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| 3. |
- Arlt, D, et al.
(författare)
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Breeding synchrony does not affect extra-pair paternity in great reed warblers
- 2004
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Ingår i: Behaviour. - : Brill. - 1568-539X .- 0005-7959. ; 141:7, s. 863-880
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Tidskriftsartikel (refereegranskat)abstract
- Breeding synchrony is hypothesised to influence the occurrence and frequency of extra-pair fertilisations (EPFs) in birds irrespective of the social mating system. The two proposed hypotheses make opposite predictions. (1) Synchronous breeding leads to a lower frequency of EPFs because males face a trade-off between mate guarding and obtaining additional matings via extra-pair copulations (EPCs) ('guarding constraint' hypothesis). (2) Synchronous breeding promotes EPFs because females are able to compare displaying males simultaneously, which provides them with more reliable cues for extra-pair mate choice ('mate assessment' hypothesis). In a study of great reed warblers (Acrocephalus arundillaceus) from 1987-1998, annual breeding was asynchronous and the frequency of EPFs was rather low (extra-pair young occurring in 6.4% of the broods). Within this population, however, there was no relationship between the frequency of EPFs and breeding synchrony, thus not favouring any of the two hypotheses. Contrary to assumptions of the hypotheses, mate guarding did not seem to constrain males from engaging in EPCs (disfavouring the 'guarding constraint' hypothesis), and females seem to have repeated opportunities to compare males irrespective of breeding synchrony (disfavouring the 'mate assessment' hypothesis). Our results suggest that breeding synchrony is not an important factor influencing patterns of EPFs in great reed warblers. The low frequency of EPFs may instead be explained by the socially polygynous mating system, where females are less constrained in their choice of a social male.
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| 4. |
- Erlinge, Sam, et al.
(författare)
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Can vertebrate predators regulate their prey?
- 1984
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Ingår i: The American Naturalist. ; 123:1, s. 125-133
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Tidskriftsartikel (refereegranskat)abstract
- Whether vertebrate predators can regulate their prey or not has long been a controversial question. At the one extreme it has been claimed that predators have no impact on prey numbers but consume only a doomed surplus (Errington 1946), and at the other that predators strongly interact with their prey causing either stable equilibria or cycles (Tanner 1975; Keith et al. 1977). However,.there are no field studies showing a regulatory effect of predation among vertebrates. Here we report on such a study.
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| 6. |
- Hansson, Bengt, et al.
(författare)
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Increase of genetic variation over time in a recently founded population of great reed warblers (Acrocephalus arundinaceus) revealed by microsatellites and DNA fingerprinting
- 2000
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 9:10, s. 1529-1538
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Tidskriftsartikel (refereegranskat)abstract
- Genetic similarity within pairs of individuals was examined using both 10 polymorphic microsatellite loci and multi-locus DNA fingerprinting profiles in a semi-isolated population of great reed warblers at Lake Kvismaren, south Central Sweden, in 1987-1993. The population was founded by a few individuals in 1978, followed by a gradual increase in numbers until 1988, since when the population has remained relatively stable with about 60 breeding birds. We have previously found that high genetic similarity between pairmates in the population during the early part of the study period reduced egg hatching success, and hence reproductive success. The measures of pairwise genetic similarity, microsatellite allele sharing and DNA fingerprinting band sharing, were highly correlated with pedigree-based relatedness. Both microsatellite and DNA fingerprinting similarities between pair-mates declined significantly over the study period, and the pattern was most pronounced in the DNA fingerprinting data. Analyses restricted to the microsatellite data showed that the average annual microsatellite similarity between pairwise combinations of individuals, as well as individual homozygosity in males, declined significantly over the study period, and that several immigrants carrying novel alleles entered the population during the study. Hence, the temporal decline in genetic similarity of mates in the population is probably a consequence of increased immigration, facilitated by the recent expansion of the species in the region. These results suggest that the population has now recovered genetically, or is in the process of recovering, from a recent founder event.
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| 7. |
- Hansson, Maria, et al.
