| 1. |
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| 2. |
- Beier, Sara, et al.
(författare)
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Pronounced seasonal dynamics of freshwater chitinase genes and chitin processing
- 2012
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 14:9, s. 2467-2479
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Tidskriftsartikel (refereegranskat)abstract
- Seasonal variation in activity of enzymes involved in polymer degradation, including chitinases, has been observed previously in freshwater environments. However, it is not known whether the seasonal dynamics are due to shifts in the activity of bacteria already present, or shifts in community structure towards emergence or disappearance of chitinolytic organisms. We traced seasonal shifts in the chitinase gene assemblage in a temperate lake and linked these communities to variation in chitinase activity. Chitinase genes from 20 samples collected over a full yearly cycle were characterized by pyrosequencing. Pronounced temporal shifts in composition of the chitinase gene pool (beta diversity) occurred along with distinct shifts in richness (alpha diversity) as well as chitin processing. Changes in the chitinase gene pool correlated mainly with temperature, abundance of crustacean zooplankton and phytoplankton blooms. Also changes in the physical structure of the lake, e.g. stratification and mixing were associated with changes in the chitinolytic community, while differences were minor between surface and suboxic hypolimnetic water. The lake characteristics influencing the chitinolytic community are all linked to changes in organic particles and we suggest that seasonal changes in particle quality and availability foster microbial communities adapted to efficiently degrade them.
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| 3. |
- Bensch, Staffan, et al.
(författare)
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Host specificity in avian blood parasites: a study of Plasmodium and Haemoproteus mitochondrial DNA amplified from birds
- 2000
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 267:1452, s. 1583-1589
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Tidskriftsartikel (refereegranskat)abstract
- A fragment of the mitochondrial cytochrome b gene of avian malaria (genera Haemoproteus and Plasmodium) was amplified from blood samples of 12 species of passerine birds from the genera Acrocephalus, Phylloscopus and Parus. By sequencing 478 nucleotides of the obtained fragments, we found 17 different mitocholdrial haplotypes of Haemoproteus or Plasmodium among the 12 bird species investigated. Only one out of the: 17 haplotypes was found in more than one host species, this exception being a haplotype detected in both blue tits (Parus caeruleus) and great tits (Parus major). The phylogenetic tree which was constructed grouped the sequences into two clades, most probably representing Haemoproteus and Plasmodium, respectively. We found two to four different parasite mitochondrial DNA (mtDNA) haplotypes in four bird species. The phylogenetic tree obtained from the mtDNA of the parasites matched the phylogenetic tree of the bird hosts poorly For example, the two tit species and the willow warbler (Phylloscopus troclilus) carried parasites differing by only 0.6% sequence divergence, suggesting that Haemoproteus shift both between species within the same genus and also between species in different families. Hence, host shifts seem to have occurred repeatedly in this parasite-host system. We discuss this in terms of the possilble evolutionary consequences for these bird species.
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| 4. |
- Berga, Mercè, et al.
(författare)
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Combined effects of zooplankton grazing and dispersal on the diversity and assembly mechanisms of bacterial metacommunities
- 2015
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 17:7, s. 2275-2287
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Tidskriftsartikel (refereegranskat)abstract
- Effects of dispersal and the presence of predators on diversity, assembly and functioning of bacterial communities are well studied in isolation. In reality, however, dispersal and trophic interactions act simultaneously and can therefore have combined effects, which are poorly investigated. We performed an experiment with aquatic metacommunities consisting of three environmentally different patches and manipulated dispersal rates among them as well as the presence or absence of the keystone species Daphnia magna. Daphnia magnareduced both local and regional diversity, whereas dispersal increased local diversity but decreased beta-diversity having no net effect on regional diversity. Dispersal modified the assembly mechanisms of bacterial communities by increasing the degree of determinism. Additionally, the combination of the D. magna and dispersal increased the importance of deterministic processes, presumably because predator-tolerant taxa were spread in the metacommunity via dispersal. Moreover, the presence of D. magna affected community composition, increased community respiration rates but did not affect bacterial production or abundance, whereas dispersal slightly increased bacterial production. In conclusion, our study suggests that predation by a keystone species such as D. magna and dispersal additively influence bacterial diversity, assembly processes and ecosystem functioning.
