a site where they occur sympatrically near Fairbanks, Alaska, to determine if pollination interactions play a role in maintaining overlapping blooming times. Seed set in each species was apparently neither enhanced nor reduced by the presence of the other species. Seed set of H. boreale was positively related to visitation rates by female Megachile giliae, the most abundant visitor to H. boreale. This bee showed no preference between the two Hedysarum species. However, worker Bombus flavifrons, the most abundant visitor to H. alpinum, preferred to forage on H. alpinum. The exhibition of strong floral constancy by visitors to the two Hedysarum species suggests that interspecific pollination may not be strong enough to cause divergence in blooming times. I found no evidence that the presence of one Hedysarum species enhances visitation to the other species. Instead, because visitation by worker B. flavifrons to H. alpinum was reduced on sympatric plots, H. alpinum may have to tolerate overlap with H. boreale to take advantage of worker B. flavifrons activity. The results of this study suggest that the two Hedysarum species may simply bloom when their best pollinators are most active.     

POLLINATOR LIMITATION IN THE FACULTATIVELY AUTOGAMOUS ANNUAL,LUPINUS NANUS (LEGUMINOSAE)

The importance of pollinator visitation for determining both maternal reproductive success and outcrossing rates was investigated in the facultatively autogamous annual, Lupinus nanus. Sixty plants in each of two adjacent sites were assigned to either a pollinator-exclusion, pollen-augmentation, or open-pollinated (control) treatment. Flower, fruit, and seed production were recorded for each plant, and outcrossing rates were determined for plants in all three treatments at each site. Pollinator-exclusion reduced the reproductive success of plants at Site 1, but had no effect on reproduction for plants at Site 2. Pollen-augmentation increased fruit production by 22% and seed production by 45% at Site 2, but had no effect on reproduction for plants at Site 1. Plants in the open-pollinated, control treatment outcrossed at intermediate rates at both sites, with plants at Site 2 (outcrossing rate, t = 0.66) outcrossing at a significantly higher rate than plants at Site 1 (t = 0.40). The pollen-augmentation treatment increased the outcrossing rate for plants at both sites (Site 1, t = 0.72; Site 2, t = 0.78). These results indicate that pollinator availability can limit maternal reproductive success for this facultatively autogamous plant species. Additionally, the intermediate outcrossing rates observed in nature for this species are not a consequence of plant characters alone, but instead result from plant characters combined with the local pollination ecology.     

SEX ALLOCATION AND OUTCROSSING RATE: A TEST OF THEORETICAL PREDICTIONS USING BROMEGRASSES (BROMUS)

Predictions of sex-allocation theory were tested by comparisons among hermaphroditic bromegrass (Bromus) species that differed in outcrossing rate. Relative maternal and paternal investment were calculated using both the ratio of pollen to seed production, and absolute allocations in units of energy, nitrogen, phosphorus, potassium, magnesium, and calcium. Outcrossing rate had a large effect on sex allocation; species having greater outcrossing rates had relatively more paternal reproductive effort. Bromus inermis was obligately outcrossing, and nearly half of its reproductive effort was devoted to pollen production. Three partially outcrossed species, B. kalmii, B. ciliatus, and B. latiglumis, invested between 5% and 11% of reproductive effort in pollen production. Paternal investment was less than 2% in the selling species B. tectorum. Estimates of sex allocation were relatively unaffected by the resource currency used in calculation. The differences among species in sex allocation were mostly due to differences in anther size and seed set.>     

AUTOGAMY AND COMPETITION FOR POLLINATORS IN HEPATICA AMERICANA (RANUNCULACEAE)

Hepatica americana is one of the earliest flowering vernal herbs in the deciduous forests of piedmont North Carolina. Unlike most other members of the spring wildflower community, its flowers are nectarless and autogamous. The number of insect visits a flower receives varies markedly through the blooming season and is lowest when H. americana is in full bloom. Potential for outcrossing as measured by the seed set of emasculated flowers follows the same pattern. The mid-season decline in insect-pollination is most likely the result of competition with Erythronium umbilicatum, which flowers concurrently with H. americana and is much more attractive to the solitary bees that are the principal early season pollen vectors. Because of this competitive disadvantage, seed set of H. americana in piedmont North Carolina would be pollination-limited if the flowers were not autogamous. Autogamy may also be favored by flowering early in the spring before pollinators are available. Opportunities for outcrossing in H. americana are primarily the result of protogyny and blooming earlier than competitors.     

