| 1. |
- Hansson, Lars-Anders, et al.
(författare)
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High zooplankton diversity in the extreme environments of the McMurdo Dry Valley lakes, Antarctica
- 2012
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Ingår i: Antarctic Science. - 1365-2079 .- 0954-1020. ; 24:2, s. 131-138
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Tidskriftsartikel (refereegranskat)abstract
- The McMurdo Dry Valley lakes of Antarctica constitute some of the harshest and most isolated freshwater environments on Earth which might be expected to limit the biogeographical expansion of many organisms. Despite this, we found that the biodiversity of rotifer zooplankton is the highest ever recorded on the Antarctic mainland. We identified in total nine rotifer taxa, of which six are new to the Antarctic continent, in Lake Hoare, and also the first sub- adult crustacean copepod belonging to the genus Boeckella. A possible explanation for the high biodiversity is that many of the recorded species have arrived in the region in relatively recent times and then established invasive populations, suggesting that their distribution pattern was previously limited only by biogeographical borders. Interestingly, we show that the cosmopolitan rotifer taxa identified are relatively abundant, suggesting that they have established viable populations. Hence, our study suggests that the biogeographical maps have to be redrawn for several species.
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| 2. |
- Hylander, Kristoffer, et al.
(författare)
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In situ survival of forest bryophytes in small-scale refugia after an intense forest fire
- 2010
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 21:6, s. 1099-1109
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Tidskriftsartikel (refereegranskat)abstract
- Question Species can persist in landscapes with recurring disturbances either by migrating to places suitable for the moment or by enduring the threatening conditions. We investigated to what extent boreal forest bryophytes survived an intense forest fire in situ and whether bryophytes had started to recolonize the area 7-8 years later. Location Tyresta National Park, eastern Sweden. Methods We recorded bryophytes in 14 burnt and 12 forest reference plots (50 x 50 m). In each plot we investigated 15 random 1-m2 micro-plots. In plots in the burnt area we also examined micro-plots at locations of all fire refugia, and in case of the forest references, of 10 potential refugia. Results We found on average three small refugia per 50 x 50-m plot; each containing on average 4.8 forest bryophytes, a level similar to that of micro-plots in the references, but significantly higher than in random micro-plots in the burnt plots (1.5 species). Many refugia were located in rocky areas, but few were in wet sites. The burnt area remained dominated by a few fire-favoured species, even if recolonization of forest bryophytes had begun. There was, however, no significant correlation between number of refugia and number of forest species in random micro-plots, leaving open the question of the importance of refugia as regulators of early succession. Conclusion We conclude that small-scale refugia can also occur for sensitive species such as forest bryophytes, and that the refugia in our case were frequently found on rocky or mesic rather than wet sites. The role of such refugia in recolonization, however, warrants further investigation.
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| 3. |
- Hylander, Samuel, et al.
(författare)
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Climate-induced input of turbid glacial meltwater affects vertical distribution and community composition of phyto- and zooplankton
- 2011
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 33:8, s. 1239-1248
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Tidskriftsartikel (refereegranskat)abstract
- Receding glaciers are among the most obvious changes caused by global warming, and glacial meltwater entering lakes generally forms plumes of particles. By taking vertical samples along a horizontal gradient from such a particle source, we found that photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) attenuated 20-25% faster close to the inflow of suspended particles compared with the more transparent part of the gradient. All sampled stations had a deep chlorophyll a (Chl a) maximum at 15-20 m which was more distinct in the transparent part of the horizontal gradient. Picocyanobacteria increased in abundance in more transparent water and their numbers were tightly correlated with the intensity of the deep Chl a maxima. Motile species of phytoplankton had a deeper depth distribution in transparent versus less transparent water. Yet other species, like Chrysochromulina parva, that can withstand high PAR intensities and low nutrient concentrations, increased in abundance as the water became more transparent. Also copepods increased in abundance, indicating that they are more successful in transparent water. We conclude that sediment input into lakes creates horizontal gradients in PAR and UVR attenuation which strongly affect both distribution and behavior of phyto-and zooplankton. The input of glacial flour creates a sub-habitat that can function as a refuge for species that are sensitive to high PAR and UVR exposure. When the glacier has vanished, this habitat may disappear. During the melting period, with heavy sediment input, we predict that competitive species in transparent waters, like Chrysocromulina, picocyanobacteria and copepods, will become less common. The deep Chl a maxima is also likely to become less developed. Hence, glacier melting will probably have profound effects on both species composition and behavior of several planktonic taxa with potential effects on the food web.
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| 4. |
- Hylander, Samuel, et al.
