Marianne Philipp

Gene flow and mode of pollination in a dry-grassland species, Filipendula vulgaris (Rosaceae)

Filipendula vulgaris is a characteristic species of dry nonacidic grasslands in Denmark. This habitat type occurs only on marginal areas not suitable for agriculture or urbanization and that are by their nature fragmented. The population genetic structure of F. vulgaris was investigated in 17 populations within two regions of Denmark, using isozyme electrophoresis. Small populations were found to have significantly fewer polymorphic loci than larger populations, but all populations maintained the same common allelic variants. The degree of isolation of individual populations did not affect the amount of genetic variation. Offspring arrays revealed a very high outcrossing rate (0.96). The field study demonstrated a very high level of gene flow between populations considering that small insects are thought to be the main pollinators of this species. An experiment to verify whether pollen transport by wind could explain the results from the field study demonstrated long-distance transport from isolated plants to bagged plants. Filipendula vulgaris pollen grains are very small and this explains why outcrossed progeny were found using pollination bags with small pore sizes. We conclude that wind pollination is indeed possible and together with insect pollination is causing the observed patterns of genetic variation. The substantial gene flow between populations may be reducing the effects of genetic drift in the small fragmented populations of F. vulgaris.

Enhancement of local species richness in tundra by seed dispersal through guts of muskox and barnacle goose

The potential contribution of vertebrate-mediated seed rain to the maintenance of plant community richness in a High Arctic ecosystem was investigated. We analyzed viable seed content in dung of the four numerically most important terrestrial vertebrates in Northeast Greenland – muskox (Ovibos moschatus), barnacle goose (Branta leucopsis), Arctic fox (Alopex lagopus) and Arctic hare (Lepus arcticus). High numbers of plant propagules were found in the dung of muskox and barnacle goose. Seeds of many plant species were found in the faeces of one vertebrate species only. Propagule composition in barnacle goose droppings was relatively uniform over samples, with a high abundance of the nutritious bulbils of Polygonum viviparum (Bistorta vivipara), suggesting that geese have a narrow habitat preference and feed selectively. Propagule composition in muskox dung was diverse and heterogeneous among samples, suggesting a generalist approach in terms of food selection and the haphazard ingestion of plant propagules with foliage. The species composition of plant propagules in dung samples was different from that of the receiving plant communities (in terms of the Sørensen and Czekanowski dissimilarity indices), and dung deposition, especially by muskox, often brought new species to the receiving community. The results suggest that endozoochorous propagule dispersal in the Arctic has a great potential in the generation and maintenance of local species richness, albeit being little specialized. It is further suggested that endozoochory is an important means of long-distance dispersal and, thereby, of plant migration in response to climate change.

Selective advantage of ray florets in Scalesia affinis and S. pedunculata (Asteraceae), two endemic species from the Galápagos

The presence of neuter ray florets in species within Asteraceae is generally believed to increase pollinator attraction. In the endemic Galápagos genus Scalesia (Asteraceae) a natural variation in the presence/absence of neuter ray florets is found. To evaluate whether the presence of ray florets plays a selective role on female reproductive success we chose two species of Scalesia, Scalesia affinis that carries ray florets and S. pedunculata that is rayless. On Santa Cruz Island capitula of S. pedunculata were equipped with fake ray florets while others were untouched. On Isabela Island ray florets were removed on half of the capitula of S. affinis. In S. affinis rayed capitula received more pollinators and more pollen, which resulted in a significantly higher embryo production. In S. pedunculata no effect on embryo production was found. The disagreement between the two species may correspond to a difference in visitation frequency, S. pedunculata receiving many more visit than S. affinis. Thus, ray floret development proved beneficial in pollinator-restricted localities.

