Abyssorum Tatricus Research Articles

Phenotypic and molecular responses of copepods to UV radiation stress in a clear versus a glacially turbid lake.

Zooplankton are exposed to multiple environmental stressors in alpine lakes. However, phenotypic and molecular responses of copepods to different environmental conditions, including ultraviolet radiation (UVR), are still not fully understood. Here, we tested whether gene expression patterns vary within the same species, Cyclops abyssorum tatricus, but in populations from different environments (a clear vs. a glacially turbid lake) when exposed to UVR. Moreover, we wanted to examine potential seasonal variation (summer vs. autumn) in copepod gene expression.We measured photoprotective compounds (mycosporine‐like amino acids and carotenoids) and antioxidant capacities in two copepod populations and studied gene expression of heat shock proteins (hsps) as indicator of stress after UVR exposure in the laboratory.Compared with the copepod population from the clear lake, the population from the turbid lake showed lower mycosporine‐like amino acid, but higher carotenoid concentrations that decreased over the season. Antioxidant capacities (both lipophilic and hydrophilic) were higher in autumn than in summer. The hsp60 and hsp90 genes were constitutively expressed, regardless of habitat origin and season, while hsp70 was upregulated after exposure to UVR (up to 2.8‐fold change). We observed stronger upregulation of hsp70 gene expression in autumn for the turbid and summer for the clear lake, with highest gene expression 24 hr post‐UVR exposure (up to 10.2‐fold change in the turbid and 3.9‐fold in the clear lake).We show how variation in phenotypic traits modulates hsp gene expression patterns, specifically hsp70 gene expression. Rapidly induced defences against cellular stress may improve survival in harsh environments such as alpine lakes, especially since these sensitive ecosystems may experience further changes in the future.

Contrasting diurnal patterns in antioxidant capacities, but not in expression of stress protein genes among copepod populations from clear versus glacially fed alpine and subalpine lakes.

Short-term changes in environmental conditions largely influence planktonic organisms, but their responses will depend on the habitat characteristics. Here we studied diurnal patterns in antioxidative metabolites (lipophilic and hydrophilic antioxidant capacities) and in the expression of stress protein genes (heat shock proteins, hsp) of copepods to identify short-term stress responses in clear and turbid alpine lakes, as well as in less transparent subalpine ones. Cyclops abyssorum tatricus showed diurnal variation in antioxidant capacities with maxima around noon in clear, but not in glacially fed, turbid lakes. Low fluctuations of these metabolites were also observed in another copepod, Acanthodiaptomus denticornis. Although levels of hsp genes differed between populations living in clear or glacially fed lakes, there was no diurnal rhythmicity in gene expression. Our data show that when planktonic organisms may be at greatest risk of oxidative damage, such as during the daytime in high UV radiation environments, they activate antioxidant responses. Conversely, in less transparent lakes, the physiological response seems to be unnecessary. The difference in gene expression levels suggests an ecological, albeit not acute, role of these genes in copepods experiencing daily environmental fluctuations.

Seasonal plasticity in photoprotection modulates UV-induced hsp gene expression in copepods from a clear lake.

Zooplankton from clear alpine lakes is exposed to stressful levels of solar UV radiation (UVR). As these pelagic organisms experience high UVR and large changes in solar radiation conditions between ice‐free and ice‐cover periods, they have evolved various strategies to minimize UVR exposure and damage. Here, we studied the relation between photoprotection levels (mycosporine‐like amino acids, carotenoids), antioxidant capacities, and gene expression of heat shock proteins (hsps) as indicator of stress in the copepod Cyclops abyssorum tatricus during the course of a year. Expression of hsp60, hsp70, and hsp90 was measured in the field (baseline expression [BE]) and after UVR exposure in the laboratory. The BE differed among genes and seasons (hsp60: high during summer, hsp70 and hsp90: high during the ice‐cover period). The gene expression of hsp70 was upregulated after exposure to UVR (up to 5.2‐fold change), while hsp60 and hsp90 were only constitutively expressed. A strong seasonal pattern was found in the photoprotective compounds and antioxidant capacities, with highest levels during the ice‐free period. The extent of upregulation of hsp70 gene expression increased with decreasing photoprotection levels and peaked 24 h post UVR exposure (9.6‐fold change) at the time of lowest photoprotection (February). Our data suggest that hsp70 gene expression is modulated by seasonal plasticity in photoprotection. This ability of adequate stress response is essential for survival in highly variable ecosystems such as alpine lakes.