(författare)
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Fish-mediated trait compensation in zooplankton
- 2012
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Ingår i: Functional Ecology. - : Wiley. - 1365-2435 .- 0269-8463. ; 26:3, s. 608-615
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Tidskriftsartikel (refereegranskat)abstract
- 1. Environmental factors fluctuate spatially and temporally, and organisms that can alter phenotype in response to these changes may increase their fitness. Zooplankton are known to be able to induce body pigmentation in response to ultraviolet radiation (UVR) and to reduce the pigmentation when exposed to fish predators. Hence, reduced pigmentation because of the presence of fish could potentially lead to UVR damage, which calls for alternative protective mechanisms. 2. We exposed zooplankton to fish cues and UVR stress to assess whether body pigmentation and cellular antioxidants are flexible predation and UVR defences. 3. Zooplankton exposed to fish predator cues (no direct predation) reduced their pigmentation by c. 30% in 20 days. However, they were able to rapidly counteract negative UVR effects by increasing the activity of antioxidant defences such as glutathione S-transferase (GST). When exposed to UVR, the GST activity increased by c. 100% in zooplankton that had previously reduced their pigmentation because of fish cues. Transparency in the zooplankton did not lead to considerably higher UVR damage, here measured as inhibition of cholinesterase (ChE). 4. We conclude that zooplankton pigmentation and antioxidant enzymes are flexible UVR defence systems, which can be induced when needed. Zooplankton may employ antioxidant defences when pigmentation is reduced to counteract predation risk and thereby rapidly respond to detrimental effects of UVR exposure, that is, they can compensate one trait with another.
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| 5. |
- Hylander, Samuel, et al.
(författare)
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Fitness costs and benefits of ultraviolet radiation exposure in marine pelagic copepods
- 2014
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Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 28:1, s. 149-158
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Tidskriftsartikel (refereegranskat)abstract
- 1Life-history theory predicts that organisms should allocate energy throughout their life such that they maximize their fitness. Copepod zooplankton are known to accumulate sunscreens (so-called mycosporine-like amino acids, MAAs) and antioxidant carotenoids to mitigate negative effects of ultraviolet radiation (UVR), but it is not well known how this affects their fitness. We followed cohorts of the marine copepod Acartia tonsa and assessed how fitness was affected by UVR exposure and a diet rich in UVR-protective sunscreens. Several fitness components including somatic growth, egg quality and nauplii production (larvae) were negatively affected by UVR, whereas other components such as size at maturity, survival and length of life were not. Nauplii production through low egg quality was the most influential life-history parameter that changed in response to UVR. There was interaction between fitness costs and food source. If copepods were fed a diet rich in UVR-screening MAAs, they were able to maintain and even increase their fitness even though they were exposed to otherwise detrimental radiation. Levels of UVR-protective carotenoids were low in the studied species and a meta-analysis revealed that marine copepods in general have much lower - by an order of magnitude - levels of carotenoids than freshwater species, while levels of MAAs are similar between the two habitats. We conclude that allocation to different fitness components to some extent is plastic although egg quality is by far the most influential factor, and this is an example of how environmental variability affects overall fitness. Fitness costs associated with UVR exposure in the absence of UVR-screening MAAs were present. Other costs such as costs for accumulating MAAs were not detected, and if present, they were outweighed by a stimulated fitness in combined UVR and MAA treatments challenging the common model that inducible defences (such as accumulation of MAAs) should come with a cost. Low levels of carotenoids in marine systems suggest high predation pressures on pigmented specimens. Accumulation of nonpigmented MAAs could hence be a key adaptation for surface-dwelling marine zooplankton to maintain or even increase their fitness when exposed to detrimental radiation.
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| 6. |
- Hylander, Samuel, et al.
(författare)
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Induced tolerance expressed as relaxed behavioural threat response in millimetre-sized aquatic organisms
- 2014
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 281:1788, s. Article ID: 20140364-
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Tidskriftsartikel (refereegranskat)abstract
- Natural selection shapes behaviour in all organisms, but this is difficult to study in small, millimetre-sized, organisms. With novel labelling and tracking techniques, based on nanotechnology, we here show how behaviour in zooplankton (Daphnia magna) is affected by size, morphology and previous exposure to detrimental ultraviolet radiation (UVR). All individuals responded with immediate downward swimming to UVR exposure, but when released from the threat they rapidly returned to the surface. Large individuals swam faster and generally travelled longer distances than small individuals. Interestingly, individuals previously exposed to UVR (during several generations) showed a more relaxed response to UVR and travelled shorter total distances than those that were naive to UVR, suggesting induced tolerance to the threat. In addition, animals previously exposed to UVR also had smaller eyes than the naive ones, whereas UVR-protective melanin pigmentation of the animals was similar between populations. Finally, we show that smaller individuals have lower capacity to avoid UVR which could explain patterns in natural systems of lower migration amplitudes in small individuals. The ability to change behavioural patterns in response to a threat, in this case UVR, adds to our understanding of how organisms navigate in the ‘landscape of fear’, and this has important implications for individual fitness and for interaction strengths in biotic interactions.
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| 7. |
- Hylander, Samuel, et al.
