Differential rates of invasion in three related alien oak gall wasps (Cynipidae: Hymenoptera)

Abstract. Three related species of oak gall wasps, Andricus corruptrix (Schlechtendal), A. kollari (Hartig) and A. lignicola (Hartig) have entered Britain since the introduction of Turkey oak, Quercus cerris L. in 1735. Their lifecycles involve alternating generations between an agamic generation on the native oak species (Q. petraea, Q. robur and their hybrid Q. x. rosacea), and a smaller, sexual generation on the alien Q. cerris. In examining the distributions of these insects and Q. cerris, we hypothesized that: (1) the invasion will spread more rapidly in places where both host trees are equally abundant than through regions where one of the tree species is substantially less common than the other; (2) interspecific competition between these bud‐galling species will lead to a negative correlation between their abundances at a particular site; (3) differential recruitment of natural enemies from the native hymenopteran fauna will slow the rate of spread in a species‐specific manner. A. kollari arrived nearly 200 years ago and is now found throughout the British Isles, wherever Turkey oak is grown. A. lignicola and A. corruptrix have been here for 30 years, after establishing in S.E. England. A. lignicola is in its final rapid stages of range expansion across England, southern Scotland and N.E. Scotland. A. corruptrix is just beginning to spread through Central and S.W. England. It has occupied proportionally fewer sites behind its invasion front than have the other two species, but is no less abundant at these sites. Nevertheless, distance leaps of up to 50 km were identified in A. lignicola in N.E. Scotland, and the possibility of long‐distance transport of infected trees through the horticulture and forestry trades remains. The co‐occurrence of mature individuals of both host Quercus species does appear to have increased their rates of colonization in A. lignicola and A. corruptrix. There is no evidence, however, to suggest that interspecific competition between the three alien gall formers is an important factor in determining their distributions and abundance within their invaded ranges. All three species have recruited parasitoids and inquilines rapidly from the native fauna; attack rates were highly variable, but showed no evidence of density dependence across sites.     

Allozyme variation in cork oak (Quercus suber L.): the role of phylogeography and genetic introgression by other Mediterranean oak species and human activities

 Genetic variation in the cork oak (Quercus suber L.) was investigated using 11 loci from seven enzyme systems in 40 populations sampled over the entire distribution of this species in the western Mediterranean Basin. Mean heterozygosity values over the polymorphic loci (Ho=0.283), the percentage of polymorphic populations (M=0.76), and the total genetic diversity (Ht=0.31) from which 11% was accounted for among-population variation, are among the highest recorded in oak species. In contrast to previous results in holm oak (Q. ilex L.), another evergreen species in the same area, cork oak possessed a smaller allele pool and a lower average number of alleles per locus and per population (A=2.0). More particularly, very few low-frequency alleles were observed in cork oak except for eight populations in which allozyme polymorphism at locus Pgi 1, diagnostic between both species, indicates that these low-frequency alleles are introgressed from holm oak. On the basis of the genetic distance estimated from allozyme frequencies, 32 of the 40 cork oak populations studied were classified into two very distinct sets which also corresponded to distinct geographic areas. One set gathered together the 18 populations from the Iberian peninsula and two adjacent areas in France, i.e. the centre of origin of cork oak, according to paleobotanical data. This set was characterized by a larger allele pool, a higher within-population genetic diversity and a lower differentiation between populations than was observed in the other set, which comprised the populations from North Africa, Sicily, Sardinia, Corsica, continental Italy and the region of Provence (southeastern France). In these more southern and eastern disjunct areas, cork oak migration from Iberia may have occurred at different periods since the end of the Tertiary. The possible effect of human activity on cork oak genetic structure, i.e. the selection of good-quality cork, acorn over-use for animal food, and even human nutrition, is discussed. Received: 3 March 1998 / Accepted: 19 March 1998     

Molecular evidence for hybrid origin of Quercus crenata Lam. (Fagaceae) from Q. cerris L. and Q. suber L.