Ciliate community structure and interactions within the planktonic food web in two alpine lakes of contrasting transparency.

Summary Climate warming is accelerating the retreat of glaciers and recently, many ‘new’ glacial turbid lakes have been created. In the course of time, the loss of the hydrological connectivity to a glacier causes, however, changes in their water turbidity and turns these ecosystems into clear ones.To understand potential differences in the food‐web structure between glacier‐fed turbid and clear alpine lakes, we sampled ciliates, phyto‐, bacterio‐ and zooplankton in one clear and one glacial turbid alpine lake, and measured key physicochemical parameters. In particular, we focused on the ciliate community and the potential drivers for their abundance distribution.In both lakes, the zooplankton community was similar and dominated by the copepod Cyclops abyssorum tatricus and rotifers including Polyarthra dolichoptera, Keratella hiemalis, Keratella cochlearis and Notholca squamula. The phytoplankton community structure differed and it was dominated by the planktonic diatom Fragilaria tenera and the cryptophyte alga Plagioselmis nannoplanctica in the glacial turbid lake, while chrysophytes and dinoflagellates were predominant in the clear one.Ciliate abundance and richness were higher in the glacial turbid lake (∼4000–27 800 Ind L−1, up to 29 species) than in the clear lake (∼570–7150 Ind L−1, up to eight species). The dominant species were Balanion planctonicum, Askenasia cf. chlorelligera, Urotricha cf. furcata and Mesodinium cf. acarus. The same species dominated in both lakes, except for Mesodinium cf. acarus and some particle‐associated ciliates, which occurred exclusively in the glacial turbid lake. The relative underwater solar irradiance (i.e. percentage of PAR and UVR at depth) significantly explained their abundance distribution pattern, especially in the clear water lake. In the glacial turbid lake, the abundance of the dominating ciliate taxa was mainly explained by the presence of predatory zooplankton.Our results revealed an unexpected high abundance and richness of protists (algae, ciliates) in the glacial turbid lake. This type of lake likely offers more suitable environmental conditions and resource niches for protists than the clear and highly UV transparent lake.

UV-induced DNA damage in Cyclops abyssorum tatricus populations from clear and turbid alpine lakes

Zooplankton from clear alpine lakes thrive under high levels of solar UV radiation (UVR), but in glacially turbid ones they are more protected from this damaging radiation. Here, we present results from experiments done with Cyclops abyssorum tatricus to assess UV-induced DNA damage and repair processes using the comet assay. Copepods were collected from three alpine lakes of differing UV transparency ranging from clear to glacially turbid, and exposed to artificial UVR. In addition, photoprotection levels [mycosporine-like amino acids (MAAs) and lipophilic antioxidant capacity] were estimated in the test populations. Similar UV-induced DNA damage levels were observed among the copepods from all lakes, but background DNA damage (time zero and dark controls) was lowest in the copepods from the glacially turbid lake, resulting in a higher relative DNA damage accumulation. Most DNA strand breaks were repaired after recovery in the dark. Low MAA concentrations were found in the copepods from the glacially turbid lake, while the highest levels were observed in the population from the most UV transparent lake. However, the highest lipophilic antioxidant capacities were measured in the copepods from the lake with intermediate UV transparency. Photoprotection and the ability to repair DNA damage, and consequently reducing UV-induced damage, are part of the response mechanisms in zooplankton to changes in water transparency caused by glacier retreat.

