Vincetoxicum Hirundinaria Research Articles

Simultaneous inbreeding modifies inbreeding depression in a plant-herbivore interaction

Because inbreeding is common in natural populations of plants and their herbivores, herbivore-induced selection on plants, and vice versa, may be significantly modified by inbreeding and inbreeding depression. In a feeding assay with inbred and outbred lines of both the perennial herb, Vincetoxicum hirundinaria, and its specialist herbivore, Abrostola asclepiadis, we discovered that plant inbreeding increased inbreeding depression in herbivore performance in some populations. The effect of inbreeding on plant resistance varied among plant and herbivore populations. The among-population variation is likely to be driven by variation in plant secondary compounds across populations. In addition, inbreeding depression in plant resistance was substantial when herbivores were outbred, but diminished when herbivores were inbred. These findings demonstrate that in plant-herbivore interactions expression of inbreeding depression can depend on the level of inbreeding of the interacting species. Furthermore, our results suggest that when herbivores are inbred, herbivore-induced selection against self-fertilisation in plants may diminish.

Genetic factors affecting food‐plant specialization of an oligophagous seed predator

Several ecological and genetic factors affect the diet specialization of insect herbivores. The evolution of specialization may be constrained by lack of genetic variation in herbivore performance on different food-plant species. By traditional view, trade-offs, that is, negative genetic correlations between the performance of the herbivores on different food-plant species favour the evolution of specialization. To investigate whether there is genetic variation or trade-offs in herbivore performance between different food plants that may influence specialization of the oligophagous seed-eating herbivore, Lygaeus equestris (Heteroptera), we conducted a feeding trial in laboratory using four food-plant species. Although L. equestris is specialized on Vincetoxicum hirundinaria (Apocynaceae) to some degree, it occasionally feeds on alternative food-plant species. We did not find significant negative genetic correlations between mortality, developmental time and adult biomass of L.equestris on the different food-plant species. We found genetic variation in mortality and developmental time of L. equestris on some of the food plants, but not in adult biomass. Our results suggest that trade-offs do not affect adaptation and specialization of L. equestris to current and novel food-plant species, but the lack of genetic variation may restrict food-plant utilization. As food-plant specialization of herbivores may have wide-ranging effects, for instance, on coevolving plant-herbivore interactions and speciation, it is essential to thoroughly understand the factors behind the specialization process. Our findings provide valuable information about the role of genetic factors in food-plant specialization of this oligophagous herbivore.

Variation and constraints of local adaptation of a long‐lived plant, its pollinators and specialist herbivores

Summary Due to geographically variable species interactions, plants may become locally adapted to their sympatric herbivores and pollinators. However, adaptation to the abiotic environment may significantly affect plant interactions with herbivores and pollinators. Local adaptation to the abiotic environment may constrain local adaptation to herbivores and pollinators under contrasting selection pressures, resulting in trade‐offs in local adaptation. We studied local adaptation of a perennial herb, Vincetoxicum hirundinaria, in a reciprocal transplant experiment among four populations and measured plant fitness, pollination success and resistance to two specialist herbivores. We also estimated local adaptation of these two herbivores and generalist pollinators to their sympatric plant populations. Local adaptation was compared with within‐population genetic variation, genetic and geographical divergence, and with divergence in terms of population size, environmental conditions and plant secondary chemistry. We further compared local adaptation to the environment, to local adaptation to herbivores and pollinators to detect possible trade‐offs in local adaptation. The existence and degree of local adaptation varied among the plant populations. Plants from two populations were locally adapted to their sympatric leaf herbivores and plants from two populations were locally adapted to their abiotic environment. Herbivores from one population were locally adapted to their sympatric plant population. Local adaptation of V. hirundinaria to the seed predator increased with increasing among‐population divergence in precipitation and temperature. Local adaptation to the seed predator and the environment increased with increasing population genetic variation. Local adaptation of V. hirundinaria in fitness and in herbivore resistance also correlated positively, suggesting lack of trade‐offs in local adaptation. Synthesis. These results demonstrate that species interactions can lead to a mosaic of locally adapted plant, herbivore and pollinator populations. In addition to natural enemies, genetic variation, the abiotic environment and mutualistic interactions contribute to the evolution of local adaptation in long‐lived plants. These results provide new insights into the patterns and causes of variation in local adaptation and are among the first to demonstrate that conflicting selection pressures within a population do not constrain local adaptation in multiple traits.

