Frequent cytoplasmic exchanges between oak species that are not closely related: Quercus suber and Q. ilex in Morocco

Chloroplast (cp) and mitochondrial (mt) DNA variation were studied in 97 populations of cork oak (Quercus suber) in Morocco; in 31 of these populations, holm oak (Quercus ilex), a clearly distinct species, also occurred and was compared with Q. suber. Three cpDNA and one mtDNA primer pairs were used in the survey, each in combination with one restriction enzyme. Six haplotypes belonging to two very divergent lineages were detected; one lineage predominates in each species, and is probably ancestral, as inferred from comparisons with other oak species. In the mixed-species populations, cytoplasmic genomes were frequently shared across species, as indicated by an introgression ratio of 0.63. This index is a new measure of the propensity of species to share locally genetic markers, varying from zero (complete differentiation) to one (no differentiation). By contrast, more closely related deciduous oak species (Q. robur, Q. petraea and Q. pubescens) have introgression ratios varying from 0.82 to 0.97. The introgression events appear to have been more frequent in the direction Q. ilex (female) x Q. suber (male), a finding which seems attributable to the flowering phenology of these two species. This asymmetry may have favoured immigration of Q. suber beyond its main range, in regions already colonized by Q. ilex. There, rare hybridization and further introgression through long distance pollen flow have established populations that are morphologically indistinguishable from Q. suber but that have cytoplasmic genomes originating from the local Q. ilex populations.     

Endemic North African Quercus afares Pomel originates from hybridisation between two genetically very distant oak species (Q. suber L. and Q. canariensis Willd.): evidence from nuclear and cytoplasmic markers

Hybridisation is a potent force in plant evolution, although there are few reported examples of stabilised species that have been created through homoploid hybridisation. We focus here on Quercus afares, an endemic North African species that combines morphological, physiological and ecological traits of both Q. suber and Q. canariensis, two phylogenetically distant species. These two species are sympatric with Q. afares over most of its distribution. We studied two Q. afares populations (one from Algeria and one from Tunisia), as well as several populations of both Q. suber and Q. canariensis sampled both within and outside areas where these species overlap with Q. afares. A genetic analysis was conducted using both nuclear (allozymes) and chloroplastic markers, which shows that Q. afares originates from a Q. suber x Q. canariensis hybridisation. At most loci, Q. afares predominantly possesses alleles from Q. suber, suggesting that the initial cross between Q. suber and Q. canariensis was followed by backcrossing with Q. suber. Other hypotheses that can account for this result, including genetic drift, gene silencing, gene conversion and selection, are discussed. A single Q. suber chlorotype was detected, and all Q. afares individuals displayed this chlorotype, indicating that Q. suber was the maternal parent. Q. afares is genetically, morphologically and ecologically differentiated from its parental species, and can therefore be considered as a stabilised hybrid species.     

Three divergent rDNA clusters predate the species divergence in Quercus petraea (Matt.) Liebl. and Quercus robur L

Quercus petraea and Quercus robur are two closely related oak species that frequently hybridize. We sequenced 70 clones containing the 5.8S and ITS2 regions of ribosomal DNA (rDNA) from these two species and did not detect a species-specific difference. Surprisingly, three divergent (up to 12.6%) rDNA families were identified in both species, indicating that they predate the speciation event. Despite a large between-rDNA-families divergence, rDNA sequences were very similar within families, suggesting ongoing concerted evolution. Expression analysis, relative-rate tests, and mutation spectrum analyses indicated that only a single rDNA family is functional. We propose that past hybridization events, combined with nucleolar dominance, were the evolutionary processes underlying the contemporary rDNA variability in Q. petraea and Q. robur.     

A Musca domestica satellite sequence detects individual polymorphic regions in insect genome.

A recombinant plasmid, pHMd.24, was constructed which contains an array of a 24 bp sequence from the genome of the Musca domestica. This sequence hybridizes to sites occurring at various genomic locations in different housefly strains. The pHMd.24 insert has a structural organisation similar to satellite DNA sequences and hybridizes to homologous repeated sequences representing a small fraction of the M. domestica genome. Interestingly, this clone reveals polymorphic fragments from DNA isolated from single houseflies, thus generating an insect DNA fingerprint. In addition, the segregation of the fragments detected by hybridisation in a M. domestica pedigree indicates a transmission that follows mendelian inheritance.     