Abstract

Random Amplified Polymorphic DNA (RAPD) and Inter-Simple Sequence Repeats (ISSR) markers were employed to examine samples from Quercus cerris, Q. suber and Q. crenata in order to test the hypothesis of the hybrid origin of Q. crenata from Q. cerris and Q. suber in a part of its distribution area where the two putative parents do not overlap at present. Leaves from 21 Q. crenata and 37 Q. cerris individual trees were collected at natural sites in northern Italy, where Q. suber is currently lacking; 21 Q. suber and six Q. crenata plants from central Italy were also analysed. Results from Unweighted Pair Group Method with Arithmetic mean (UPGMA) analysis and principal component analysis (PCA) implied that exchange of neutral markers has been considerable between the three species, while differences in morphological characters have remained comparatively stable. The Mantel test indicated low correlation between RAPD- and ISSR-based similarity matrices, showing that the two screening techniques reveal unrelated estimates of genetic relationships. Hybrid indices computed for both markers displayed an intermediate position of Q. crenata individuals between the two putative parents shifted toward Q. cerris. Results from the present study corroborate the hypothesis of a hybrid origin for Q. crenata occurring in northern Italy, and suggest asymmetrical backcrossing with Q. cerris acting as the recurrent parent.     

Human and non-human determinants of forest composition in southern Spain: evidence of shifts towards cork oak dominance as a result of management over the past century

Aims Both human and non‐human determinants have shaped Mediterranean forest structure over the last few millennia. The effects of recent human activities on forest composition, however, remain poorly understood. We quantified changes in forest composition during the past century in the mixed forests of Quercus suber (cork oak) and Q. canariensis (Algerian oak), and explored the effects of forest management and environmental (climate, topography) factors on forest structure at various spatial and temporal scales. Location Mountains north of the Strait of Gibraltar (southern Spain). Methods First, we quantified 20th‐century changes in species composition from a series of inventories in nine mixed forests (c. 40,000 ha), and examined them in terms of the management practices and environmental conditions. Second, we analysed present‐day Q. suber and Q. canariensis stand structure along environmental gradients at two spatial scales: (1) that of the forest landscape (c. 284 ha), combining local inventories and topographic variables and using a digital elevation model; and (2) regional (c. 87,600 km²), combining data from the Spanish Forest Inventory for the Andalusia region and estimates of climatic variables. Results Historical data indicate anthropogenic changes in stand composition, revealing a sharp increase in the density of cork oaks over the last century. Forest management has favoured this species (for cork production) at the expense of Q. canariensis. The impact of management is imprinted on the present‐day forest structure. The abundance of both species increases with annual mean precipitation, and they coexist above 800 mm (the minimum threshold for Q. canariensis). Quercus suber dominates in most of the stands, and species segregation in the landscape is associated with the drainage network, Q. canariensis being clearly associated with moister habitats near streams. Main conclusions Our study quantitatively exemplifies a recent human‐mediated shift in forest composition. As a result of forest management, the realized niche of the cork oak has been enlarged at the expense of that of Q. canariensis, providing further evidence for humans as major drivers of oak forest composition across the Mediterranean. Recent regeneration problems detected in Q. suber stands, a reduced demand for wood products, conservation policies, and climate change augur new large‐scale shifts in forest composition.     

Fungal Endophytic Communities in Healthy and Declining Quercus robur L. and Q. cerris L. Trees in Northern Italy

Healthy and declining English oak (Quercus robur) and Turkey oak (Q. cerris) in north‐western Italy, in a plain oak forest showing decline for oak puzzle disease, were tested to assess possible variations in the composition of their fungal endophytic communities and their relation to the health status of trees. Samples collected in spring (buds) and in autumn (leaves, annual shoots and twigs) were surface‐sterilized, cut into fragments and placed on potato dextrose agar for a month; 26 fungal species were isolated, the most frequent being Tubakia dryina, Dendrodochium sp., Eutypella sp. and a sterile mycelium. Correspondence analysis showed significant qualitative differences between assemblages inhabiting twigs and herbaceous tissues that were due to the low frequency of Tubakia dryina in twigs and its higher frequency in buds, leaves and shoots. Tubakia dryina was isolated more frequently from leaves of declining oaks and from buds of healthy oaks; Monochaetia monochaeta showed a preference for healthy trees, especially leaves and buds. According to the Shannon–Wiener index, endophytic fungal communities of leaves, twigs and buds of declining English oak were poorer than those of declining Turkey oak, but there were no significant differences between healthy hosts.     