Climate change and longterm patch dynamics of a perennial herb

Many perennial herbs are patchily distributed across the landscape. How such patch systems change over time is poorly known. What are the rates of patch establishment, extinction and area growth, and to what degree are changes synchronous and exhibiting trends? Can, for example, climate change signals be discerned? These questions are of interest also concerning the long-term population dynamics of the insects utilizing patchy plant resources. All patches of Vincetoxicum hirundinaria, a long-lived, patchily distributed herb, were mapped within a 12km2 area in SE Sweden. Patch areas were measured in 1977 and then almost yearly from 1990 to 2008.None of the original patches went extinct, but eleven new patches were established during the 32-year study period. However, the new patches combined represented only 0.6% of the total patch area in 2008. Average patch size did not change up to the early 1990s, but thereafter most patches grew slowly and steadily in size. This increase coincided with a climate shift towards longer growing seasons with warmer, sunnier and wetter summers. Larger patches and patches where plants had more flowers per shoot expanded faster.The patch system is presently not in equilibrium and this is probably the result of the new climatic regime. The number of patches increases steadily, most patches increase synchronously in size, and there is a positive feed back of patch size on rate of increase. Still, rates of increase are low, and in a three decade perspective the distribution of plant resources at the landscape scale remains essentially unchanged.

Plant chemistry and local adaptation of a specialized folivore.

Local adaptation is central for creating and maintaining spatial variation in plant-herbivore interactions. Short-lived insect herbivores feeding on long-lived plants are likely to adapt to their local host plants, because of their short generation time, poor dispersal, and geographically varying selection due to variation in plant defences. In a reciprocal feeding trial, we investigated the impact of geographic variation in plant secondary chemistry of a long-lived plant, Vincetoxicum hirundinaria, on among-population variation in local adaptation of a specialist leaf-feeding herbivore, Abrostola asclepiadis. The occurrence and degree of local adaptation varied among populations. This variation correlated with qualitative and quantitative differences in plant chemistry among the plant populations. These findings provide insights into the mechanisms driving variation in local adaptation in this specialized plant-herbivore interaction.

First Report of Black Swallow-Wort as an Alternate Host of the Two-Needle Pine Stem Rust Pathogen, Cronartium flaccidum, in France.

Stem rust disease, caused by Cronartium flaccidum (Alb. & Schwein.) G. Winter, is among the most destructive diseases of the two-needle hard pine in the Northern Hemisphere, including Scots pine but also several Mediterranean pines in southern Europe (2,3). This heteroecious rust has numerous alternate herbaceous hosts spanning different plant families, thereby contributing to epidemic outbreaks when environmental conditions for infection are optimal (2,3). The main alternate host in Europe is the white swallow-wort, Vincetoxicum hirundinaria Medik, a herbaceous perennial in the milkweed family (Asclepiadaceae). At the southwestern edge of its distribution, V. hirundinaria co-occurs with the black swallow-wort, V. nigrum (L.) Moench and cases of misidentification between the two species are not uncommon. Little to no disease occurs to V. nigrum likely because phenanthroindolizidine alkaloid antimicrobial compounds are produced in the weed. In 1918, occurrence of C. flaccidum was reported in Spain and Portugal on black and white swallow-worts albeit as C. asclepadium (1). In the early summer of 2011, at Saint Clément de Rivière in southern France, we detected orange-yellow rust pustules on the lower leaf surfaces of several black swallow-worts growing near Aleppo pines (Pinus halepensis). These orange-yellow pustules were erumpent uredinia in groups (range = 137 to 400 μm in diameter) with peridia that broke with the production of uredinospores. The latter were moderately echinulate, light yellow, broadly ellipsoid (length = 23 ± 4 μm and range = 11 to 33 μm; width = 15 ± 2 μm and range = 9 to 20 μm) with walls of 1 to 2 μm thick (mean 1.3 ± 0.2 μm). Hair-like columnar telia (length = 1123 ± 131 μm and range = 976 to 1280 μm; width = 136 ± 28 μm and range = 104 to 176 μm) were mostly formed from uredinia. Telia were hypophyllous and reddish orange. Teliospores were orange-yellow and ellipsoidal to cylindrical (length 26.3 ± 6.2 μm and range 13.5 to 46 μm; width = 10.5 ± 1.8 μm and range = 6.9 to 14.9 μm). Morphological features of these fruiting structures were consistent with those of C. flaccidum (Alb. & Schwein.) G. Winter on white swallow-worts (2). Additional confirmation was provided by sequencing the two internal transcribed spacer regions (ITS1 and ITS2) and the 5.8S gene (4). The sequence was 843 bp long (GenBank Accession No. JN802139), 99.7% similar to C. flaccidum found on Melampyrum in Finland (Accession No. JF13709), and 99.4% similar to C. flaccidum found on pines in Italy (Accession No. X83900). Voucher material has been deposited at the Herbarium of Montpellier's University under the collection Accession No. MPUØ188846. To our knowledge, this is the first report of the occurrence of uredinia and telia of C. flaccidum on black swallow-worts clearly identified in France. The occurrence of the rust on this understory vine is of critical importance for the economic sustainability of pine forests in France, especially when they are heavily constrained by drought and fire.

