Few immigrant phytophagous insects on woody plants in Europe: legacy of the European crucible?

Exotic phytophagous insects are invading forest ecosystems worldwide. So far, 109 invasive insects on woody plants, 57 from North American (NA), and 52 from Asia (A) have established populations in European forests. Four orders account for about 84% of the immigrants: Homoptera 39%, Lepidoptera 13%, Coleoptera 19%, and Hymenoptera 13%. The majority of these invasive species (63% of NA and 77% of A) live on deciduous trees, of which 36% have been introduced from NA and Asia. The remaining insect species (37% NA and 25% A) live on various conifers, of which 53% have also been introduced. Most (57%) of the NA insects feeding on coniferous plants live upon their introduced, native host plants. These data suggest that many NA immigrant phytophagous species in Europe have been successful in establishing permanent populations because their native hosts preceded or accompanied them into Europe and/or were asexually reproducing species. We propose that fewer invasive phytophagous insects have become established in European compared to North American woodlands because of the unique legacy of the European Pleistocene/Holocene crucible (i.e. endless cycles of populations contracting into highly disparate, dispersed metapopulation refugia and eventually expanding out of them) on European species and ecosystems that caused highly diminished heterogeneity. This translates to fewer and less penetrable tri-trophic niches in Europe due to fewer and less available host plants, but greater zootic resistance per niche derived from more competition-hardened competitors and possibly natural enemies. Moreover, many European species are probably superior invasion specialists because the crucible favored traits that are conducive to success in highly subdivided, and extinction-prone metapopulations: asexual reproduction, polyploidy, and other traits especially conducive to persistence under stress, and explosive growth/spread under amelioration.     

Does enemy release matter for invasive plants? evidence from a comparison of insect herbivore damage among invasive,non-invasive and native congeners

One of the most popular single-factor hypotheses that have been proposed to explain the naturalization and spread of introduced species is the enemy release hypothesis (ERH). One ramification of the ERH is that invasive plants sustain less herbivore damage than their native counterparts in the invaded range. However, introduced plants, invasive or not, may experience less herbivore damage than the natives. Therefore, to test the role of natural enemies in the success of invasive plants, studies should include both invasive as well as non-invasive introduced species. In this study, we employed a novel three-way comparison, in which we compared herbivore damage among native, introduced invasive, and introduced non-invasive Eugenia (Myrtaceae) in South Florida. We found that introduced Eugenia, both invasive and non-invasive, sustained less herbivore damage, especially damage by oligophagous and endophagous insects, than native Eugenia. However, the difference in insect damage between introduced invasive and introduced non-invasive Eugenia was not significant. Escape from herbivores may not account for the spread of invasive Eugenia. We would not have been able to draw this conclusion without inclusion of the non-invasive Eugenia species in the study.     

Morphological description of two bucephalid trematodes collected from freshwater fishes in the Uji River, Kyoto, Japan

The morphology of two species of bucephalids (Bucephalidae; Digenea; Trematoda), which since 1999 has caused a fish disease at the Uji River, Kyoto Prefecture, Japan, is described. Parabucephalopsis parasiluri Wang, 1985 was first recorded in the Uji River in 2000, and Prosorhynchoides ozakii (Nagaty, 1937) in 2005. The definitive host of both species is the Lake Biwa catfish (Silurus biwaensis), and the second intermediate hosts include many fish species from several families. P. parasiluri is an introduced parasite that invaded with its first intermediate host, golden mussels (Limnoperna fortunei), from the Asian continent. P. ozakii may also be an introduced species, although its first intermediate host has not been identified.     

The exotic mammals of Argentina

Exotic mammals in South America represent about 20% of world mammal introductions. The aim of our paper is to provide a global assessment of the exotic mammals of Argentina, their pathways, impacts, and a synthesis of their attributes as potential invasive species. We reviewed and compiled data from a diversity of sources and databases on alien mammals occurring in feral state exclusively. We recorded 18 species of exotic mammals for Argentina. The majority of introductions occurred between the 18th and 19th centuries and their ports of entry were located in temperate ecosystems, between 34° and 55° SL. Most of their entry pathways were associated with human activities (e.g. sport hunting, food and fur industry). The exotic mammals occupy ecoregions similar to their original distributions, but most of them have experienced a range expansion to novel habitats. The fauna of exotic mammals of Argentina represents a good opportunity to understand the dynamics of the invasion process as they represent a diversity of ecological groups and environmental contexts.     

