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1. The dispersal of aquatic plant propagules is highly facilitated in streams due to flow. As many aquatic plants predominantly spread through vegetative propagules, the specific retention and thus drift distance of dispersed plant fragments largely contribute to the rapid spread along the course of a stream. 2. We determined fragment retention for four aquatic plant species (Elodea canadensis, Myriophyllum spicatum, Ceratophyllum demersum, Salvinia natans; representing four different common morpho-structural groups) in sections of small to mediumsized German streams with different levels of stream sinuosity. 3. The number of fragments showed a logistic decline over drift distance. In two small streams, 90% of drifting fragments were retained at distances (D 90) of only 5-9 m and 19-70 m, while higher D 90 values of 116-903 m and 153-2,367 m were determined for sections of a medium-sized stream. The likelihood of retention thereby decreased significantly with increasing stream size and was reduced in straightened stream sections. 4. Differences in retention were more strongly related to fragment buoyancy rather than fragment size and morphology. Increasing buoyancy significantly lowered the likelihood of fragment retention over drift distance by a factor of 3-8, whereas contrasting effects were documented for size and morphology of fragments. 5. The relevance of different obstacles was highly stream section-specific and depended on obstacle abundance, distribution, and the degree of submergence/ emergence. 6. Our findings elucidate the dynamic retention patterns of plant fragments and highlight the strong interplay between extrinsic (stream) and intrinsic (fragment) properties. We conclude that straightened lowland streams of intermediate size promote the rapid dispersal of invasive aquatic plants and are particularly prone to invaders producing large amounts of small and highly buoyant plant fragments. Information on the species-specific fragment colonisation dynamics in the field is further required to improve our understanding of the vegetative dispersal capacity of invasive aquatic plants in stream ecosystems.

Amphibian clutches are colonized by diverse but poorly studied communities of micro-organisms. One of the most noted ones is the unicellular green alga, Oophila amblystomatis, but the occurrence and role of other micro-organisms in the capsular chamber surrounding amphibian clutches have remained largely unstudied. Here, we undertook a multi-marker DNA metabarcoding study to characterize the community of algae and other micro-eukaryotes associated with agile frog (Rana dalmatina) clutches. Samplings were performed at three small ponds in Germany, from four substrates: water, sediment, tree leaves from the bottom of the pond, and R. dalmatina clutches. Sampling substrate strongly determined the community compositions of algae and other micro-eukaryotes. Therefore, as expected, the frog clutch-associated communities formed clearly distinct clusters. Clutch-associated communities in our study were structured by a plethora of not only green algae, but also diatoms and other ochrophytes. The most abundant operational taxonomic units (OTUs) in clutch samples were taxa from Chlamydomonas, Oophila, but also from Nitzschia and other ochrophytes. Sequences of Oophila “Clade B” were found exclusively in clutches. Based on additional phylogenetic analyses of 18S rDNA and of a matrix of 18 nuclear genes derived from transcriptomes, we confirmed in our samples the existence of two distinct clades of green algae assigned to Oophila in past studies. We hypothesize that “Clade B” algae correspond to the true Oophila, whereas “Clade A” algae are a series of Chlorococcum species that, along with other green algae, ochrophytes and protists, colonize amphibian clutches opportunistically and are often cultured from clutch samples due to their robust growth performance. The clutch-associated communities were subject to filtering by sampling location, suggesting that the taxa colonizing amphibian clutches can drastically differ depending on environmental conditions.

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The pale summer sedge caddisfly, Limnephilus hyalinus Hagen, 1861 (Limnephilidae, the Northern Caddisflies), is widespread in North America. Genome skimming by Illumina sequencing allowed assembly of a complete 15,168 bp circular mitogenome from L. hyalinus consisting of 78.0% AT nucleotides, 22 tRNAs, 13 protein-coding genes, two rRNAs and a control region in the ancestral insect gene order. Limnephilus hyalinus COX1 features an atypical CGA start codon while ATP8, NAD1, NAD5, and NAD6 exhibit incomplete stop codons. The mtTERM binding site is conserved between the Trichoptera and the Lepidoptera. Phylogenetic reconstruction reveals a monophyletic Order Trichoptera, Family Limnephilidae, and genus Limnephilus.