Very long diapause and extreme resistance to population disturbance in a galling insect

1. Some insects have a prolonged diapause – a dormancy that extends over more than 1 year. In most species prolonged diapause involves one or a few extra years, but in extreme cases diapause may surpass 10 years. Few cases of very long diapause have been described, and very little is known about the population consequences of the temporal refuge formed by the diapausing individuals. 2. The gall midge Contarinia vincetoxici Kieffer galls the flowers of a long-lived herb Vincetoxicum hirundinaria Med. After completing development, larvae leave the galls for the ground where they enter diapause. Extending an earlier published inoculation experiment, we show that the diapause may last up to at least 13 years, with a median duration of at least 6 years. 3. The gall midge is attacked by two parasitoid species. Dissections of gall midge larvae for presence of parasitoids revealed that Omphale salicis Haliday had a maximum 2 year diapause and Synopeas acuminatus Kieffer a maximum 4 years. The very long diapause of the gall midge may thus provide a temporal refuge from these enemies. 4. In a 15-year field experiment all galls were removed every year from six isolated habitat patches. Density changes in experimental populations were not statistically different from control populations for over a decade. After 14–15 years a modest decline could be observed. This slow response illustrates that prolonged diapause in C. vincetoxici provides a very strong population buffer against mortality during the galling stage.

The role of inbreeding and outbreeding in herbivore resistance and tolerance in Vincetoxicum hirundinaria

Inbreeding via self-fertilization may have negative effects on plant fitness (i.e. inbreeding depression). Outbreeding, or cross-fertilization between genetically dissimilar parental plants, may also disrupt local adaptation or allelic co-adaptation in the offspring and again lead to reduced plant fitness (i.e. outbreeding depression). Inbreeding and outbreeding may also increase plant vulnerability to natural enemies by altering plant quality or defence. The effects of inbreeding and outbreeding on plant size and response to herbivory in the perennial herb, Vincetoxicum hirundinaria, were investigated. Greenhouse experiments were conducted using inbred and outbred (within- and between-population) offspring of 20 maternal plants from four different populations, quantifying plant germination, size, resistance against the specialist folivore, Abrostola asclepiadis, and tolerance of simulated defoliation. Selfed plants were smaller and more susceptible to damage by A. asclepiadis than outcrossed plants. However, herbivore biomass on selfed and outcrossed plants did not differ. The effects of inbreeding on plant performance and resistance did not differ among plant populations or families, and no inbreeding depression at all was found in tolerance of defoliation. Between-population outcrossing had no effect on plant performance or resistance against A. asclepiadis, indicating a lack of outbreeding depression. Since inbreeding depression negatively affects plant size and herbivore resistance, inbreeding may modify the evolution of the interaction between V. hirundinaria and its specialist folivore. The results further suggest that herbivory may contribute to the maintenance of a mixed mating system of the host plants by selecting for outcrossing and reduced susceptibility to herbivore attack, and thus add to the growing body of evidence on the effects of inbreeding on the mating system evolution of the host plants and the dynamics of plant-herbivore interactions.