(författare)
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Characterization of two distinct aryl hydrocarbon receptor (AhR2) genes in Atlantic salmon (Salmo salar) and evidence for multiple AhR2 gene lineages in salmonid fish
- 2003
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Ingår i: Gene. - 1879-0038. ; 303, s. 197-206
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Tidskriftsartikel (refereegranskat)abstract
- The aryl hydrocarbon receptor (AhR) mediates the toxicity of several environmental contaminants, e.g. 2,3,7,8-tetrachlorodibenzo-p-dioxin, and other halogenated hydrocarbons in vertebrates. This receptor initiates the transcription of several biotransformation enzymes, which in turn are responsible for causing severe harm to biological tissue. Here we describe the isolation and complete characterization of the first two AhR genes from the teleost fish Atlantic salmon (Salmo salar). The predicted amino acid sequences contain regions characteristic of other vertebrate AhRs including basic helix-loop-helix (bHLH) and PER-ARNT-SIM (PAS) domains but show little similarity to other vertebrate AhRs across the C-terminal half. Furthermore, they do not contain distinct Q-rich domains as found in the mammalian AhR, which is in line with previously described fish AhR genes. The salmon cDNAs encode 1106 and 1107 putative residues, respectively, approximately 50 amino acids longer than previously characterized AhR genes. Phylogenetic analyses demonstrated that the two salmon AhR sequences cluster within the AhR subfamily of the bHLH-PAS family, in a clade containing fish AhR2 genes. Although the two AbR2 forms are 92% identical at the amino acid level, the distribution of sequence differences and the presence of both forms in 30 tested individuals suggest that they are not allelic but derived from separate loci. Interestingly, they are not orthologs of the rainbow trout (Oncorhynchus mykiss) AhR2alpha and beta genes and the new salmon loci are therefore here designated AhR2gamma and AhR2delta. In line with this, PCR with DNA from rainbow trout revealed a new trout AhR locus that was more similar to the two salmon genes than to the trout AhR2alpha and beta genes, suggesting that the rainbow trout possesses at least three distinct AhR2 genes. The presence of multiple AhR genes in these species is probably a consequence of the genome duplications that occurred in the early evolution of fish and later also specifically in the salmonid lineage. Reverse transcription-PCR analyses revealed that both AhR2gamma and AhR2delta are transcribed in the liver, spleen and muscles of adult salmon.
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| 8. |
- Hansson, Maria, et al.
(författare)
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Polychlorinated biphenyl load, aryl hydrocarbon receptor, and cytochrome P4501A1 induction in a wild population of Atlantic salmon (Salmo salar) from the Baltic Sea
- 2006
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Ingår i: Environmental Toxicology and Chemistry. - 0730-7268. ; 25:8, s. 2197-2207
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Tidskriftsartikel (refereegranskat)abstract
- The toxicity induced by several environmental pollutants is mediated by the aryl hydrocarbon receptor (AHR), which controls the expression of many biotransformation genes, such as cytochrome P4501A1 (CYP1A1). Previous studies have indicated that fish populations can evolve tolerance to persistent chlorinated pollutants by down-regulating the AHR pathway. Here, we measure to what extent tissue loads of polychlorinated biphenyl (PCB) congeners and AHR genotypes contribute to biotransformation capacity in wild, foraging Atlantic salmon (Salmo salar L.) from the Baltic Sea. In muscle, the sum of the 21 most common PCB congeners (ΣPCB) was correlated with three extracted AHR agonists (PCBs 77/110, 118/123/149, and 105/132/153). Both the AHR agonists as well as ΣPCB were correlated with lipid content. The ΣPCB, controlled for the effects of sex and lipid content in muscle tissue, did not predict mRNA transcript levels of the measured AHRs (AHR2α, AHR2γ, and AHR2δ) or CYP1A1 in liver. However, all AHR2 mRNA transcript levels were positively correlated with CYP1A1 level. In turn, the CYP1A1 level was negatively correlated with concentration of the muscle-tissue antioxidant astaxanthin, suggesting that astaxanthin is depleted when biotransformation processes (CYP1A1) are activated. No correlation was found between ethoxyresorufin-O-deethylase activity and ΣPCB, CYP1A1, or antioxidant levels. In 5′-flanking regions of the AHR2 genes, we identified multiple allelic variants that were used for genotyping. The mRNA transcript level of AHR2α was significantly associated with the AHR2α 5′-flanking region genotype and with the interaction of the genotype and individual PCB level. These results suggest that in wild Atlantic salmon from the Baltic Sea, active production of AHR2 mRNA by means of PCB exposure may be affected by genetic polymorphisms at the AHR2 loci.
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| 9. |
- Hansson, Maria, et al.
(författare)
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Polychlorinated biphenyl (PCB) load, lipid reserves and biotransformation activity in migrating Atlantic salmon from River Mörrum, Sweden.
