| 1. |
- Allander, Klas, et al.
(författare)
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Temporal variation and reliability of blood parasite levels in captive Yellowhammer males Emberiza citrinella
- 1997
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Ingår i: Journal of Avian Biology. - : JSTOR. - 0908-8857 .- 1600-048X. ; 28:4, s. 325-330
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Tidskriftsartikel (refereegranskat)abstract
- The temporal variation of blood parasites in captive Yellowhammer males was studied in order to investigate possible costs of parasites. Birds were caught in the wild in early April and kept in aviaries during the study period. Blood samples were taken, body mass measured, and moult was scored twelve times for the same individuals from April to October. Blood parasites were detectable in smears during the whole study period with an intensity peak coinciding with breeding in the wild. Young birds had more parasites and a consistently higher body mass than older birds. There was no relationship between parasite intensity and mass in older birds but possibly one in young birds. Parasites did not seem to affect moult in either age class. Repeatability of parasite counts of smears from the same individual was very high and smears are therefore a reliable method for estimating parasite intensity. We conclude that blood parasites are probably most severe during, but occur in their hosts long after, the breeding season. Possible costs of parasites outside the breeding season require further study.
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| 2. |
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| 3. |
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| 4. |
- Sterky, Fredrik, et al.
(författare)
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Gene discovery in the wood-forming tissues of poplar : Analysis of 5,692 expressed sequence tags
- 1998
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 95:22, s. 13330-13335
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Tidskriftsartikel (refereegranskat)abstract
- A rapidly growing area of genome research is the generation of expressed sequence tags (ESTs) in which large numbers of randomly selected cDNA clones are partially sequenced. The collection of ESTs reflects the level and complexity of gene expression in the sampled tissue, To date, the majority of plant ESTs are from nonwoody plants such as Arabidopsis, Brassica, maize, and rice. Here, we present a large-scale production of ESTs from the wood-forming tissues of two poplars, Populus tremula L, x tremuloides Michx, and Populus trichocarpa 'Trichobel.' The 5,692 ESTs analyzed represented a total of 3,719 unique transcripts for the two cDNA libraries, Putative functions could be assigned to 2,245 of these transcripts that corresponded to 820 protein functions. Of specific interest to forest biotechnology are the 4% of ESTs involved in various processes of cell wall formation, such as lignin and cellulose synthesis, 5% similar to developmental regulators and members of known signal transduction pathways, and 2% involved in hormone biosynthesis. An additional 12% of the ESTs show ed no significant similarity to any other DNA or protein sequences in existing databases. The absence of these sequences from public databases may indicate a specific role for these proteins in wood formation. The cDNA libraries and the accompanying database are valuable resources for forest research directed toward understanding the genetic control of wood formation and future endeavors to modify wood and fiber properties for industrial use.
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| 5. |
- Sundberg, Jan
(författare)
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Female Yellowhammers (Emberiza-Citrinella) Prefer Yellower Males - A Laboratory Experiment
- 1995
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Ingår i: Behavioral Ecology and Sociobiology. - 0340-5443 .- 1432-0762. ; 37:4, s. 275-282
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Tidskriftsartikel (refereegranskat)abstract
- The importance of male plumage coloration as a signal of male dominance and a cue for female choice in the monogamous yellowhammer, Emberiza citrinella, was tested in two sets of experiments in an indoor aviary. Dominance was tested by introducing two individuals, with no previous experience of each other, in an aviary with food and water. Aggression occurred more often between two males than between a male and a female and more frequently between pairs of males including at least one old male than between two young males. Dominance was not related to male colour in trials between males of the same age class, but it was in trials between an old and a young male, often differing in colour. Thus, age may be a more important determinant of dominance than colour. Female preference for more colourful males was tested by allowing hormone-induced females to choose between a more and a less colourful dummy male. Females spent more time in front of more colourful than drabber males and also more often perched beside colourful males than duller individuals. Although male colour cannot be ruled out as a dominance signal, the results suggest that male colour is primarily used as a signal in mate choice. Female choice may hence be responsible for maintenance of bright plumage in the male yellowhammer.
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| 6. |
- Sundberg, Jan, et al.
(författare)
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Old, colourful male yellowhammers, Emberiza citrinella, benefit from extra-pair copulations
- 1996
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472 .- 1095-8282. ; 52, s. 113-122
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Tidskriftsartikel (refereegranskat)abstract
- The frequency of extra-pair paternity was determined in broods of the yellowhammer using single-locus DNA fingerprinting. Of 32 analysed clutches, 69% contained at least one extra-pair young. Out of 123 nestlings, 37% were extra-pair sired young. The extra-pair male could be assigned to 23 (50%) nestlings. Successful extra-pair males were all at least 3 years old although both younger and older males suffered from extra-pair paternity. Extra-pair males were also significantly more colourful than pair males, but did not differ in other characters. Colour did not differ between males with or without extra-pair young. The frequency of extra-pair young was not related to breeding density and identified extra-pair males were not necessarily nearest neighbours, giving further evidence that extra-pair males are not chosen at random. Since females do not obtain anything but sperm from extra-pair males, the results suggest that females prefer older and more colourful males, contributing good or attractive genes, as indicated by their plumage. Consequently, old, colourful extra-pair males, and possibly females, are likely to benefit from extra-pair copulations.
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| 7. |
- Sundberg, Jan
(författare)
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Parasites, plumage coloration and reproductive success in the yellowhammer, Emberiza citrinella
- 1995
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Ingår i: Oikos. - : JSTOR. - 0030-1299 .- 1600-0706. ; 74:2, s. 331-339
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Tidskriftsartikel (refereegranskat)abstract
- The prevalence and intensity of haematozoan parasites, with special emphasis on Haemoproteus coatneyi, was studied in relation to male plumage coloration, and reproductive success in a population of yellowhammers (Emberiza citrinella). Parasite prevalence and intensity were found to vary with time in season, emphasising the need to take samples during times of developed infection. Males were found with a peak intensity during the early breeding period and females slightly later, during the nestling period. The hypothesis of parasite-mediated sexual selection, according to which bright plumages have evolved in relation to degree of parasite infection, was tested. Male colour was found to reliably reveal the intensity of parasites during the breeding period. Males with high parasite intensity produced fewer fledglings. In spite of the negative correlation between parasite load and colour, males with more colour did not produce more offspring. No cost of parasites was found in females, and pairing was not assortative with respect to parasite infection. However, contrary to the hypothesis, no relationship between male colour and number of fledglings was found. Conclusively, some support was found for the hypothesis of parasite-mediated sexual selection, i.e. bright male plumages in the yellowhammer may thus have evolved or is maintained as a signal of level of parasite infection since a reduced reproductive success may be a cost imposed by high parasite load.
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