New records of Cynipidae (Hymenoptera) from Italy

New records of Cynipid gall wasps and inquilines for the Italian peninsula and Sicily and their new host plants for the Palaearctic Region are listed and commented on. Among them we find: Cerroneuroterus cerrifloralis (Müllner 1901) as new for Italy and new for the Palaearctic region as host on Quercus suber; Andricus multiplicatus Giraud 1859 on Q. suber, as new host for the Palaearctic region; Aylax papaveris (Perris 1839), reported in Italy over a century ago, but later overlooked; Cerroneuroterus minutulus (Giraud 1859), also reported more than a century ago from Sicily, but later overlooked. Among the inquilines are here listed: Synergus variabilis Mayr 1872, emerged from Janetia cerris (Kollar 1850) galls (Diptera Cecidomyiidae), and found for the first time in the Palaearctic Region as host on Q. suber; Saphonecrus haimi (Mayr 1872) and Saphonecrus barbotini Pujade-Villar & Nieves-Aldrey 1986, are new records for Italy.     

Out of Anatolia: longitudinal gradients in genetic diversity support an eastern origin for a circum-Mediterranean oak gallwasp Andricus quercustozae

Many studies have addressed the latitudinal gradients in intraspecific genetic diversity of European taxa generated during postglacial range expansion from southern refugia. Although Asia Minor is known to be a centre of diversity for many taxa, relatively few studies have considered its potential role as a Pleistocene refugium or a potential source for more ancient westward range expansion into Europe. Here we address these issues for an oak gallwasp, Andricus quercustozae (Hymenoptera: Cynipidae), whose distribution extends from Morocco along the northern coast of the Mediterranean through Turkey to Iran. We use sequence data for a fragment of the mitochondrial gene cytochrome b and allele frequency data for 12 polymorphic allozyme loci to answer the following questions: (1) which regions represent current centres of genetic diversity for A. quercustozae? Do eastern populations represent one refuge or several discrete glacial refugia? (2) Can we infer the timescale and sequence of the colonization processes linking current centres of diversity? Our results suggest that A. quercustozae was present in five distinct refugia (Iberia, Italy, the Balkans, southwestern Turkey and northeastern Turkey) with recent genetic exchange between Italy and Hungary. Genetic diversity is greatest in the Turkish refugia, suggesting that European populations are either (a) derived from Asia Minor, or (b) subject to more frequent population bottlenecks. Although Iberian populations show the lowest diversity for putatively selectively neutral markers, they have colonized a new oak host and represent a genetically and biologically discrete entity within the species.     

Invaders on the move: parasitism in the sexual galls of four alien gall wasps in Britain (Hymenoptera: Cynipidae)

