Kristine Vander Mijnsbrugge

Morphological and AFLP-based Differentiation within the Taxonomical Complex Section Caninae (subgenus Rosa)

BACKGROUND AND AIMS The taxonomical structure of the polymorphic subgenus Rosa section Caninae is highly complex due to the combination of some unusual features: the unique polyploid chromosomal constitution, the heterogamic canina meiosis, the ability to hybridize interspecifically, and the predominantly matroclinal inheritance. Although most taxonomists agree on the subdivision of the section into three morphologically well-defined groups (Rubigineae, Vestitae, and Caninae), they disagree on the existence of smaller groups such as Tomentellae. The aim was to gain insight in the taxonomical structure and investigate the interpopulation differentiation of the polymorphic section Caninae by analysing morphological and AFLP-based characters of the seven most common Belgian dog-rose taxa. METHODS The intersubsectional and -specific relationships within the dog-roses were examined using morphological and molecular-genetic markers. AFLP data were analysed with basic descriptive genetic statistics because of the lack of Hardy-Weinberg equilibrium due to the polyploid genetic structure and heterogamic meiosis. KEY RESULTS Both the morphological and AFLP-based analyses supported the subdivision of the dog-roses in three well-defined though partly overlapping groups, Rubigineae, Vestitae and Caninae. However, it was not possible to distinguish between the morphologically well-defined taxa within the same subsection using AFLP-based data. In addition, the results suggested a high similarity of Rosa balsamica with subsection Caninae taxa. Small-scale geographical AFLP-based differentiation was observed within several dog-rose taxa. Surprisingly, individuals sampled at one locality and belonging to morphologically distinct dog-rose taxa displayed higher genetic similarities in comparison to their congeners sampled at different localities. CONCLUSIONS The hybridogenic character of the dog-roses was reflected in the vague boundaries between the subsections and on the species level within the subsections. Indications were found for current or historical hybridization on the genetic structure of the population. No morphological or AFLP-based evidence was obtained to support the existence of the separate subsection Tomentellae.

A combined morphometric and AFLP based diversity study challenges the taxonomy of the European members of the complex Prunus L. section Prunus

Multivariate analysis of both endocarp and leaf morphometrics is combined with cluster analysis and Bayesian inference of AFLP markers to assess the morphologic and genetic variation of five European members of Prunus section Prunus (P. cerasifera, P. domestica, P. insititia, P. spinosa, and P. × fruticans). Endocarp morphometrics separate most Prunus taxa studied, but overlap remains between P. domestica and P. cerasifera, and P. spinosa and P. × fruticans. Leaf morphometrics yield better separation of P. domestica and P. cerasifera, but do not allow distinction between P. spinosa and P. × fruticans. Both cluster analysis and PCoA of AFLP markers equally produce three distinct clusters. A first consists of all P. cerasifera samples and the sole P. cocomilia; a second cluster includes all individuals of P. domestica and P. insititia; and a third group comprises all P. spinosa and P. × fruticans samples.

Conservation approaches for autochthonous woody plants in Flanders

Abstract Autochthonous genetic resources of woody plants have become seriously endangered in Flanders because of the particularly low and fragmented forest cover, centuries of intensive forest use in this highly populated area and the wide-spread usage of non-autochthonous planting stock in reforestation and landscape plantings. Intraspecific hybridisation between remnant autochthonous populations and foreign genotypes, which can show inadequate adaptation, may influence the autochthonous genetic constitution and fitness in the long term. As several European countries face similar problems, the objective of this paper is to outline the conservation measures that are taken in Flanders. The central aim is to maintain and create the necessary conditions for natural and flexible evolution of the genetic diversity of autochthonous trees and shrubs. An inventory survey to locate remaining autochthonous populations was started in 1997 and will be completed in 2006. Relict populations are preserved in clonal banks. Central issues are the production of autochthonous planting stock through in situ seed collection, the approval of seed sources and stands and the creation of seed orchards. Conservation actions are discussed.

An evaluation of seed zone delineation using phenotypic and population genomic data on black alder Alnus glutinosa

Summary 1. Delineation of seed zones or provenance regions to preserve local adaptation is a common practice in forestry and restoration, as locally adapted plants generally possess relatively high levels of productivity and resistance. Provenance trials typically quantify the degree of phenotypic divergence among individuals and populations raised under common conditions, which is time-consuming and potentially confounded by phenotypic plasticity and maternal effects. 2. Here, we put forward population genomics, the screening of individual genomes for the genetic signature of adaptation, as a fast and reliable strategy to evaluate seed zone delineation. To illustrate the value of this approach, we quantified the degree of genomic adaptation within and among Belgian black alder Alnus glutinosa provenances and compared results with traditional provenance trials. Distant European reference regions were included to validate the approaches, as larger environmental differences at a European scale are expected to result in larger adaptive responses. 3. Local provenances did not perform better than foreign provenances at the scale of Belgian seed zones, in contrast to the comparisons with the distant European regions. A significant site effect indicated that plastic responses rather than local adaptation explain phenotypic differences among seed zones. The common garden revealed little evidence for adaptation for all measured traits, both among seed zones and among distant regions. 4. The number and strength of genetic outliers was not significantly larger among Belgian seed zones than within these seed zones, but was significantly larger between Belgian seed zones and the distant European reference regions. 5. Synthesis and applications. The lack of adaptive divergence among Belgian seed zones supports an expansion of current provenance regions into larger seed zones. The results also show that population genomics can be an accurate and time-efficient resource to assist decisions on seed sourcing. This highlights the importance of raising awareness of the potential benefits of this novel approach among policy makers, foresters and restoration practitioners.

