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Recent decades have seen a shift in agricultural land use from pasture to arable combined with increased use of fertilisers and pesticides. In this quite hostile landscape matrix, pollinator movements between native vegetation remnants may be impeded. Linear landscape elements (LLEs) in farmland can function as biological corridors by facilitating pollinator movements and pollen flow between fragmented plant populations. The type of landscape matrix surrounding LLEs and plant populations, and LLE habitat quality may influence the effectiveness of LLEs as corridors for pollen dispersal through the availability of floral resources and nesting opportunities for pollinators. Using fluorescent dyes as pollen analogues, we investigated dye dispersal patterns between fragmented populations of the rare insect-pollinated Primula vulgaris connected by existing LLEs. We examined how dye deposition on P. vulgaris and within LLEs (on other co-flowering insect-pollinated species) could be influenced by the surrounding matrix type (pasture, arable field), the recipient population traits of P. vulgaris (flowering population size, flower display, flowering plant density and co-flowering floral resources) and by LLE traits (LLE length and co-flowering floral resources). Dye dispersal through corridors was significantly higher when the landscape matrix surrounding P. vulgaris recipient populations and LLEs consisted of pastures rather than arable fields (or a mix of both), even after accounting for differences in floral resources. A higher cover and diversity of insect-pollinated plants increased dye deposition when co-flowering within small P. vulgaris populations, but led to dye loss within LLEs. Large P. vulgaris populations appeared more attractive thereby increasing heterospecific dye deposition in the LLEs. Our study shows that farming practices shifting from pastures to maize arable fields have a negative impact on dye dispersal patterns, and so possibly affect pollen dispersal of P. vulgaris, likely through a reduced pollinator service. Corridor effectiveness depends on the type of surrounding matrix, and the abundance of floral resources directly influences dye dispersal patterns. Preserving the remaining pastureland is essential, but restoring rich flowering vegetation at field boundaries and along LLEs may also promote corridor effectiveness for pollen dispersal.

Ceratophyllum spp., Callitriche spp., Zannichellia spp. and Potamogeton pectinatus L. are widespread submerged macrophyte species, often occurring at high abundance and forming an integral part of the vegetation of many types of shallow aquatic systems. Several species occur in both freshwater and brackish water habitats. Most have a mixed reproduction system and can reproduce sexually by seeds and propagate asexually by rhizomes, turions, root tubers or axillary tubers. It is hypothesized that sexual propagules are more important than vegetative fragments to ensure long-distance-dispersal, which in case of frequent bird or water flow-mediated dispersal should lead to lowered genetic differentiation. At a regional level, we used dominant ISSR markers in a multi-species approach and observed the largest clonal differentiation between brackish water and freshwater populations of the western European lowland (Belgium). Differentiation was pronounced at taxon level (e.g. Zannichellia), as a salinity gradient (P. pectinatus) or as a coastal-to-inland conductivity gradient (Callitriche obtusangula). These differences and trends suggested a very limited dispersal at regional level across both habitats and regions. To test the hypothesis whether vegetative reproduction and dispersal may have an important function in maintenance of the species at local scale, we investigated the microsatellite diversity and clonal distribution within and between populations of P. pectinatus from a single catchment, representing upstream forest ponds and downstream river sites along the Woluwe (Brussels, Belgium). Clonal diversity was low on average, however, with a higher number of multilocus genotypes in upstream forest ponds than in downstream river sites. A few but abundant clones were present along various stretches of the river indicating clonal spread and establishment over larger distances within the river. Clonal dispersal at a local scale was more pronounced in river than in pond habitats, indicating a higher relative importance of water flow than bird-mediated dispersal for establishment of P. pectinatus in river sites. Dispersal of seeds and establishment of seedlings were assumed more effective within ponds than in river habitats. Upstream forest ponds can be regarded as source populations and refuges of clonal diversity for recolonization of the more stressful downstream river habitat.

