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"Fontaneto, Diego"
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Long-distance passive dispersal in microscopic aquatic animals
Given their dormancy capability (long-term resistant stages) and their ability to colonise and reproduce, microscopic aquatic animals have been suggested having cosmopolitan distribution. Their dormant stages may be continuously moved by mobile elements through the entire planet to any suitable habitat, preventing the formation of biogeographical patterns. In this review, I will go through the evidence we have on the most common microscopic aquatic animals, namely nematodes, rotifers, and tardigrades, for each of the assumptions allowing long-distance dispersal (dormancy, viability, and reproduction) and all the evidence we have for transportation, directly from surveys of dispersing stages, and indirectly from the outcome of successful dispersal in biogeographical and phylogeographical studies. The current knowledge reveals biogeographical patterns also for microscopic organisms, with species-specific differences in ecological features that make some taxa indeed cosmopolitan with the potential for long-distance dispersal, but others with restricted geographic distributions.
Journal Article
Meiofauna as a model to test paradigms of ecological metacommunity theory
The metacommunity concept incorporates spatial dynamics into community ecology, shedding light on how local and regional processes interact in structuring ecological communities, and to which measure they are deterministic or stochastic. We reviewed metacommunity studies on freshwater meiobenthos published since 2004, when the main principles of metacommunity theory were conceptualized. The studies (together 19) were observational, focused mainly on ostracods, and rarely on rotifers and nematodes. In accordance with general expectations, the prevalent structuring force was species sorting. Ostracods showed more dispersal limitations than nematodes and rotifers, and there was very little support for dispersal surplus. We discussed the role of body size, dispersal mode, and attachment to sediment for the meiofauna dispersal. Effects of metacommunity context (habitat connectivity, spatial extent, and environmental heterogeneity), study design (e.g., sample size), and statistical approach could not be sufficiently disentangled due to the low number of studies. Local stochasticity, consistent with neutral theory and patch dynamics, was indicated for taxa with weak specialization and metacommunities in small habitats. Our understanding of meiofaunal metacommunities is only fragmentary and it would highly benefit from direct comparisons of taxa with different species traits and between different spatial scales, and studies incorporating temporal dynamics and hypothesis-driven experiments.
Journal Article
Biodiversity analyses in freshwater meiofauna through DNA sequence data
Microscopic animals (also referred to as meiofauna) in freshwater habitats include several common, abundant and species-rich phyla, whose patterns of diversity are poorly known. Several approaches using DNA sequence data can be used to improve our knowledge on their biodiversity. In this review, we focus on studies using DNA data for taxonomy, and for environmental studies through metabarcoding on freshwater meiofauna. The results of the literature survey reveal that the use of DNA data is still rather limited. We screen the available literature on the topic and analyse the details of the current use and choices of the methods in freshwater meiofauna, the potential problems and limitations, and the flawed parts that still need to be improved. We conclude the review with a perspective on the still unexploited potentials in future applications to address biodiversity shortfalls in species diversity and taxonomy, and in the ecological and biogeographical patterns of species distribution.
Journal Article
Effects of Ailanthus altissima Invasion and Removal on High-Biodiversity Mediterranean Grasslands
Ailanthus altissima is one of the worst invasive plants in Europe in several habitat types, including high-biodiversity grasslands. The aim of this work was to evaluate the impact of the invasive A. altissima on high-biodiversity grassland vegetation and the effects of its removal on the recovery of native plant communities. The study area was within the Alta Murgia National Park (SE Italy). Seventeen vegetation quadrats were sampled in invaded grasslands and nine quadrats were sampled in nearby uninvaded areas. A. altissima was removed from six quadrats, which were sampled for two years after plant removal. Cluster analysis and non-metric multidimensional scaling ordination were used to identify and visualize the general vegetation pattern. Generalised Linear Models with different error structures were used to analyse the effects of A. altissima on native grasslands and vegetation recovery after removal. Results showed that the invasion of A. altissima changed drastically the community composition, reduced plant richness and diversity. Invaded stands had a greater presence of ruderal and widely distributed taxa, as opposed to a lesser presence of endemic and Mediterranean ones. The differences in the community composition between invaded and uninvaded quadrats became clearly detectable when A. altissima plants exceeded a threshold of 1 m of height and 50% of coverage. After A. altissima removal, the recovery of the grassland community was not completely achieved after two years.