Species distinction in Irish populations of Quercus petraea and Q. robur: morphological versus molecular analyses

BACKGROUND AND AIMS: Populations of oak (Quercus petraea and Q. robur) were investigated using morphological and molecular (AFLP) analyses to assess species distinction. The study aimed to describe species distinction in Irish oak populations and to situate this in a European context. METHODS: Populations were sampled from across the range of the island of Ireland. Leaf morphological characters were analysed through clustering and ordination methods. Putative neutral molecular markers (AFLPs) were used to analyse the molecular variation. Cluster and ordination analyses were also performed on the AFLP markers in addition to calculations of genetic diversity and F-statisitcs. KEY RESULTS: A notable divergence was uncovered between the morphological and molecular analyses. The morphological analysis clearly differentiated individuals into their respective species, whereas the molecular analysis did not. Twenty species-specific AFLP markers were observed from 123 plants in 24 populations but none of these was species-diagnostic. Principal Coordinate Analysis of the AFLP data revealed a clustering, across the first two axes, of individuals according to population rather than according to species. High F(ST) values calculated from AFLP markers also indicated population differentiation (F(ST) = 0.271). Species differentiation accounted for only 13 % of the variation in diversity compared with population differentiation, which accounted for 27 %. CONCLUSIONS: The results show that neutral molecular variation is partitioned more strongly between populations than between species. Although this could indicate that the populations of Q. petraea and Q. robur studied may not be distinct species at a molecular level, it is proposed that the difficulty in distinguishing the species in Irish oak populations using AFLP markers is due to population differentiation masking species differences. This could result from non-random mating in small, fragmented woodland populations. Hybridization and introgression between the species could also have a significant role.     

Genetic variation and differentiation within a natural community of five oak species (Quercus spp.)

Chloroplast DNA and two categories of nuclear markers - isozymes and microsatellites - were used to examine a very rich natural community of oaks (Quercus spp.) situated in west-central Romania. The community consists of five oak species: Q. robur, Q. petraea, Q. pubescens, and Q. frainetto - that are closely related -, and Q. cerris. A total of five chloroplast haplotypes was identified. Q. cerris was fixed for a single haplotype. The other four species shared the two most common haplotypes. One haplotype was confined to Q. robur and a very rare one was restricted to Q. petraea. Both types of nuclear markers revealed a larger genetic variation for Q. pubescens and Q. petraea than for Q. frainetto and Q. robur, although the differences between species are in most cases not significant. At the nuclear level, Q. cerris could be clearly separated from the other four oak species confirming the taxonomic classification. Regardless of the estimate used, the levels of polymorphism revealed by microsatellites were much higher than those based on isozymes. For the four closely related species the overall genetic differentiation was significant at both categories of nuclear markers. Several loci, such as Acp-C for isozymes, and ssrQpZAG36 and ssrQrZAG96 for microsatellites were very useful to discriminate among species. However, the level of differentiation varied markedly between pairs of species. The genetic affinities among the species may reflect different phylogenetic distances and/or different rates of recurrent gene flow at this site.     

QTL analysis of leaf morphological characters in a Quercus robur full-sib family (Q. robur x Q. robur ssp. slavonica)

The distinction between white oak species (section Quercus sensu stricto) is largely based on leaf morphological characters. There is, however, considerable within-species variation and no single species-diagnostic character, possibly due to phenotypic plasticity and/or underlying genetic variation. The aim of the present study was to identify quantitative trait loci (QTL) underlying the high within-species variation for leaf morphological characters in an F(1) full-sib family derived from a cross between Q. robur and Q. robur ssp. slavonica. In accordance with an earlier QTL mapping study in an intraspecific Q. robur full-sib family, polygenic inheritance was detected for leaf morphological characters that are used to discriminate between the species Quercus robur and Q. petraea. QTLs were distributed over ten linkage groups, showed a moderate effect in terms of phenotypic variance explained (PVE) in the mapping pedigree (3.6-9.6%), but accounted for a considerable amount of the parental differences. Co-localisation of QTLs on the same linkage group in different genetic backgrounds was found for the number and percentage of intercalary veins (NV, PV) on linkage group 3 and for NV on linkage group 5, revealing a high congruence in the relative QTL positions. The generally low correspondence of the other QTLs in the different mapping pedigrees may be an effect of the genetic background and of the environment. In conclusion, leaf morphological characters were found to be under polygenic control, and a comparison to earlier published results led to the identification of two QTLs that were stable across different genetic backgrounds.     