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| 5. |
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| 6. |
- Berga Quintana, Mercè
(författare)
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Assembly Mechanisms in Aquatic Bacterial Communities : The Role of Disturbances, Dispersal and History
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Environmental conditions, biotic interactions, dispersal and history have been suggested to be important processes influencing the spatial distribution of organisms and thus to affect community assembly. Understanding how these processes influence community assembly is important, particularly because community diversity and composition are suggested to be relevant for ecosystem functioning. Moreover, bacteria are strongly contributing to nutrient and carbon cycle. Bacteria are highly abundant and ubiquitous, and thus it is relevant to study how they are assembled. This thesis aims to gain insight on the role of these processes on aquatic bacterial community assembly, diversity and functioning. The studies included in this thesis involve transplant and microcosm experiments performed in the lab as well as manipulation experiments and field surveys in a natural rock pool systems. Bacterial community composition was addressed by analysis of 16S rRNA gene and community functioning by measuring bacterial production, community respiration and the ability to use different carbon substrates. This thesis highlights that species sorting is a very important assembly mechanism for bacterial communities, but also finds that other processes such as dispersal and history contribute to the patterns observed. Dispersal caused rescuing effects compensating for losses of diversity; at the same time it increased the similarity between communities. Moreover, bacteria have shown a high level of functional plasticity when colonizing a new locality. Interestingly, past environmental conditions explained the structure of bacterial communities better than present-day environmental conditions. Disturbances and biotic interactions are also important in the assembly of communities. Disturbance caused temporary shifts in bacterial function and changes in composition, the magnitude of which depended on the intensity and the frequency of the disturbance. However, natural aquatic bacterial communities showed quite high resilience capacities. Competition can shift the proportion of generalists and specialists species whereas predation or trophic interactions have been found to decrease diversity and to modify the importance of stochasticity. Both caused alterations of community functioning. Finally, this thesis shows that the diversity-functioning relationship is context dependent. Further research should be directed to understanding the intensity and direction of changes in composition and how this affects the functionality of bacterial communities
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| 7. |
- Berggren, Terese, et al.
(författare)
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Warmer water increases early body growth of northern pike (Esox lucius), but mortality has larger impact on decreasing body sizes
- 2021
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 79, s. 771-781
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Tidskriftsartikel (refereegranskat)abstract
- Large fish species often display truncated size distributions related to harvest. In addition, temperature, food availability and density dependence affect body growth and together with natural mortality influence population size structure. Here we study changes in body growth, size distributions and mortality in both harvested and nonharvested populations of northern pike (Esox Lucius) over 50 years along the Baltic Sea coast and in Lake Malaren, Sweden. For coastal pike, body growth has increased coincidentally with increasing water temperatures, yet in the last two decades there has been a decrease of larger individuals. In Lake Malaren, in contrast, size distributions and body growth were stationary despite similar increases in water temperature. A dominance of slow-growing individuals in older age classes was evident in all studied populations, also in the no-take zone, suggesting other factors than fishing contribute to the mortality pattern. We propose that increasing temperatures have favoured body growth in coastal areas, but this has been counteracted by increased mortality, causing pike sizes to decline. To regain larger coastal pike, managers need to consider multiple measures that reduce mortality.
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| 8. |
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| 9. |
- Bergström, Ulf, et al.