Screening of Eurasian plants for insecticidal and growth inhibition activity against Spodoptera littoralis larvae

This paper presents the results of a screening of plant extracts obtained from 134 plant species of the Eurasian region for chronic toxicity and larval inhibition in Spodoptera littoralis larval growth. The extracts from Ailanthus altissima, Ajuga chamaepitys; Ajuga reptans, Angelica archangelica, Artemisia campestris, Buphtalmum salicifolium, Camellia sinensis, Chenopodium bonus-henricus, Eupatorium cannabinum, Foeniculum vulgare, Lythrum salicaria, Lythrum virgatum, Mentha arvensis, Mentha longifolia, Mentha suaveolens,Potentila argentea, Potentila fruticosa, Seseli pallasii and Vincetoxicum hirundinaria were selected, which caused both 100% larval mortality and growth inhibition higher than 75% after application of 15 mg dose of the extract in 1 g of food. Lethal doses and the effect of LD50 on growth inhibition and antifeedant were estimated in order to determine the differences in efficiency of the selected extracts based on the mortality results, the extract from A. archangelica seeds could be chosen as the most efficient one for its LD50 was significantly lower (0.4 mg/g) compared to the other extracts. Key words: Spodoptera littoralis, plant extracts, botanical insecticides, antifeedancy, acute toxicity.

Performance of potential European biological control agents of Vincetoxicum spp. with notes on their distribution

Exploratory surveys were conducted in Europe to locate potential biological control agents of Vincetoxicum nigrum and Vincetoxicum rossicum and to collect known specialist herbivores of Vincetoxicum hirundinaria (Abrostola asclepiadis, Chrysolina a. asclepiadis, Eumolpus asclepiadeus and Euphranta connexa). Development of the most abundant herbivores found attacking leaves, roots, and developing seeds was evaluated in the laboratory on three Vincetoxicum spp. Field surveys revealed that the highest diversity of herbivores was associated with the abundant and widespread V. hirundinaria. No new herbivores were reported from V. hirundinaria or V. nigrum, but the leaf-feeding noctuid Hypena opulenta was recorded for the first time attacking V. rossicum and V. scandens in Ukraine. Based upon larval survival and development and adult fecundity, the leaf feeders A. asclepiadis, C. a. asclepiadis, and H. opulenta, perform better on V. nigrum and V. rossicum than on V. hirundinaria. Larval performance of the root feeder E. asclepiadeus followed a similar pattern, but adult fecundity of this insect did not vary among host plant species. Immature development time of the pre-dispersal seed feeder E. connexa is similar among hosts, but larvae grow larger on V. nigrum and V. hirundinaria than on V. rossicum. All herbivores are promising biological control agents of Vincetoxicum in North America and we have prioritized host range testing with H. opulenta and E. asclepiadeus.

Susceptibility of Pedicularis spp. to Cronartium ribicola and C. flaccidum in Finland

Summary Aeciospores of Cronartium ribicola and C. flaccidum were collected from several locations in Finland and used to inoculate Pedicularis spp. and some known and suspected alternate hosts in 2008–2009. In all trials, C. ribicola formed uredinia and telia on leaves of Ribes nigrum. No uredinia or telia of C. ribicola formed on older leaves of Pedicularis spp. but both uredinia and telia were found on young leaves of P. palustris ssp. palustris. Cronartium flaccidum produced uredinia and/or telia on leaves of P. palustris ssp. palustris, P. lapponica, Vincetoxicum hirundinaria and Melampyrum sylvaticum. Neither rust infected P. sceptrum-carolinum, Vaccinium myrtillus, Calluna vulgaris or Ledum palustre. Similar to rusts in Asia and North America, the results showed that European C. ribicola exhibit more variable host reactions and wider alternate host ranges than earlier described. Pedicularis palustris may play a role in the spread of Cronartium in natural forests.