QTL analysis of leaf morphological characters in a Quercus robur full-sib family (Q. robur × Q. robur ssp. slavonica)

The distinction between white oak species (section Quercus sensu stricto ) is largely based on leaf morphological characters. There is, however, considerable within-species variation and no single species-diagnostic character, possibly due to phenotypic plasticity and/or underlying genetic variation. The aim of the present study was to identify quantitative trait loci (QTL) underlying the high within-species variation for leaf morphological characters in an F₁ full-sib family derived from a cross between Q. robur and Q. robur ssp. slavonica . In accordance with an earlier QTL mapping study in an intraspecific Q. robur full-sib family, polygenic inheritance was detected for leaf morphological characters that are used to discriminate between the species Quercus robur and Q. petraea . QTLs were distributed over ten linkage groups, showed a moderate effect in terms of phenotypic variance explained (PVE) in the mapping pedigree (3.6–9.6%), but accounted for a considerable amount of the parental differences. Co-localisation of QTLs on the same linkage group in different genetic backgrounds was found for the number and percentage of intercalary veins (NV, PV) on linkage group 3 and for NV on linkage group 5, revealing a high congruence in the relative QTL positions. The generally low correspondence of the other QTLs in the different mapping pedigrees may be an effect of the genetic background and of the environment. In conclusion, leaf morphological characters were found to be under polygenic control, and a comparison to earlier published results led to the identification of two QTLs that were stable across different genetic backgrounds.     

Genome scanning for interspecific differentiation between two closely related oak species [Quercus robur L. and Q. petraea (Matt.) Liebl.

Interspecific differentiation values (G(ST)) between two closely related oak species (Quercus petraea and Q. robur) were compiled across different studies with the aim to explore the distribution of differentiation at the genome level. The study was based on a total set of 389 markers (isozymes, AFLPs, SCARs, microsatellites, and SNPs) for which allelic frequencies were estimated in pairs of populations sampled throughout the sympatric distribution of the two species. The overall distribution of G(ST) values followed an L-shaped curve with most markers exhibiting low species differentiation (G(ST) < 0.01) and only a few loci reaching >10% levels. Twelve percent of the loci exhibited significant G(ST) deviations to neutral expectations, suggesting that selection contributed to species divergence. Coding regions expressed higher differentiation than noncoding regions. Among the 389 markers, 158 could be mapped on the 12 linkage groups of the existing Q. robur genetic map. Outlier loci with large G(ST) values were distributed over 9 linkage groups. One cluster of three outlier loci was found within 0.51 cM; but significant autocorrelation of G(ST) was observed at distances <2 cM. The size and distribution of genomic regions involved in species divergence are discussed in reference to hitchhiking effects and disruptive selection.     

The Description of Clones of Quercus robur L. and Q. petraea (Matt.) Liebl. with Microsatellites and AFLP in an Ancient Woodland

Abstract: In densely populated areas autochthonous Quercus robur L. (pedunculate oak) and Q. petraea (Matt.) Liebl. (sessile oak) (Fagaceae) populations have been maintained as ancient devastated woodlands. The continuous cutting, grazing and resprouting of such woodlands has enabled the development of clonal structures. For conservation purposes, an analysis of the actual number, size and spatial distribution of clones is necessary, especially when there is an interest in genetic variation of the population. This study describes for the first time - based on microsatellite and AFLP™ analysis - clones in an autochthonous mixed Q. robur and Q. petraea population that has been coppiced and grazed for several centuries. Based on six microsatellite loci and 69 polymorphic AFLP markers, only 14 unique genotypes were detected in a plot that consisted of 80 trees. Clones were observed for both Q. robur and Q. petraea. The largest clone diameters were observed for Q. robur, with distances up to 5.8 m. The observed clone sizes may indicate the age of the trees.     

