Microbial stowaways – waterbirds as dispersal vectors of aquatic pro- and microeukaryotic communities

Aim: Waterbirds are important dispersal vectors of multicellular organisms such as macrophytes, aquatic macroinvertebrates, and zooplankton. However, no study to date has focused on their potential role in dispersing aquatic microbial communities. Here, we carried out the first explicit study on passive transport (endozoochory) of prokaryotes and unicellular microeukaryotes by waterbirds based on a metagenomic approach. By directly comparing the dispersed set of organisms to the source pool of a natural metacommunity, we aimed for a realistic estimate of the overall importance of waterbird zoochory for natural microbial communities. Location: Seewinkel region of Austria and Hungary. Taxon: Prokaryotes and unicellular microeukaryotes. Methods: In 2017 and 2018, water samples from natural aquatic habitats along with fresh droppings of the dominant greylag goose (Anser anser) and four other waterbird species were collected in a well-delineated habitat network of temporary saline ponds (soda pans). Their prokaryotic and microeukaryotic communities were identified via 16S and 18S rRNA gene amplicon sequencing and compared across years and waterbird species. Results: We found that up to 40% of the dominant aquatic microbial OTUs were transported by A. anser. OTU richness in A. anser droppings was lower, but compositional variation was higher compared to the aquatic communities, probably resulting from stochastic pick-up of microbes from multiple aquatic habitats. We furthermore found that prokaryote species composition of bird droppings followed the interannual turnover in the aquatic communities. Finally, we found species-specific differences among different waterbird species. Among them, the planktivore filter-feeder northern shovelers (Anas clypeata) collected and dispersed a more species-rich subset of microeukaryotes than shorebirds or geese. Main conclusions: Overall, our study provides the first quantitative empirical evidence of endozoochory in natural microorganism communities. These results imply that waterbirds may be crucial in maintaining ecological connectivity between discrete aquatic habitats at the level of microbial communities. Keywords: aquatic microorganisms, bacteria, connectivity, dispersal, endozoochory, phytoplankton, protists, waterbirds

Insect Preservation Methods Allow Quantification of Dispersing Microorganisms by Scanning Electron Microscopy

Insects may act as dispersal vectors for microbes where microbes can temporarily adhere to insect exoskeletons. Microbes carried by honey bees (Apis mellifera) may experience a range of dispersal outcomes, from successful colonisation of a new habitat to predation by grooming bees, partly depending on their location on the bee exoskeleton and the carried population size. I tested four methods for handling collected bees, and examined the bees in a scanning electron microscope, imaging and counting microbial cells attached to tarsal claws. Freeze-dried bees carried more microbial cells than bees that were pinned and air-dried, preserved in 96% ethanol then dried by CO2 critical-point drying, or bees washed with potassium phosphate then preserved in 96% ethanol, but some microbes were found on bees from every treatment. The similarity in microbial passengers found between air-dried and ethanol-preserved bees suggests that examination by electron microscopy could be used to address questions regarding microbial dispersal by pollinators already present in collections associated with other pollination research.

The Invasive Macroalga Rugulopteryx okamurae: Substrata Plasticity and Spatial Colonization Pressure on Resident Macroalgae

The present study constitutes the first evaluation of the space colonization strategies performed by Rugulopteryx okamurae when co-occurring with the resident macroalgal community in the introduced areas. Since the first apparition of the nonindigenous macroalga in the Strait of Gibraltar, its high propagation capacity together with its colonization ability has enhanced the establishment success of the species in detriment of the resident biota. In this study, we carried out observational surveys during 2017–2020 in order to assess the coverage levels of R. okamurae on different lighting conditions, surface orientations, and substrata types (artificial and natural). Results revealed that, beyond the high percent coverages already reported at illuminated and semi-illuminated natural rocky habitats, R. okamurae is able to settle on a wide variety of artificial substrata. The settlement performance of the species was also investigated and different mechanisms underlying the space colonization were proposed. Thus, R. okamurae was observed interacting with 43 resident macroalgal species at generally illuminated rocky habitats of the northern Strait coasts. Six colonization mechanisms were proposed for spatial growth scenarios. Overall, results pointed out that, in most of the cases where the invasive species co-occur with the resident community, R. okamurae would be favored as regards spatial growth success. Competitive interactions and environmental factors which influence results obtained must be addressed in order to fully predict impacts on resident communities. Moreover, together with previous scientific works, overall data provided in this study highlight the need to urgent implement management measures focused on habitats susceptible to be invaded, as well as studies on the ecology and dispersal vectors of R. okamurae in the Strait of Gibraltar and adjacent areas.

Changing climate requires shift from refugia to sanctuaries for floodplain forests

Context Riparian areas are considered to undergo major alterations under changing climate, making floodplain habitats targets for conservation and landscape planning. Protected areas might provide sanctuaries especially for sessile riparian plant species, but these niches are not always persistent over time. Objectives We investigate if plant species of floodplain forests are provided with suitable habitat within currently protected areas and if these refugia persist. A coupled-modelling approach is used to gain spatially explicit information on new areas for sanctuaries. Methods We use species distribution models to predict the niche of 12 Salicion albae and 7 Fraxinion floodplain forest species along rivers in Switzerland, under current, moderate and extreme climate change scenarios up to 80 years to the future (2100). The spread of plant species from current habitat to suitable future habitat is simulated using dispersal vectors and life history traits. Results Salicion albae species are more flexible under both climate change scenarios than Fraxinion species. The main limitation for the spread of species is their dispersal ability, as only a minority of the suitable cells is colonized during the simulation process. The predicted future presence within currently protected areas decreases under both climate change scenarios in the model. Conclusions Current protected floodplains do not provide persistent refugia for the plants studied, but might still be of importance to other organisms. Planning of sanctuaries for riparian plant species and communities need to focus on connectivity along rivers to maintain viable source populations in dynamic riverine landscapes under changing climate.

