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.

Two alien species in Europe,Impatiens glanduliferaandI. balfourii, are closely related, have similar growth rates and reproductive capacities, and are very attractive to pollinators. Nevertheless, onlyI. glanduliferais a highly invasive alien species in Europe, whileI. balfouriiis non-invasive. We assumed that the varying levels of invasiveness are driven by differences in the floating ability of their seeds, which may determine the invasion success of riparian alien plants, such as theImpatiensspecies. By mimicking two types of aquatic conditions, we determined seed floating ability for each species from younger and older populations. We also analyzed four seed traits: seed viability, surface, shape and coat structure. Seeds of the non-invasiveI. balfouriifloat less well than seeds of the invasiveI. glandulifera. We also found that the seeds ofI. balfouriifrom the younger population have a higher floating ability in comparison with that of the seeds from the older population. The results forI. glanduliferawere the opposite, with decreased floating ability in the younger population. These differences were associated with seed surface, shape and coat structure. These results indicate that the floating ability ofI. balfouriiseeds may increase over time following its introduction into a given area, while in the case ofI. glandulifera, this ability may gradually decrease. Therefore, the former species, currently regarded as a poor disperser, has the potential to become invasive in the future, whereas the latter does not seem to benefit from further investments in the floating ability of its seeds.

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.