Natural hybridisation among Quercus glabrescens,Q. rugosa and Q. obtusata (Fagaceae): Microsatellites and secondary metabolites markers

• Natural hybridisation has significant ecological, genetic and evolutionary consequences altering morphological and chemical characters of individuals. Quercus glabrescens, Q. rugosa and Q. obtusata are white oak species well separated by their morphological characters when they occur in allopatry in Mexican temperate forests. However, in sympatry, individuals with atypical morphology have been observed, suggesting hybridisation events.
• In this study, we determined, with microsatellites and secondary metabolites, if interspecific gene flow occurs when these three oak species coexist in sympatry. In total, 180 individuals belonging to seven populations [three allopatric (one for each parental species) and four sympatric sites] were analysed.
• Allopatric populations represent well‐defined genetic groups and the sympatric populations showed genetic evidence of hybridisation between Q. glabrescens × Q. rugosa and Q. glabrescens × Q. obtusata. The hybridisation percentage varied between sites and combination of involved species. We registered the presence of unique flavonoid compounds for Q. glabrescens (caffeic acid and flavonol 2), Q. rugosa (flavonol 5) and Q. obtusata (flavonol 1). Three compounds (quercetin rhamnoside, flavonol 3 and alkyl coumarate) were expressed in all taxa. Finally, the hybrid genotypes identified in this study (Q. glabrescens × Q. rugosa and Q. glabrescens × Q. obtusata) showed specific chemical profiles, resulting from a combination of those of their parental species.
• These results show that hybridisation events between these oak species alter chemical expression of secondary metabolites, creating a mosaic of resources and conditions that provide the substrate for different combinations of foliar‐associated species such as herbivores, endophytic fungi or epiphyte plants.

     

Past distribution and ecology of the cork oak (Quercus suber) in the Iberian Peninsula: a pollen-analytical approach

Abstract.  This study presents pollen-analytical data from continental and offshore Iberian Peninsula sites that include pollen curves of Quercus suber , to provide information on the past distribution and ecology of the cork oak ( Q. suber ). Results centre on a new pollen record of Navarrés (Valencia, eastern Spain), which shows that the cork oak survived regionally during the Upper Pleistocene and was important during a mid-Holocene replacement of a local pine forest by Quercus -dominated communities. This phenomenon appears linked to the recurrence of fire and reinforces the value of the cork oak for reforestation programmes in fire-prone areas. In addition to Navarrés, other Late Quaternary pollen sequences (Sobrestany, Casablanca-Almenara, Padul, SU 8103, SU8113, 8057B) suggest last glacial survival of the cork oak in southern and coastal areas of the Peninsula and North Africa. Important developments also occur from the Late Glacial to the middle Holocene, not only in the west but also in the eastern Peninsula. It is suggested that, in the absence of human influence, Q. suber would develop in non-monospecific forests, sharing the arboreal stratum both with other sclerophyllous and deciduous Quercus and Pinus species.     

Differences in fine-scale genetic structure and dispersal in Quercus ilex L. and Q. suber L.: consequences for regeneration of mediterranean open woods

Cork oak (Quercus suber L.) and holm oak (Q. ilex L.) are among the most important tree species (economically and ecologically) in the Western Mediterranean region, where they define unique open woods (created and maintained by man) known as 'dehesas' in Spain. However, these formations are under increasing threat due to the lack of regeneration. We have analysed spatial genetic structure in a mixed parkland; inferences about gene dispersal have also been performed, according to the isolation by distance model. Noticeable differences have been detected between the species, despite their similar ecological roles. Restricted effective dispersal leads to kin structures in cork oak, up to 70 m, while no genetic structure is observed in holm oak. Our results suggest a very effective dispersal for the latter, with a local historical gene flow estimated between 55 and 95 m. This is the first time regeneration of Mediterranean oak parklands has been assessed from a genetic perspective. Effective gene flow detected for holm oaks allows us to discount the risk of inbreeding over successive generations. Thus, regeneration of Q. ilex dehesas will just require action directed to help the settlement of the saplings (such as limiting grazing). However, in those cases where densities are too low, more intense forestation (such as plantation and/or establishment of appropriate shelter) will be needed. The 'density threshold' for initiating regeneration will probably be higher for cork oak, due to its more limited dispersal and minor full-light tolerance.     

