Ferenc Lakatos

Mitochondrial and microsatellite DNA markers reveal a Balkan origin for the highly invasive horse‐chestnut leaf miner Cameraria ohridella (Lepidoptera, Gracillariidae)

Biological invasions usually start with a small number of founder individuals. These founders are likely to represent a small fraction of the total genetic diversity found in the source population. Our study set out to trace genetically the geographical origin of the horse‐chestnut leafminer, Cameraria ohridella, an invasive microlepidopteran whose area of origin is still unkown. Since its discovery in Macedonia 25 years ago, this insect has experienced an explosive westward range expansion, progressively colonizing all of Central and Western Europe. We used cytochrome oxidase I sequences (DNA barcode fragment) and a set of six polymorphic microsatellites to assess the genetic variability of C. ohridella populations, and to test the hypothesis that C. ohridella derives from the southern Balkans (Albania, Macedonia and Greece). Analysis of mtDNA of 486 individuals from 88 localities allowed us to identify 25 geographically structured haplotypes. In addition, 480 individuals from 16 populations from Europe and the southern Balkans were genotyped for 6 polymorphic microsatellite loci. High haplotype diversity and low measures of nucleotide diversities including a significantly negative Tajima’s D indicate that C. ohridella has experienced rapid population expansion during its dispersal across Europe. Both mtDNA and microsatellites show a reduction in genetic diversity of C. ohridella populations sampled from artificial habitats (e.g. planted trees in public parks, gardens, along roads in urban or sub‐urban areas) across Europe compared with C. ohridella sampled in natural stands of horse‐chestnuts in the southern Balkans. These findings suggest that European populations of C. ohridella may indeed derive from the southern Balkans.

Evidence for a recent horizontal transmission and spatial spread of Wolbachia from endemic Rhagoletis cerasi (Diptera: Tephritidae) to invasive Rhagoletis cingulata in Europe.

The widespread occurrence of Wolbachia in arthropods and nematodes suggests that this intracellular, maternally inherited endosymbiont has the ability to cross species boundaries. However, direct evidence for such a horizontal transmission of Wolbachia in nature is scarce. Here, we compare the well‐characterized Wolbachia infection of the European cherry fruit fly, Rhagoletis cerasi, with that of the North American eastern cherry fruit fly, Rhagoletis cingulata, recently introduced to Europe. Molecular genetic analysis of Wolbachia based on multilocus sequence typing and the Wolbachia surface protein wsp showed that all R. cingulata individuals are infected with wCin2 identical to wCer2 in R. cerasi. In contrast, wCin1, a strain identical to wCer1 in R. cerasi, was present in several European populations of R. cingulata, but not in any individual from the United States. Surveys of R. cingulata from Germany and Hungary indicated that in some populations, the frequency of wCin1 increased significantly in just a few years with at least two independent horizontal transmission events. This is corroborated by the analysis of the mitochondrial cytochrome oxidase II gene that showed association of wCin1 with two distinct haplotypes in Germany, one of which is also infected with wCin1 in Hungary. In summary, our study provides strong evidence for a very recent inter‐specific Wolbachia transmission with a subsequent spatial spread in field populations.

The phylogenetic relationships of seven European Ips (Scolytidae, Ipinae) species.

In Central Europe seven Ips species are characterized by differences in morphology, structure of galleries, host specificity and aggressiveness. These species were analysed by allozyme markers and by sequencing 567 bp of the mitochondrial cytochrome oxidase I gene, in order to define their phylogenetic relationships. Orthotomicus erosus and Tomicus minor were taken as outgroup species. The data revealed high inter‐specific and low intra‐specific sequence divergence. Plotting the observed sequence divergence caused by transversions (Tv) and transitions (Ts) and the level of saturation for Ts and Tv of each codon position showed that the third positions were highly saturated by multiple substitutions. Maximum parsimony analysis produced two groups: (1) I. typographus, I. cembrae, I. amitinus, I. duplicatus and I. acuminatus; (2) I. mannsfeldi, I. sexdentatus and the two outgroups. In all analyses the species of the first cluster were put together and I. typographus and I. cembrae, and I. mannsfeldi and O. erosus emerged as sister pairs.