INBREEDING EFFECTS IN CLARKIA TEMBLORIENSIS (ONAGRACEAE) POPULATIONS WITH DIFFERENT NATURAL OUTCROSSING RATES

Inbreeding depression is commonly observed in natural populations. The deleterious effects of forced inbreeding are often thought to be less pronounced in populations with self-pollinating mating systems than in primarily outcrossing populations. We tested this hypothesis by comparing the performance of plants produced by artificial self- and cross-pollination from three populations whose outcrossing rate estimates were 0.03, 0.26, and 0.58. Outcrossing rates and inbreeding coefficients were estimated using isozyme polymorphisms as genetic markers. Analysis of F statistics suggests that biparental inbreeding as well as self-fertilization contribute to the level of homozygosity in the seed crop. Biparental inbreeding will reduce the heterozygosity of progeny produced by outcrossing, relative to random outcrossing expectations, and hence will reduce the effects of outcrossing versus self-fertilization. Heterotic selection may increase the average heterozygosity during the life history. Selfed and outcrossed seeds from all three populations were equally likely to germinate and survive to reproduce. However, inbreeding depression was observed in fecundity traits of plants surviving to reproduction in all three populations. Even in the population whose natural self-fertilization rate was 97%, plants grown from seed produced by self-pollination produced fewer fruits and less total seed weight than plants grown from outcrossed seed. There was no detectable inbreeding depression in estimated lifetime fitness. Inbreeding effects for all reproductive yield characters were most severe in the accession from the most outcrossing population and least severe in the accession from the most self-fertilizing population.     

Sequential decline in fruit resource allocation within inflorescences of Sagittaria trifolia: a test of non‐uniform pollination hypothesis

Flowering plants often exhibit declining resource investment to floral organs, fruits and seeds temporally or spatially in an inflorescence. To account for such variances, non‐uniform pollination hypothesis, which highlights various mating environments each flower experiences, provides adaptive significance for allocation patterns but with controversial supports. Sagittaria trifolia (Alismataceae) was used to examine differences in seed number, seed weight and germination rate among sequential fruits within inflorescences. Ovule number was also investigated to evaluate allocation patterns in the floral stage. To test the non‐uniform pollination hypothesis, we used three polymorphic microsatellite loci of S. trifolia to estimate the seed outcrossing rate in proximal and distal fruits. The results showed that the seed number, average seed weight and seed germination rate of S. trifolia gradually decreased from proximal to distal fruits within inflorescences. The percent of decrease in seed number between two contiguous fruits was 14.68 ± 3.22%, which was much stronger than the percent of decrease in ovule number at 6.95 ± 1.60%. Both proximal and distal fruits within inflorescences had high outcrossing rates (81.5 ± 5.0%, proximal; 82.3 ± 6.9%, distal) and they did not differ significantly. Overall, there was an acropetal decline of resource allocation to fruits within inflorescences of S. trifolia. Allocation pattern to ovules was not a limiting factor for seed production. The lack of difference in outcrossing rate between proximal and distal fruits indicated that the allocation strategy was probably not caused by non‐uniform pollination, but more likely position effects.     

