The under-ice microbiome, a five-year study at Lake Tovel

Little is known about changes in microbial abundance and community composition during persistent ice cover of lakes. Here, the under-ice 16S rRNA diversity was assessed for different pelagic layers and compared between years (2015, 2017, 2018, 2019, 2020) at Lake Tovel (1177 m above sea level; Italy). Functional profiling of amplicon sequences variants (ASVs) was also done with Piphillin. Environmental parameters (chemistry, temperature, light climate, oxygen concentration) were linked to the observed diversity patterns. Despite relatively uniform temperature and chemistry profiles, the pelagic and hypolimnetic microbiome of different years were different as assessed by a Principal Coordinates Analysis. The under-ice light climate was a driving factor of the observed differences and related to different precipitations patterns. These results underline how a changing climate also influences life under ice

CO2 evolution in surface waters of Lake Tovel

Lake Tovel, a mountain lake (1177 m a.s.l.), is regularly samples during the ice-free season from 1995 onwards. Based on chemical data and the PhreeQC software, the CO2 content in the surface is calculated and the CO2 flux to the atmosphere is assessed. Lake Tovel shows considerable variability, coinciding with changing dissolved oxygen concentrations in the hypolimnion. Possible relationships will be discussed

Cryptic diversity of Synchaeta spp. (Rotifera, Monogononta) in mountain lakes: relationships with environmental parameters

Cryptic species (i.e. distinct species that are morphologically similar) may have different ecological requirements and their merging into one species can bias the assessment of the main ecological drivers of biodiversity. We investigated the environmental parameters influencing the occurrence of Synchaeta species (S. pectinata, S. grandis, S. lakowitziana, S. tremula/oblonga - monogonont rotifers) in 17 waterbodies of the Trentino-South Tyrol region in the Eastern Alps. To improve taxonomic resolution in phylogenetic analysis, a marine Synchaeta (i.e. S. cf. cecilia) from the United Kingdom was also sampled and sequences from GenBank were downloaded. While Synchaeta species were morphologically identified based on trophi structure, cryptic species were identified based on the generalised mixed Yule coalescent (GMYC) model. We performed multivariate ordination both for morphospecies (i.e. unresolved complexes of cryptic species), a common practice in limnological studies based on morphological taxonomy, and for putative cryptic species, made possible by DNA taxonomy. We expected that resolving complexes of cryptic species could provide more information than using morphospecies. Out of the overall phylogenetic tree with 48 haplotypes from 203 individuals, the GMYC model indicated the presence of 14 GMYC entities, 11 from lakes in the Eastern Alps, 2 from Canada, and one from the U.K. Synchaeta pectinata showed five GMYC entities and S. tremula showed two; all individuals, for which the identification to S. tremula or S. oblonga was not possible, clustered in one monophyletic clade, here called S. tremula/oblonga, that showed additional evidence of three GMYC entities. Environmental-based multivariate ordination on cryptic species explained a significantly higher proportion of variance than that based on morphospecies. Occurrence of putative cryptic species was mainly related to total phosphorus. Moreover, different cryptic species within the same morphospecies showed different, and even opposite, preferences for total phosphorus. In addition, the same GMYC entity of S. tremula/oblonga found in Trentino-South Tyrol was also present in Canada and the same haplotype of S. pectinata found in Trentino-South Tyrol was also found in the U.K. This wide geographical distribution of haplotypes and cryptic species indicated the absence of dispersal barriers in Synchaet

Sexual species are separated by larger genetic gaps than asexual species in rotifers.

Why organisms diversify into discrete species instead of showing a continuum of genotypic and phenotypic forms is an important yet rarely studied question in speciation biology. Does species discreteness come from adaptation to fill discrete niches or from interspecific gaps generated by reproductive isolation? We investigate the importance of reproductive isolation by comparing genetic discreteness, in terms of intra- and interspecific variation, between facultatively sexual monogonont rotifers and obligately asexual bdelloid rotifers. We calculated the age (phylogenetic distance) and average pairwise genetic distance (raw distance) within and among evolutionarily significant units of diversity in six bdelloid clades and seven monogonont clades sampled for 4211 individuals in total. We find that monogonont species are more discrete than bdelloid species with respect to divergence between species but exhibit similar levels of intraspecific variation (species cohesiveness). This pattern arises because bdelloids have diversified into discrete genetic clusters at a faster net rate than monogononts. Although sampling biases or differences in ecology that are independent of sexuality might also affect these patterns, the results are consistent with the hypothesis that bdelloids diversified at a faster rate into less discrete species because their diversification does not depend on the evolution of reproductive isolation