(författare)
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Long-term decline in northern pike (Esox lucius L.) populations in the Baltic Sea revealed by recreational angling data
- 2022
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- In the Baltic Sea, the large predatory fish northern pike (Esox lucius L.) is important for both recreational fisheries and ecosystem functioning. As existing fishery-independent surveys do not adequately monitor pike populations, a general lack of knowledge on population status and trends poses challenges for management. Here we use recreational angling data as an alternative method to describe pike population development along the Swedish Baltic Sea coast from 1938 onwards and assess the change over time in potential mortality factors by estimating harvest by fisheries and consumption by large predators. Data from a Swedish national register on trophy-sized pike (>12 kg) showed that numbers and maximum sizes peaked in 1990-1995, after which declines in both metrics are evident. In logbooks from a sport fishing club in the Stockholm archipelago, a simultaneous decrease in maximum sizes of pike was observed, together with a decrease in the total number of pike caught per fishing day. Jointly, these data indicate a decline in the abundance of large pike since around 1990. While commercial pike fisheries in the Baltic Sea have decreased continuously since the 1950s, recreational fishing increased after 1985, when Swedish coastal waters were made open access to anglers. The declines in large pike starting in the 1990s could, thus, have been driven by an increase in mortality from recreational fisheries, which at the time primarily practiced catch and kill. Since the 2000s, bag and slot length limits, spawning closures, and a general increase in catch-and-release fishing has reduced the landings of pike in recreational fisheries. Despite these fisheries regulations and higher release rates the decline in catches of large pike has continued, indicating an effect of other mortality factors. The strong growth of grey seal (Halichoerus grypus) and great cormorant (Phalacrocorax carbo sinensis) populations suggest that predation pressure on pike has increased over time. In the Stockholm archipelago these two predators were estimated to remove 5-18 times (range based on different diet composition estimates) more pike biomass than total fisheries landings in 2014-2017. To improve the situation for northern pike in the Baltic Sea managers need to consider both fisheries restrictions and measures to decrease predation pressure and increase recruitment. Catch data from recreational fisheries may be used to evaluate such management efforts by providing information on the population development of this keystone species.
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| 10. |
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| 11. |
- Dahlin, Iris, et al.
(författare)
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Fishing cyprinids for food - Evaluation of ecosystem effects and contaminants in cyprinid fish
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We conclude that a coastal cyprinid fishery may have positive effects on the ecosystem and with regard to levels of toxic contaminants, the fish is safe for humans to eat. There is, however, a need to scale up the targeted cyprinid fishery in order to evaluate and quantify the effects on the ecosystem. Scaling up from the pilot scale fisheries requires a change in consumer’s attitude and product development, so that larger quantities of cyprinid fish can be harvested and sold. Several wild fish stocks in the Baltic Sea are in poor condition and today the supply of fish for human consumption in Sweden heavily relies on farmed and imported fish. At the same time, eutrophication and climate change has led to increasing populations of cyprinid fish (e.g. bream, roach, ide) in many coastal areas of the Baltic Sea, which threatens to violate Swedish and international environmental goals. During recent years, there has been an increased interest to fish cyprinids for human consumption in Finland and Sweden. This report evaluates potential ecosystem effects resulting from an increased cyprinid fishery, and how to monitor and assess these effects in the Baltic Sea. We also assess potential barriers to increased cyprinid fisheries for human consumption due to food safety issues resulting from environmental contaminants and market incentives for fishers. In a literature review on biomanipulation targeting cyprinids in lakes, we show that removing cyprinids as a measure to improve water quality has been successful in around 60% of the cases where it has been tested. In the Baltic Sea, however, there have only been a few pilot projects of biomanipulation of cyprinids. Differences between coastal areas and lakes makes it unlikely that the same success rate as in lakes would also apply to coastal areas, especially when considering lowering of nutrient concentrations. Still, we think that a sustainable fishery targeting cyprinids may promote at least positive effects on water transparency and macrophytes in the Baltic Sea on a longer time-scale. In line with results from our literature review, we suggest a monitoring program for evaluation of a targeted cyprinid fishery in coastal areas. Based on the potential ecosystem effects of a cyprinid fishery we suggest that monitoring should prioritize fish community composition, water transparency, chlorofyll α, and submerged macrophytes. For more thorough scientific evaluations, the monitoring program should also include abundance of phyto- and zooplankton, as well as and nutrient and oxygen levels. An increased use of cyprinids from the Baltic Sea as human food will also have societal impacts. To examine if human consumption of cyprinid fish entails any increased risk of exposure to contaminants, we analysed concentration levels of several toxins (mercury, cadmium, dioxins, PCBs, PFAS and PBDE) in bream, ide and roach from five sites along the Swedish coast of the northern Baltic Sea. Our results show that, based on the regulations in Sweden today, cyprinids meet all health regulations for human food. Based on recommendations of weekly intake there are no apparent health risks of consuming cyprinid fish from the Baltic Sea at least weekly. However, since knowledge and regulations of certain environmental toxins are poor or non-existent, we believe it is important to conduct a more comprehensive study, especially for PFAS. An increased fishery targeting cyprinids would diversify the small-scale coastal fishery in Sweden, but the currently low demand makes it risky for fishers to invest in equipment and distribution becomes relatively expensive.