Tetranucleotide microsatellites for the barnacle Megabalanus coccopoma (Darwin, 1854)

The barnacle Megabalanus coccopoma is indigenous to the tropical Pacific Ocean, but was recently introduced to the coastal waters of the southeastern U.S.A. As part of a larger effort to investigate the population dynamics of this introduction, we designed 13 microsatellite primers specific to M. coccopoma and developed the accompanying polymerase chain reaction (PCR) conditions. We tested these primers on 42 individuals of M. coccopoma collected from two sampling locations in coastal Georgia, USA. The 13 loci developed showed means of 24.5 alleles per locus, 0.93 expected heterozygosity, 0.67 observed heterozygosity, and 0.91 polymorphic information content. The high variation observed within these microsatellite loci makes them useful tools for testing hypotheses related to population genetics, including source-sink dynamics for range expansions and rates of self-fertilization and outcrossing.     

Effects of competition and mowing on growth and reproduction of the invasive plant Erigeron annuus at two contrasting altitudes

Invasive plants are often abundant at frequently disturbed sites such as roadsides, because they benefit from reduced competition or increased nutrient availability. In Switzerland, roadsides are subjected to regular mowing, and to persist in these sites, plants must be able to compensate for the biomass removal. However, the ability to tolerate competition and mowing might decline under less favourable growth conditions, such as those at higher altitudes. I investigated how competition and mowing affect growth and reproduction of Erigeron annuus (L.) Pers., an invasive plant common on Swiss roadsides, and how these effects change with altitude. The experiment was replicated in common gardens at altitudes of 400 m and 1,000 m asl, representing growth conditions in the main distribution area of E. annuus and at its altitudinal limit, respectively. Vegetative growth was negatively affected by competition at both sites, but especially at 1,000 m. The number of capitula was not affected by competition at 400 m, but was reduced at 1,000 m. Plants regrew vigorously after mowing in both gardens. The effects of mowing on reproductive output were positive at 400 m, but negative at 1,000 m. These results imply that E. annuus is able to tolerate competition and mowing at low altitudes, but both of these factors hinder its reproduction at higher altitudes.

---

Zusammenfassung  Invasive Neophyten kommen an gest?rten Standorten besonders h?ufig vor, da sie dort weniger Konkurrenz oder eine h?here N?hrstoffverfügbarkeit vorfinden. In der Schweiz sind regelm?ssig gem?hte Strassenr?nder wichtige Lebensr?ume und Ausbreitungskorridore für invasive Pflanzen. Offenbar gelingt es den Pflanzen, die Mahdverluste zu kompensieren und sich dennoch zu vermehren. Die F?higkeit von Pflanzen, Konkurrenz oder St?rungen zu ertragen, nimmt in der Regel unter ungünstigen Wachstumsbedingungen ab. Deshalb k?nnte man erwarten, dass invasive Pflanzen mit zunehmender Meeresh?he aufgrund des k?lteren Klimas durch Konkurrenz und Mahd st?rker betroffen werden. Hier wurde untersucht, ob Konkurrenz und Mahd das Wachstum und die Fortpflanzung des einj?hrigen Berufkrauts, Erigeron annuus (L.) Pers., je nach Meeresh?he unterschiedlich beeinflussen. Dazu wurde ein Experiment in zwei G?rten auf 400 und 1,000 m ü.M. angelegt, wobei der obere Garten der heutigen Verbreitungsgrenze von E. annuus entspricht. Konkurrenz reduzierte das vegetative Wachstum an beiden Orten, jedoch st?rker auf 1,000 m. Die Anzahl Blütenk?pfe wurde nur auf 1,000 m durch Konkurrenz reduziert. Nach einer Mahd trieben die Pflanzen in beiden G?rten schnell wieder aus. Die Mahd erh?hte die Anzahl Blütenk?pfe auf 400 m und senkte sie auf 1,000 m. Diese Ergebnisse bedeuten, dass E. annuus in tiefen Lagen Mahd und Konkurrenz ertragen kann, w?hrend in h?heren Lagen beide Faktoren seiner Ausbreitung entgegenwirken.