Genetic structure of Japanese populations of an ambrosia beetle, Xylosandrus germanus (Curculionidae: Scolytinae)

We examined the genetic structures of 13 Japanese populations of an ambrosia beetle, Xylosandrus germanus (Curculionidae: Scolytinae), to understand the effects of geographical barriers on the colonization dynamics of this species. The genetic structure was studied using portions of the mitochondrial cytochrome oxidase I (COI) gene. A phylogenetic analysis revealed three distinct lineages (clades A, B and C) within X. germanus. Clade A contained 21 haplotypes from all 13 populations; whereas clade B contained eight haplotypes from Hokkaido (Sapporo and Furano), Iwate and Nagano populations; and clade C contained only a single a haplotype from the Hokkaido (Furano) population. In the analysis of molecular variance (amova), the greatest amount of genetic variation was detected between populations in Hokkaido and those in Honshu and other southern islands. Between these two groups of populations, all the values of the coefficient of gene differentiation were significantly larger than zero, except for the Hokkaido (Sapporo) versus Nagano comparison. Our results confirm that for X. germanus, gene flow has been interrupted between Hokkaido and Honshu since the last glacial maximum.

Insight into the Genetic Components of Community Genetics: QTL Mapping of Insect Association in a Fast-Growing Forest Tree

Identifying genetic sequences underlying insect associations on forest trees will improve the understanding of community genetics on a broad scale. We tested for genomic regions associated with insects in hybrid poplar using quantitative trait loci (QTL) analyses conducted on data from a common garden experiment. The F2 offspring of a hybrid poplar (Populus trichocarpa x P. deltoides) cross were assessed for seven categories of insect leaf damage at two time points, June and August. Positive and negative correlations were detected among damage categories and between sampling times. For example, sap suckers on leaves in June were positively correlated with sap suckers on leaves (P<0.001) but negatively correlated with skeletonizer damage (P<0.01) in August. The seven forms of leaf damage were used as a proxy for seven functional groups of insect species. Significant variation in insect association occurred among the hybrid offspring, including transgressive segregation of susceptibility to damage. NMDS analyses revealed significant variation and modest broad-sense heritability in insect community structure among genets. QTL analyses identified 14 genomic regions across 9 linkage groups that correlated with insect association. We used three genomics tools to test for putative mechanisms underlying the QTL. First, shikimate-phenylpropanoid pathway genes co-located to 9 of the 13 QTL tested, consistent with the role of phenolic glycosides as defensive compounds. Second, two insect association QTL corresponded to genomic hotspots for leaf trait QTL as identified in previous studies, indicating that, in addition to biochemical attributes, leaf morphology may influence insect preference. Third, network analyses identified categories of gene models over-represented in QTL for certain damage types, providing direction for future functional studies. These results provide insight into the genetic components involved in insect community structure in a fast-growing forest tree.

Analysing the effect of stand density and site conditions on structure and growth of oak species using Nelder trials along an environmental gradient: experimental design, evaluation methods, and results

BackgroundMost current approaches in forest science and practice require information about structure and growth of individual trees rather than - or in addition to - sum and mean values of growth and yield at forest stand level as provided by classic experimental designs. By inventing the wheel design, Nelder provided the possibility to turn to the individual tree as basic information unit. Such trials provide valuable insights into the dependency of growth on stand density at particular sites.MethodsHere, we present an extension of the original design and evaluation by Nelder. (i) We established Nelder wheels along an environmental gradient through Europe in atlantic climate in Belgium and Germany, Mediterranean climate in Italy, continental climate in Hungary as well as on high land climate in Mexico. Such disjunct Nelder wheels along an environmental gradient can be regarded and analysed as a two-factor design with the factors of site condition and stand density. (ii) We present an advanced statistical approach to evaluate density dependent growth dynamics of trees planted in form of the Nelder design, which considers spatio-temporal autocorrelation. (iii) We prove the usefulness of the methods in improving ecological theory concerning density related productivity, trade-offs between facilitation and competition, and allometric relations between size variables.ResultsFirst evaluations based on remeasured Nelder wheels in oak (Quercus roburL.) show a size growth differentiation during the first observation period. In particular, height growth is accelerated under higher competition indicating facilitation effects. We detect furthermore a high variability in allometric relations.ConclusionsThe proposed design, methods, and results are discussed regarding their impact on forest practice, model building, and ecological theory. We conclude that the extended Nelder approach is highly efficient in providing currently lacking individual tree level information.

Wolbachia endosymbionts in haplodiploid and diploid scolytine beetles (Coleoptera: Curculionidae: Scolytinae).