No inbreeding depression in an outcrossing alpine species: The breeding system of Campanula thyrsoides

Plants that live in fragmented landscapes, where populations are isolated from each other and in which long-distance dispersal is essential for colonization of empty sites, reproduction should be favoured by self-compatibility (Baker's law). Nevertheless, outcrossing mechanisms, such as self-incompatibility and dichogamy, are common in many species and are often maintained by inbreeding depression in the fitness of selfed progeny. Here, we studied the breeding system and the consequences of selfing and sister mating in Campanula thyrsoides, a short-lived perennial monocarp, which is found in the naturally fragmented landscape of the Alps. An experiment with controlled pollinations was set up in the common garden with plants grown from seeds originating from 14 seed families, collected in the siliceous Central Alps, where this plant is found on isolated carbonate bearing outcrops.Our results indicate that C. thyrsoides has a strong self-incompatibility system (SI) with no or low seed set in selfed flowers compared to outcrossed and sister-crossed flowers. Moreover, the SI system in C. thyrsoides did not break down with flower age as in some other Campanula species. Surprisingly, there was no significant difference in seed set, seed weight, germination percentage, seedling survival and size between outcrossed and sister-crossed offspring, which indicates no inbreeding depression.We suggest that the absence of inbreeding depression in this outcrossing species might be a result of frequent bottlenecks during colonization of the isolated habitats in the alpine landscape.     

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.     

Costs of selfing prevent the spread of a self‐compatibility mutation that causes reproductive assurance

In flowering plants, shifts from outcrossing to partial or complete self‐fertilization have occurred independently thousands of times, yet the underlying adaptive processes are difficult to discern. Selfing's ability to provide reproductive assurance when pollination is uncertain is an oft‐cited ecological explanation for its evolution, but this benefit may be outweighed by costs diminishing its selective advantage over outcrossing. We directly studied the fitness effects of a self‐compatibility mutation that was backcrossed into a self‐incompatible (SI) population of Leavenworthia alabamica, illuminating the direction and magnitude of selection on the mating‐system modifier. In array experiments conducted in two years, self‐compatible (SC) plants produced 17–26% more seed, but this advantage was counteracted by extensive seed discounting—the replacement of high‐quality outcrossed seeds by selfed seeds. Using a simple model and simulations, we demonstrate that SC mutations with these attributes rarely spread to high frequency in natural populations, unless inbreeding depression falls below a threshold value (0.57 ≤ δ_threshold ≤ 0.70) in SI populations. A combination of heavy seed discounting and inbreeding depression likely explains why outcrossing adaptations such as self‐incompatibility are maintained generally, despite persistent input of selfing mutations, and frequent limits on outcross seed production in nature.     

DISTANCE BETWEEN MATES AFFECTS SEEDLING CHARACTERS IN A POPULATION OF IMPATIENS CAPENSIS (BALSAMINACEAE)

We tested for the presence of an optimal outcrossing distance in a population of Impatiens capensis, an annual herb that possesses a mixed mating system, by measuring fitness components for offspring of parents that were separated by distances of 2, 10, or 50 m. Heavier seed weights and later seed maturation enhanced probabilities of emergence and subsequent survival, but emergence and survival were unaffected by outcrossing distance. Path analysis showed that most characteristics of seeds and seedlings were positively correlated. Effects of maternal family were strong through the first month of growth. Analyses of covariance reveal that, as anticipated, the effects of maternal family, seed weight, and seed maturation date declined over time. Seeds that were produced late in the season were heavier than early seeds, and late seeds germinated at later dates than early seeds. Surprisingly, although late germination dates were associated with taller plants after 1 and 3 months of growth, late germination resulted in lighter dry weights at maturity. The distance between parents had a negative direct effect on seed weight but a positive effect on height after 1 month. Height at 1 month responded positively to outcrossing distance and negatively to the square of distance when seed weight, collection date, and maternal family were held constant. This implies an optimal outcrossing distance for height at 1 month, which we estimate as 29 m using a quadratic procedure. However, path analysis suggests that the apparent optimum is due to a negative correlation between the interparent distance and seed weight.     