The new checklist of the Italian Fauna: Rotifera

5openInternationalInternational coauthor/editorWe present a data set reporting the checklist of the species of the phylum Rotifera for Italy, updating the one previously published in the series ‘Checklist delle Specie della Fauna d'Italia’ in 1995. The records of the updated checklist refer to the 483 taxa at the species and subspecies level currently known from national Italian territories (119 Bdelloidea, 362 Monogononta, 2 Seisonacea) at the regional level (22 terrestrial and nine marine geographical units). The records refer to various freshwater, limno-terrestrial, and marine coastal habitats. The previous checklist reported 245 taxa (54 Bdelloidea, 189 Monogononta, 2 Seisonacea): three taxa were removed because currently considered not valid and 241 were added,scanning 21 papers we found that were published between 1993 and 2020, expanding the regional records and including four papers older than 1993 with overlooked records in the previous checklist. The Rotifera data are part of the updated Checklist of the Italian Fauna, which is viewable on the LifeWatch Italy platform at https://www.lifewatchitaly.eu/en/initiatives/checklist-fauna-italia-en/checklist and is freely available on the LifeWatch Italy Data Portal (https://dataportal.lifewatchitaly.eu/data). The checklist will be dynamically updated with new records; this paper describes the state of the art of the data set regarding Rotifera on May 2021.openFontaneto, D.; Bertani, I.; Cancellario, T.; Rossetti, G.; Obertegger, U.Fontaneto, D.; Bertani, I.; Cancellario, T.; Rossetti, G.; Obertegger, U

Multi annual comparisons of summer and under ice phytoplankton communities of a mountain lake

Little is known on the dynamics of under-ice phytoplankton communities. We investigated phytoplankton communities in the upper (0-20 m) and lower (30-35 m) layer of oligotrophic Lake Tovel, Brenta Dolomites (Italy) over six years during summer and under ice. Winter conditions were different from one year to another with respect to ice thickness and snow cover. Proxies for light transmission (Secchi disk transparency, light attenuation) were similar between seasons, even though the incident solar radiation was lower in winter. Algal richness and chlorophyll-a were not different between seasons while biomass was higher during summer. In four of the six years, Bacillariophyta dominated during summer and Miozoa (class Dinophyceae) under ice while in two years Bacillariophyta also dominated under ice. Generally, a shift to larger size classes from summer to under ice was observed for Bacillariophyta, Chlorophyta, and Ochrophyta (class Chrysophyceae) while Dinophyceae showed the opposite pattern. No strong links between phytoplankton community composition and abiotic factors (under-ice convective mixing, snow on ice, under-ice light) were found. We suggest that inter-species relationships and more precise indicators of under-ice light should be considered to better understand under-ice processes

A georeferenced dataset of Italian occurrence records of the phylum Rotifera

We report a dataset of known and published occurrence records of Italian taxa from species (and subspecies) to family rank of the phylum Rotifera; we considered only Bdelloidea, Monogononta, and Seisonacea, and did not include Acanthocephala. The dataset in-cludes 15,525 records (12,015 of which with georeferenced coordinates) of 584 valid species and subspecies names and other taxa at family level, gathered from 332 published papers. The published literature spans the period from 1838 to 2022, with the lowest number of papers published during the first half of the twentieth century, followed by an increasing number of papers, from 20 to more than 60 in each decade. The Italian regions with the highest number of records and species are Emilia-Romagna, Lombardy, and Piedmont, whereas no records are known for Molise. The number of species known from each region mostly mirrors sampling efforts, measured as the number of publications per region. The dataset is available through the Open Science Framework (OSF), and all the georeferenced occurrence data have been uploaded to the Global Biodiversity Information Facility (GBIF). ial use only

A georeferenced dataset of Italian occurrence records of the phylum Rotifera

We report a dataset of known and published occurrence records of Italian taxa from species (and subspecies) to family rank of the phylum Rotifera; we considered only Bdelloidea, Monogononta, and Seisonacea, and did not include Acanthocephala. The dataset includes 15,525 records (12,015 of which with georeferenced coordinates) of 584 valid species and subspecies names and other taxa at family level, gathered from 332 published papers. The published literature spans the period from 1838 to 2022, with the lowest number of papers published during the first half of the twentieth century, followed by an increasing number of papers, from 20 to more than 60 in each decade. The Italian regions with the highest number of records and species are Emilia-Romagna, Lombardy, and Piedmont, whereas no records are known for Molise. The number of species known from each region mostly mirrors sampling efforts, measured as the number of publications per region. The dataset is available through the Open Science Framework (OSF), and all the georeferenced occurrence data have been uploaded to the Global Biodiversity Information Facility (GBIF)

Dissolved oxygen dynamics under ice: three winters of high-frequency data from Lake Tovel, Italy

