Allelopathic effects of <Emphasis Type="Italic">Ceratiola ericoides</Emphasis> (Empetraceae) on germination and survival of six Florida scrub species

Allelopathic inhibition of germination by Florida scrub plants has been demonstrated in the greenhouse and lab, but not in the field. We studied the allelopathic effects of Florida rosemary (Ceratiola ericoides) roots, leaves, and litter leachates on field germination and three-month survival of six Florida scrub species, three habitat generalists (Lechea deckertii, Palafoxia feayi, and Polygonella robusta), and three rosemary scrub specialists (Hypericum cumulicola, Lechea cernua, and Polygonella basiramia). We used AIC and model averaging to evaluate support for a series of non-exclusive hypotheses. Species varied in germination (2.7–24.6%) and survival (39.2–71%) percentages, and in their sensitivity to leachates. Germination of scrub species was most negatively affected by leaf > root > litter leachates, although not all species followed the overall trend. Additional germination suppression by leachate combinations (relative to single leachates) was minimal. Sites did not vary in germination, but seedling survival did differ among sites. This study further documents the negative impact of Florida rosemary leachates on the germination of co-occurring plant species. Allelopathy may be partly responsible for bare sand gaps in Florida rosemary scrub, and therefore be one of the forces structuring Florida rosemary scrub ecosystems.     

Microhabitat of critically endangered Lupinus aridorum (Fabaceae) at wild and introduced locations in Florida scrub

Elucidating microhabitat preferences of a rare species are critical for its conservation. Lupinus aridorum McFarlin ex Beckner (Fabaceae) is a critically endangered plant known only from a few locations in imperiled Florida scrub habitat and nothing is known about its preferred microhabitat. Our goals were threefold. First, determine whether L. aridorum has multiple cytotypes because this can influence its spatial distribution. Second, measure how microhabitat characteristics at locations supporting wild L. aridorum vary from random locations, which will provide information about microhabitat characteristics that influence the spatial distribution of individuals. Third, measure whether microhabitat characteristics differ between locations supporting wild or introduced plants, which will provide information about the realized and fundamental niche. Our research determined that L. aridorum is diploid and grew, on average, in areas closer to trees and shrubs, with lower soil moisture, and with a greater mixture of detritus than random locations. Some microhabitat characteristics at locations where L. aridorum were introduced were similar to microhabitat supporting wild L. aridorum, but multiple soil characteristics differed as did the plant community, which contained more nonnative plant species near introduced plants. Therefore, the realized niche is narrower than the fundamental niche. Overall, information about the microhabitat of L. aridorum can be used to design appropriate management programs to conserve and restore populations of this plant species and species that occupy a similar niche in imperiled Florida scrub.     

Influence of community structure on the spatial distribution of critically endangered Dicerandra immaculata var. immaculata (Lamiaceae) at wild, introduced, and extirpated locations in Florida scrub

Community structure at local scales is a major factor controlling population and community dynamics of plant species. Dicerandra immaculata Lakela var. immaculata (Lamiaceae) is a critically endangered plant known only from a few locations in scrub habitat in Florida. Using seven sites where populations of D. immaculata were wild, introduced, and/or extirpated, we sought to answer the following questions: (1) how do habitat characteristics at locations supporting wild D. immaculata plants vary from random locations within the same habitat; (2) how do habitat characteristics differ between wild and extirpated populations; and (3) how do habitat characteristics differ between wild and introduced populations? At locations of wild D. immaculata, community structure had fewer woody stems, shorter understory vegetation, lower percent canopy coverage, and lower percent ground cover of detritus than random locations and locations with extirpated D. immaculata. In addition, bare ground decreased at extirpated locations because other plant species expanded their coverage, water saturation of the soil increased, diversity of shrubs decreased, and composition of the overstory changed compared to that of wild locations. Habitat characteristics associated with introduced plants were more similar to characteristics at randomly chosen locations than those with wild plants. However, introduced plants tended to occupy locations that had drier soil, a higher abundance of conspecifics, and a higher proportion of woody understory plants than that of random locations. Overall, gaps in the canopy and at ground level are likely essential for survival and recruitment of D. immaculata.     