Four alien, host-alternating cynipid gall wasps are established in the British Isles: Andricus kollari, A. lignicola, A. quercuscalicis and A. corruptrix. Their current distributions divide Britain into four zones; all four invaders are present in the south and south-east of Britain, whereas only A. kollari is present in the far north of Scotland. The rank order, according to how far north the distributions of the four invading cynipid species reach, is: A. corruptrix→ A. quercuscalicis→ A. lignicola→ A. kollari. The life cycles of all four cynipid species involve a sexual generation in spring on Quercus cerris, and an agamic generation in autumn on Q. robur. Here we studied the parasitoid attack by four pteromalid species on the sexual generations of the invaders. We collected and reared the galls of all four species at eight sites from the south to the north of the country (two sites per zone). The geographical locations of the sites reflect the invasion history and thus the residence time of the alien species in the four zones. At each site we measured the densities of all host galls on Q. cerris and of both obligatory host-tree species. We also took a series of measures, such as host-tree density and mean host-tree size, to further characterize the tree stands. These measures are referred to as local parameters. Host densities varied between sites and between years. In A. kollari, galling rates were highest in the middle of the country (zone 2) in 1994, whereas in 1995 they increased from the south to the north. In A. lignicola, galling rates in both years were lowest at the sites in zone 3 (closest to its distribution boundary). In A. quercuscalicis, galling rates were found to be lowest at the site most to the north-west in both years, again the one furthest away from the area where this species was first recorded. Mortality caused by parasitoid attack differed from less than 10% to as high as 70% and varied between host species, sites and years. In four out of six cases the historical/regional variables (north/south and east/west) correlated significantly with parasitoid attack rates that were characteristically lowest at sites close to the distribution boundaries. Of the local factors, we found parasitoid attack rates correlated negatively in one case with host density, whereas they correlated positively in four cases with the density of alternative hosts of the parasitoids. In one of the models the local density of Q. cerris trees correlated negatively with parasitoid attack on A. quercuscalicis. For all three host species the terms retained in the minimal adequate models obtained for 1994 and 1995 differed, which might indicate that these communities of native parasitoids and invading host have not yet settled in any definite structure.     

The Balearic Islands: a reservoir of cpDNA genetic variation for evergreen oaks

Aim To analyse the role of the Balearic Islands as a refuge area for evergreen Quercus (cork oak: Quercus suber L., holm oak: Q. ilex L., kermes oak: Q. coccifera L.), by using molecular, historical and palaeobotanical data. Location The Western Mediterranean Basin (Balearic Islands, eastern Iberia, Provence, Sardinia, Corsica, Sicily, Malta, Italy, Northern Africa). Methods We sampled 108 populations and used the PCR‐RFLP technique with five universal cpDNA primers to define haplotypes in the sampled populations. Diversity, differentiation parameters and spatial analysis of the populations, using a spatial version of amova , were linked to the geological history of the Western Mediterranean Basin in order to explain the present spatial pattern of the evergreen Quercus populations in the Balearics. Results Evergreen Quercus cpDNA shows a complex structure, with remnants of ancient diversity in the Balearics. Balearic populations of holm oak are related to Iberian populations, while for cork and kermes oaks, we found both Tyrrhenian and Iberian haplotypes. Main conclusions The complex spatial patterns of cpDNA in Balearic evergreen Quercus appears explicable in terms of a combination of physical (vicariance and long distance dispersal) and biological (introgressive hybridization) factors. The Balearics constitute a glacial refuge area and a reservoir of genetic variation with traces of ancient diversity from Messinian–Pliocene stages.     

Proteomic analysis from haploid and diploid embryos of Quercus suber L. identifies qualitative and quantitative differential expression patterns

Quercus suber L. is a Mediterranean forest species with ecological, social and economic value. Clonal propagation of Q. suber elite trees has been successfully obtained from in vitro‐derived somatic and gametic embryos. These clonal lines play a main role in breeding and genetic studies of Q. suber. To aid in unravelling diverse genetic and biological unknowns, a proteomic approach is proposed. The proteomic analysis of Q. suber somatic and gametic in vitro culture‐derived embryos, based on DIGE and MALDI‐MS, has produced for the first time proteomic data on this species. Seventeen differentially expressed proteins have been identified which display significantly altered levels between gametic and somatic embryos. These proteins are involved in a variety of cellular processes, most of which had been neither previously associated with embryo development nor identified in the genus Quercus. Some of these proteins are involved in stress and pollen development and others play a role in the metabolism of tannins and phenylpropanoids, which represent two of the major pathways for the synthesis of cork chemical components. Furthermore, the augmented expression levels found for specific proteins are probably related to the homozygous state of a doubled‐haploid sample. Proteins involved in synthesis of cork components can be detected at such early stages of development, showing the potential of the method to be useful in searching for biomarkers related to cork quality.     

