Acanthoecid choanoflagellates from the Atlantic Arctic Region - a baseline study

Biogeographical distribution of Hartaetosiga strains (Choanoflagellatea, Craspedida, Salpingoecidae) including morphological and transcriptomic data from a transect across the Atlantic Ocean

The genus Hartaetosiga Carr, Richter and Nitsche, 2017 comprised up to now only three species, H. gracilis (Kent) Carr, Richter, Nitsche, 2017, H. balthica (Wylezich and Karpov) Carr, Richter and Nitsche, 2017 and H. minima (Wylezich and Karpov) Carr, Richter and Nitsche, 2017. Based on distinct molecular data these species were relocated from the strictly freshwater genus Codosiga (Ehrenberg) Bütschli, 1878 to a new genus comprising brackish and marine species. During the cruise MSM82/2 across the Atlantic Ocean in 2019, surface water samples were taken from 15 stations along a transect ranging from 35°S to 23°N. We were able to isolate and cultivate 14 strains of the genus Hartaetosiga. Morphometric data showed no distinct morphological traits allowing for a species delineation, indicating a cryptic species complex within the genus. Based on cultivation, morphological data, and molecular analyses, we recorded H. gracilis for the first time from off-shelf waters of the Atlantic Ocean and could describe a new species, H. australis n. sp. This new species was recorded from sampling stations in the Southern Hemisphere only, which may indicate a potential biogeographic restriction likely caused by the Equatorial Counter Current (ECC), dividing the northern and southern surface waters.

Contrasting sea ice conditions shape microbial food webs in Hudson Bay (Canadian Arctic)

The transition from ice-covered to open water is a recurring feature of the Arctic and sub-Arctic, but microbial diversity and cascading effects on the microbial food webs is poorly known. Here, we investigated microbial eukaryote, bacterial and archaeal communities in Hudson Bay (sub-Arctic, Canada) under sea-ice cover and open waters conditions. Co-occurrence networks revealed a <3 µm pico‒phytoplankton-based food web under the ice and a >3 µm nano‒microphytoplankton-based food web in the open waters. The ice-edge communities were characteristic of post-bloom conditions with high proportions of the picophytoplankton Micromonas and Bathycoccus. Nano‒ to micro‒phytoplankton and ice associated diatoms were detected throughout the water column, with the sympagic Melosira arctica exclusive to ice-covered central Hudson Bay and Thalassiosira in open northwestern Hudson Bay. Heterotrophic microbial eukaryotes and prokaryotes also differed by ice-state, suggesting a linkage between microbes at depth and surface phytoplankton bloom state. The findings suggest that a longer open water season may favor the establishment of a large phytoplankton-based food web at the subsurface chlorophyll maxima (SCM), increasing carbon export from pelagic diatoms to deeper waters and affect higher trophic levels in the deep Hudson Bay.

Loricate choanoflagellates (Acanthoecida) from warm water seas. IX. Coronoeca gen. nov., Polyfibula Manton and spiny forms of Parvicorbicula Deflandre

The ambition to generate an overview of warm water loricate choanoflagellate biodiversity, based on a classic morphometric approach, is here completed by analyses of a range of tiny forms with anterior spines or projections and in most cases also a posterior pedicel. The warm water study complements previously obtained results from the more extensively studied temperate and polar regions of the world's oceans. It thus contributes to a significantly more balanced approach to global diversity patterns for these organisms. The current survey includes taxa such as Polyfibula elatensis, Parvicorbicula pedicellata, as well as a range of primarily undescribed and taxonomically challenging species, that are in an interim approach allocated to Coronoeca gen. nov. (C. kosmaniae sp. nov., C. conicella sp. nov., C. superpositus (Booth) comb. nov., C. marchantii sp. nov., C. tongiae sp. nov., and C. patongiensis sp. nov.). The analysis of warm water acanthoecid biodiversity has revealed in total 80 species from the six geographic regions sampled, corresponding to approximately 50% of all loricate species described. Nineteen species are previously undescribed forms. The Andaman Sea, Thailand, and West Australia are in a global context the most species-rich regions with 62 and 64 species respectively.

Loricate choanoflagellates (Acanthoecida) from warm water seas. VIII. Crinolina Thomsen and Diaphanoeca Ellis

The loricate choanoflagellate genera Diaphanoeca Ellis and Crinolina Thomsen encompass a total of ten species. The majority of these are recorded from the warm water regions reported on here. A distinct morphological dichotomy characterizes the genus Diaphanoeca as currently circumscribed. The species distribute themselves within a 'D. grandis subgroup' and a 'D. pedicellata subgroup' distinguished on e.g., the position of the protoplast inside the lorica chamber and the elaboration of the anterior projections. We are, while awaiting in particular further molecular evidence, taking a conservative approach and abstain from dealing with the subgroup issue at the generic level. The examination of material from the warm water regions of the world's oceans has resulted in the description of D. sargassoensis sp.n., D. pseudoundulata sp.n., and D. throndsenii sp.n., and a thorough re-examination of D. undulata. Species of Crinolina share multiple features with in particular the D. grandis species subgroup. It is yet relevant, both in a morphological and molecular perspective, to retain the genus Crinolina which remains unambiguously defined based on the posteriorly open lorica. A high level of agreement is found when contrasting morphological and molecular based phylogenetic schemes.

Temperature sensitivities of metazoan and pre-metazoan Src kinases

Homologous enzymes from different species display functional characteristics that correlate with the physiological and environmental temperatures encountered by the organisms. In this study, we have investigated the temperature sensitivity of the nonreceptor tyrosine kinase Src. We compared the temperature dependencies of c-Src and two Src kinases from single-celled eukaryotes, the choanoflagellate Monosiga brevicollis and the filasterean Capsaspora owczarzaki. Metazoan c-Src exhibits temperature sensitivity, with high activity at 30 °C and 37 °C. This sensitivity is driven by changes in substrate binding as well as maximal velocity, and it is dependent on the amino acid sequence surrounding tyrosine in the substrate. When tested with a peptide that displays temperature-dependent phosphorylation by c-Src, the enzymatic rates for the unicellular Src kinases show much less variation over the temperatures tested. The data demonstrate that unicellular Src kinases are temperature compensated relative to metazoan c-Src, consistent with an evolutionary adaptation to their environments.