Associations of plant fitness, leaf chemistry, and damage suggest selection mosaic in plant–herbivore interactions

The geographic mosaic theory of coevolution states that variation in species interactions forms the raw material for coevolutionary processes, which take place over large geographic scales. One key assumption underlying the process of coevolution in plant-herbivore interactions is that herbivores exert selection on their host plants and that this selection varies among plant populations. We examined spatial variation in the existence and strength of phenotypic selection on host plant resistance exerted by specialist herbivores in 17 archipelago populations of the perennial herb Vincetoxicum hirundinaria (Asclepiadaceae). In these highly fragmented populations, V. hirundinaria is consumed by the larvae of two specialist herbivores: the folivorous moth Abrostola asclepiadis and the seed predator Euphranta connexa. Selection imposed on host plants by these herbivores was examined by analyzing the associations between levels of herbivory, plant fitness, and contents of a number of leaf chemicals reflecting plant resistance to and quality for the herbivores. We found extensive spatial variation in the levels of herbivory and in plant fitness. More importantly, the impact of both leaf herbivory and seed predation on plant fitness varied among plant populations, indicating spatial variation in phenotypic selection. In addition, leaf chemistry varied widely among plant populations, reflecting spatial variation in plant quality as food for the herbivores. However, leaf compounds influenced folivory similarly in all the studied plant populations, and interestingly, some of the compounds were associated with the intensity of seed predation. Finally, some of the leaf compounds were associated with plant fitness, and the strength and direction of these associations varied among plant populations. The observed spatial variation in the strength of the interactions between V. hirundinaria and its specialist herbivores suggests a geographic selection mosaic. Because the occurrence and strength of spatial variation varied between the two specialist herbivores, our results highlight the importance of considering multiple enemies when trying to understand evolution of interactions between plants and their herbivores.

Antifeedant activity of plant extracts on Leptinotarsa decemlineata Say. and Spodoptera littoralis Bois. larvae

Antifeedant activities of methanol extracts obtained from 75 plant species of the Eurasian region were assessed on Spodoptera littoralis and Leptinotarsa decemlineata larvae. Significant differences in antifeedant activity were found in the highest tested dose of 500 μg/cm 2, not only among individual extracts but also between both pest species tested. S. littoralis larvae were less sensitive to the extracts, when 43 extracts showed antifeedant activity lower than 50%, and an effectiveness in the range of 50–95% was found in 13 extracts. Out of all tested extracts, only the extracts obtained from the plants Angelica archangelica, Imperatoria ostruthium, Psoralea bituminosa and Vincetoxicum hirundinaria showed antifeedant activity higher than 95%, and their effective doses (ED 50) were estimated as 44, 34, 72 and 11 μg/cm 2, respectively. L. decemlineata larvae were very sensitive to all the tested extracts. Only 15 extracts showed antifeedant effectiveness lower than 50%. The highest number of extracts (42) showed effectiveness in the range of 50–95%. 23 extracts were chosen for subsequent tests; antifeedant effectiveness higher than 95% was determined for these extracts. Out of 23 extracts, 3 extracts obtained from A. archangelica, Grindelia camporum and Inula auriculata showed the highest effectiveness, when ED 50 lower than 1 μg/cm 2.

Associations of plant fitness, leaf chemistry, and damage suggest selection mosaic in plant-herbivore interactions

The geographic mosaic theory of coevolution states that variation in species interactions forms the raw material for coevolutionary processes, which take place over large geographic scales. One key assumption underlying the process of coevolution in plant–herbivore interactions is that herbivores exert selection on their host plants and that this selection varies among plant populations. We examined spatial variation in the existence and strength of phenotypic selection on host plant resistance exerted by specialist herbivores in 17 archipelago populations of the perennial herb Vincetoxicum hirundinaria (Asclepiadaceae). In these highly fragmented populations, V. hirundinaria is consumed by the larvae of two specialist herbivores: the folivorous moth Abrostola asclepiadis and the seed predator Euphranta connexa. Selection imposed on host plants by these herbivores was examined by analyzing the associations between levels of herbivory, plant fitness, and contents of a number of leaf chemicals reflecting plant resistance to and quality for the herbivores. We found extensive spatial variation in the levels of herbivory and in plant fitness. More importantly, the impact of both leaf herbivory and seed predation on plant fitness varied among plant populations, indicating spatial variation in phenotypic selection. In addition, leaf chemistry varied widely among plant populations, reflecting spatial variation in plant quality as food for the herbivores. However, leaf compounds influenced folivory similarly in all the studied plant populations, and interestingly, some of the compounds were associated with the intensity of seed predation. Finally, some of the leaf compounds were associated with plant fitness, and the strength and direction of these associations varied among plant populations. The observed spatial variation in the strength of the interactions between V. hirundinaria and its specialist herbivores suggests a geographic selection mosaic. Because the occurrence and strength of spatial variation varied between the two specialist herbivores, our results highlight the importance of considering multiple enemies when trying to understand evolution of interactions between plants and their herbivores.