Gene flow and population structure in Armeria maritima

Gene flow distances and population structure were studied in populations of Armeria maritima (Mill). Willd. in Denmark. Gene flow was studied by direct methods using seed and pollen dispersal distances. Pollen flow in four experimental populations, where honey-bees were pollinators, surpassed the diameter of each experimental population. Seed dispersal was restricted and was used to partition a coastal grassland population into local populations. The structure of this population was analysed with a population genetic model that formulated a sequence of hypotheses about the action of natural selection and the geographical subdivision of the total population into local populations. The variation at a morphological marker locus was used for this purpose: the presence of hairs on the flower stalk in this species is determined by a dominant allele. The estimated pollen pools in the six local populations were homogeneous, and there was no evidence of deviation from random mating in any of the local populations. The genotypic distributions were homogeneous in the local populations and accorded with Hardy–Weinberg proportions. There was no evidence of selection at the studied locus, accordingly, the studied population was panmictic and its genotypic distribution could be described with a single parameter, the allele frequency at the marker locus.

Climate Change Influences on Species Interrelationships and Distributions in High-Arctic Greenland

Biotic communities in Northeast Greenland have an insular character as a consequence of the complex geomorphologic nature of the ice-free land and its interdigitation with glacial ice and the sea. Post Pleistocene movements of most plants and animals into the region have generally followed East and North Greenland coastal routes, and the majority of the plants have North American affinities. Climatic change, bringing about reduction in the extent of sea ice adjacent to the coast and changes in seasonality and associated precipitation and air movements, influences patterns of activity, growth, reproduction and dispersal of all life forms present. Climate associated changes in the biotic communities of the region are altering inter-species interactions, notably pollination, seed dispersal and plant-herbivore relations. Sexual reproduction and dispersal of propagules, primarily seeds, are essential processes underlying maintenance of genetic biodiversity in plant communities in Northeast Greenland. Wind and water transport of seeds are primary methods by which plants disperse and become established in the High Arctic, but birds and mammals are also involved. In Northeast Greenland, dispersal of viable seeds may occur by passage through the guts of geese and muskoxen. Research at Zackenberg on the role of insects in pollination of flowering plants has shown that Diptera species, primarily flies, dominate among the insect species visiting flowers each summer. Diptera, Lepidoptera (butterflies and moths), Hymenoptera (bumble bees and small wasps) and one Hemiptera (true bugs) species have constituted the primary pollinators at Zackenberg. Arctic willow Salix arctica, white arctic bell heather Cassiope tetragona and mountain avens Dryas octopetala, are the primary species represented in the pollen present on pollinating insects at Zackenberg. The effects of climate warming that may enhance environmental conditions for plant growth in Northeast Greenland and accelerate invasion of new species will also be tied to the relationship of specific plant species to their insect pollinators. Those plants that are self pollinated may have an initial advantage in an environment where insects and their plant relationships are being altered by the changing climate. An increase in growth and dispersal of shrubs in the Arctic is occurring as a consequence of climate warming. Increases in shrubs with more upright growth form, especially willows, will generate microhabitats not previously present in the High Arctic. The new habitats will make possible the invasion of new insect, mammal and bird herbivores, as well as their parasites and predators. (Less)

How a heterostylous plant species responds to life on remote islands: a comparative study of the morphology and reproductive biology of Waltheria ovata on the coasts of Ecuador and the Galápagos Islands

Heterostylous reproductive systems are usually absent on oceanic island. Self-compatibility would, generally, be advantageous for long-distance dispersing species, as it provides reproductive assurance when density of mates is low. The heterostylous reproductive system, often associated with an incompatibility system, may be a constraint on the colonization of remote habitats. It is, therefore, surprising that the distylous shrub Waltheria ovata has colonized all of the Galápagos Islands, situated more than a thousand kilometres off the shore of Ecuador. The present study confirmed the reciprocal herkogamy of W. ovata. A comparison of mainland and the Galápagos Island populations showed a reduction in flower size, including distance between anthers and stigmas and size of anthers on the islands. Some reductions are quite large but not significantly different, mainly due to a high degree of variation among populations on the islands. The pin morph of W. ovata has undergone the most radical adaptive changes in morphology. Pollination experiments of W. ovata disclosed a leak in the incompatibility system on the Galápagos Islands, allowing higher selfing rates as well as intra-morph seed set compared to the mainland populations. This was most pronounced in the thrum morph. The deficient distylous reproductive system may be an adaptation to a pollinator and mate sparse environment on the Galápagos Islands. We conclude that the heterostylous mating system has changed in response to colonization of the Galápagos Islands, giving room for reproductive assurance by seed set after selfings and intra-morph pollinations.

