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Some algal species have extended their native range. Problems in settling on a proper definition of 'alien' for microorganisms have made it difficult to unequivocally assess whether their spread was natural or resulted from human intervention. As direct evidence seems to be virtually non-existent, the only option is to rely on circumstantial evidence. In this paper, we discuss the expansion routes of three cyanobacteria species: Cylindrospermopsis raciborskii, Raphidiopsis mediterranea and Cuspidothrix issatschenkoi. We analyse the information available for these species, which are commonly regarded as alien, in order to establish the context in which the migration and evolution of these microorganisms should be understood, so that a proper assessment of their geographic expansion can be made. A more complete picture of the expansion and evolution of microorganisms must combine many types of information, including the history of local expansions, ecological ranges, and data from studies in morphology, ecology, genetics and paleolimnology.

Aim The aim of the study was to test the role of racoon (Procyon lotor), an invasive alien species, in the spread of microorganisms. We tested whether the spread of microorganisms can be detected by sampling microbial DNA sourced from the raccoon body, thus facilitating biodiversity research. Location Warta Mouth National Park, western Poland. Methods We used the V4 hyper‐variable region of the 18S ribosomal RNA gene and Illumina MiSeq amplicon sequencing to identify microorganisms present on the body surface of raccoons. Results Out of 170 DNA samples, we obtained 15 PCR products that contained the target sequences of freshwater or terrestrial microorganisms. We found that raccoons carry and spread chlorophytes, alveolates, amoeboids and fungi on their body surface. We identified 16 different microbial organisms. The sequences of four organisms, Micronuclearia podoventralis (amoeboid), Parachloroidium lobatum and Jaagichlorella roystonensis (chlorophyta), and Mortierella polygonia (fungi), exhibited 100% identity to the best GenBank hit and were thus identified to the species level. The two chlorophyte species, Parachloroidium lobatum and Jaagichlorella roystonensis, are particularly noteworthy, as they were first described recently, in 2013 and 2019, respectively, and knowledge about their global distribution is very scarce. Main conclusions We demonstrated that raccoons may effectively spread terrestrial and aquatic microorganisms. By utilizing this novel source of microbial DNA, we also showed that mammals may be effective living samplers. This perspective is worth exploring, as in some cases it may efficiently reduce the burden required in traditional sampling and provide valuable insights into local biodiversity and distributions of species.

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Two articles published in Diversity and Distributions (Green, 2015;Reynolds et al., 2015) demonstrate the role of waterbirds in dispersing alien species and claim that this phenomenon has been largely neglected. Setting out priorities for the future, they focus on the need to improve our understanding of the problem if it is to be successfully managed. We argue that birds are vectors of the secondary spread of alien species already introduced by human agency, rather than the pathway of their primary introduction. The challenge presented by unaided dispersal pathways, such as birds, will not be significantly reduced by future advances in our understanding of their mechanisms. The three-stage hierarchical approach, recommended by the Convention on Biological Diversity, remains the best management option for biological invasions, irrespective of the level of knowledge about their pathways.Keywords biological invasions, invasion pathways, invasion vectors, secondary spread, three-stage hierarchical approach, unaided pathways.Two articles published in Diversity and Distributions (Green, 2015;Reynolds et al., 2015) discussed the role of waterbirds in dispersing alien species. The authors provide empirical evidence for such dispersal of 79 alien plant species and eight alien invertebrates, including some of the worst aquatic invaders and the most widely distributed alien terrestrial plant species. In setting out priorities for the future, these authors stress that improving our knowledge of different aspects of this problem is a basic prerequisite of its proactive and effective management. However, they give little practical advice on how this management should be realized. We argue that stopping primary introductions of new alien species and preventing their establishment are the two most important conditions for avoiding their further spread not only by birds but also through other unaided pathways, such as wind or sea currents. Once alien species capable of such hitchhiking have been introduced and established, their containment may be virtually impossible even if we make great progress in understanding the mechanisms of that phenomenon.Reynolds et al. and Green provide a set of priorities for future field and experimental research. They postulate, among other things, that improving predictions of invasive alien species spread by waterbirds requires an understanding of the nature and scale of waterbird movement and foraging ecology, baseline identification of the alien organisms being dispersed by waterbirds in different parts of the globe, the effects of gut passage, the viability and condition of propagules landing at new sites, propagule selectivity and retention, and whether multiple bird species may be spreading a particular alien organism. We claim that our knowledge of some of these aspects is already good enough to lead us to conclude that further progress will add little, regrettably, to our arsenal of practical means to tackle avian dispersal of alien species.For example, most cases of endozoochory...

Although closely related, Impatiens glandulifera and Impatiens balfourii differ in their invasiveness in Europe; only the former is highly invasive there. Following the assumptions of the enemy release hypothesis (ERH), we tested whether these differences may be explained by the levels of seed infestation by pathogenic fungi. Using seeds collected along the Swiss-Italian border, we recorded four true pathogens of seeds: Fusarium culmorum, F. oxysporum, F. sporotrichoides, and Giberella avenacea. In Italy the seeds of I. balfourii were infected by fungal pathogens more often than those of I. glandulifera, while in Switzerland both species were under the same level of pressure. However, the overall differences in pathogen abundance were consistent with the ERH: seeds of the more invasive species were attacked less. This could be a result of differences between the communities of fungal pathogens attacking the seeds of both species in each country. The number of colonies of secondary pathogens (Cladosporium cladosporioides, Alternaria alternata) correlated negatively with the number of colonies of true pathogens; we suggest that the secondary pathogens may have prevented the occurrence of the true pathogens. The reason for the between-country differences in the fungal pathogen communities is unclear. A possible explanation is that Italy and Switzerland differ in their road and greenarea maintenance work schemes, which may have influenced pathogen pressure on seeds. This study is one of the few that offers results indicating that release from enemies may be crucial to the invasion success of plants as early as the seed stage. Keywords Biological invasions Á Seed enemies Á Seedborne fungi Á Seed antagonists Á Obligatory pathogens Á Enemy release hypothesis Communicated by Timothy Bell.

The enemy release hypothesis (ERH) attributes the invasive behavior of some alien species to decreased pressure from natural enemies, as they have been left behind in the hosts' native range. The majority of research supports this idea, but some studies confirm it only partially or even contradict it. Here, we present the results of ERH tests of three Impatiens species studied in southern Poland in 2010-2011. Two of them are alien and invasive in Europe (Impatiens glandulifera, I. parviflora) and one is native (I. noli-tangere). We compared the three species in terms of the percentage of all leaves showing symptoms of disease and/or damage, and also the number of pests recorded on the monitored plants.In 1071 individual plant controls, we assessed 17 180 leaves, 7552 of which showed symptoms of disease/damage, and we recorded 5721 invertebrates, 5220 of them were pests. Rusts and spots were the predominant symptoms and Aphidoidea were the dominant group of pests. Comparisons of the two alien and one native Impatiens did not confirm the ERH in 90% of the performed tests. Most of the differences between the species were not significant, and most of the significant ones contradicted the ERH. The only results confirming the ERH were found in comparisons between I. parviflora and I. noli-tangere. The tests between two alien species showed that I. parviflora was under higher pest pressure, while I. glandulifera had more disease and damage symptoms, thus, plant-enemy relations differed between the two balsams. In summary, the presented results add evidence that the success of some alien species may depend on factors related to biotic and/or abiotic conditions in ways that are not explained by the enemy release hypothesis.