Thomas Weisse

University of Innsbruck, Innsbruck, Tyrol, Austria

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Publications (84)156.32 Total impact

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    ABSTRACT: Since ciliates rarely possess structures that easily fossilize, we are limited in our ability to use paleontological studies to reconstruct the early evolution of this large and ecologically important clade of protists. Tintinnids, a group of loricate (house-forming) planktonic ciliates, are the only group that has a significant fossil record. Putative tintinnid fossils from rocks older than Jurassic, however, possess few to no characters that can be found in extant ciliates; these fossils are best described as ‘incertae sedis eukaryotes’. Here, we review the Devonian fossil Nassacysta reticulata and propose that it is likewise another incertae sedis eukaryote due to the lack of any unambiguous ciliate characters. Future tintinnid fossil descriptions would be most helpful if: (i) neutral terminology is used in the descriptions but ciliate-specific terminology in the interpretations; (ii) the current ciliate classification is used, although fossil data may expand or modify classifications based on modern forms; (iii) close collaboration with specialists studying extant ciliates is done; and (iv) editors include an expert of extant ciliates in the review process.
    Full-text · Article · Sep 2015 · Marine Micropaleontology
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    Full-text · Book · Feb 2015
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    Full-text · Book · Feb 2015
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    ABSTRACT: We assessed long-term aquatic biodiversity patterns, with a focus on functional diversity (FD), by using sedimentary Chironomidae and Cladocera assemblages in four mountain lakes in the Austrian Alps. The objectives were to detect whether the invertebrate communities exhibited similar recent diversity trends in climate-sensitive alpine lakes, to observe how lake-specific limnological shifts affect biodiversity, and to test the relationship between taxonomic diversity (TD) and FD for paleolimnological biodiversity evaluations. We applied traditional TD indices to the sedimentary assemblages and used an FD index that was based on functional traits of the encountered taxa of both invertebrate groups. There were some similar long-term trends in invertebrate FD and TD among the lakes; e.g. chironomid diversity increased in two lakes and cladoceran diversity in three lakes toward the twentieth and twenty-first century, but in general the diversity patterns were variable between lakes. Overall, FD had a positive relationship with TD suggesting that functionality can be used in paleolimnological studies as a measure of biodiversity. However, cladoceran taxon richness did not correlate with FD in two lakes suggesting that TD is not always a surrogate for FD. Furthermore, TD of chironomids tended to increase more pronouncedly than FD in the top core sections indicating that increasing TD does not necessarily enhance FD and that different taxonomic entities may play similar functional roles in ecosystems. Accordingly, when evaluating biodiversity and ecological redundancy, functionality of the species pool should be carefully considered and highlighted also in paleolimnological research.
    Full-text · Article · Jan 2015 · Aquatic Sciences
  • Thomas Weisse