AFLP markers demonstrate local genetic differentiation between two indigenous oak species [ Quercus robur L. and Quercus petraea (Matt.) Liebl.] in Flemish populations

The nuclear genetic variation within and between four sessile ( Q. petraea) and six pedunculate ( Q. robur) autochthonous Flemish oak populations was investigated with AFLP markers. One sessile and one pedunculate oak population were additionally screened for detailed leaf characteristics using an image analysis system. Principal coordinate analysis on the AFLP data classified the oaks in two main groups, according to their taxonomic status. No species-specific AFLP markers were found using four primer combinations, but marker frequency differences up to 71% were recorded between both species. Analysis of the genetic structure showed that the divergence between species, as observed by ordination, was significant. Both species revealed similar diversity levels. A smaller though significant differentiation was also revealed for both species among populations within species. Molecular and morphology based approaches showed a high degree of consistency. Screening of 60 AFLP primer combinations using a bulking strategy did not allow identifying species-specific markers, which supports the conclusions reached in previous studies. The distribution of genetic variability at the species and at the population level is discussed.     

Comparison of Isoprene Emission, Intercellular Isoprene Concentration and Photosynthetic Performance in Water-Limited Oak (Quercus pubescens Willd. and Quercus robur L.) Saplings

Abstract: The influence of prolonged water limitation on leaf gas exchange, isoprene emission, isoprene synthase activities and intercellular isoprene concentrations was investigated under standard conditions (30 °C leaf temperature and 1000 μmol photons m^-2 s^-1 PPFD) in greenhouse experiments with five-year-old pubescent oak ( Quercus pubescens Willd.) and four-year-old pedunculate oak ( Quercus robur L.) saplings. Net assimilation rates proved to be highly sensitive to moderate drought in both oak species, and were virtually zero at water potentials (Ψ_pd) below - 1.3 MPa in Q. robur and below - 2.5 MPa in Q. pubescens . The response of stomatal conductance to water stress was slightly less distinct. Isoprene emission was much more resistant to drought and declined significantly only at Ψ_pd below - 2 MPa in Q. robur and below - 3.5 MPa in Q. pubescens . Even during the most severe water stress, isoprene emission of drought-stressed saplings was still approximately one-third of the control in Q. robur and one-fifth in Q. pubescens . Isoprene synthase activities were virtually unaffected by drought stress. Re-watering led to partial recovery of leaf gas exchange and isoprene emission. Intercellular isoprene concentrations were remarkably enhanced in water-limited saplings of both oak species during the first half of the respective drought periods with maximum mean values up to ca. 16 μl l^-1 isoprene for Q. pubescens and ca. 11 μl l^-1 isoprene for pedunculate oak, supporting the hypothesis that isoprene serves as a short-term thermoprotective agent in isoprene-emitting plant species.     

Hybridisation and colonisation dynamics in European oaks

Summary

Extensive hybridisation between the two sympatric species Quercus petraea and Q.robur is suggested by the near lack of genetic differentiation between the two species and supported by controlled crosses and mating system analysis in mixed stands. Further ecological and genetic evidence suggest that hybridisation does not impede the ecological specialisation of the two species, raising the issue of its evolutionary significance in oaks. Preferential unidirectional hybridization (pollen Q. petraea to ovule Q. robur) has been shown in various mixed stands and facilitates the introduction of sessile oak in existing pedunculate stands. If this unidirectional trend is reinforced in later backcrosses, then hybridisation leads to the dispersal of Q. petraea in existing stands of Q. robur. Hybridisation can therefore be seen as a ‘pollen-mediated’ dispersal mechanism, and has most likely contributed to the rapid migration of Q. petraea in Europe. Given the extant distribution of the species in Europe, migration through pollen swamping should be seen at the edges of the natural distribution of Q. petraea where the demographic imbalance of the two species will reinforce backcrosses.     

Detection of herpes simplex virus type-2 DNA restriction fragments in human cervical carcinoma tissue.

DNA extracted from eight human cervical carcinomas, one lymph node metastasis and related control tissue was examined for the presence of herpes simplex virus (HSV) DNA sequences. Southern blot transfers of tumour and control DNA were hybridised with radioactively labelled cloned probes representing 70% of the HSV-2 genome. Specific hybridisation to HSV DNA sequences was observed in one of eight carcinoma tissues analysed. Hybridisation of HSV-2 DNA probes to BamHI and XhoI restriction enzyme fragments of tumour cell DNA which co-migrated with authentic HSV-2 viral fragments identified co-linear HSV-2 DNA sequences comprising 3% of the HSV-2 genome, between map coordinates 0.582 and 0.612. The remaining eight tumour and all control tissues analysed, showed no specific hybridisation to any of the probes used at levels of sensitivity which would detect 0.5 copies/cell of HSV-2 DNA restriction fragments of 2 kb or greater.     