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| 12. |
- Eklöf, Johan S., 1978-, et al.
(författare)
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Effects of seasonal spawning closures on pike (Esox lucius L.) and perch (Perca fluviatilis L.) catches and coastal food webs in the western Baltic Sea
- 2023
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 263
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Tidskriftsartikel (refereegranskat)abstract
- Marine protected areas have become one of the main tools in the battle to curb marine biodiversity loss and habitat degradation. Yet, implementation of permanent fishery closures has often generated resource user conflicts that ultimately undermine conservation goals. Here we assessed the influence of an alternative and often more accepted measure – seasonal fish spawning closures – on large predatory fish and coastal food webs in the western Baltic Sea (Sweden). In spring 2017, we conducted a multivariable field survey in 11 seasonal closures and 11 paired references areas open to fishing. In each area, pike was sampled through angling, and perch and mesopredators through gillnet surveys. To assess trophic cascades, we measured zooplankton abundance and loss of tethered gammarids from predation. Catches per unit effort of northern pike (Esox lucius) – the main target species in recreational fisheries – were ca. 2.5 times higher per unit effort in closures than reference areas; an effect that may be caused by higher abundance and/or higher catchability of pike in the absence of fishing. Catch and weight per unit effort of the more common predator European perch (Perca fluviatilus), and the mesopredators roach (Rutilus rutilus) and three-spined stickleback (Gasterosteus aculeatus) in survey nets were, however, unaffected by closures. Moreover, a previously hypothesized trophic cascade from perch to zooplankton via three-spined stickleback was supported by the analyses, but appeared independent of closures. Yet, predation risk for tethered gammarid amphipods (a prey of stickleback and an important grazer on macroalgae) was three times higher in fished areas than in closures; a cascading closure effect that may potentially be caused by small predatory fish being less active in protected areas to avoid pike predation. Overall, our results suggest that spawning closures impact pike abundance and/or behavior and could help limit the effects of fishing, but that more research is needed to disentangle i) what mechanism(s) that underlie the protection effect on pike catches, ii) the apparently weaker closure impacts on other fish species, as well as iii) the potential for cascading effects on lower trophic levels. Therefore, new seasonal spawning closures should be implemented in addition to (and not instead of) much-needed permanent closures, which have well-known effects on the wider ecosystem.
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| 13. |
- Erlandsson, Johan, et al.