Las especies de Splachnaceae (Bryophyta) de Tierra del Fuego, Argentina: las esporas y sus modos de dispersión

The Splachnaceae family is a bryological component of the temperate forests of Nothofagus in the Fuegian region of Argentina. It is represented by the Tayloria genera with three species, T. dubyi (endemic), T. magellanica, T. mirabilis, and Tetraplodon, with a single specie Tetraplodon fuegianus. They grow on organic substrates of animal origin and are the only family among mosses in the area in which entomochory is observed (i.e. dispersion of spores through insects). From herbarium material, the taxonomic features of gametophytes and sporophytes which allow species to be identified are described. Spores were studied with OM and SEM. Dispersal vectors for Tayloria mirabilis and morfo-ecological adaptations associated with entomochory were observed and analyzed. Mosses are differentiated from their leaves and the morphology and color of the sporophyte capsules. The spores, similar in the studied species, are dispersed in sticky masses, they are spheroidal, monoletes, 8-13 μm of diameter with a pitted-reticulate ornamentation. The dispersing agents mostly correspond to the order Diptera. The Splachnaceae family has developed adaptive strategies in relation to substrate (coprophilous gametophytes), in striking and showy sporophytes morphologies and in a particular dispersal mode of the spores by insects. All these morpho-ecological adaptations contribute to an effective action of the dispersing agents in the muscinal biocenosis.

New alien taxa of the genus Cornus (Cornaceae) recorded in Lithuania and Latvia

Plants of the genus Cornus are valued for their ornamental qualities, are often grown in gardens, parks, or other public plantings, and form various shelterbelts. This increases the likelihood that these bird-dispersed plants will escape from their sites. This paper provides information on the first record of C. mas in Lithuania in 2021 at two sites. This species is currently considered a casual alien species, but may become locally naturalised in the future. This study confirmed that C. sericea is widespread in Lithuania, and the oldest herbarium specimen of the species was collected in 1997. Cornus sericea, like C. alba, is naturalised and potentially invasive in Lithuania. The alien subspecies of C. sanguinea (C. sanguinea subsp. australis) was found for the first time in Lithuania and Latvia in 2018. Available data show that this subspecies is naturalised in both countries, and its abundance in some areas in Lithuania indicates that it may become an invasive plant. The paper discusses dispersal vectors, occupied habitats, and the potential for spreading three alien Cornus taxa.

Strong sexual selection does not induce population differentiation in a fish species with high dispersal potential: the curious case of the worm pipefish Nerophis lumbriciformis (Teleostei: Syngnathidae)

High levels of population differentiation are a common demographic pattern in syngnathids, even at small geographical scales. This is probably the end result of the common life history traits observed within the family, involving limited dispersal capabilities and strong habitat dependency. The worm pipefish, Nerophis lumbriciformis, which displays all these characteristics, also presents an additional variable potentially able to promote population differentiation: high sexual selection intensity, especially at the extremes of its distribution. Nevertheless, an early life pelagic stage, which presumable allows for admixture, could prevent population structuring. Here, we assessed the phylogeography of N. lumbriciformis through the amplification of the cytochrome b, 12S and 16S rDNA mitochondrial markers as well as the rhodopsin nuclear marker, performed upon 119 individuals. We observed a genetically homogeneous population with indications of extensive gene flow. We tentatively attribute this finding to the dispersal potential of the species’ pelagic larvae, supported by marine currents acting as major dispersal vectors. We also detected a signal of expansion towards the poles, consistent with the current climate change scenario. Despite the marked latitudinal differences in the phenotype of reproducing worm pipefish, the absence of clear population structuring suggests that phenotypic plasticity can have a significant role in the expression of sexual selection-related traits.

Ungulates as dispersal vectors of non-native plants.

Ungulates are present worldwide with 257 recorded species, including livestock. They cover different functional gradients, be it feeding regime, digestive strategy, body size, body mass, fur characteristics or sociality. All these specificities may intervene at different stages of animal-mediated plant dispersal. Ungulates move diaspores from both native and non-native plants, through endo- and epizoochory. Initially introduced by humans, non-native plants bearing specific traits can be carried over long distances and to new environments by ungulates. These vectors can further free local resources necessary for the germination and the subsequent growth of the released diaspores. We first looked at trait-based plant community changes at different timescales in the presence of different native ungulates. We then reviewed the literature on endozoochory, regurgitation and fur-epizoochory assisted by ungulates, focusing on the dispersal of non-native plants. We made an overall assessment of ungulate-mediated non-native plant dispersal by biogeographical zone and dispersal mode, and then provided additional information on plant growth form and taxonomy, vectors and associated modes of dispersal. Results are presented for four main ungulate families: Cervidae, Bovidae, Suidae and Equidae. For each family, we highlight our findings either by ungulate if sufficiently represented (e.g. <i>Odocoileus virginianus, Bison bison, Bos taurus</i>) or by group of species. According to their feeding regime, grazers dispersed solely forbs and graminoids whereas omnivores also dispersed plants from other growth forms (i.e. cactus, vine, shrub and tree). Numerous non-native plants are dispersed by ungulates around the world, but this is probably the visible part of the iceberg, as only 32 ungulates (i.e. 12%) have been studied as vectors so far, suggesting their overall contribution is certainly underrated.