- 2009
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491 .- 1873-6424. ; 157:12, s. 3396-3403
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Tidskriftsartikel (refereegranskat)abstract
- Atlantic salmon accumulate high levels of contaminants such as polychlorinated biphenyls (PCBs) in their lipids during the adult growth phase spent at sea. The lipids are later utilized during migration for swimming and biological adaptations. We hypothesize that migrating salmons' biotransformation processes are affected by the high levels of built-up PCBs compared to salmon that in a pre-migrational stage. For these analyses we sampled adult Atlantic salmon during migration in the Swedish River Mörrum and measured the 21 most common PCB congeners ( summation operatorPCB) and lipid levels in muscle tissue, aryl hydrocarbon receptor (AHR2) and cytochrome P4501A1 (CYP1A1) transcript levels as well as ethoxyresorufin-O-deethylase activity (EROD) in liver. We also determined which AHR2 genotypes the salmon carried. We show that EROD activity is correlated to CYP1A1 level but not to summation operatorPCB concentration. summation operatorPCB concentration does not predict levels of neither the AHR2 nor CYP1A1 genes. We find no associations between specific AHR2 transcription levels and AHR2 genotypes or a correlation between AHR2 and CYP1A1 transcription levels, which is in direct contrast to pre-migrational adult salmon from the Baltic Sea. When we compare River Mörrum to salmon we have previously sampled in the Baltic Sea we show that migrating salmon have significantly lower lipid levels in their muscles; higher muscle concentrations of summation operatorPCB on a lipid basis; and significantly lower CYP1A1 and EROD levels compared to salmon from the Baltic Sea. Also, transcript levels of three out of four AHR2 genes are significantly different. In conclusion, migrating Swedish Atlantic salmon carry higher concentrations of PCBs in their lipids compared to salmon in the Baltic Sea, but have lower activation of biotransformation genes and enzymes. Our results indicate that accumulated pollutants from the Baltic Sea are deactivated inside the migrating salmon's lipid tissues and increase in concentration when migration is initiated thereby limiting their impact on biotransformation processes.
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| 10. |
- Hansson, Maria, et al.
(författare)
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Unprecedented genomic diversity of AhR1 and AhR2 genes in Atlantic salmon (Salmo salar L.)
- 2004
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Ingår i: Aquatic Toxicology. - : Elsevier BV. - 1879-1514 .- 0166-445X. ; 68:3, s. 219-232
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Tidskriftsartikel (refereegranskat)abstract
- Aryl hydrocarbon receptor (AhR) genes encode proteins involved in mediating the toxic responses induced by several environmental pollutants. Here, we describe the identification of the first two AhR1 (alpha and beta) genes and two additional AhR2 (alpha and beta) genes in the tetraploid species Atlantic salmon (Salmo salar L.) from a cosmid library screening. Cosmid clones containing genomic salmon AhR sequences were isolated using a cDNA clone containing the coding region of the Atlantic salmon AhR2gamma as a probe. Screening revealed 14 positive clones, from which four were chosen for further analyses. One of the cosmids contained genomic AhR sequences that were highly similar to the rainbow trout (Oncorhynchus mykiss) AhR2alpha and beta genes. SMART RACE amplified two complete, highly similar but not identical AhR type 2 sequences from salmon cDNA, which from phylogenetic analyses were determined as the rainbow trout AhR2alpha and beta orthologs. The salmon AhR2alpha and beta encode proteins of 1071 and 1058 residues, respectively, and encompass characteristic AhR sequence elements like a basic-helix-loop-helix (bHLH) and two PER-ARNT-SIM (PAS) domains. Both genes are transcribed in liver, spleen and muscle tissues of adult salmon. A second cosmid contained partial sequences, which were identical to the previously characterized AhR2gamma gene. The last two cosmids contained partial genomic AhR sequences, which were more similar to other AhR type 1 fish genes than the four characterized salmon AhR2 genes. However, attempts to amplify the corresponding complete cDNA sequences of the inserts proved very difficult, suggesting that these genes are non-functional or very weakly transcribed in the examined tissues. Phylogenetic analyses of the conserved regions did, however, clearly indicate that these two AhRs belong to the AhR type 1 clade and have been assigned as the Atlantic salmon AhR1alpha and AhR1beta genes. Taken together, these findings demonstrate that multiple AhR genes are present in Atlantic salmon genome, which likely is a consequence of previous genome duplications in the evolutionary past of salmonids. Plausible explanations for the high incidence of AhR genes in fish and more specifically in salmortids, like rapid divergences in specialized functions, are discussed.
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