    No preview · Article · Jul 2014 · Limnologica - Ecology and Management of Inland Waters
  • Thomas Weisse
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    ABSTRACT: Application of deep sequencing technologies to environmental samples and some detailed morphological studies suggest that there is a vast, yet unexplored rare ciliate biosphere, tentatively defined in terms of operational taxonomic units. However, very few studies complemented molecular and phylogenetic data with morphological and ecological descriptions of the species inventory. This is mainly because the sampling effort increases strongly with decreasing species abundance. In spite of this limited knowledge, it is clear that species that are rare under certain environmental conditions (temporal rare biosphere) may become abundant when the physical, chemical and biological variables of their habitat change. Furthermore, some species may always be present in low numbers if their dispersal rates are exceedingly high (accidental rare biosphere). An intriguing question is whether there are some species that are always rare, i.e. in every suitable environment. This permanent rare biosphere is conceptually different from the temporal rare biosphere. This review characterizes typical aquatic habitats of the rare ciliate biosphere, portrays different scenarios under which some or even many species may be permanently rare (background fauna), and identifies some fundamental questions that need to be addressed to achieve a better understanding of the population dynamics of the rare ciliate biosphere. This article is protected by copyright. All rights reserved.
    No preview · Article · May 2014 · Journal of Eukaryotic Microbiology
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    ABSTRACT: We investigated the ecology and life strategy of Glaucomides bromelicola (family Bromeliophryidae), a very common ciliate in the reservoirs (tanks) of bromeliads, assessing its response to food quality and quantity and pH. Further, we conducted competition experiments with the frequently coexisting species Bromeliothrix metopoides (family Colpodidae). In contrast to B. metopoides and many other colpodean ciliates, G. bromelicola does not form resting cysts, which jeopardizes this ciliate when its small aquatic habitats dry out. Both species form bactivorous microstomes and flagellate-feeding macrostomes. However, only G. bromelicola has a low feeding threshold and is able to adapt to different protist food. The higher affinity to the local bacterial and flagellate food renders it the superior competitor relative to B. metopoides. Continuous encystment and excystment of the latter may enable stable coexistence of both species in their natural habitat. Both are tolerant to a wide range of pH (4-9). These ciliates appear to be limited to tank bromeliads because they either lack resting cysts and vectors for long distance dispersal (G. bromelicola) and/or have highly specific food requirements (primarily B. metopoides).
    Preview · Article · Jun 2013 · Journal of Eukaryotic Microbiology
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    Thomas Weisse · Nicole Laufenstein · Guntram Weithoff
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    ABSTRACT: The planktonic food web in extremely acidic mining lakes is restricted to a few species that are either acidophilic or acidotolerant. Common metazoans inhabiting acidic mining lakes with a pH below 3 include rotifers in the genera Cephalodella and Elosa. The life history response of Cephalodella acidophila to three environmental key factors, pH (2, 3.5, 5.0 and 7.0), temperature (10, 17.5 and 25 °C) and food concentration (10 000, 35 000 and 50 000 algal cells per mL), was investigated in a full factorial design using life-table experiments. The effect of each of the three environmental variables investigated on the rotifer life cycle parameters (life span, fecundity and population growth rate) differed. C. acidophila is a stenoecious species with a pH optimum in the range 3–4 and a comparably high food threshold. Combining the laboratory results with field data, we conclude that C. acidophila is severely growth limited in its natural habitat. However, low pH alone is not harmful as long as temperatures are moderate to warm and food is abundant. The population of C. acidophila in the field is maintained mainly due to release from competitors and predators.
    Full-text · Article · May 2013 · Freshwater Biology