Under-ice dissolved oxygen (DO) metabolism and DO depletion are poorly understood, limiting our ability to predict how changing winter conditions will affect lake ecosystems. We analyzed under-ice DO dynamics based on high-frequency (HF) data at two depths (5 and 25 m) for three winters (January-March 2014, 2015, and 2016) in oligotrophic Lake Tovel (1178 m above sea level; maximum depth 39 m). Specifically, we assessed diel metabolic rates based on HF data of DO, temperature, and light for winter 2016 and seasonal DO depletion rates based on HF data of DO for all three winters. For 2016, calculations of metabolic rates were possible only for 34% and 3% of days at 5 and 25 m, respectively; these metabolic rates generally indicated net heterotrophy at both depths. Low success in modeling metabolic rates was attributed to low diel DO variability and anomalous diel DO patterns, probably linked to under-ice physical processes. Seasonal DO patterns for the three winters showed increasing, decreasing, or stable DO trends at 5 m while at 25 m patterns always showed decreasing DO trends but with different rates. Our multiyear study permitted us to hypothesize that the observed intraannual and interannual differences in DO depletion can be attributed to variable snow cover determining the penetration of radiation and thus photosynthesis. This study brings new insights to DO dynamics in ice-covered systems, highlights the challenges linked to under-ice lake metabolism, and advocates for a modeling approach that includes physical processes

ZOOPLANKTON IN ANCIENT AND OLIGOTROPHIC LAKE OHRID (EUROPE) IN ASSOCIATION WITH ENVIRONMENTAL VARIABLES

Analiziran je sastav zooplanktona u geološki starom, tektonskom Ohridskom jezeru (Makedonija, jugoistočna Europa). Glavni cilj rada bio je utvrditi sezonske i prostorne značajke funkcionalnih hranidbenih skupina zooplanktona i njihovu povezanost s uvjetima okoliša. Najveća produkcija zooplanktona utvrđena je u metalimniju, u kojem su biomasa fitoplanktona i brojnost zooplanktona postigle najveće vrijednosti. Utvrđeno je 16 pelagičkih vrsta od kojih dvije endemične: Arctodiaptomus steindachneri (Richard, 1897) i Cyclops ochridanus (Kiefer, 1932). Zooplankton pelagijala bio je zastupljen s niskom brojnošću, 25 ± 22 ind. L-1, a najveći udio, 60 %, postigli su veslonošci. Unutar trofičke skupine mikrofaga, prevladavali su tijekom ljeta kolnjaci s vrstom Kellicottica longispina (Kellicott, 1879), a naupliji veslonožaca prevladavali su u proljeće Eudiaptomus gracilis (Sars, 1862) and C. achridanus i jesen C.achridanus. Ova trofička skupina hrani se suspenzijom bakterija i detritusa, te je tijekom istraživanog razdoblja zauzimala afotički hipolimnij. Predatori su uglavnom bili zastupljeni s kopepoditima i odraslim veslonošcima u metalimniju. Na njihove populacije su značajno i pozitivno utjecali: temperatura (r = 0.417, p = 0.001), otopljeni kisik (r = 0.463, p = 0.0001) te najizraženije biomasa fitoplanktona (r = 0.708, p < 0.00001). Ovo istraživanje među prvima razmatra zooplankton Ohridskog jezera kao važnu kariku unutar hranidbene mreže ovog oligotrofnog ekosustava.Zooplankton is studied in the ancient, tectonic, oligomictic and oligotrophic Lake Ohrid (Macedonia, South Eastern Europe). The main aim of this study was to assess the seasonal and spatial patterns of the zooplankton functional feeding guilds in relation to the environmental conditions. Metalimnion of the lake was detected as the most productive environment, where biomass of the phytoplankton and abundance of the zooplankton reached their maxima. Pelagial zooplankton of low abundance (25 ± 22 ind. L-1) consisted of 16 species including two endemic copepods, Arctodiaptomus steindachneri (Richard, 1897) and Cyclops ochridanus (Kiefer, 1932). Copepods obtained remarkable share (60%) in the zooplankton assemblage. Microphagous zooplankton was mainly comprised of the most abundant rotifer Kellicottia longispina (Kellicott, 1879) in summer, and copepod nauplii during the spring Eudiaptomus gracilis (Sars, 1862) and C.ochridanus, and autumn C.ochridanus. Due to their requirements for the bacterio-detritus suspension, this microphagous zooplankton occupied aphotic hypolimnion during the entire study period. Raptorials were typically represented by copepodites and adult copepods in the metalimnion, and were significantly and positively affected by temperature (r = 0.417, p = 0.001), dissolved oxygen (r = 0.463, p = 0.0001) and, particularly, phytoplankton biomass (r = 0.708, p < 0.00001). This is the first study in which the link between the lower and higher trophic levels is investigated in Lake Ohrid