Seasonal variations of gas exchange, photosynthetic pigments, and antioxidants in Turkey oak (Quercus cerris L.) and Hungarian oak (Quercus frainetto Ten.) of different age

Seasonal changes in physiological and biochemical parameters were studied in 35-, 55- and 140-year-old trees of Turkey oak (Quercus cerris L.) and Hungarian oak (Q. frainetto Ten.), growing in natural stands in Eastern Balkan Mountains (Bulgaria). During the seasonal drought period (August), assimilation activity, transpiration rate, stomatal conductance and water potential had a seasonal minimum in all the studied tree ages and species. The foliar concentrations of glutathione, ascorbate, α-tocopherol, as well as photosynthetic pigments in oak leaves were significantly affected by season. With the increasing age of the studied trees, we observed a decrease of the physiological activity and an increase of the antioxidants’ accumulation. Both the species were drought tolerant and anisohydric, where Q. frainetto exhibited higher rates of gas exchange than Q. cerris. Moreover, they differed in the extent of increase in the foliar antioxidants and carotenoids.     

Buds buried in bark: the reason why <Emphasis Type="Italic">Quercus suber</Emphasis> (cork oak) is an excellent post-fire epicormic resprouter

Key message

Cork oak has buds protected by the full thickness of its substantial phellem, thus explaining why it is the only European tree that can epicormically resprout after higher intensity fire.

Abstract

Epicormic resprouting has various ecological advantages over basal resprouting. However, after higher intensity fires epicormic resprouting is rare as it is difficult for trees and shrubs to keep both their buds and vascular cambia alive. Quercus suber (cork oak) is the only European tree that can resprout epicormically after higher intensity fires. Q. suber develops very thick bark and it has been assumed, without anatomical evidence, that the bark protects the epicormic buds. We investigated if developmental anatomy could explain why Q. suber is an excellent post-fire epicormic resprouter. We examined buds from mature Q. suber trees, macroscopically using a stereo microscope and microscopically using semi-thin microtome sections. Q. suber produced buds in the foliage leaf axils and the bud scale axils. With the commencement of extensive phellem (cork) production the base of the epicormic buds remained at, or just below, the level of the phellogen and thus cork began to bury the buds, although a narrow tube connected each bud to the bark surface. Q. suber epicormic buds became deeply buried in the phellem and would be protected from heat by the full phellem thickness. With its rapid and substantial development of phellem Q. suber had well-protected epicormic buds even in relatively small diameter stems. These results provide the anatomical evidence to show why Q. suber is a noted epicormic resprouter after crown fire.

     

Phylogeography and cryptic variation within the Lacerta viridis complex (Lacertidae, Reptilia)

It is well known that the current genetic pattern of many European species has been highly influenced by climatic changes during the Pleistocene. While there are many well known vertebrate examples, knowledge about squamate reptiles is sparse. To obtain more data, a range‐wide sampling of Lacerta viridis was conducted and phylogenetic relations within the L. viridis complex were analysed using an mtDNA fragment encompassing part of cytochrome b, the adjacent tRNA genes and the noncoding control region. Most genetic divergence was found in the south of the distribution range. The Carpathian Basin and the regions north of the Carpathians and Alps are inhabited by the same mitochondrial lineage, corresponding to Lacerta viridis viridis. Three distinct lineages occurred in the south‐eastern Balkans — corresponding to L. v. viridis, L. v. meridionalis, L. v. guentherpetersi— as well as a fourth lineage for which no subspecies name is available. This distribution pattern suggests a rapid range expansion of L. v. viridis after the Holocene warming, leading to a colonization of the northern part of the species range. An unexpected finding was that a highly distinct genetic lineage occurs along the western Balkan coast. Phylogenetic analyses (Bayesian, maximum likelihood, maximum parsimony) suggested that this west Balkan lineage could represent the sister taxon of Lacerta bilineata. Due to the morphological similarity of taxa within the L. viridis complex this cryptic taxon was previously assigned to L. v. viridis. The distribution pattern of several parapatric, in part highly, distinct genetic lineages suggested the existence of several refuges in close proximity on the southern Balkans. Within L. bilineata sensu stricto a generally similar pattern emerged, with a high genetic diversity on the Apennine peninsula, arguing for two distinct refuges there, and a low genetic diversity in the northern part of the range. Close to the south‐eastern Alps, three distinct lineages (L. b. bilineata, L. v. viridis, west Balkan taxon) occurred within close proximity. We suggest that the west Balkan lineage represents an early offshoot of L. bilineata that was isolated during a previous Pleistocene glacial from the more western L. bilineata populations, which survived in refuges on the Apennine peninsula.     