(författare)
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UV protective compounds transferred from a marine dinoflagellate to its copepod predator
- 2010
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 389:1-2, s. 38-44
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Tidskriftsartikel (refereegranskat)abstract
- Planktonic organisms living in surface waters can be exposed to harmful levels of ultraviolet radiation (UVR), but few studies have examined accumulation of UV protective compounds in marine zooplankton. Zooplankters are suggested to lack the ability to synthesize these substances and hence must accumulate them from their algal food. Here, we show that both phytoplankton (dinoflagellates) and their zooplankton grazers (copepods) respond strongly to UVR exposure by, respectively, synthesizing and accumulating the natural sunscreens mycosporine-like amino acids (MAAs). In our experiment, the MAAs content increased approximately four times in dinoflagellates exposed to UVR and PAR, as compared to non-UVR controls only receiving PAR (PAR = photosynthetically active radiation). The elevated MAAs level in the dinoflagellates was mirrored in the copepods, which accumulated more MAAs when exposed to UVR as compared to a non-UVR treatment. Overall, copepods accumulated approximately 2-5% of the total MAAs pool. Other UV protective compounds, like carotenoids, were however not accumulated by the copepods. The ability of some species to produce or accumulate photoprotective compounds may lead to increased fitness, and thus these taxa may become more dominant in plankton communities. (C) 2010 Elsevier B.V. All rights reserved.
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| 8. |
- Hylander, Samuel, et al.
(författare)
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Vertical distribution and pigmentation of Antarctic zooplankton determined by a blend of UV radiation, predation and food availability
- 2013
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Ingår i: Aquatic Ecology. - : Springer Science and Business Media LLC. - 1386-2588 .- 1573-5125. ; 47:4, s. 467-480
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Tidskriftsartikel (refereegranskat)abstract
- Selection pressure induced by simultaneously occurring environmental threats is a major evolutionary driver for organisms in terrestrial, as well as in aquatic ecosystems. For example, protection against ultraviolet radiation (UVR) and predation include both morphological and behavioral components. Here we address those selective pressures on zooplankton by performing a latitudinal monitoring, combined with mechanistic experiments in the Antarctic Southern Ocean, where the UVR-threat is extremely high. We assessed vertical distributions of zooplankton along the Antarctic coast showing that animals were most abundant at 20-80 m and tended to avoid the surface at sites with clear water. UVR-threat disappeared at between 9 and 15 m at sites with low and high water transparency, respectively. Light levels were, however, sufficient for visual fish predation down to approximately 19 and 37 m, respectively. The few zooplankton that were present in surface waters had high levels of non-pigmented UVR-protective compounds (mycosporine-like amino acids) compared to deeper dwelling zooplankton. Overall they had low levels of red pigmented UVR-protective compounds (carotenoids), suggesting high predation on pigmented individuals. In a complementary laboratory study we showed that levels of UVR-protective compounds increased considerably when zooplankton were exposed to UVR in the absence of predator cues. The recently developed transparency-regulator hypothesis predicts that UVR avoidance is an important driver to diel vertical migration in transparent waters, such as in Antarctica. We, however, conclude that copepods resided well below the level where UVR had diminished to very low levels and that predator avoidance or food availability are more likely drivers of zooplankton vertical depth distribution in transparent marine systems.
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| 9. |
- Hylander, Samuel, et al.
(författare)
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Vertical migration mitigates UV effects on zooplankton community composition
- 2010
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 32:7, s. 971-980
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Tidskriftsartikel (refereegranskat)abstract
- Several zooplankton species are susceptible to ultraviolet radiation (UV), suggesting that UV may shape zooplankton community composition. Little is known, however, about the quantitative effects of long-term UV exposure in relation to biological processes. Therefore, we studied effects of UV on behaviour, population dynamics and reproduction of several zooplankton taxa. We identified different strategies regarding daytime vertical distribution: a strong response to UV threat, illustrated by Daphnia; a weak, albeit significant response, such as in copepods; and lastly, a stationary position in a depth refuge, as in Chydorus and Eurycercus. The relative abundances of the different zooplankton species were similar and only Daphnia and copepod nauplii displayed a slight decrease in relative abundance in response to UV treatment. Daphnia also reacted to the UV threat by increasing resting egg production, whereas long-term population dynamics for all studied species were surprisingly similar between treatments, despite considerable differences in UV exposure for several months. We conclude that zooplankton communities at temperate latitudes are able to survive increased UV levels due to efficient defences, suggesting that future potential increases in UV radiation may result in only moderate impacts on zooplankton population dynamics and community composition.
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| 10. |
- Jönsson, Mikael, et al.
(författare)
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Foraging success of juvenile pike Esox lucius depends on visual conditions and prey pigmentation
- 2011
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 79:1, s. 290-297
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Tidskriftsartikel (refereegranskat)abstract
- Young-of-the-year pike Esox lucius foraging on copepods experienced different foraging success depending on prey pigmentation in water visually degraded by brown colouration or algae. Both attack rate and prey consumption rate were higher for E. lucius foraging on transparent prey in brown water, whereas the opposite was true in algal turbid water. Pigments in copepod prey may have a cryptic function in brown water instead of a photo-protective function even if prey-size selectivity was stronger than selection based on pigmentation in juvenile E. lucius. (C) 2011 The Authors Journal of Fish Biology (C) 2011 The Fisheries Society of the British Isles
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