Plasmid-homologous sequences in the chromosome of plasmidless Coxiella burnetii Scurry Q217.

Chromosomal DNA from Coxiella burnetii Scurry Q217 was screened for the presence of plasmid-homologous sequences. Total DNA from Scurry Q217 was digested with NotI, and the resulting DNA fragments were separated by contour-clamped homogeneous electric field pulsed-field gel electrophoresis (CHEF-PFGE). Following hybridization with biotin-labeled QpH1 plasmid as a probe, two DNA fragments of 40 and 170 kb were identified as targets. These fragments were cloned, and subclones containing QpH1-homologous sequences were completely sequenced. The physical mapping of DNA fragments was achieved by PCR with primers derived from adjacent fragments, and a total of 18,360 bp was sequenced. Within the QpH1-homologous region spanning 16,624 bp, homology was as high as 99%. Deletions were identified within EcoRI fragments A(H)-C(H)-K(H)-B(H) (13,490 bp) and J(H)-G(H)-E(H)-L+-D(H) (6,509 bp) and in fragment A(H) alone (619 bp). An insertion of 744 bp was identified within the JDc region of Scurry Q217. A search for putative coding regions identified a total of 17 open reading frames (ORFs). Compared to plasmid QpH1, 6 ORFs were identical, 5 ORFs were different in size, 6 ORFs were newly generated, and 25 ORFs were lost. It was found that plasmid-homologous sequences in Scurry Q217 were of chromosomal origin.     

Potential host plants of Corythucha arcuata (Het., Tingidae) in Europe: a laboratory study

Abstract:  The oak lace bug Corythucha arcuata (Say) (Het., Tingidae), native to North America, was found in Europe on Quercus robur L. and other oaks in the spring of 2000. The potential host plant range of this species in Europe and its development time were investigated in a laboratory study. An assay was performed on leaf cuts of different plant species. On the deciduous European oaks ( Q. robur , Quercus pubescens Willd, Quercus petraea (Mattuschka) Liebl., Quercus cerris L.), as well as Rubus ulmifolius Schott. and Rubus idaeus L., most of the lace bugs (>50%) reached the adult stage; on Castanea sativa Mill., Rubus caesius L. and Rosa canina L., a reduced number of individuals (<25%) reached the adult stage. No nymphs survived on Quercus rubra L. (mentioned in literature as a host plant), on the evergreen oaks Quercus suber L. and Quercus ilex L., on Malus domestica Borkh. and four tested maple species. On plant species where the lace bug reached the adult stage, the development time varied from 13 to 27 days. On European deciduous oak species, the development time was longer on leaves taken in late summer (September) than on those of late spring (June); on the contrary, such differences were not observed on Rubus species, and Castanea sativa .     

Contrasting nuclear and cytoplasmic exchanges between phylogenetically distant oak species (Quercus suber L. and Q. ilex L.) in Southern France: inferring crosses and dynamics

Gene flow is particularly frequent in the genus Quercus (oaks), especially between closely related species. We focus here on Quercus ilex and the cork-producing Quercus suber , which occasionally hybridize although they are phylogenetically markedly separated. Morphological observations were combined with both allozymic and chloroplastic diagnostic markers to characterize hybridization and introgression and to infer their dynamics in two French regions (French Catalonia and Provence), which are separated by several hundred kilometres. Some hybrids were found in both regions, indicating recent hybridization events. As expected from previous studies, most hybrids resulted from ♀ Q. ilex  × ♂ Q. suber crosses, but our data showed that the reciprocal cross is also possible. Partial independence between nuclear and chloroplastic introgression was observed in the two species. Nuclear introgression was limited in both species and both regions, with no preferred direction. In Provence, chloroplastic introgression was very rare in both species. Conversely, all Q. suber individuals from French Catalonia were introgressed by Q. ilex chlorotypes. This might be explained by introgression in the Iberian Peninsula antedating the first occurrence of the two species in French Catalonia. We also observed a new chlorotype that was created locally, and was exchanged between the two species. However, the two species still remain genetically differentiated. The dynamics and complexity of exchanges and the factors determining them (including human management of Q. suber ) are discussed.