(författare)
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Spatial structure of body size of European flounder (Platichthys flesus L.) in the Baltic Sea
- 2017
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 189, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- The spatial structure of fish species is important for stock identification and management. The European flounder (Platichthys flesus L) shows morphological differences across the Baltic Sea Proper. However, it is not known whether flounders cluster into several distinct areas based on morphological characters, indicating discrete sub-populations, or whether they show continuous morphological variation along space indicating a more continuous population structure. Here, we study the spatial structure of body length and length-at-age distributions of the European flounder (Platichthys flesus L.) across the Baltic Sea Proper (International Council for the Exploration of the Sea (ICES) subdivisions 25-28) using high spatial resolution data (ICES rectangles) from fishery independent surveys 2008-2014. Our results are in agreement with genetic data suggesting a continuous gradient of decreasing body length from southwest to north-east. Further, we observed distance decay in the spatial synchrony of temporal changes in the length distributions, such that the temporal trends were correlated among adjacent ICES rectangles but independent across the whole study area. Length-at-age and maturity patterns that were calculated for each subdivision also showed a consistent spatial difference where SD 28 was significantly different from SD 25 and 26. Our results indicate that the European flounder in the Baltic Sea consists of several loosely defined sub-populations, which may warrant a reconsideration of assessment models, management targets and regulations across subdivisions. (C) 2017 Elsevier B.V. All rights reserved.
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| 14. |
- Faulks, Leanne, et al.
(författare)
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Genetic and morphological divergence along the littoral–pelagic axis in two common and sympatric fishes : perch, Perca fluviatilis (Percidae) and roach, Rutilus rutilus (Cyprinidae)
- 2015
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Ingår i: Biological Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4066 .- 1095-8312. ; 114:4, s. 929-940
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Tidskriftsartikel (refereegranskat)abstract
- Individuals are constantly in competition with one another and, on both ecological and evolutionary timescales, processes act to reduce this competition and promote the gain of fitness advantages via diversification. Here we have investigated the genetic (AFLP) and morphological (geometric morphometrics) aspects of the littoral–pelagic axis, a commonly observed resource polymorphism in freshwater fishes of postglacial lakes. We found a large degree of variation in the genetic and morphological divergence between littoral and pelagic perch and roach across Swedish lakes. Although there was evidence of assortative mating (elevated kinship values) in both species, we could not find any significant coupling of morphology and genetic divergence. Instead, there was evidence that the extent of resource polymorphism may be largely caused by phenotypic plasticity. These results suggest that assortative mating, which can lead to genetically determined adaptive divergence, does occur in these species, particularly perch, but not according to genetically fixed morphological traits. The behavioural mechanisms facilitating associative mating need to be investigated to explore the interaction between phenotypic plasticity and adaptive genetic divergence and their roles in diversification.
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| 15. |
- Faulks, Leanne, et al.
(författare)
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Intraspecific Niche Variation Drives Abundance-Occupancy Relationships in Freshwater Fish Communities
- 2015
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 186:2, s. 272-283
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Tidskriftsartikel (refereegranskat)abstract
- A positive relationship between occupancy and average local abundance of species is found in a variety of taxa, yet the mechanisms driving this association between abundance and occupancy are still enigmatic. Here we show that freshwater fishes exhibit a positive abundance-occupancy relationship across 125 Swedish lakes. For a subset of 9 species from 11 lakes, we estimated species-specific diet breadth from stable isotopes, within-lake habitat breadth from catch data for littoral and pelagic nets, adaptive potential from genetic diversity, abiotic niche position, and dispersal capacity. Average local abundance was mainly positively associated with both within-lake habitat and diet breadth, that is, species with larger intraspecific variation in niche space had higher abundances. No measure was a good predictor of occupancy, indicating that occupancy may be more directly related to abundance or abiotic conditions than to niche breadth per se. This study suggests a link between intraspecific niche variation and a positive abundance-occupancy relationship and implies that management of freshwater fish communities, whether to conserve threatened or control invasive species, should initially be aimed at niche processes.
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| 16. |
- Faulks, L. K., et al.