Allelopathic effects and root distribution of Ceratiola ericoides (Empetraceae) on seven rosemary scrub species

We studied the root distribution and the effects of leachates from the dominant shrub in rosemary scrub, Florida rosemary (Ceratiola ericoides), on germination of seven subordinate rosemary scrub species. For rosemary scrub specialists, (Eryngium cuneifolium and Hypericum cumulicola), germination was suppressed by the leaf and litter leachates. For species that are not found exclusively in rosemary scrub (Liatris ohlingerae, Polygonella basiramia, Paronychia chartacea, and Palofoxia feayi) litter and leaf leachate did not suppress germination significantly. Species limited to gaps in rosemary scrub (E. cuneifolium, H. cumulicola, and Lechea deckertii) showed reduced germination from rosemary leachates while species not limited to rosemary-free gaps (L. ohlingerae and P. feayi) were not affected by rosemary leachates. Rosemary root abundance was greatest near shrubs, at a shallow depth, and at sites not recently burned. As rosemary scrub patches age, rosemary roots are more likely to interact with herbaceous species in gaps.     

Linking the patterns in soil moisture to leaf water potential, stomatal conductance, growth, and mortality of dominant shrubs in the Florida scrub ecosystem

Patterns in soil moisture availability affect plant survival, growth and fecundity. Here we link patterns in soil moisture to physiological and demographic consequences in Florida scrub plants. We use data on different temporal scales to (1) determine critical soil moisture content that leads to loss of turgor in leaves during predawn measurements of leaf water status (Ψ _crit), (2) describe the temporal patterns in the distribution of Ψ _crit, (3) analyze the strength of relationship between rainfall and soil moisture content based on 8 years of data, (4) predict soil moisture content for 75 years of rainfall data, and (5) evaluate morphological, physiological and demographic consequences of spring 2006 drought on dominant shrubs in Florida scrub ecosystem in the light of water-uptake depth as determined by stable isotope analysis (δ¹⁸O). Based on 1998–2006 data, the soil moisture content at 50 cm depth explained significant variation in predawn leaf water potential of two dominant shrubs, Quercus chapmanii and Ceratiola ericoides (r ²?=?0.69). During 8 years of data collection, leaves attained Ψ _crit only during the peak drought of 2000 when the soil moisture fell below 1% by volume at 50 and 90 cm depth. Precipitation explained a significant variation in soil moisture content (r ²?=?0.62). The patterns in predicted soil moisture for 75 year period, suggested that the frequency of drought occurrence has not increased in time. In spring 2006, the soil reached critical soil moisture levels, with consequences for plant growth and physiological responses. Overall, 24% of plants showed no drought-induced damage, 51% showed damage up to 50%, 21% had intense leaf shedding and 2% of all plants died. Over the drought and recovery period (May–October 2006), relative height growth was significantly lower in plants with greater die-back. All species showed a significant depression in stomatal conductance, while all but deep-rooted palms Sabal etonia and Serenoa repens showed significantly lower predawn (Ψ _pd) and mid-day (Ψ _md) leaf water potential in dry compared to wet season. Plants experiencing less severe die-back exhibited greater stomatal conductance, suggesting a strong relationship between physiology and morphology. Based on results we suggest that the restoration efforts in Florida scrub should consider the soil moisture requirements of key species.     