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    ABSTRACT: We investigated the recently described colpodid ciliate Bromeliothrix metopoides in a series of laboratory experiments to reveal the environmental factors that constrain this species to its peculiar habitat, i.e. the tanks of bromeliads. Our results demonstrated that the various life stages of this ciliate (bacterivorous theronts and microstome trophonts, flagellate-feeding macrostomes) have specific demands in terms of food quality and quantity. Bromeliothrix required a high food threshold (>1.4mgCL(-1)) in order to thrive. Food quality also affected resting cyst formation of B. metopoides when the experimental containers dried out. Its maximum growth rates (μmax=4.71d(-1), i.e. 6.8doublingsd(-1)) belong to the highest ones recorded thus far for free-living ciliates. The pH niche of B. metopoides was relatively wide (pH ∼4 to >9) under optimal food conditions. However, its high sensitivity to unfavourable environmental conditions let the population collapse within several hours. We conclude that B. metopoides is a boom and bust ciliate that is specifically adapted to its peculiar habitat but virtually unviable in other environments.
    Preview · Article · Mar 2013 · European Journal of Protistology
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    ABSTRACT: We investigated the morphology, phylogeny of the 18S rDNA, and pH response of Oxytricha acidotolerans sp. nov. and Urosomoida sp. (Ciliophora, Hypotricha) isolated from two chemically similar acid mining lakes (pH∼2.6) located at Langau, Austria, and in Lusatia, Germany. Oxytricha acidotolerans sp. nov. from Langau has 18 frontal-ventral-transverse cirri but a very indistinct kinety 3 fragmentation so that the assignment to Oxytricha is uncertain. The somewhat smaller species from Lusatia has a highly variable cirral pattern and the dorsal kineties arranged in the Urosomoida pattern and is, therefore, preliminary designated as Urosomoida sp. The pH response was measured as ciliate growth rates in laboratory experiments at pH ranging from 2.5 to 7.0. Our hypothesis was that the shape of the pH reaction norm would not differ between these closely related (3% difference in their SSU rDNA) species. Results revealed a broad pH niche for O. acidotolerans, with growth rates peaking at moderately acidic conditions (pH 5.2). Cyst formation was positively and linearly related to pH. Urosomoida sp. was more sensitive to pH and did not survive at circumneutral pH. Accordingly, we reject our hypothesis that similar habitats would harbour ciliate species with virtually identical pH reaction norm.
    Full-text · Article · Sep 2012 · European Journal of Protistology
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    ABSTRACT: We investigated the morphology, phylogeny, and pH response of two undescribed Oxytricha species isolated from two acid mining lakes (pH ~2.6) located in Lusatia (Germany) and Langau (Austria). The Langau species, tentatively named Oxytricha acidotolerans by Weisse et al. (2011, Ecosphere), is about 60-80 × 25-40 µm in life, has an ordinary 18-cirri pattern, about 24 adoral membranelles, 3 µm long dorsal bristles, three caudal cirri, two macronuclear nodules, two micronuclei, and six dorsal kineties. The species from Lusatia is highly variable in the main characters (body size, shape, infraciliature, nuclear apparatus) making a useable description almost impossible. Both species differ by 3% in their SSU rDNA and occur in a cluster containing, inter alia, other oxytrichids like Onychodromopsis flexilis, Cyrtohymena citrina, and Paraurostyla weissei. However, Oxytricha granulifera, the type species of Oxytricha, is distinctly separated, demonstrating the immature taxonomy of this group. Our ecological hypothesis was that the shape of the pH reaction norm would not differ between our closely related species. Ciliate growth rates measured in the laboratory were calculated from changes in cell numbers vs. time. Results revealed a broad pH niche for O. acidotolerans, with positive growth rates over the entire pH range investigated, peaking at moderately acidic conditions (pH 5.2). Cyst formation was positively and linearly related to pH. Oxytricha sp. from Lusatia was more sensitive to pH and did not survive at circum-neutral pH. Our experimental results characterize O. acidotolerans as an acidotolerant species, while Oxytricha sp. is acidophilic. We reject our hypothesis that similar habitats would harbour ciliate species with virtually identical pH reaction norm. Supported by the Austrian Science Fund (FWF) Projects P20118-B17 (TW) and P23415-B17 (HB).
    No preview · Conference Paper · Mar 2012
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    Thomas Weisse