Summary 1. Habitat fragmentation in agricultural landscapes has reduced the population sizes of many plant species while increasing their spatial isolation. Restoration or maintenance of the connectivity by gene flow between the fragmented patches may be determinant to sustaining viable populations, especially for insect-pollinated species. Functional biological corridors facilitating pollen flow between remnants in a human-dominated matrix might achieve this. 2. Dye dispersal was investigated for the extremely fragmented insect-pollinated herb Primula vulgaris, using fluorescent dye particles as pollen analogues, in a study site comprising 20 populations, of which 13 pairs were physically connected by a linear landscape elements (LLEs, ditches), and 11 pairs were not connected by an LLE. The dye deposition events were used to fit a model of pollen dispersal at the landscape level. We examined whether existing LLEs in the intensively used agricultural landscape act as functional corridors for pollen dispersal. The effects of LLE length and size and plant density of the recipient population on the dispersal patterns were tested. 3. Dye dispersal showed a leptokurtic decay distribution, with 80% of the dye transfers occurring at less than 85.1 m, and a maximal distance of 1010.8 m. The mean distance travelled by fluorescent dye particles based on the dye dispersal model was δ = 87 m. 4. Dye dispersal between populations was found to be significantly higher when populations were connected by an LLE, than when populations were unconnected. For the group of population pairs connected by an LLE, dye deposition significantly decreased with the distance to dye source, but was not related to recipient population size and plant density. 5. Synthesis. Our study is, to our knowledge, the first to demonstrate that existing LLEs in an intensively used farmland may act as functional biological corridors facilitating pollen dispersal through pollinator movements. The maintenance or restoration of a network of populations connected by LLEs, but also by other landscape structures (e.g. population relays in vegetation patches and networks of small elements allowing indirect connections) should be strongly encouraged.

Background and aims – Due to habitat fragmentation and degradation many plant species have been led to near extinction, remaining as a few extremely small and isolated populations. Preserving such remnant populations requires the most appropriate management strategies to apply in complementarity with the usual habitat restoration. These require an adequately evaluated genetic and demographic status. Methods – We investigated population genetic variation of three remnant populations of Primula vulgaris (Noord-Drenthe, The Netherlands) using six microsatellite loci, for comparison with fifteen populations from Flanders (Belgium), showing similar fragmentation history and population sizes. Key Results – Noord-Drenthe populations show lower genetic variation and higher between-population genetic differentiation, but lower F IS values than populations from Flanders. This suggests stronger genetic erosion and gene flow disruption than in Flanders, but also a substantial genetic diversity retained by old-aged individuals, contributing to maintain low levels of inbreeding. Such a situation might await P. vulgaris in Flanders in the future. Conclusions – Given the very small number and size of populations, a genetic rescue programme is needed through active reinforcements of the existing populations and creation of new populations. Seedlings used for rescue can be obtained from seeds collected in the field, but also from outcrosses between remnant populations, to maximize genetic diversity.

Pollinator movement in the intensive agricultural landscape using fluorescent dye particles: Primula vulgaris as a model species.

Microsatellite loci were developed for Primula vulgaris, a distylous, insect-pollinated, long-lived perennial herb. Primula vulgaris is rare and declining in Belgium. Eighteen microsatellite primer pairs were tested on 267 P vulgaris individuals and on 246 individuals of its common congener Primula elatior to test for cross-species amplification. Only three polymorphic microsatellite loci amplified successfully in R vulgaris and only two in P. elatior. Between 4 and 11 alleles were found per locus in P vulgaris and 8-11 alleles per locus in P. elation Expected heterozygosity ranged from 0.496-0.620 and from 0.830-0.880 for P vulgaris and P. elatior, respectively.

Magnetic moment direction of Tb in [Fe(40 A)/Tb(x A)]30 multilayers (x=20 and 10) has been studied by the low-temperature nuclear orientation technique in the temperature range of 5–50 mK and in the external magnetic field (Bext) range of 0–1 T, applied along the sample plane. The γ-ray anisotropy of the 299 keV160Tb line was monitored. The perpendicular magnetic anisotropy (PMA) of the Tb magnetic moments has been found at zero Bext for both systems. The PMA effect increased when the Tb layer thickness decreased.

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

In flowering plants, pollen dispersal is often the major contributing component to gene flow, hence a key parameter in conservation genetics and population biology. A cost-effective method to assess pollen dispersal consists of monitoring the dispersal of fluorescent dyes used as pollen analogues. However, few comparisons between dye dispersal and realized pollen dispersal have been performed to validate the method. We investigated pollen dispersal in two small populations of the insect-pollinated herb Primula elatior from urban forest fragments using direct (paternity analyses based on microsatellite DNA markers) and indirect (fluorescent dyes) methods. We compared these methods using two approaches, testing for the difference between the distance distributions of observed dispersal events and estimating parameters of a dispersal model, and related these results to dye dispersal patterns in three large populations. Dye and realized (based on paternity inference) pollen dispersal showed exponential decay distributions, with 74.2-94.8% of the depositions occurring at less than 50m and a few longer distance dispersal events (up to 151m). No significant difference in curve shape was found between dye and realized pollen dispersal distributions. The best-fitting parameters characterizing the dye dispersal model were consistent with those obtained for realized pollen dispersal. Hence, the fluorescent dye method may be considered as reliable to infer realized pollen dispersal for forest herbs such as P. elatior. However, our simulations reveal that large sample sizes are needed to detect moderate differences between dye and realized pollen dispersal patterns because the estimation of dispersal parameters suffers low precision.

Genetic differentiation of submerged plant populations and taxa between habitats