OUTCROSSING RATE AND INBREEDING DEPRESSION IN TWO ANNUAL MONOECIOUS HERBS,BEGONIA HIRSUTA AND B. SEMIOVATA

Most models of mating-system evolution predict inbreeding depression to be low in inbred populations due to the purging of deleterious recessive alleles. This paper presents estimates of outcrossing rates and inbreeding depression for two highly selfing, monoecious annuals Begonia hirsuta and B. semiovata. Outcrossing rates were estimated using isozyme polymorphisms, and the magnitude of inbreeding depression was quantified by growing progeny in the greenhouse produced through controlled selfing and outcrossing. The estimated single-locus outcrossing rate was 0.03 ± 0.01 (SE) for B. hirsuta and 0.05 ± 0.02 for B. semiovata. In both species, the seed production of selfed flowers was on average 12% lower than that of outcrossed flowers (B. hirsuta P = 0.07, B. semiovata P < 0.05, mixed model ANOVAs). There was no significant effect of crosstype on germination rate or survival, but selfed offspring had a lower dry mass than outcrossed offspring 18 weeks after planting in both species (on average 18% lower in B. hirsuta and 31% lower in B. semiovata). Plants that were the products of selfing began flowering later than plants produced through outcrossing in B. semiovata, but not in B. hirsuta. The effects of crosstype on seed production (B. semiovata), days to first flower and offspring dry mass (both species) varied among maternal parents, as indicated by significant crosstype x maternal parent interactions for these characters. Both species showed significant inbreeding depression for total fitness (estimated as the product of seed production, germination rate, survival and dry mass at 18 weeks). In B. hirsuta, the average total inbreeding depression was 22% (range -57%-98%; N = 23 maternal parents), and in B. semiovata, it was 42% (-11%-84%; N = 21). This study demonstrates that highly selfing populations can harbor substantial inbreeding depression. Our findings are consistent with the hypothesis that a high mutation rate to mildly deleterious alleles contributes to the maintenance of inbreeding depression in selfing populations.     

Experimental and genetic analyses reveal that inbreeding depression declines with increased self‐fertilization among populations of a coastal dune plant

Theory predicts that inbreeding depression (ID) should decline via purging in self‐fertilizing populations. Yet, intraspecific comparisons between selfing and outcrossing populations are few and provide only mixed support for this key evolutionary process. We estimated ID for large‐flowered (LF), predominantly outcrossing vs. small‐flowered (SF), predominantly selfing populations of the dune endemic Camissoniopsis cheiranthifolia by comparing selfed and crossed progeny in glasshouse environments differing in soil moisture, and by comparing allozyme‐based estimates of the proportion of seeds selfed and inbreeding coefficient of mature plants. Based on lifetime measures of dry mass and flower production, ID was stronger in nine LF populations [mean δ = 1?(fitness of selfed seed/fitness of outcrossed seed) = 0.39] than 16 SF populations (mean δ = 0.03). However, predispersal ID during seed maturation was not stronger for LF populations, and ID was not more pronounced under simulated drought, a pervasive stress in sand dune habitat. Genetic estimates of δ were also higher for four LF (δ = 1.23) than five SF (δ = 0.66) populations; however, broad confidence intervals around these estimates overlapped. These results are consistent with purging, but selective interference among loci may be required to maintain strong ID in partially selfing LF populations, and trade‐offs between selfed and outcrossed fitness are likely required to maintain outcrossing in SF populations.     

A ROLE FOR NONADAPTIVE PROCESSES IN PLANT GENOME SIZE EVOLUTION?