Body distribution and source of mycosporine-like amino acids in the cyclopoid copepod Cyclops abyssorum tatricus

Mycosporine-like amino acids (MAAs) are an important family of photoprotective compounds accumulated by zooplankton, but little is known about their localization in the body or their source in natural lake populations. Here, we assessed first, the distribution of MAAs in the body of the copepod Cyclops abyssorum tatricus and second, measured stable isotope signatures (dC, dN) in different life stages of the copepod, as well as in seston and benthic primary producers to reveal the potential source of these compounds in a UV transparent alpine lake. The stable isotope analysis showed that this copepod was herbivorous throughout its ontogeny, from nauplius to adult. Mixing models based on the stable isotope signatures suggest that this copepod feeds predominantly on the ,20-mm size fraction of seston. These models also indicated that the probability of feeding in the upper water layers was high in the ice-cover period, but that the copepod switched to deep water layers in the ice-free period following the maximum of phytoplankton biomass. The higher MAA concentration found in C. abyssorum tatricus during the ice-free period was not connected with an enhanced availability in the food source, but seems to be the result of an active accumulation. The highest MAA content in the body of C. abyssorum tatricus females was found in eggs. Our results indicate that MAAs in this copepod are efficiently accumulated through the diet (mainly nanophytoplankton) and transferred to the nauplii as an important strategy to provide photoprotection for the first life stages.

Seasonal and ontogenetic changes of mycosporine-like amino acids in planktonic organisms from an alpine lake

We studied the quantitative and qualitative mycosporine-like amino acid (MAA) composition in phytoplankton and the copepod Cyclops abyssorum tatricus from an alpine lake over a 15-month period. Up to eight MAAs were identified in the samples, with shinorine being predominant. The MAAs occurred year round and showed a strong seasonal pattern. Compared with ice-cover periods, concentrations during the summer were on average 3.6 and 3.0 times higher in phytoplankton and C. abyssorum tatricus, respectively. During the summer, the contents of MAAs in phytoplankton decreased with depth, suggesting their photoprotective role. Chlorophyll a-specific concentrations of MAAs in phytoplankton correlated significantly with the incident solar radiation and ultraviolet (UV) water transparency (r(2) ≤ 0.36), however, the strongest relationship was found with water temperature (r(2) = 0.67). In zooplankton, highest contents of MAAs were found in eggs, nauplii, and young copepodids, presumably providing a high level of photoprotection for progeny. Proportions of the dominant MAAs in the copepod showed seasonal and ontogenetic variations, which were consistent with relative changes in the predominant MAA, but not other abundant MAAs, in phytoplankton. Considering a time lag of approximately 1 month between the synthesis and subsequent accumulation of these compounds, MAA concentrations in late copepodid to adult life stages were significantly correlated to those in phytoplankton. Annual patterns in MAAs with high concentrations during periods of elevated environmental stress are consistent with the idea that these compounds play an important role in protecting aquatic organisms against UV damage.

The effect of different methanol concentrations and temperatures on the extraction of mycosporine-like amino acids (MAAs) in algae and Zooplankton

Mycosporine-like amino acids (MAAs) are a family of intracellular UV-absorbing compounds involved in the protection of aquatic organisms against solar UV radiation. These compounds have been identified and quantified in many marine and freshwater organisms, however, no standard method to analyze these compounds is available. Consequently, protocols to extract MAAs largely differ, for example, in the type of solvent, concentrations, temperatures, and times used. In this study, we tested whether the concentrations of MAAs are affected by extraction at different temperatures and methanol (MeOH) concentrations. Natural assemblages of freshwater phytoplankton, the cyclopoid copepod Cyclops abyssorum tatricus, and the marine alga Porphyra sp. were used as test organisms. The MAAs shinorine, palythine, MAA 331, asterina-330, and porphyra-334 present in the organisms examined were generally best extracted at 45 °C in 25 % aqueous MeOH. In Porphyra sp. and natural freshwater phytoplankton, the mean total MAA concentrations obtained with this protocol were respectively -13 and ∼3 times higher than when extracted in 100% MeOH at 4 °C. In Cyclops, concentrations of MAAs were also highest when extracted in 25 % MeOH at 45 °C, but there was no statistically significant difference among the different protocols (P = 0.079). Depending on the organism examined, both MeOH concentration and temperature affected extraction efficiency and final MAA concentration. Our results stress the need for a priori testing the influence of these variables to assure that the highest concentration is obtained without altering the qualitative MAA composition. Based on these results, direct comparison of MAA concentrations reported in the scientific literature should be done with caution.