Spatio‐temporal variation in fruit production and seed predation in a perennial herb influenced by habitat quality and population size

Summary In patchily distributed plant species, seed production is likely to be influenced both by local abiotic factors affecting plant size and conditions for fruit maturation, and by population characteristics affecting the intensity of interactions with mutualists and antagonists. However, the relative importance of these effects is poorly known. We used multiple regression and path models to examine the importance of abiotic factors (sun exposure, soil depth) and population characteristics (size, density and connectivity) for variation in flower and fruit production and intensity of seed predation among 39 populations of the long‐lived herb Vincetoxicum hirundinaria in three consecutive years. In addition, we manipulated water availability in a field experiment and recorded short‐term and long‐term effects on fruit output, and conducted a supplemental hand‐pollination experiment. Flower production varied little, while fruit initiation, fruit abortion and fruit predation varied considerably among years. Sun exposure and soil depth affected fruit production per plant indirectly and positively through their effects on flower number. Population density affected fruit production negatively through its effect on flower number. Both fruit initiation and the proportion of fruits attacked by the tephritid fly Euphranta connexa were related positively to population size. The number of full‐size fruits per plant was related positively to sun exposure and population size in two years each, and related negatively to population density in one year. However, because of seed predation, the number of intact mature fruits was related significantly to population characteristics in only one of three years. The field experiments showed that both shortage of water and insufficient pollination may limit fruit set in V. hirundinaria. Synthesis. These results demonstrate that the relative importance of local abiotic conditions and population characteristics may vary considerably along the chain of events from flower formation to intact fruit, and also among years. They further show that, at least in species with a naturally patchy distribution, connectivity may be relatively unimportant for variation in reproductive output compared to effects of habitat quality, population size and density.

Finnish Cronartium ribicola does not infect alternate hosts of Cronartium flaccidum

SummarySusceptibility of the main alternate hosts of Cronartium flaccidum, Vincetoxicum spp. and Melampyrum spp., to C. ribicola was investigated by artificial inoculations on detached leaves in the laboratory and on whole plants in the greenhouse. Neither uredinia nor telia developed on the leaves of either Vincetoxicum hirundinaria, Vincetoxicum nigrum, Melampyrum sylvaticum, Melampyrum pratense, Melampyrum nemorosum, Melampyrum arvense, Melampyrum cristatum or Melampyrum polonicum following inoculation by the 26 aeciospore sources collected from Pinus strobus, Pinus monticola, Pinus flexilis and Pinus peuce in 2000–2003. The results suggest that Finnish C. ribicola does not infect the main alternate hosts of C. flaccidum. Cronartium ribicola and C. flaccidum can thus be identified reliably by inoculations on their main alternate hosts.

Diversity of MAPs in some plant communities of Stara Planina

The high floristic diversity of Stara Planina was the starting base for the research of medicinal and aromatic plants (MAPs) in individual forest and meadow communities. The sites Javor and Prelesje, forest community Fagetum moesiacae montanum B. Jov. 1953, pioneer community of birch Betuletum verrucosae s.l. and meadow community Agrostietum vulgaris (capillaris) Pavlovic, Z. 1955, were researched as follows: soil types, floristic composition and structure of the community, percentage of MAPs, as well as the selection of species which, according to the predetermined criteria can be recommended for further exploitation. The study shows that the soil of the forest communities is eutric brown, and meadow soils are dystric and eutric humus-siliceous. The percentage of MAPs in the floristic structure of the study sites in forest and meadow communities is 32.35%. The following species can be recommended for the collection and utilisation: Hypericum perforatum L., Asperula odorata L., Dryopteris filix-mas (L) Schott. Urtica dioica L., Euphorbia amygdaloides L., Prunella grandiflora L. Tanacetum vulgare L., Achillea millefolium L., Rumex acetosa L., Campanula glomerata L., Stachys officinalis (L) Trevis., Plantago lanceolata W. et K., Potentilla erecta (L) Rauchel, Chamaespartium sagittale (L) P. Gibbs. Cynanchum vincetoxicum (L) Pers., Euphrasia stricta Host., Fagus moesiaca (Matt) Liebl. and Fragaria vesca L.