    No preview · Article · Feb 2012 · European Journal of Protistology
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    Michael Moser · Thomas Weisse
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    ABSTRACT: This study investigated two mining lakes located in the north of Lower Austria. These lakes arose 45 years ago when open cast lignite mining ceased. The lakes are separated by a 7-m wide dam. Due to the oxidation of pyrite, both lakes have been acidified and exhibit iron, sulphate, and heavy metal concentrations several orders of magnitude higher than in circumneutral lakes. The water column of both lakes is divided into two layers by a pronounced chemocline. The smaller mining lake (AML), with pH close to of 2.6, is the most acidic lake in Austria, whereas flooding with stream water and by drainage from the surrounding fields neutralized the adjacent larger pit lake. The goal of our study was to investigate the effect of flooding on its physical, chemical and biological properties, in comparison to the pristine AML. Even relative to other extremely acidic lakes, the flora and fauna in the AML was reduced and composed of only two flagellate, one ciliate, and one rotifer species. The simplified pelagic food web in the mixolimnion consisted of heterotrophic bacteria, the mixotrophic flagellates Chlamydomonas acidophila and Ochromonas sp., the ciliate Oxytricha sp., and the rotifer Cephalodella sp. The latter two are as yet undescribed new species. The heliozoan Actinophrys sp. that may act as top predator occurred only in low abundance. The euglenid Lepocinclis buetschlii formed a stable deep chlorophyll maximum (DCM) at 7 m depth. Highest cell numbers of L. buetschlii in the DCM exceeded 10(8) L(-1). The neutralized mining lake harboured higher plankton diversity similar to that of natural circumneutral lakes. A peak of at least 16 different phytoplankton taxa was observed during summer. The zooplankton consisted of several copepod species, daphnids and other cladocerans, and at least six different rotifer species. Several fish species occurred in the neutralized lake. Although the effect of non-permanent flooding was largely sustainable, interannual fluctuations of the pH affected the plankton community and reduced its species diversity.
    Preview · Article · Dec 2011
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    ABSTRACT: It is currently controversially discussed if the same freshwater microorganisms occur worldwide wherever their required habitats are realized, i.e., without any adaptation to local conditions below the species level. We performed laboratory experiments with flagellates and ciliates from three acidic mining lakes (AML, pH similar to 2.7) to investigate if similar habitats may affect similar organisms differently. Such man-made lakes provide suitable ecosystem models to test for the significance of strong habitat selection. To this end, we analyzed the growth response of three protist taxa (three strains of the phytoflagellate Chlamydomonas acidophila, two isolates of the phytoflagellate Ochromonas and two species of the ciliate genus Oxytricha) by exposing them to lake water of their origin and from the two other AML in a cross-factorial design. Population growth rates were measured as a proxy for their fitness. Results revealed significant effects of strain, lake (= habitat), and strain X habitat interaction. In the environmentally most adverse AML, all three protist taxa were locally adapted. In conclusion, our study demonstrates that (1) the same habitat may affect strains of the same species differently and that (2) similar habitats may harbor ecophysiologically different strains or species. These results contradict the 'everything is everywhere' paradigm.
    Full-text · Article · Dec 2011 · Ecosphere
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    ABSTRACT: We describe a new species of Cephalodella, C. acidophila n. sp., from the plankton of two extremely acidic mining lakes (pH <3) in Austria and Germany. The species is morphologically closely related to Cephalodella delicata Wulfert. It shares with the latter an almost identical trophi morphology and anatomical organization, but differs clearly by form and length of its toes, larger body size, and ecology. Laboratory experiments revealed that the species is acidophilic, i.e. it thrives at low pH (<4) and does not survive at circumneutral conditions. The species occurs in man-made habitats at low to moderate abundance (usually 5-22 individuals l -1) and in stock cultures thrives on the green alga Chlamydomonas acidophila. The easily cultured species has previously been used in various experimental studies, but has onlynow been recognized as an undescribed species.
    No preview · Article · Jul 2011 · Zootaxa
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    Michael Moser · Thomas Weisse
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    ABSTRACT: Strains of the green alga Chlamydomonas acidophila and two chrysomonads, Ochromonas spp., isolated from each of two similar acid mining lakes (AMLs) with extremely low pH (∼2.6) were investigated to consider a possible synergistic stress effect of low pH and unfavourable temperature. We measured flagellate growth rates over a combination of four pH (2.5, 3.5, 5.0 and 7.0) and three temperatures (10, 17.5 and 25°C) in the laboratory. Our hypothesis was that, under highly acidic conditions (pH <3), an obligate acidophil species (C. acidophila) would be less sensitive to the combined stress of pH and temperature than acidotolerant species (Ochromonas spp.). We expected that the difference of the fundamental vs. realized pH niche would be greater in the latter. Another chrysomonad, Poterioochromonas malhamensis strain DS, served as a reference for a closely related neutrophil species. Surprisingly, C. acidophila did not survive temperatures >27°C. The lowest temperature tested reduced growth rates of all three chrysomonad strains significantly. Since all chrysomonads were tolerant to high temperature, growth rate of one Ochromonas spp. strain was measured exemplarily at 35°C. Only at this high temperature was the realized pH niche significantly narrowed. We also recorded significant intraspecific differences within the C. acidophila strains from the two AML, illustrating that the niche width of a species is broader than that of individual clones.
    Preview · Article · Jul 2011 · Journal of Plankton Research