UV-absorbing mycosporine-like compounds in planktonic and benthic organisms from a high-mountain lake

We investigated the occurrence, concentration and composition of mycosporines (mycosporine-like amino acids, MAAs) in planktonic organisms and epilithic cyanobacteria from a clear water high-mountain lake situated in the Central Alps, Austria. Two bi-substituted MAAs were identified by HPLC in extracts made of 1996 plankton samples with 90 % aqueous methanol, i.e. asterina-330 (&= = 330 nm) and shinorine (km = 334 run). Extracts with 20 % aqueous methanol for 2 h at 45 “C revealed the additional presence of another MAA tentatively identified as palythine (&.,, = 320nm) in the 1998 planktonic assemblage. In the upper 3 m of the water column the total concentration of MAAs decreased exponentially with depth, but the maxima for both absolute and chlorophyll-a specific concentrations were. observed close to the bottom at 8.5 m depth. This was explained by the accumulation of MAAs in the copepod’cyclops abyssorum tatricus that stays in deep water, during daytime. The copepodite III stage contained the 3 MAAs found in phytoplankton but also the mono-substituted compound, mycosporine-glycine (mycosporine-gly: & = 310 nm). The concentration of MAAs in C. abyssorum tatricus was highest for shinorine (1.45 % of the dry weight) and lowest for mycosporine-gly (0.02 % of the dry weight). Epilithic cyanobacteria had a more diverse MAA spectrum than plankton, and produced not only asterina-330 and shinorine but also palythinol (&, = 332 nm), mycosporine-gly and two unidentified compounds with &,,, = 330 and 340nm. The composition and also the relative abundance of the cyanobacterial MAAs changed with depth. Mycosporine-gly was found at the lakeshore where Gloeocapsa sp. dominates, but it was absent at 0.5 and 2.5 m depth dominated by Schizothrix sp. and Tolipothrix sp., respectively. We could not detect any MAAs in the cysts of the red snow alga Chlamydomonas nivalis, which develops on top of the winter cover shortly be’ Authors’ addresses: University of Innsbruck, InstitutGof Zoology and Limnology, Technikerstr. 25, A-6020 Innsbruck, Austria. E-mail: ruben.sommaruga@uibk.ac.at. 2 Max-Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany. * Author for correspondence. 0003-9136/99/0144-0255 $3.75

Survivorship of Cyclops abyssorum tatricus (Cyclopoida, Copepoda) and Boeckella gracilipes (Calanoida, Copepoda) under ambient levels of solar UVB radiation in two high-mountain lakes

