Turbidity, Waterfowl Herbivory, and Propagule Banks Shape Submerged Aquatic Vegetation in Ponds

The aquatic vegetation in nutrient-rich shallow lakes and ponds is structured by the interplay of multiple biotic and abiotic drivers. We tested the contribution of the macrophyte propagule bank and the delayed as well as direct impact of waterbirds on submerged aquatic vegetation in a peri-urban pond system. To clarify the functional hierarchy of predictor variables, effects of herbivorous waterfowl and propagule bank potential were ranked relative to environmental, phytoplankton, and zooplankton indicators. Two aspects of the aquatic vegetation – community composition and total pond-scale cover – were discriminated. Within vegetation communities, phytoplankton biovolume and waterfowl herbivory during summer were linked to low macrophyte abundance, whereas propagule density of angiosperms was positively associated with specific assemblages of submerged macrophytes. High algal biovolume and summer waterfowl grazing seemed to affect maximal pond-scale cover of submerged aquatic vegetation. The presence of waterfowl in cold and spring periods was unrelated to vegetation structure in the consecutive main growth season. In addition, availability of propagules in the sediment did not automatically prompt pond-wide vegetation cover (especially when overruled by high waterfowl densities), nor did it guarantee a position in the submerged macrophyte community. Nonetheless, propagule bank potential was related to the waterbody’s general ecological status, since turbid ponds exhibited impoverished propagule reserves compared to ponds residing in a clear, macrophyte-dominated state. Inadequate recruitment therefore represents a plausible bottleneck for macrophyte establishment. We conclude that phytoplankton-caused turbidity and high waterfowl biomass densities greatly restrict submerged macrophyte abundance. Propagule banks also participate in structuring submerged aquatic vegetation, though a stronger role is reserved for herbivorous waterfowl

Report of a Pest Risk Analysis for Hydrocotyle ranunculoides

Hydrocotyle ranunculoides originates from the American continent and was introduced into the EPPO region as an ornamental plant for tropical aquaria and garden ponds, where it is still sold under its correct name, sometimes under other names (H. vulgaris, H. leucocephala, and H. natans which is a synonym of H. ranunculoides). The plant was first recorded as naturalised in the south-east of the UK in the 1980s (Newman, 2003). Naturalisation in the Netherlands and in Belgium was recorded in the last decade of the twentieth century (Baas & Duistermaat, 1999; Baas & Holverda, 1996; Krabben & Rotteveel, 2003; Verloove 2006, Invasive Species in Belgium Website). Deleterious impacts have been reported in these three countries. The species is also recorded in France, Ireland, Italy, Germany (see EPPO, 2009) but several EPPO countries are still free from H. ranunculoides and there are concerns that it may be able to enter and establish in further countries. This PRA assesses the risks of its further introduction into other EPPO countries and its current and predicted impact. An initial EPPO PRA was performed and approved in 2005. After the proposal of listing this species in the Directive 2000/29, the European Food Safety Authority reviewed the initial PRA and made some comments. The initial PRA is therefore revised in the view of the EFSA comments and of information having become available after the initial PRA (EFSA, 2007)

Contrasting Effects of Historical Sea Level Rise and Contemporary Ocean Currents on Regional Gene Flow of Rhizophora racemosa in Eastern Atlantic Mangroves

Mangroves are seafaring taxa through their hydrochorous propagules that have the potential to disperse over long distances. Therefore, investigating their patterns of gene flow provides insights on the processes involved in the spatial genetic structuring of populations. The coastline of Cameroon has a particular geomorphological history and coastal hydrology with complex contemporary patterns of ocean currents, which we hypothesize to have effects on the spatial configuration and composition of present-day mangroves within its spans. A total of 982 trees were sampled from 33 transects (11 sites) in 4 estuaries. Using 11 polymorphic SSR markers, we investigated genetic diversity and structure of Rhizophora racemosa, a widespread species in the region. Genetic diversity was low to moderate and genetic differentiation between nearly all population pairs was significant. Bayesian clustering analysis, PCoA, estimates of contemporary migration rates and identification of barriers to gene flow were used and complemented with estimated dispersal trajectories of hourly released virtual propagules, using high-resolution surface current from a mesoscale and tide-resolving ocean simulation. These indicate that the Cameroon Volcanic Line (CVL) is not a present-day barrier to gene flow. Rather, the Inter-Bioko-Cameroon (IBC) corridor, formed due to sea level rise, allows for connectivity between two mangrove areas that were isolated during glacial times by the CVL. Genetic data and numerical ocean simulations indicated that an oceanic convergence zone near the Cameroon Estuary complex (CEC) presents a strong barrier to gene flow, resulting in genetic discontinuities between the mangrove areas on either side. This convergence did not result in higher genetic diversity at the CEC as we had hypothesized. In conclusion, the genetic structure of Rhizophora racemosa is maintained by the contrasting effects of the contemporary oceanic convergence and historical climate change-induced sea level rise