Genetic Variation in Four Species of Pedicularis (Scrophulariaceae) within a Limited Area in West Greenland

Four closely related species of Pedicularis (Scrophulariaceae), an abundant plant genus in the Arctic, with different breeding systems were analyzed for amount and distribution of genetic variation at three sites at Qeqertarsuaq, West Greenland. Isozyme variation was found in two enzyme systems (phosphogluconate dehydrogenase and phosphoglucomutase) in only one of the of the species (P. lanata). Average genetic diversity (He) was 0.028, including monomorphic loci. Compared to the other three species investigated, P. lanata possesses the breeding system with the highest capacity for outcrossing in the study area and also shows the greatest morphological variation within is geographic distribution. There seems thus to be accordance between the morphological variation, breeding system and the population genetic results.

Modelling Gene Flow between Fields of White Clover with Honeybees as Pollen Vectors

The portion-dilution model is a parametric restatement of the conventional view of animal pollination; it predicts the level of pollinator-mediated gene dispersal. In this study, the model was applied to white clover (Trifolium repens) and its most frequent pollinator, the honeybee (Apis mellifera). One of the three parameters in the portion-dilution model is the mean number of flowers a pollinator visits in one foraging bout. An alternative method to estimate this parameter was developed that was not depending on pollinator hive-seeking behaviour. The new estimation method, based on nectar collection, seems to be a good alternative, when reliable observation on visiting behaviour of pollinators is not possible. The gene flow in white clover was modelled. Where fields were assumed to be well separated, and only a low fraction of bees travelled between fields, the gene flow was estimated to be 0.7%, but subjected to large uncertainty. In a worst case scenario with adjacent fields—one with a genetically modified (GM) T. repens cultivar and the other with a conventional T. repens cultivar—and where all arriving bees were expected to transfer GM pollen, the median gene flow was modelled to be 7% with an estimated 95% percentile of 70%. The results show that the European Union threshold limit of 0.9% GM admixture for food and feed will likely be exceeded at times and especially organic farmers that do not accept GM admixture and often have clover and clover–grass fields might face challenges with admixture of GM.

The Effect of a Seed-Sucking Bug on Seed Germination of an Arctic Cushion Plant

Abstract: Seeds of Arctic plants face numerous threats prior to dispersal. The growing season varies across years in terms of degree days, and herbivory, predation, and pathogens are critical threats. In this study the results of different densities of the Arctic seed bug, Nysius groenlandicus (Heteroptera), piercing the seed coat of Silene acaulis and sucking out nutritional content were observed. In order to study the effect of Nysius groenlandicus on seed mass and germination of Silene acaulis, seeds were placed in Petri dishes with different densities of seed bugs. The herbivory affected the seed mass, leading to an average mass loss of 3.0% in fed-upon seeds compared to non-fed-upon seeds. However, the average seed mass lost seemed independent of the densities of seed bugs. A significant negative correlation between seed mass loss and number of germinations for seeds exposed to seed bugs was found. Furthermore, the germination speed of the seeds increased with increasing density of Nysius groenlandicus. The significance of this interaction is discussed, and we hypothesize that feeding might benefit the establishment of seedlings.

Synopsis of subcategories and recommended methods

The different subcategories listed in Chapter 3 are examined in relation to the risk assessment of GMPs in natural and agricultural ecosystems. Methods which are suitable as test procedures for specific items are suggested. Subcategories lacking relevant methods are indicated in the margin as “need for new methods” and commented on, while interesting research subjects which have had little investigation are marked “research need”. For the discussion of subjects under the categories “Genetic engineering techniques”, “Inserted trait” and “Test procedures”, see Chapters 8, 9 and 10, respectively. A list of the references for each subcategory is shown in Section 6.1 and a list of reviews for each category is shown in Section 6.2.