Journal Article
Potential niche displacement in species of aquatic bdelloid rotifers between temperate and tropical areas
Bdelloids are commonly found in freshwaters or limno-terrestrial habitats. No formal attempt has yet been performed to define bdelloid niche and to identify whether species respond in a clear, consistent, and quantifiable fashion to environmental parameters. Therefore, we analysed the correlation between the occurrence of common Rotaria species in Thailand and environmental variables, including limnological, climatic, and biotic features. We followed two approaches to determine the niche of the investigated species: performing regression models for each species and reconstructing the niche spaces occupied by each species using n-dimensional hypervolumes. The effect of local-scale limnological and large-scale climatic variables was almost negligible at explaining the occurrence and distribution of Rotaria species. Surprisingly, primary productivity, known in temperate areas to be a major positive correlate of the occurrence of R. neptunia, appeared to have no effect on this species when measured as chlorophyll a, and a negative effect when measured as cyanobacterial productivity. Biotic variables revealed that different Rotaria species have a similar response to environmental variables. Two main messages are supported: (i) no clear environmental features unambiguously affected bdelloids species; (ii) features that are relevant for limnological processes at temperate latitudes may not be applicable for explaining processes in tropical latitudes.
Journal Article
Drivers of species knowledge across the tree of life
Knowledge of biodiversity is unevenly distributed across the Tree of Life. In the long run, such disparity in awareness unbalances our understanding of life on Earth, influencing policy decisions and the allocation of research and conservation funding. We investigated how humans accumulate knowledge of biodiversity by searching for consistent relationships between scientific (number of publications) and societal (number of views in Wikipedia) interest, and species-level morphological, ecological, and sociocultural factors. Across a random selection of 3019 species spanning 29 Phyla/Divisions, we show that sociocultural factors are the most important correlates of scientific and societal interest in biodiversity, including the fact that a species is useful or harmful to humans, has a common name, and is listed in the International Union for Conservation of Nature Red List. Furthermore, large-bodied, broadly distributed, and taxonomically unique species receive more scientific and societal attention, whereas colorfulness and phylogenetic proximity to humans correlate exclusively with societal attention. These results highlight a favoritism toward limited branches of the Tree of Life, and that scientific and societal priorities in biodiversity research broadly align. This suggests that we may be missing out on key species in our research and conservation agenda simply because they are not on our cultural radar.
Journal Article
widely used small subunit 18S rDNA molecule greatly underestimates true diversity in biodiversity surveys of the meiofauna
Molecular tools have revolutionized the exploration of biodiversity, especially in organisms for which traditional taxonomy is difficult, such as for microscopic animals (meiofauna). Environmental (eDNA) metabarcode surveys of DNA extracted from sediment samples are increasingly popular for surveying biodiversity. Most eDNA surveys use the nuclear gene-encoding small-subunit rDNA gene (18S) as a marker; however, different markers and metrics used for delimiting species have not yet been evaluated against each other or against morphologically defined species (morphospecies). We assessed more than 12,000 meiofaunal sequences of 18S and of the main alternatively used marker [Cytochrome c oxidase subunit I (COI) mtDNA] belonging to 55 datasets covering three taxonomic ranks. Our results show that 18S reduced diversity estimates by a factor of 0.4 relative to morphospecies, whereas COI increased diversity estimates by a factor of 7.6. Moreover, estimates of species richness using COI were robust among three of four commonly used delimitation metrics, whereas estimates using 18S varied widely with the different metrics. We show that meiofaunal diversity has been greatly underestimated by 18S eDNA surveys and that the use of COI provides a better estimate of diversity. The suitability of COI is supported by cross-mating experiments in the literature and evolutionary analyses of discreteness in patterns of genetic variation. Furthermore its splitting of morphospecies is expected from documented levels of cryptic taxa in exemplar meiofauna. We recommend against using 18S as a marker for biodiversity surveys and suggest that use of COI for eDNA surveys could provide more accurate estimates of species richness in the future.
Journal Article
Evolutionary dynamics of transposable elements in bdelloid rotifers
Transposable elements (TEs) are selfish genomic parasites whose ability to spread autonomously is facilitated by sexual reproduction in their hosts. If hosts become obligately asexual, TE frequencies and dynamics are predicted to change dramatically, but the long-term outcome is unclear. Here, we test current theory using whole-genome sequence data from eight species of bdelloid rotifers, a class of invertebrates in which males are thus far unknown. Contrary to expectations, we find a variety of active TEs in bdelloid genomes, at an overall frequency within the range seen in sexual species. We find no evidence that TEs are spread by cryptic recombination or restrained by unusual DNA repair mechanisms. Instead, we find that that TE content evolves relatively slowly in bdelloids and that gene families involved in RNAi-mediated TE suppression have undergone significant expansion, which might mitigate the deleterious effects of active TEs and compensate for the consequences of long-term asexuality.
Journal Article