Haplodiploidy is a sex determination system in which fertilized diploid eggs develop into females and unfertilized haploid eggs develop into males. The evolutionary explanations for this phenomenon include the possibility that haplodiploidy can be reinforced by infection with endosymbiotic bacteria, such as Wolbachia. The subfamily Scolytinae contains species with haplodiploid and diploid sex determination systems. Thus, we studied the association with Wolbachia in 12 diploid and 11 haplodiploid scolytine beetles by analyzing wsp and multilocus sequence typing (MLST) of five loci in this endosymbiont. Wolbachia genotypes were compared with mitochondrial (COI) and nuclear (EF) genotypes in the scolytines. Eight of the 23 scolytine species were infected with Wolbachia, with haplodiploids at significantly higher rates than diploid species. Cloning and sequencing detected multiple infections with up to six Wolbachia strains in individual species. Phylogenetic analyses of wsp and five MLST genes revealed different Wolbachia strains in scolytines. Comparisons between the beetle and Wolbachia phylogenies revealed that closely related beetles were infected with genetically different Wolbachia strains. These results suggest the horizontal transmission of multiple Wolbachia strains between scolytines. We discuss these results in terms of the evolution of different sex determination systems in scolytine beetles.

Occurrence of soilborne Phytophthora species in declining broadleaf forests in Hungary

Invasive Phytophthora species are responsible for severe tree diseases in many forest ecosystems in Europe. In Hungary, the symptoms were first noted when P. alni infection led to a serious decline and mortality of alder stands in the late 1990s. Between 2001 and 2009, over 300 soilborne Phytophthora isolates were collected from declining broadleaf forests in Hungary, and 10 Phytophthora species identified based on morphological traits and the molecular characteristics of the internally transcribed spacer (ITS) regions of the nuclear ribosomal DNA. The most diverse species spectrum, found in diseased alder stands, included P. gonapodyides, P. gregata, P. inundata, P. lacustris, P. megasperma, P. plurivora, one informally designated taxon: P. taxon hungarica, and one unnamed species P. sp.1. P. cactorum and P. plurivora isolates were prevalent in the soil of a declining eastern black walnut forest, and three species, P. gonapodyides, P. multivora and P. plurivora were recovered from a declining oak stand. More than one ITS-based genotype was identified for four species, including six genotypes for P. gonapodyides, and two each for P. cactorum, P. plurivora and P. inundata. The high genetic diversity of the P. gonapodyides isolates may indicate that the species is indigenous to the region. In contrast, the frequently recovered, widely distributed P. lacustris with a single ITS genotype may represent a recent colonizer. The P. multivora isolates are, to date, the first reported from a European native forest.

Occurrence and Diversity of Soilborne Phytophthoras in a Declining Black Walnut Stand in Hungary

Abstract The paper reports on the occurrence and impact of Phytophthora species in a declining eastern black walnut (Juglans nigra) stand in West Hungary. The health condition of the trees was investigated and soil samples were taken from the rhizosphere of the trees two times per year in 2011 and 2012 in order to isolate Phytophthora species. Altogether 20 trees were selected for investigations. The species identity of the isolates was determined by morphological and molecular methods. Phytophthora cactorum and Phytophthora plurivora were found as supposedly responsible for the decline of the trees. The abundance of the two species was changing at the different sampling times, presumably due to the different weather conditions. The intraspecific diversity of both species was estimated based on the ITS1-5.8S-ITS2 sequences of the isolates. Kivonat Phytophthora fajok gyakorisága és diverzitása egy pusztuló feketedió állományban Magyarországon. A tanulmány egy pusztuló nyugat-magyarországi fekete dió (Juglans nigra ) állományban előforduló Phytophthora fajokról, és azok faállományra gyakorolt hatásáról tudósít. A szerzők vizsgálták a faállomány egészségi állapotát, illetve talajmintákat gyűjtöttek a fák gyökérzónájából a Phytophthora fajok kitenyésztése céljából. A vizsgálatokat 20 megjelölt fán végezték, 2011-ben és 2012-ben, évente 2-2 alkalommal. Az izolátumok azonosítása morfológiai és molekuláris genetikai módszerekkel történt. Phytophthora cactorum-ot és Phytophthora plurivora-t találtak, mint a pusztulás valószínűsíthető okát. A két faj gyakorisága eltérő volt a különböző mintavételi időpontokban, feltehetően az eltérő időjárási viszonyok miatt. A két faj diverzitását az izolátumok ITS1 - 5.8S - ITS2 szekvenciái alapján becsülték.

Sudden Phytophthora Dieback of Wild Cherry Trees in Northwest Hungary

Abstract During a regular survey of declining forests in 2011, sudden dieback symptoms were observed on scattered wild cherry trees (Prunus avium) in a mixed deciduous forest stand, located in the flood plain area of the Rába River, in northwest Hungary. In this study, we correlated both soil conditions and presence of Phytophthora spp. to dieback of cherry trees. Two Phytophthora species, P. polonica and P. plurivora, were isolated from the rhizosphere soil of the dying trees. By contrast, only P. polonica was recovered from the necrotic tissues of symptomatic roots. Stem and root inoculation tests on cherry seedlings showed pathogenicity of both species, although P. polonica proved to be more virulent. This is the first report of natural infections of P. polonica.