(författare)
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Adaptive major histocompatibility complex (MHC) and neutral genetic variation in two native Baltic Sea fishes (perch Perca fluviatilis and zander Sander lucioperca) with comparisons to an introduced and disease susceptible population in Australia (P-fluviatilis) : assessing the risk of disease epidemics
- 2016
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 88:4, s. 1564-1583
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Tidskriftsartikel (refereegranskat)abstract
- This study assessed the major histocompatibility complex (MHC) and neutral genetic variation and structure in two percid species, perch Perca fluviatilis and zander Sander lucioperca, in a unique brackish ecosystem, the Baltic Sea. In addition, to assess the importance of MHC diversity to disease susceptibility in these populations, comparisons were made to an introduced, disease susceptible, P. fluviatilis population in Australia. Eighty-three MHC class II B exon 2 variants were amplified: 71 variants from 92 P. fluviatilis samples, and 12 variants from 82 S. lucioperca samples. Microsatellite and MHC data revealed strong spatial genetic structure in S. lucioperca, but not P. fluviatilis, across the Baltic Sea. Both microsatellite and MHC data showed higher levels of genetic diversity in P. fluviatilis from the Baltic Sea compared to Australia, which may have facilitated the spread of an endemic virus, EHNV in the Australian population. The relatively high levels of genetic variation in the Baltic Sea populations, together with spatial genetic structure, however, suggest that there currently seems to be little risk of disease epidemics in this system. To ensure this remains the case in the face of ongoing environmental changes, fisheries and habitat disturbance, the conservation of local-scale genetic variation is recommended.
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| 17. |
- Garnier, Aurélie, et al.
(författare)
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Coastal darkening exacerbates eutrophication symptoms through bottom-up and top-down control modification
- 2023
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 68:3, s. 678-691
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Tidskriftsartikel (refereegranskat)abstract
- Coastal eutrophication due to excessive anthropogenic nutrient loading is a major threat worldwide, and especially in estuaries and semi-enclosed waterbodies, like the brackish Baltic Sea. In addition, coastal waters may become darker (coastal darkening) due to increased input of colored compounds from terrestrial run-off and sediment resuspension. Still, the effects of darkening on coastal food web responses to eutrophication are unknown. In a mesocosm experiment with benthic and pelagic habitats, we manipulated nutrient loading, presence of fish and light availability to disentangle bottom-up and top-down control of eutrophication symptoms in ambient and darkened waters. Overall, we found higher pelagic Chlorophyll a concentrations (a proxy of algal biomass) with darkening and with nutrient enrichment in both clear and dark waters. Albeit fish had a strong impact on zooplankton and zoobenthos, they had no cascading effect on algae. We conclude that coastal darkening due to changes in land use and climate change can pose an additional challenge concerning the recovery of coastal waters from eutrophication.
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| 18. |
- Gårdmark, Anna, et al.
(författare)
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Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates?
- 2012
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 69, s. 1448-1456
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Tidskriftsartikel (refereegranskat)abstract
- Mortality of small pelagic fish due to marine mammals is generally considered to be low compared with other sources of mortality. With recent recoveries of marine mammal predators worldwide, this may no longer hold. The grey seal (Halichoerus grypus) population in the Bothnian Sea has increased fivefold since 1985. Its main prey, herring (Clupea harrengus), is a key species for fisheries in the region. Yet, current stock assessments assume constant natural mortality, leading to a risk of biased stock estimates with increasing predation and misleading analyses of herring population dynamics. We estimated grey seal predation from diet data and reanalysed herring spawning stock biomass (SSB) during 1973-2009. Accounting for predation increased the herring SSB 16% (maximum 19%), but this was within the confidence intervals when ignoring predation. Although mortality in older individuals was inflated when accounting for seal predation, this did not change the conclusions about drivers of herring dynamics. Accounting for grey seal predation is important for abundance estimates of old herring, but currently not for SSB estimates, given the great uncertainties in the standard assessment. The grey seal impact on Bothnian Sea herring will need to be reassessed if stock age composition, grey seal feeding preferences, or total stock development change.
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| 19. |
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| 20. |
- Hasselquist, Dennis, et al.