Effects of harvesting dates and frequencies on above and below-ground dynamics in Belgian wet grasslands

A trial was established to assess the effects of harvesting dates and frequencies on the species, biomass and nutrient dynamics in wet grasslands in Belgium. Above and below-ground developments wer...

The population genomic signature of environmental selection in the widespread insect-pollinated tree species Frangula alnus at different geographical scales

The evaluation of the molecular signatures of selection in species lacking an available closely related reference genome remains challenging, yet it may provide valuable fundamental insights into the capacity of populations to respond to environmental cues. We screened 25 native populations of the tree species Frangula alnus subsp. alnus (Rhamnaceae), covering three different geographical scales, for 183 annotated single-nucleotide polymorphisms (SNPs). Standard population genomic outlier screens were combined with individual-based and multivariate landscape genomic approaches to examine the strength of selection relative to neutral processes in shaping genomic variation, and to identify the main environmental agents driving selection. Our results demonstrate a more distinct signature of selection with increasing geographical distance, as indicated by the proportion of SNPs (i) showing exceptional patterns of genetic diversity and differentiation (outliers) and (ii) associated with climate. Both temperature and precipitation have an important role as selective agents in shaping adaptive genomic differentiation in F. alnus subsp. alnus, although their relative importance differed among spatial scales. At the ‘intermediate’ and ‘regional’ scales, where limited genetic clustering and high population diversity were observed, some indications of natural selection may suggest a major role for gene flow in safeguarding adaptability. High genetic diversity at loci under selection in particular, indicated considerable adaptive potential, which may nevertheless be compromised by the combined effects of climate change and habitat fragmentation.

Conservation measures for Rosa arvensis Huds. in Flanders (Belgium) based on congruent genetic and phenotypic population differentiation

Rosa arvensis is a naturally rare and scattered indigenous wild rose species in Flanders, the northern part of Belgium. As is the case for many light demanding woody species in this area, it is currently threatened by habitat fragmentation and destruction due to high human pressure. Recent inventories revealed a restricted distribution pattern for this rose, concentrated mainly in two regions of the south western part of Flanders. Surprisingly, strong differentiation was observed among natural populations in these two proximate regions in both an AFLP-based and a morphological analysis. A common garden experiment indicated a partly genetic basis for the morphological divergence. Additionally, the AFLP analysis of roses sampled in the same forested area within one of the two regions resulted in two differentiated gene pools. Possible causes for the observed differentiation can be adaptive divergence, founder effects and/or historical hybridisation with dogroses. Together, the congruent genetic and morphometric differentiation between the two geographic regions urges a cautious approach in conservation programs.

A combination of fruit and leaf morphology enables taxonomic classification of the complex Q. robur L. – Q. x rosacea Bechst. – Q. petraea (Matt.) Liebl. in autochthonous stands in Flanders

Abstract Hybrids between Quercus robur and Q. petraea have been a sought topic of many studies in Europe during the last decades. Here, leaf and fruit morphology were studied in five oak stands where both species occur naturally intermixed. The stands are relicts of old, possibly medieval coppice wood. Twenty two leaf characters and nine fruit characters were assessed on three leaves and three fruits per tree and for thirty trees per stand. A principal component analysis (PCA) resulted in a bimodal distribution with restricted overlap along the first component when both leaf and fruit data were processed together. For leaf and fruit data separately, the analysis produced only continuous clusters of trees. Two types of putative hybrids can be defined that either show a petiole length of the leaf (PL) according to Q. robur and a petiole length of the fruit (FP1) according to Q. petraea, or vice versa. These hybrids cluster within both groups of the PCA analysis, but not all are situated close to or in the intermediate area between the groups. A lowered mean relative number of developed acorns in the hybrid groups in comparison to their putative maternal parent, based on the assumption of matroclinal inheritance of PL, is observed. This might indicate a reduced ability for successful fertilisation in the hybrids. These results suggest the presence of putative hybrids and introgressed forms within the morphological distinct Q. robur and Q. petraea groups and argument for a taxonomically defined Q. x rosacea based on PL and FP1 limits.