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    Thomas Weisse · Erland McIsaac
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    ABSTRACT: We measured bacterial abundance, biomass, production rates, and grazing losses to protozoans in three oligotrophic British Columbia lakes and analyzed bacteria abundance and lake productivity data from 11 other lakes, most fertilized with inorganic nutrients to increase their productivity for juvenile salmon. Bacteria contributed about 24% to the phytoplankton-bacteria carbon biomass in the most ultraoligotrophic lakes, and their relative contribution declined to < 11% with increasing lake productivity. At increasingly high nutrient loadings to the lakes, bacteria abundance increased and was closely correlated with phytoplankton biomass and productivity. Heterotrophic nanoflagellate (HNF) abundance was positively correlated with bacterial numbers. Grazing experiments revealed that HNF were the primary pathway for moving bacterial production to higher trophic levels in oligotrophic British Columbia lakes, and predation by the ciliate and rotifer microzooplankton community appeared to exert top-down control over the abundance of HNF and the transfer of carbon from bacteria. The HNF and microzooplankton, in turn, were affected by the abundance of crustacean mesozooplankton, principally copepods in our experiments.
    Preview · Article · Apr 2011 · Canadian Journal of Fisheries and Aquatic Sciences
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    Michael Moser · Thomas Weisse
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    ABSTRACT: We investigated the effect of pH on the competition of two closely related chrysomonad species, Poterioochromonas malhamensis originating from circumneutral Lake Constance, and Ochromonas sp. isolated from a highly acidic mining lake in Austria (pH ∼2.6). We performed pairwise growth experiments between these two species at four different pH ranging from 2.5 to 7.0. Heterotrophic bacteria served as food for both flagellates. Results were compared to growth rates measured earlier in single species experiments over the same pH range. We tested the hypothesis that the acidotolerant species benefits from competitive release under conditions of acid stress. The neutrophilic strain numerically dominated over the acidotolerant strain at pH 7.0, but was the inferior competitor at pH 2.5. At pH 3.5 and 5.0 both strains coexisted. Surprisingly, P. malhamensis prevailed over Ochromonas sp. under moderately acidic conditions, i.e. at the pH where growth rates of the latter peaked when grown alone. Since bacterial food was not limiting, resource competition is improbable. It appears more likely that P. malhamensis ingested cells of its slightly smaller competitor. Adverse effects mediated via allelopathy, either directly on the competing flagellate or indirectly by affecting its bacterial food, might also have affected the outcome of competition.
    Preview · Article · Feb 2011 · European Journal of Protistology
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    C D JERSABEK · G WEITHOFF · T WEISSE
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    ABSTRACT: We describe a new species of Cephalodella, C. acidophila n. sp., isolated from the plankton of two extremely acidic mining lakes (pH <3) in Austria and Germany. The species is morphologically closely related to Cephalodella delicata Wulfert. It shares with the latter an almost identical trophi morphology and anatomical organization, but differs clearly by form and length of its toes, larger body size, and ecology. Laboratory experiments revealed that the species is acidophilic, i.e. it thrives at low pH (<4) and does not survive at circumneutral conditions. The species occurs in its man-made habitats at low to moderate abundance (usually 5–22 individuals l-1) and in stock cultures thrives on the green alga Chlamydomonas acidophila. The easily cultured species has previously been used in various experimental studies, but has only now been recognized to represent an undescribed species.
    Full-text · Article · Jan 2011 · Zootaxa
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    ABSTRACT: Acidic mining lakes (pH <3) are specific habitats exhibiting particular chemical and biological characteristics. The species richness is low and mixotrophy and omnivory are common features of the plankton food web in such lakes. The plankton community structure of mining lakes of different morphometry and mixing type but similar chemical characteristics (Lake 130, Germany and Lake Langau, Austria) was investigated. The focus was laid on the species composition, the trophic relationship between the phago-mixotrophic flagellate Ochromonas sp. and bacteria and the formation of a deep chlorophyll maximum along a vertical pH-gradient. The shallow wind-exposed Lake 130 exhibited a higher species richness than Lake Langau. This increase in species richness was made up mainly by mero-planktic species, suggesting a strong benthic/littoral - pelagic coupling. Based on the field data from both lakes, a nonlinear, negative relation between bacteria and Ochromonas biomass was found, suggesting that at an Ochromonas biomass below 50 μg C L(-1), the grazing pressure on bacteria is low and with increasing Ochromonas biomass bacteria decline. Furthermore, in Lake Langau, a prominent deep chlorophyll maximum was found with chlorophyll concentrations ca. 50 times higher than in the epilimnion which was build up by the euglenophyte Lepocinclis sp. We conclude that lake morphometry, and specific abiotic characteristics such as mixing behaviour influence the community structure in these mining lakes.
    Full-text · Article · May 2010 · Limnologica - Ecology and Management of Inland Waters

Publication Stats

2k Citations
156.32 Total Impact Points

Institutions

  • 2013-2015
    • University of Innsbruck
      • Institute of Ecology
      Innsbruck, Tyrol, Austria
  • 2002-2012
    • Austrian Academy of Sciences
      • Institute for Limnology
      Wien, Vienna, Austria
  • 2011
    • Fisheries and Oceans Canada
      Ottawa, Ontario, Canada
  • 2001
    • University of Cologne
      • Zoological Institute
      Köln, North Rhine-Westphalia, Germany
  • 1988-1996
    • Universität Konstanz
      Constance, Baden-Württemberg, Germany
  • 1985-1986
    • Christian-Albrechts-Universität zu Kiel
      Kiel, Schleswig-Holstein, Germany