(författare)
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Temporal patterns of occurrence and transmission of the blood parasite Haemoproteus payevskyi in the great reed warbler Acrocephalus arundinaceus
- 2007
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Ingår i: Journal of Ornithology = Journal fur Ornithologie. - : Springer Science and Business Media LLC. - 0021-8375 .- 1439-0361. ; 148:4, s. 401-409
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Tidskriftsartikel (refereegranskat)abstract
- We studied the prevalence and intensity of the haemosporidian blood parasite Haemoproteus payevskyi in great reed warblers at Lake Kvismaren (6 years) and Lake Segersjo (3 years) in Sweden. Based on microscopic inspection of slides from 282 adult birds, 20.6% showed infection of H. payevskyi in circulating red blood cells in at least 1 year. For parasite prevalence, there was no difference between years, sex, and age classes. However, parasite intensity was higher in females than in males, and this was most pronounced in 1-year-old birds. Individuals scored to carry parasites in year (n) were more likely to show parasite infection year (n + 1) than birds scored to be parasite-free in year (n) . None of 99 juvenile birds examined at the breeding site in late summer, 4-9 weeks after hatching, showed infection of H. payevskyi. Parasite intensity in infected adult birds decreased in the course of the breeding season and no new or relapse infections were observed during this period. Thus, our data imply that in the great reed warbler, a long-distance migrant to tropical Africa, transmission of H. payevskyi occurs on wintering sites or at stopover sites during migration.
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| 21. |
- Herlevi, Heidi, et al.
(författare)
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Environmental abundances of the non-native round goby Neogobius melanostomus influence feeding of native fish predators
- 2023
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Ingår i: Journal of Fish Biology. - : Wiley-Blackwell. - 0022-1112 .- 1095-8649. ; 102:6, s. 1340-1357
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Tidskriftsartikel (refereegranskat)abstract
- The authors assessed the importance of the round goby Neogobius melanostomus as prey for three native predatory fish species, Atlantic cod Gadus morhua, European perch Perca fluviatilis and northern pike Esox lucius, in a northern and southern area of the Baltic Proper, using a combination of visual analysis and DNA metabarcoding of predator stomach contents. To explore the influence of environmental abundances of N. melanostomus on predation, they related the occurrence of N. melanostomus in predator diets to its abundance in survey fishing. Gadus morhua and E. lucius in the southern area showed the highest tendency to feed on N. melanostomus when it was abundant, as N. melanostomus occurred in up to 100% of stomachs and constituted up to 88% of the total diet volume proportion. The diet contribution of N. melanostomus was associated with N. melanostomus abundances for G. morhua and E. lucius, and when N. melanostomus was abundant, these predators exhibited lower prey richness and a higher degree of piscivory. G. morhua and P. fluviatilis also fed less on crustacean prey when N. melanostomus was abundant. The high importance of N. melanostomus in diets of native fish predators may modify indirect interactions between N. melanostomus and native prey species in invaded coastal communities.
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| 22. |
- Hesson, Jenny C., 1980-
(författare)
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Clearing up Culex Confusion : A Basis for Virus Vector Discrimination in Europe
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mosquito species of the Culex genus are the enzootic vectors for several bird-associated viruses that cause disease in humans. In Europe, these viruses include Sindbis (SINV), West Nile and Usutu viruses. The morphologically similar females of Cx. torrentium and Cx. pipiens are potential vectors of these viruses, but difficulties in correctly identifying the mosquito species have caused confusion regarding their respective distribution, abundance, ecology, and consequently their importance as vectors. Species-specific knowledge from correctly identified field material is however of crucial importance since previous research shows that the relatively unknown Cx. torrentium is a far more efficient SINV vector than the widely recognized Cx. pipiens. The latter is involved in the transmission of several other viruses, but its potential importance for SINV transmission is debated.In this thesis I describe the development of a molecular method for species identification, based on reliably identified males of Cx. torrentium and Cx. pipiens. This identification method was then used in consecutive studies on the distribution and relative abundance of the two species in Sweden and 12 other European countries, SINV field infection rates in mosquitoes identified to species level, and evaluation of potential trap bias associated with common sampling techniques.The results showed that Cx. torrentium is a far more common species in Europe than previously assumed. In Sweden and Finland, it is the dominant species, accounting for 89% of the sampled Culex population. In central Europe, it is equally common to Cx. pipiens, while Cx. pipiens dominates south of the Alps Mountain range. Larvae of both species are often found together in both artificial containers (e.g. car tires) and natural sites. Also, a trapping bias against Cx. torrentium was revealed for CDC-traps. For the first time, SINV was isolated from species-identified Cx. torrentium and Cx. pipiens mosquitoes caught in the field, with Cx. torrentium being superior in infection rates (36/1,000 vs. 8.2/1,000). Future studies on SINV, as well as other mosquito-borne bird viruses in Europe, can hopefully gain from the baseline information provided here, and from principles of vector discrimination discussed in the thesis.