Population History, Mating System, and Fitness Variation in a Perennial Herb with a Fragmented Distribution

Abstract: Patterns of genetic diversity are strongly influenced by the history of populations, which is often ignored when examining the viability of populations. We studied the relationship of population size, genetic variation, and fitness in the perennial herb Vincetoxicum hirundinaria (Asclepiadaceae) in the southwestern archipelago of Finland, where this species occurs commonly on many of the islands and its distribution is highly fragmented. We measured the magnitude and distribution of genetic variation in this species to examine how patterns of genetic diversity reflect population history, especially the colonization pattern of the islands and the mating system. Additionally, we used the genetic data to interpret previous results that suggest that fitness variation among populations is not directly related to population size. We found a high level of genetic variation (He=0.396) and a low level of genetic differentiation ( FST=0.052) among the populations. In contrast to several rare plant species, the level of genetic variation ( He) was not correlated with population size or with male or female fitness of the plants. Our results also indicated that inbreeding is common in all populations regardless of their size (mean FIS=0.460) but that it does not correlate significantly with male or female fitness traits. The observed patterns of genetic variation suggest that this species has a mixed mating system. Taken together, these results indicate that the studied populations are of recent common ancestry but may also have relatively high levels of current gene flow. The differences between our results and those from previous studies of rare plant species with a fragmented distribution pattern emphasize the importance of considering whether fragmentation is caused by recent human activities or whether it reflects a distribution pattern characteristic of the species when evaluating the conservation needs of the species.

Variation in the mating system of Vincetoxicum hirundinaria (Asclepiadaceae) in peripherial island populations.

Self-fertility may be selected for in small and isolated plant populations of normally outcrossing species. In addition, adaptations for self-fertility are likely to arise in island populations and in populations that are located at the border of the species range. The mating system of Vincetoxicum hirundinaria (Asclepiadaceae) is examined in island populations that are located at the northern border of the species range. Pollination experiments were conducted under glasshouse conditions with plants from four populations. The frequencies of self-fertile individuals were relatively high and did not differ among populations. Cross-pollination resulted in higher fruit set than self-pollination. However, fruit-set from self-pollination and cross-pollination did not differ in the self-fertile individuals. Interestingly, the proportion of aborted fruits was on average higher following cross-pollination than following self-pollination. No differences were observed in seed number or seed mass between self- and cross-pollinated fruits. Pollen tube growth following self- and cross-pollinations was indistinguishable. The results of this study revealed that V. hirundinaria possess a mixed-mating system in the studied island populations. Evidence was also provided for a late-acting self-incompatibility system commonly observed in Asclepiadaceae. No clear signs of inbreeding depression were observed in the early stages of development.

Cronartium flaccidum produces uredinia and telia on Melampyrum nemorosum and on Finnish Vincetoxicum hirundinaria

SummaryUredinia and telia were produced on Melampyrum nemorosum through inoculations with Cronartium flaccidum aeciospores collected from northern Finland, proving that M. nemorosum serves as the telial host of C. flaccidum. Melampyrum nemorosum plants were either grown from seeds collected from several geographical provenances or transplanted from natural forest stands. They were inoculated with several geographical aeciospore sources of C. flaccidum in a greenhouse. Vincetoxicum hirundinaria, M. pratense and M. sylvaticum were used as positive controls. Detached leaves of Melampyrum spp. and V. hirundinaria were also inoculated but uredinia and telia formed only on V. hirundinaria. Most of the aeciospore sources from northern Finland produced abundant uredinia and telia both on M. nemorosum from two geographical locations and on V. hirundinaria in the greenhouse. Statistically significant differences were observed in the dimensions of artificially produced telia, teliospores and urediniospores among the tested alternate hosts and spore sources. The results suggest that M. nemorosum is susceptible to C. flaccidum and therefore may play a role in southern Fennoscandia as an alternate host but it has potentially a greater role in central and eastern Europe, where M. nemorosum occurs commonly.