Early Summer Drought Stress During the First Growing Year Stimulates Extra Shoot Growth in Oak Seedlings (Quercus petraea)

More severe summer droughts are predicted for mid-latitudes in Europe. To evaluate the impact on forest ecosystems and more specifically on forest regeneration, we studied the response to summer drought in oak seedlings (Quercus petraea). Acorns were collected from different mother trees in three stands in Belgium, sown in pots and grown in non-heated greenhouse conditions. We imposed drought on the seedlings in early summer by first watering the pots to saturation and then stopping any watering. Weight of the pots and stomatal conductance were regularly measured. Re-watering followed this drought period of 5 weeks. Height of the seedlings and apical bud development were observed. Stomatal resistance increased toward the end of the experiment in the drought-treated group and was restored after re-watering. The seedlings from the drought treatment displayed a higher probability to produce additional shoot growth after re-watering (p ≤ 0.05). A higher competition for water (two plants per pot) increased this chance. Although this chance was also higher for smaller seedlings, the actual length of the extra growth after re-watering was higher for larger seedlings (p ≤ 0.01). Both in the drought-treated and in the control group the autochthonous provenance growing on a xeric site produced less extra shoots compared to the two other provenances. Finally, stressed plants showed less developed apical buds compared to the control group after re-watering, suggesting a phenological effect on the growth cycle of oaks (p ≤ 0.0001). The higher chance for an extra shoot growth after the drought period can be considered as a compensation for the induced growth arrest during the drought period.

Morphological dissection of leaf, bud and infructescence traits of the interfertile native A. glutinosa and non-native A. incana in Flanders (northern part of Belgium)

Key messageSpontaneous hybrids in natural regenerations ofA. glutinosacannot be excluded ifA. incanais occurring in the neighbourhood, and has to be taken into account when restoring swamp forests.AbstractSwamp forests with A. glutinosa are endangered in Flanders due to habitat destruction and fragmentation, and therefore restoration is promoted. At the other hand, frequent plantations of A. incana, a non-native species in Flanders (northern part of Belgium), may facilitate spontaneous hybrids between the two species as they are interfertile. We assessed phenotypic variability of both species and putative hybrids using nine leaf, five infructescence and eight bud characters, and additionally height growth. We focussed on a field trial established with seeds collected in fifteen autochthonous A. glutinosa stands and on A. incana trees of unknown origin sampled at five locations in Flanders. We applied geometric morphometric methods, principal component analyses and mixed modelling methods. We found three individuals with intermediate morphological traits between A. glutinosa and A. incana among the eleven pedigrees in one of the two natural A. glutinosa populations where also planted A. incana was present. Their height growth was variable and only one of the three fructified, with seeds showing a normal germination success. These individuals can be hybrids with intermediate features between the parental species or they may display the natural variability of the latter with overlapping traits. Other individuals with intermediate leaf shape but less intermediate features for other leaf, bud and infructescence characters, found in the pedigrees of additional four A. glutinosa populations, may point to the relative wide natural variability for leaf shape within the parental species. Alternatively, these may concern backcrossed individuals or matro/patroclinal inheritance in hybrids. An inter-population variance study showed that several leaf characters are under a relative genetic control, underlining the importance of vegetative organs in taxonomic treatment of species complexes. The occurrence of spontaneous hybrids in natural regenerations of A. glutinosa cannot be excluded if A. incana is present in the neighbourhood, and has to be taken into account both in seed collections for the creation of autochthonous planting stock as when restoring swamp forests.Spontaneous hybrids in natural regenerations of A. glutinosa cannot be excluded if A. incana is occurring in the neighbourhood, and has to be taken into account when restoring swamp forests. Swamp forests with A. glutinosa are endangered in Flanders due to habitat destruction and fragmentation, and therefore restoration is promoted. At the other hand, frequent plantations of A. incana, a non-native species in Flanders (northern part of Belgium), may facilitate spontaneous hybrids between the two species as they are interfertile. We assessed phenotypic variability of both species and putative hybrids using nine leaf, five infructescence and eight bud characters, and additionally height growth. We focussed on a field trial established with seeds collected in fifteen autochthonous A. glutinosa stands and on A. incana trees of unknown origin sampled at five locations in Flanders. We applied geometric morphometric methods, principal component analyses and mixed modelling methods. We found three individuals with intermediate morphological traits between A. glutinosa and A. incana among the eleven pedigrees in one of the two natural A. glutinosa populations where also planted A. incana was present. Their height growth was variable and only one of the three fructified, with seeds showing a normal germination success. These individuals can be hybrids with intermediate features between the parental species or they may display the natural variability of the latter with overlapping traits. Other individuals with intermediate leaf shape but less intermediate features for other leaf, bud and infructescence characters, found in the pedigrees of additional four A. glutinosa populations, may point to the relative wide natural variability for leaf shape within the parental species. Alternatively, these may concern backcrossed individuals or matro/patroclinal inheritance in hybrids. An inter-population variance study showed that several leaf characters are under a relative genetic control, underlining the importance of vegetative organs in taxonomic treatment of species complexes. The occurrence of spontaneous hybrids in natural regenerations of A. glutinosa cannot be excluded if A. incana is present in the neighbourhood, and has to be taken into account both in seed collections for the creation of autochthonous planting stock as when restoring swamp forests.