Genetics and morphology in a Borrichia frutescens and B. arborescens (Asteraceae) hybrid zone

Interspecific plant hybridization is a common and evolutionarily important phenomenon. Here, the results of a study of hybridization in the Florida Keys between two species of sea oxeye daisy, Borrichia frutescens and B. arborescens, are reported. Nuclear and chloroplast genetic loci, log-likelihood assignment tests, and maximum likelihood estimates of genealogical class frequencies were used to identify hybrid and parent genotypes, to investigate the utility of leaf and flower morphology for hybrid identification, and to study symmetry and degree of introgression between the species. Genetic analyses confirmed the identity of the hybrid and parent plants that were used for the morphological studies. Together, leaf and flower morphology can be used to identify hybrid and parental types with moderate accuracy (4% error rate). Population genetic analyses indicate that, in spite of a significant level of hybridization, pure B. frutescens and B. arborescens are persisting in the hybrid zone. Of the nonparentals, about 18% appear to be F(1) hybrids, over 50% F(2) hybrids, and the remainder backcrossed individuals but only with the B. frutescens parent. It is postulated that the hybrid zone in the Florida Keys is being maintained by a combination of positive assortative mating and clonal reproduction.     

Habitat and microsite influence demography of two herbs in intact and degraded scrub

Identifying environmental factors associated with vital rate variation is critical to predict population consequences of environmental perturbation. We used matrix models to explore effects of habitat and microsite on demography of two widespread herbs, Chamaecrista fasciculata (partridge pea) and Balduina angustifolia (yellow buttons). We evaluated models simulating population dynamics in common microsites (shrub, litter, bare sand) within two habitats (intact, degraded Florida scrub) using data on experimental populations initiated by sowing seeds, and natural seed production. Models included four stages (seed bank, small vegetative, large vegetative, reproductive) and three vital rates (survival, growth, fecundity), summarized in sixteen transitions. We conducted life table response experiments to assess contributions of each habitat and microsite to population growth rates. We found that (1) C. fasciculata had greatest population growth in degraded habitat and litter microsites, (2) B. angustifolia had similar population growth between habitats and greatest in bare sand microsites, (3) advancing growth transitions of C. fasciculata had greatest elasticity on population growth in degraded habitat, shrub, and litter, as did seed survival in intact habitat and bare sand, (4) seed survival and advancing growth transitions of B. angustifolia had greatest elasticity on population growth in both habitats, as did seed survival in shrub and litter, and advancing growth in bare sand. Greater population growth of C. fasciculata in degraded scrub is probably explained by release from belowground competition; B. angustifolia may be most affected by competition with shrubs. Microsites in intact scrub were not ecologically equivalent to those in degraded scrub emphasizing that intact scrub is ecologically complex and critical to preserve.     

Decoupling litter barrier and soil moisture influences on the establishment of an invasive grass

Background and aims

Through recruitment, plants establish in novel environments. Recruitment also is the stage where plants undergo the highest mortality. We investigate the recruitment niche for Microstegium vimineum, an annual grass from East Asia spreading throughout eastern North American forests.

Methods

Current observational and greenhouse research indicates that M. vimineum recruitment may be inhibited by leaf litter and promoted by soil moisture; we use field studies to experimentally test how these factors influence M. vimineum germination, seedling survival and reproduction. Specifically, we introduce M. vimineum seeds into forest microhabitats with experimentally varied levels of soil moisture and leaf litter.

Results

Soil moisture increases M. vimineum germination regardless of leaf litter thickness and ameliorates seedling mortality in deep leaf litter. Seed production per m² increases with watering, reflecting higher germination and survival, whereas per capita seed production increases with leaf litter thickness, reflecting density-dependent limits on seed production.

Conclusions

The interactive effects of varied levels of soil moisture and leaf litter thickness on key M. vimineum life history stages highlight the need to consider multiple drivers, such as rainfall and local forest disturbance, when assessing how soil properties influence the establishment of invasive plants.     