Phylogeography,population genetics and conservation of the European red deer Cervus elaphus

• 1 During the Last Glacial Maximum, European red deer Cervus elaphus occurred in refugia in Iberia/southern France, Italy, the Balkans and the Carpathians. Most of Europe, including large parts of the east and north‐east, is now inhabited by red deer from the western lineage. The eastern lineage is largely confined to south‐eastern Europe; a third lineage comprises Sardo‐Corsican and Barbary red deer.
• 2 Sardo‐Corsican, Barbary and Mesola red deer are genetically unique units. They exhibit low levels of genetic diversity and deserve particular protection, since conservation strategies should target genetic information.
• 3 Hybridization between sika Cervus nippon and red deer occurs rarely, but may lead to extensive introgression, particularly in parts of the British Isles. Further expansion of both species may lead to increased hybridization in continental Europe.
• 4 Although hunting has an impact on red deer gene pools, the main threat today is habitat fragmentation in human‐dominated landscapes. The resulting increase in genetic drift and inbreeding reduces variability in isolated populations and may lead to inbreeding depression. To support vital meta‐populations, migration corridors should be established.

     

Discovery of an oak gall wasp (Hymenoptera: Cynipidae) inducing galls on deciduous oak trees in India

We report for the first time the occurrence of an oak gall wasp Andricus mukaigawae (Mukaigawa) (Hymenoptera: Cynipidae) on the deciduous oak Quercus griffithii Hook. F & Thomson ex Miq. in India. Andricus mukaigawae is the only cynipid species that has been observed to induce galls on deciduous oak species in India to date. In addition, this is the first record of a gall wasp species with a distribution extending all the way from the eastern Palearctic region to the Indian subcontinent, suggesting the existence of a close relationship between cynipid faunas on deciduous oak trees in the two regions.     

A comprehensive assessment of the transcriptome of cork oak (Quercus suber) through EST sequencing

Background

Cork oak (Quercus suber) is one of the rare trees with the ability to produce cork, a material widely used to make wine bottle stoppers, flooring and insulation materials, among many other uses. The molecular mechanisms of cork formation are still poorly understood, in great part due to the difficulty in studying a species with a long life-cycle and for which there is scarce molecular/genomic information. Cork oak forests are of great ecological importance and represent a major economic and social resource in Southern Europe and Northern Africa. However, global warming is threatening the cork oak forests by imposing thermal, hydric and many types of novel biotic stresses. Despite the economic and social value of the Q. suber species, few genomic resources have been developed, useful for biotechnological applications and improved forest management.

Results

We generated in excess of 7 million sequence reads, by pyrosequencing 21 normalized cDNA libraries derived from multiple Q. suber tissues and organs, developmental stages and physiological conditions. We deployed a stringent sequence processing and assembly pipeline that resulted in the identification of ~159,000 unigenes. These were annotated according to their similarity to known plant genes, to known Interpro domains, GO classes and E.C. numbers. The phylogenetic extent of this ESTs set was investigated, and we found that cork oak revealed a significant new gene space that is not covered by other model species or EST sequencing projects. The raw data, as well as the full annotated assembly, are now available to the community in a dedicated web portal at http://www.corkoakdb.org.