Genome sizes vary widely among species, but comprehensive explanations for the emergence of this variation have not been validated. Lynch and Conery (2003) hypothesized that genome expansion is maladaptive, and that lineages with small effective population size (N_e) evolve larger genomes than those with large N_e as a consequence of the lowered efficacy of natural selection in small populations. In addition, mating systems likely affect genome size evolution via effects on both N_e and the spread of transposable elements (TEs). We present a comparative analysis of the effects of N_e and mating system on genome size evolution in seed plants. The dataset includes 205 species with monoploid genome size estimates (corrected for recent polyploidy) ranging from 2Cx = 0.3 to 65.9 pg. The raw data exhibited a strong positive relationship between outcrossing and genome size, a negative relationship between N_e and genome size, but no detectable N_e× outcrossing interaction. In contrast, phylogenetically independent contrast analyses found only a weak relationship between outcrossing and genome size and no relationship between N_e and genome size. Thus, seed plants do not support the Lynch and Conery mechanism of genome size evolution. Further work is needed to disentangle contrasting effects of mating systems on the efficacy of selection and TE transmission.     

Significant differences in outcrossing rate,self‐incompatibility,and inbreeding depression between two widely hybridizing species of Geum

Geum urbanum and Geum rivale are two widely hybridizing perennial herbs. Estimation of the breeding systems of these taxa using nuclear microsatellite markers scored in mother–progeny arrays demonstrated that, in pure populations, G. urbanum is predominantly selfing (outcrossing rate, t = 0.058 to 0.177), whereas G. rivale is predominantly outcrossing (t = 0.686–0.775). Theory suggests that hybridization between inbreeding and outcrossing species can potentially generate novel inbreeding lineages. However, the establishment of such lineages may be restricted either by self‐incompatibility loci or deleterious recessive alleles derived from the outcrossing parent. To assess the likelihood that hybridization between G. urbanum and G. rivale will generate novel inbreeding lineages, self‐incompatibility and inbreeding depression were investigated in the two taxa. Seed set in the absence of pollinators, and after controlled self‐ and cross‐pollination, was measured to study self‐incompatibility. Inbreeding depression was measured by estimating the relative fitness of offspring from controlled self‐and cross‐pollinations. Geum urbanum was fully self‐compatible [self‐compatibility index (SCI) = 1] and bagged flowers showed full seed set. By contrast, only 3% of bagged flowers set seed in G. rivale and controlled self‐pollinations showed a 60–80% reduction in seed set compared to controlled outcross pollinations (SCI = 0.28). There was no evidence for inbreeding depression in G. urbanum, although significant, albeit low levels of inbreeding depression were detected in one of two G. rivale populations (δ = 0.33). The implication of these results is that if genetic material from G. rivale was incorporated into a hybrid with a selfing morphology, the establishment of this selfing lineage could be compromised by self‐incompatibility and inbreeding depression. The wider implications of these results for evolution in hybrid swarms between G. urbanum and G. rivale are discussed. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 977–990.     

Inbreeding depression and selfing rates in a self-compatible,hermaphroditic species,Schiedea membranacea (Caryophyllaceae)

Inbreeding depression and selfing rates were investigated in Schiedea membranacea (Caryophyllaceae), a hermaphroditic species endemic to the Hawaiian Islands. Most theoretical models predict high inbreeding depression in outcrossing hermaphroditic species and low inbreeding depression in inbreeding species. Although high outcrossing rates and high levels of inbreeding depression are characteristic of many species of Schiedea, self- fertilization is common among relatives of hermaphroditic S. membranacea, and high selfing rates and low levels of inbreeding depression were predicted in this species. Sixteen individuals grown in the greenhouse were used to produce selfed and outcrossed progeny. Inbreeding depression, which was evident throughout the stages measured (percentage viable seeds per capsule, mean seed mass, percentage seed germination, percentage seedling survival, and biomass after 8 mo), averaged 0.70. Inbreeding depression among maternal families varied significantly for all measured traits and ranged from −0.12 to 0.97. Using isozyme analysis, the multilocus selfing rate varied from 0.13 to 0.38 over 4 yr. Contrary to the initial prediction of high selfing and low inbreeding depression based on phylogenetic relationships within Schiedea, low selfing rates and high levels of inbreeding depression were found in S. membranacea. These results indicate that outcrossing is stable in this species and maintained by high levels of inbreeding depression.