Positive Effects of Non-Native Grasses on the Growth of a Native Annual in a Southern California Ecosystem

Fire disturbance is considered a major factor in the promotion of non-native plant species. Non-native grasses are adapted to fire and can alter environmental conditions and reduce resource availability in native coastal sage scrub and chaparral communities of southern California. In these communities persistence of non-native grasses following fire can inhibit establishment and growth of woody species. This may allow certain native herbaceous species to colonize and persist beneath gaps in the canopy. A field manipulative experiment with control, litter, and bare ground treatments was used to examine the impact of non-native grasses on growth and establishment of a native herbaceous species, Cryptantha muricata. C. muricata seedling survival, growth, and reproduction were greatest in the control treatment where non-native grasses were present. C. muricata plants growing in the presence of non-native grasses produced more than twice the number of flowers and more than twice the reproductive biomass of plants growing in the treatments where non-native grasses were removed. Total biomass and number of fruits were also greater in the plants growing in the presence of non-native grasses. Total biomass and reproductive biomass was also greater in late germinants than early germinants growing in the presence of non-native grasses. This study suggests a potential positive effect of non-native grasses on the performance of a particular native annual in a southern California ecosystem.     

Does genetic introgression improve female reproductive performance? A test on the endangered Florida panther

Genetic introgression has been suggested as a management tool for mitigating detrimental effects of inbreeding depression, but the role of introgression in species conservation has been controversial, partly because population-level impacts of genetic introgressions are not well understood. Concerns about potential inbreeding depression in the endangered Florida panther (Puma concolor coryi) led to the release of eight female Texas pumas (P. c. stanleyana) into the Florida panther population in 1995. We used long-term reproductive data (1995–2008) collected from 61 female Florida panthers to estimate and model reproduction probability (probability of producing a litter) and litter size, and to investigate the influence of intentional genetic introgression on these parameters. Overall, 6-month probability of reproduction (±1SE) was 0.232 ± 0.021 and average litter size was 2.60 ± 0.09. Although F₁ admixed females had a lower reproduction probability than females with other ancestries, this was most likely because kittens born to F₁ females survive better; consequently, these females are unavailable for breeding until kittens are independent. There was no evidence for the effect of ancestry on litter size or of heterozygosity on probability of reproduction or litter size. In contrast, earlier studies have shown that genetic introgression positively affected Florida panther survival. Our results, along with those of earlier studies, clearly suggest that genetic introgression can have differential effects on components of fitness and highlight the importance of examining multiple demographic parameters when evaluating the effects of management actions.     

Predation and cryptic coloration in a managed landscape

Protective forms of animal color, such as crypsis, are thought to reduce the probability of detection by visual predators. However, because crypsis is ostensibly intuitive, the working hypothesis of cryptic coloration is seldom tested. Additionally because crypsis is a background-specific adaptation, events which alter habitat structure and substrate composition are likely to affect rates of predation on cryptic animals; animal colors that are cryptic against one visual background may be conspicuous against different visual backgrounds. Populations of Sceloporus woodi, a cryptic diurnal lizard, occupy clear-cut stands of sand pine scrub and prescribe-burned longleaf pine habitat within the Ocala National Forest. Here, we used a combination of clay models resembling S. woodi, and spectral analysis, to examine the effects of spatial heterogeneity and model-substrate contrast on rates of predation. The rate of attack on clay models differed between substrate types and habitats, and was highest when clay models were conspicuous against the local visual background. The dorsal color of models greatly contrasted open sand and dead wood, but had similar reflectance values to leaf litter, suggesting that models were most cryptic on leaf litter. We conclude that crypsis is adaptive in this species, and that variation in rates of attack between sampling locations is related to changes in substrate composition due to management history. For instance, the data suggest that the rate of attack on clay models would decrease in response to succession in sand pine scrub, because aging in sand pine scrub results in increased amounts of leaf litter and decreased amounts of open sand. Overall, the results of this study support the theory of protective coloration.     