Stepping-stone populations in linear landscape elements increase pollen dispersal between urban forest fragments

Background and aims – Understanding how to ensure connectivity by gene flow between insect-pollinated plant populations is essential for designing functional ecological networks in a human-dominated matrix such as in urban settings. Linear landscape elements (LLEs) might contribute to such connectivity by increasing pollen transfer. Methods – Pollen dispersal was investigated for the insect-pollinated herb Primula elatior in urban forest remnants, using fluorescent dye as a pollen analogue, in three study sites comprising population pairs located in fragments connected or not by a wooded LLE. We examined whether the presence of a small patch of plants of P. elatior placed within the LLE (stepping-stone population) might increase pollen dispersal compared to an LLE where P. elatior is absent. Key results – Dye dispersal showed a leptokurtic decay distribution, with most dye transfer events at short distances (80% at less than 15.4–114.8 m) and a maximal distance of 647.5 m. Populations not connected by an LLE, separated by distances of 249 m or more, did not exchange dye, whereas populations that were connected by LLEs (up to 602 m) did show interpopulation dye transfer, suggesting that LLEs function as biological corridors facilitating dye dispersal. The presence of a stepping-stone population of P. elatior within the LLE increased between-population dye transfers (between 1.8 and 3.3 times the proportion of visited individuals) and deposition distances, compared to an LLE with no stepping stone, at least when pollen flow already existed. Conclusions – These results provide evidence that LLEs may be more effective for pollen dispersal when serving as both movement conduit and habitat. In urban settings, developing a network of core populations connected by LLEs comprising small, even temporary, stepping-stone populations should be encouraged

Seagrass radiation after Messinian salinity crisis reflected by strong genetic structuring and out-of-Africa scenario (Ruppiaceae).

Many aquatic plant and seagrass species are widespread and the origin of their continent-wide ranges might result from high gene flow levels. The response of species when extending northwards since the Last Glacial Maximum can be opposed to the structuring of their populations that survived glaciation cycles in southern regions. The peri-Mediterranean is a complex series of sea basins, coastlines, islands and river deltas with a unique history since the Messinian Crisis that potentially influenced allopatric processes of aquatic life. We tested whether vast ranges across Europe and the peri-Mediterranean of a global seagrass group (Ruppia species complexes) can be explained by either overall high levels of gene flow or vicariance through linking population genetics, phylogeography and shallow phylogenetics. A multigene approach identified haplogroup lineages of two species complexes, of ancient and recent hybrids with most of the diversity residing in the South. High levels of connectivity over long distances were only observed at recently colonized northern ranges and in recently-filled seas following the last glaciation. A strong substructure in the southern Mediterranean explained an isolation-by-distance model across Europe. The oldest lineages of the southern Mediterranean Ruppia dated back to the period between the end of the Messinian and Late Pliocene. An imprint of ancient allopatric origin was left at basin level, including basal African lineages. Thus both vicariance in the South and high levels of connectivity in the North explained vast species ranges. Our findings highlight the need for interpreting global distributions of these seagrass and euryhaline species in the context of their origin and evolutionary significant units for setting up appropriate conservation strategies

Molecular evaluation of population Genetic structure of common wild citrus fruit (Citrus medica L.) for developing in situ conservation in the Ha Giang and Tuyen Quang provinces of vietnam

A study was conducted on the dynamic of wild Citrus medica populations in the study areas of the Ha Giang and Tuyen Quang provinces. Genetic structure and gene flow were investigated in representative populations of the area, with a view to develop an in-situ conservation strategy. High levels of intra-population variation, but very low levels of differentiation among populations, indicate that the sampled populations of C. medica have been recently derived from a common ancestor. No significant difference between Ha- and Tu-populations in genetic variation within populations was found, whereas low, but significant differentiation between the two groups, was present. The establishment of a preliminary life graph allows identification of the main factors in the survival and growth of wild populations, which will usefully guide management operations.SCOPUS: cp.kinfo:eu-repo/semantics/publishe

Perspectives for genetic rescue of the extremely fragmented Primula vulgaris populations in The Netherlands: reflecting the future of Belgian populations?

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

Perspectives for genetic rescue of the extremely fragmented Primula vulgaris populations in The Netherlands: reflecting the future of Belgian populations?

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

Analysis of Molecular Variance.

<p>AMOVA) of <i>Ruppia cirrhosa</i> cpDNA haplotypes from 106 sites divided over two continental parts and over twelve seas or regions (d.f. = degree of freedom).</p