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| 23. |
- Hesson, Jenny C., et al.
(författare)
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Geographic distribution and relative abundance of the sibling vector species Culex torrentium and Culex pipiens in Sweden
- 2011
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Ingår i: Vector Borne and Zoonotic Diseases. - : Mary Ann Liebert Inc. - 1530-3667 .- 1557-7759. ; 11:10, s. 1383-1389
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Tidskriftsartikel (refereegranskat)abstract
- Culex torrentium and Culex pipiens are sibling species and potential viral vectors that coexist in Europe. Larvae and females of the two species are morphologically almost identical, and reliable identification can only be done on males. To investigate the distribution and relative abundance of the two species in Sweden, we collected Culex larvae from sites spread over the country, identified them as Culex pipiens/torrentium based on morphology, and identified them to species using a recently developed restriction enzyme method. Cx. torrentium was the dominant species (89%, n = 1012) and it occurred in 48 of the 49 sites investigated, and also dominated in most of the study sites. The proportion of Cx. pipiens larvae in relation to Cx. torrentium collected at each site decreased with both increasing latitude and altitude, and the presence of Cx. pipiens decreased with latitude. In addition, Cx. pipiens/torrentium females were sampled with Centres for Disease Control light traps baited with carbon dioxide. The overall country mean was 4.0 Cx. pipiens/torrentium caught per trap night, with decreasing numbers of Cx. pipiens/torrentium caught per trap night with increasing latitude. Thus, the abundance of Cx. pipiens/torrentium decreased, but the proportion Cx. torrentium increased, with increasing latitude. This is the first study that shows the vast dominance of Cx. torrentium over Cx. pipiens in Sweden. The unexpected dominance of Cx. torrentium highlights the importance of distinguishing between the two species in studies of Culex-borne arboviruses in Europe.
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- Hesson, Jenny Christina, et al.
(författare)
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Temporal Variation in Sindbis Virus Antibody Prevalence in Bird Hosts in an Endemic Area in Sweden
- 2016
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 11:8
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Tidskriftsartikel (refereegranskat)abstract
- Sindbis virus (SINV) is a mosquito-borne bird virus that occasionally causes human disease in Fennoscandia, suggested to have cyclic 7-year intervals between outbreaks. Reliable data on human infections in Sweden is however lacking. Here we investigated the SINV antibody prevalence among birds in a Swedish area endemic to SINV to scrutinize if a cyclic variation in antibody prevalence is present in the natural host of SINV. Serum from birds were sampled in the summers of 2002-2004 and 2009 in the floodplains of the River Dalalven in central Sweden, with 2002 and 2009 representing hypothesized years of SINV outbreaks. A total of 963 birds from 52 species (mainly passerines) were tested for the presence of SINV antibodies using a plaque reduction neutralization test. The highest SINV antibody prevalence was found in Turdidae species, specifically Fieldfare, Redwing and Song thrush in which more than 70% of sampled individuals had antibodies to SINV in 2009. The SINV antibody prevalence significantly varied between years with 2% in 2002, 8% in 2003, 14% in 2004 and 37% in 2009. Antibodies were found equally often in hatchlings and in adults and increased from early to late in the season. Clearly, the SINV antibody prevalence was not elevated in the bird hosts in the predicted outbreak year 2002, thus solid evidence of a cyclic occurrence of SINV in Sweden is still lacking.
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