Effects of Hurricanes on Rare Plant Demography in Fire‐Controlled Ecosystems

Hurricanes have dramatic effects on forest vegetation, but their effects on shrublands have rarely been studied. We analyzed the effects of three 2004 hurricanes—among the strongest on record in Florida—on vital rates of 12 rare plant species of pyrogenic interior Florida scrub and sandhill. Tree damage varied by vegetation type (being highest in areas with Pinus clausa) and was associated with debris deposition. Most rare species were minimally impacted by hurricanes. The two most frequently damaged species were the shrubs Prunus geniculata (11% of individuals) and Asimina obovata (7%); both were resilient to damage. Prunus geniculata had little mortality during the hurricane year but damaged plants had a temporary (1‐yr) reduction in relative growth rate. Prunus geniculata flowering was unaffected by hurricane damage. Hurricane damage had no effects on vital rates of A. obovata, Eriogonum longifolium var. gnaphalifolium, or Chrysopsis highlandsensis. Other species suffered little or no observable hurricane damage. Of 12 species analyzed, nine had similar annual survival in hurricane and nonhurricane years. Relatively low survival in the hurricane year (compared with other years) was linked to prehurricane drought or prescribed fire in two of three species. Thus, the 2004 hurricanes did not have important effects on populations of interior Florida scrub and sandhill plants, especially herbaceous species. This is in marked contrast to dramatic demographic responses to fire in central Florida and strong effects of hurricanes in coastal Florida, highlighting that these different disturbances may have divergent effects on vegetation and populations over short distances.     

Breeding system of the critically endangered Lakela’s Mint and influence of plant height on pollinators and seed output

Understanding reproductive systems of rare plants is critical for conservation efforts. Lakela's Mint, Dicerandra immaculata Lakela var. immaculata, is an endangered plant endemic to an approximately 4.8-km long area in Florida, USA. We used an experimental garden and three populations of Lakela's Mint to determine: (1) what is the breeding system (autonomous, asexual, self-fertile, cross-fertile) and are insects necessary for reproduction; (2) which native and nonnative insect species visit flowers and is the frequency of visits to a plant influenced by its height; (3) does the number of flowers visited within a plant by individual insects differ among native and nonnative insect species and due to plant height; and (4) is seed output influenced by plant height? Our results indicate that the breeding system of Lakela's Mint was facultative outcrossing. Insect-pollinated flowers produced more seeds than flowers that reproduced autonomously or asexually. The honey bee Apis mellifera L., a nonnative species, was the most frequent visitor to plants and visited more flowers within plants than native pollinators, but its behavior was not influenced by plant height. Native pollinators such as Bombus impatiens Cresson were attracted more frequently to shorter plants, but visited fewer flowers than on taller plants. Despite having fewer total and pollinated flowers, shorter plants had a higher output of intact seeds than taller plants, which could be due to differences in efficiency between native and nonnative pollinators or other factors. Our results add insight into factors influencing seed output and interactions between pollinators and rare plants.     

Reproduction strategies in introduced Nymphoides peltata populations revealed by genetic markers

To determine whether introduced Nymphoides peltata populations reproduced vegetatively or sexually, microsatellites were used to study the genetic structure of the species in Sweden. Leaves from 156 plants and seeds from 4 plants were sampled from 7 water-systems and analysed. A total of 10 genotypes were found among the 156 leaves. Seeds accounted for one additional genotype per seed. Lack of genetic variation and entirely vegetative reproduction dominated in the introduced N. peltata populations although sexual reproduction was found in one water-system. However, even where the species reproduced sexually, vegetative reproduction constituted an important part of the total reproduction.     

Self-pollination and inbreeding depression in Acacia dealbata: Can selfing promote invasion in trees?

The ability to self-fertilise may promote invasiveness in plants by assuring reproduction when mate and pollinator availabilities are inadequate, provided that the benefit of increased fecundity via selfing is not outweighed by inbreeding depression. However, knowledge of breeding systems and inbreeding depression has been lacking for most introduced plants. In this study of the invasive Australian tree Acacia dealbata in its introduced range in South Africa, controlled pollination experiments indicated that the study population was at least partially self-compatible and had a high capacity for autonomous self-pollination. However, we found substantial inbreeding depression, with seeds per fruit, progeny survival and progeny growth being lower after self- than after cross-pollination. Progeny arising from self-pollination also had a higher frequency of certain traits – yellow colouration of leaves and pink or white colouration of stems – which were associated with lower rates of survival. High inbreeding depression in A. dealbata must detract from the reproductive assurance benefit of self-fertilisation, casting doubt on the hypothesis that self-fertilisation contributes to invasiveness in this species. As high inbreeding depression has also been reported in other self-compatible trees, future studies should elucidate whether self-fertilisation contributes to invasiveness of trees by assessing both reproductive assurance benefits and inbreeding depression costs over the lifetime of progeny.     