     

High-frequency variation of tree-ring width of some native and alien tree species in Latvia during the period 1965–2009

The plasticity of climate-growth relationships of trees is one of the main factors determining the climate-induced changes in forest productivity and composition. In this study, high-frequency variation of tree-ring width (TRW) of four native and three alien tree species and two hybrids of Populus L. growing in Latvia (hemiboreal zone) was compared using a principal component analysis based on TRW indices for the period 1965–2009. The effect of climatic factors was assessed using a bootstrapped correlation analysis. Influence of common climatic factors related to the length of the vegetation season, winter temperature, and water regime in summer was traced in the TRW of the studied species and hybrids. The combination and effect of the identified factors differed by species (and hybrids), to a certain extent explaining the diversity of TRW patterns. Nevertheless, some similarities among the species were also observed, suggesting the plasticity of growth response. Scots pine was generally sensitive to winter temperatures, but Norway spruce was mainly sensitive to summer water regime, while black alder was sensitive to winter temperatures and precipitation in spring. In contrast, silver birch showed the lowest sensitivity to the tested climatic factors (demonstrating sensitivity to winter precipitation in a few sites), suggesting tolerance to weather fluctuations. The TRW of the alien species was primarily sensitive to climatic factors related to water regime in the summer of the year preceding the formation of tree-ring, implying differences in mechanisms regulating wood increment. Nevertheless, temperature in the dormant period was significant for European larch in a few sites, suggesting sensitivity to cold damage. The variation of TRW of Populus hybrids diverged from others, as their growth was negatively correlated with the temperature in autumn, spring, and summer and positively correlated with water balance. Although the annual water balance in Latvia is positive, the effect of water deficit on tree growth was apparent.     

Introduced Siberian chipmunks are more heavily infested by ixodid ticks than are native bank voles in a suburban forest in France

By serving as hosts for native vectors, introduced species can surpass native hosts in their role as major reservoirs of local pathogens. During a 4-year longitudinal study, we investigated factors that affected infestation by ixodid ticks on both introduced Siberian chipmunks Tamias sibiricus barberi and native bank voles Myodes glareolus in a suburban forest (Forêt de Sénart, Ile-de-France). Ticks were counted on adult bank voles and on adult and young chipmunks using regular monthly trapping sessions, and questing ticks were quantified by dragging. At the summer peak of questing Ixodes ricinus availability, the average tick load was 27-69 times greater on adult chipmunks than on adult voles, while average biomass per hectare of chipmunks and voles were similar. In adult chipmunks, individual effects significantly explained 31% and 24% of the total variance of tick larvae and nymph burdens, respectively. Male adult chipmunks harboured significantly more larvae and nymphs than adult females, and than juveniles born in spring and in summer. The higher tick loads, and more specifically the ratio of nymphs over larvae, observed in chipmunks may be caused by a higher predisposition - both in terms of susceptibility and exposure - to questing ticks. Tick burdens were also related to habitat and seasonal variation in age- and sex-related space use by both rodents. Introduced chipmunks may thus have an important role in the dynamics of local vector-borne pathogens compared with native reservoir hosts such as bank voles.     

Parsimony dictates a human introduction: on the use of genetic and other data to distinguish between the natural and human-mediated invasion of the European snail Littorina littorea in North America

Two centuries of historical, archaeological, paleontological, geological, oceanographical and biological data conclusively indicate that the periwinkle snail Littorina littorea was introduced to North America from Europe either by Norse explorers 1000 years ago or by European colonists after 1840. Available genetic data do not indicate ancient divergence of North American and European L. littorea and thus do not challenge all other evidence that it was introduced from Europe by humans.