Conclusions

This genomic resource represents the first trancriptome study in a cork producing species. It can be explored to develop new tools and approaches to understand stress responses and developmental processes in forest trees, as well as the molecular cascades underlying cork differentiation and disease response.     

Cytosolic ascorbate peroxidase in some species of the Quercus genus

ABSTRACT

Six species of the Quercus genus (Quercus ilex L., Q. coccifera L., Q. suber L., Q. trojana Webb, Q. macrolepis Kotschy, Q. cerris L.) have been screened for cytosolic ascorbate peroxidase (APX) by means of native polyacrylamide gel electrophoresis (PAGE). A single isozyme was found in five species (Q. trojana, Q. suber, Q. cerris, Q. macrolepis and Q. coccifera), while Q. ilex shows two different APX proteins. The data showed marked similarities among Q. trojana, Q. suber, Q. cerris and Q. macrolepis with respect to the electrophoretic mobility. The validity of APX electrophoretic patterns in systematic studies is discussed.     

Expression of DNA methyltransferases is involved in Quercus suber cork quality

Cork oak (Quercus suber) is an important Portuguese species, mainly due to the economic value of the cork it produces. Cork results from phellogen, a meristematic tissue, which can locally produce lenticels or have discontinuities, originating “defects”: pores and nail inclusions that are detrimental to cork industrial use. Epigenetic processes control plant development and its deregulation can lead to altered phenotypes; therefore, the study of epigenetic players in the phellogen is important to understand the emergence of cork's defects. DNA methyltransferases (DNMTs) and one protein associated to MET1 (DMAP1) were characterized in Q. suber, and their gene expression was analyzed in phellogen and contiguous differentiating cell layers of trees producing high and low quality cork, after the evaluation of their defects by physical and image analysis methods. All classes of DNMTs (MET, DRM, and CMT) with the respective canonical motifs were identified in Q. suber. The expression analyses of these genes showed that QsDRM2 was the most active methyltransferases in the cells analyzed, and that all the genes were differentially expressed in trees with distinct cork quality, with a tendency for higher expression levels in low quality producers. Interestingly, the global methylation level was higher in cells with low expression of DNA methyltransferases. A positive and significant correlation was obtained between QsDMAP1 gene expression and the percentage of cork defects. This work provides the first evidence that cork quality in Q. suber is likely influenced by epigenetic mechanisms.     

Rodent acorn selection in a Mediterranean oak landscape

Quercus suber, Quercus ilex and Quercus coccifera (Cork, Holm and Kermes oaks, respectively) are common evergreen oak species that coexist in the landscapes of the western part of the Mediterranean basin. Rodents are the main acorn predators and thus one of the main factors for understanding recruitment patterns in oaks. In this paper we analyse to what extent mice prefer acorns from one oak species over another in three oak species studied using acorn removal experiments and video tape recordings. Twenty labelled acorns from each of the three Quercus species (60 acorns) were placed in 40 cm×40 cm quadrats on each plot. Because selection might vary as a result of the vegetation context, we performed the trials in the five main vegetation types within the study area (four replicates in each vegetation type) in order to control for habitat influences on rodent acorn preferences (a total of 20 plots). The removal of 1,200 acorns occurred within 68 days. Mice removed 98.7% of the acorns. Q. ilex acorns were preferred over Q. suber and Q. coccifera in all vegetation types except in pine forest, where no acorn preferences were detected. Acorn removal rates differed with vegetation type, correlating positively with shrub cover. The distance at which acorns were displaced by rodents (mean =4.6 m±5.1 SD) did not differ between acorn species, but varied among vegetation types. Bigger acorns of Q. coccifera were selected only after Q. ilex and Q. suber acorns were depleted, while no size selection was detected for the latter two species. Thus, we conclude that rodents show preference for some oak acorns and that landscape context contributes significantly to rodent activities and decisions.