The interaction between propagule pressure,habitat suitability and density‐dependent reproduction in species invasion

Seedling recruitment limitations create a demographic bottleneck that largely determines the viability and structure of plant populations and communities, and pose a core restriction on the colonization of novel habitat. We use a shade‐tolerant, invasive grass, Microstegium vimineum, to examine the interplay between seed and establishment limitations – phenomena that together determine recruitment success but usually are investigated individually. We add increasing amounts of seed to microhabitats containing variable levels of leaf litter thickness – with reduced leaf litter simulating disturbance – to investigate whether reduced seed limitation overcomes the establishment limitation posed by litter cover. We do this across gradients in understory light, moisture and temperature, and quantify germination, survival, and then per capita adult biomass and reproduction in order to understand the implications for invasion across the landscape. We find that the combined effects of seed and establishment limitation influence recruitment; however, propagule pressure overwhelms the inhibitory effects of leaf litter thickness. Leaf litter reduces germination by 22–57% and seedling survival by 13–15% from that observed on bare soil. However, density‐dependent reproduction compensates as 1–3 plants can produce far more seeds (approx. 525) than are required for persistence. As such, just a few plants may establish in understory forest habitat and subsequently overwhelm establishment barriers with copious propagule production. These results, for a widespread, invasive plant, are consistent with the emerging perspective for native plants that seed and establishment limitation jointly influence recruitment. The ability for an exotic plant species to compensate for low population densities with high per capita seed production, that then overrides establishment limitations, makes its invasive potential daunting. Further work is required to test if this is a common mechanism underlying plant invasions.     

Microhabitat distribution of two Florida scrub endemic plants in comparison to their habitat-generalist congeners

Habitat-specialist species may be restricted to a narrower range of microhabitats than habitat-generalist species. We addressed this hypothesis by comparing microhabitats of two pairs of congeners that differ in habitat specificity and co-occur in one distinct habitat type, Florida rosemary scrub. We characterized microhabitats of rosemary scrub specialists, Polygonella basiramia and Lechea cernua, their habitat-generalist congeners, Polygonella robusta and Lechea deckertii, and random points in the rosemary scrub habitat. Plants of both habitat specialists occurred in microhabitats with significantly more bare sand than plants of habitat-generalist species and random points. Plants of all four species occurred in microhabitats that were farther from dominant shrubs, Ceratiola and Quercus spp., than random points. Seedlings of both habitat specialists grew larger in bare sand microhabitats, whereas ground lichens and litter did not affect seedling growth of the habitat generalists. As the time since fire increases, bare sand cover decreases, Ceratiola density increases, Quercus density remains constant, and shrubs become taller. Physical characteristics, such as soil temperature, soil carbon, and soil moisture, differ slightly with respect to microhabitat. Our results suggest that P. basiramia and L. cernua are specialized on bare sand microhabitats that characterize their preferred habitat, rosemary scrub. Microhabitat specialization may limit the distribution of these rare species.     