We performed in situ experiments during the summer of 1995 and 1996 to assess the potential effect of solar ultraviolet B (UVB) radiation (290-320 nm) on the survival of Cyclops abyssorum tatricus Kozminski and Boeckella gracilipes Daday. These species are numerically dominant within the crustacean zooplankton living in two high-mountain lakes, one located in the Austrian Alps (Gossenkollesee (GKS), 2417 m above sea level, maximum depth 9.9 m) and another in the Chilean Andes (Laguna Negra, 2700 m above sea level, maximum depth 320 m). The copepods were incubated in quartz tubes (1 l) or in quartz tubes wrapped with Mylar D® to exclude most of the UVB radiation. The organisms were exposed at 0.5 m depth for 10-72 h on cloudless days. Both lakes were very transparent to UVB and 10% of the surface radiation at the nominal wavelength of 305 nm was still present at 9.6 m in GKS and at 12.8 m in Laguna Negra. These species migrate verti- cally and have a maximum daytime distribution close to the bottom (C.abyssorum tatricus) or below 15 m depth (B.gracilipes). Both species were red, but the carotenoid concentration was higher in C.abyssorum tatricus than in B.gracilipes (6.5 and 2.3 µg mg-1 dry weight, respectively). UV-absorbing compounds with a maximum absorption at ~334 nm were also detected. Cyclops abyssorum tatricus was highly resistant to UVB radiation and no significant lethal effect was observed. Boeckella gracilipes had a mortality ~5 times higher in the treatment receiving full sunlight than in the Mylar treatment (3.2%) only when exposed for 70 h. The resistance of B.gracilipes was higher than that reported in the literature for the same species, suggesting the existence of intraspecific differences in UV sensitivity.

Population dynamics and production of crustacean zooplankton in two mountain lakes in the Italian Alps (Lake Paione Superiore and Lake Malghette).

We estimated production of three populations of zooplanktonic crustacea from two lakes in the Italian Alps sampled within the EC-Project MOLAR (ENV-CT95-0007) "Measuring and modelling the dynamic response of remote mountain lake ecosystems to environmental change" (Lake Paione Superiore) and the EC- Guideline 78/659 "On the amelioration and the protection of freshwaters suitable for fish life" (Lake Malghette). The former is a fishless lake, while the latter, in addition to the native Phoxynus phoxynus, hosts populations of Salmo trutta fario and Oncorhynchus mykiss. The Allen curve method was used to estimate production of Acanthodiaptomus denticornis and Daphnia longispina in Lake Malghette and of Cyclops abyssorum tatricus in Lake Paione Superiore. Values of daily production of the three populations are similar to those found by other Authors in oligotrophic and high mountain environments.

The ecology of Cyclops abyssorum tatricus Kozminski in Norway

The ecology of <i>Cyclops abyssorum tatricus</i> Kozminski in Norway

The effect of fish predation on Cyclops life cycle

Two populations of Cyclops abyssorum tatricus studied in neighbouring alpine lakes in Tatra Mountains (southern Poland) differed in their life cycles. In the lake with planktivorous fishes, Cyclops was typically monocyclic, with highly synchronized reproduction during two winter months, while in the fishless lake its reproduction was asynchronous and continued for six months. Direct and indirect effects of fish predation on Cyclops life cycles are discussed.

Survival of Cyclops abyssorum tatricus (Copepoda, Crustacea) in alpine lakes stocked with planktivorous fish1

Results of field sampling and experiments suggest a strategy enabling Cyclops abyssorum tatricus to be the sole crustacean survivor in alpine lakes stocked with brook char. Reproductive pattern and population spatial distribution, egg resistance to char digestive enzymes, as well as the absence of cladocerans which would otherwise compete with Cyclops nauplii for scarce food resources, all ensure the survival of this planktonic crustacean.

Food of brook charr in extreme oligotrophic conditions of an alpine lake

A stunted form of Salvelinus fontinalis has persisted since its introduction in 1948 in ultra oligotrophic Zielony Lake in the Tatra Mountains, southern Poland, despite extremely poor available food. The charr shifts from feeding on airborne insects to benthic chironomid larvae when the lake is frozen in October, and to the sole planktonic crustacean survivor (Cyclops abyssorum tatricus) when access to the sediments becomes difficult due to oxygen depletion in April–May. The plankton food resource enables the charr to survive till June, when the ice-cover breaks up. Due to charr predation the old Cyclops generation becomes extinct in May, but Cyclops eggs hatch after passing through the charr intestine unharmed. Each new Cyclops generation explodes due to the absence of cannibalistic adults, which have been removed by the charr, and persists in high densities until the next April–May when the egg-carrying females (highly selected by the charr) appear again to focus the charr attention on planktonic food resources.