Eco-evolutionary litter feedback as a driver of exotic plant invasion

Many studies have examined positive feedbacks between invasive plant traits and nutrient cycling, but few have investigated whether feedbacks arise from introduction of pre-adapted species or from eco-evolutionary feedback that develops after introduction. Eco-evolutionary feedback could occur between an invader's leaf tissue C:N ratio and its response to litter accumulation. Previous modeling predicts that occurrence of this feedback would be reflected by: (1) field data showing higher litter:biomass ratios in the invasive range; (2) high C:N genotypes benefiting more from experimental litter additions than low C:N genotypes; (3) this beneficial effect on high C:N genotypes inducing a critical transition toward invader dominance when a critical amount of litter is added to a native species-dominated community experiencing low nutrient conditions. Here, we empirically tested these predictions for the invasive grass Phalaris arundinacea, which has undergone post-introduction evolutionary change toward attaining higher C:N ratios under high nutrient conditions. We performed a biogeographical comparison of litter:biomass ratios in the native (Europe) and invasive (USA) range, and an experiment with mesocosms from the invasive range under low nutrient conditions. Low and high C:N Phalaris genotypes were introduced into native-dominated and bare mesocosms, to which varying litter amounts were added. The biogeographical comparison revealed that litter:biomass ratios were higher in the invasive range. The mesocosm experiment showed that when grown in isolation, only high C:N genotypes responded positively to litter. This effect, however, was not strong enough to stimulate Phalaris when exposed to competition with native species. Our results suggest that eco-evolutionary feedback between Phalaris’ C:N ratio and litter accumulation could occur, but only under high nutrient conditions. Our experiments suggest that eco-evolutionary feedback may select for specialist rather than superior genotypes. Hence, genotypic variation induced by post-introduction admixture may be subject to context-dependent selection due to eco-evolutionary feedback, increasing trait variation within invasive populations.     

Partial hybridization in wide crosses between cultivated sunflower and the perennial Helianthus species H. mollis and H. orgyalis

To obtain introgressed sunflower lines with improved disease resistance, interspecific crosses were performed with foreign perennial species. We report on several unusual features displayed by these hybrid plants. The methods used to produce the kernels affected yield and genotypes of progeny. Phenotypic traits and DNA markers were investigated in 97 plants derived from cross-pollination between annual diploid cultivated sunflower (Helianthus annuus) and the perennial diploid species H. mollis or H. orgyalis, and the reverse reciprocal crosses. The level of hybridization in progeny was determined using RAPD and RFLP markers. Hybridization was performed by leaving embryos to develop normally on the head (classical crossing) or using embryo rescue. All observed plants derived from H. mollis were diploid (2n = 34). Phenotypes were predominantly similar to the female when cultivated sunflower was the female parent. Progeny from crosses using a wild species as the female parent resembled that parent. Thus, reciprocal crosses led to different progeny. F1 sister progeny shared different sets of molecular markers representing a few of those of the wild species used as the pollen donor. Our results indicate mechanisms leading to the unusual event of partial hybridization. Possible mechanisms behind these unusual events and their possible impact on evolution are discussed.     

Interspecific hybridisation and interaction with cultivars affect the genetic variation of Ulmus minor and Ulmus glabra in Flanders

Interspecific hybridisation and gene flow from cultivated plants may have profound effects on the evolution of wild species. Considering the cultural history and past use of Ulmus minor and Ulmus glabra trees in Flanders (northern Belgium), we investigated the extent of human impact on the genetic variation of the remaining, supposedly indigenous elm populations. We therefore examined the rate of interspecific hybridisation, which is expected to be higher under human influence, the occurrence of clones within and among locations, the presence of cultivars and their possible offspring. Based on results produced using 385 amplified fragment length polymorphic (AFLP) markers, 46 % of the 106 investigated Flemish elms appeared to be F1 hybrids or backcrosses to one of the parent species, while no F2 hybrids (F1?×?F1 progeny) were found. Clonality was mainly found among U. minor and hybrids, which are more likely to form root suckers or sprouts as opposed to U. glabra. The majority of the studied locations (76 % of the locations with multiple samples) showed evidence of clonal reproduction. Several, sometimes distant, locations shared a multilocus lineage. We also found indications of gene flow from cultivated elms into native species. It is conceivable that reproductive material has been moved around extensively, obscuring the natural genetic structure of the elm populations. The results help guide the Flemish elm genetic resources conservation programme.