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Sökning: WFRF:(Birkhead Tim)

  • Resultat 1-9 av 9
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  • Mills, James A, et al. (författare)
  • Archiving Primary Data: Solutions for Long-Term Studies.
  • 2015
  • Ingår i: Trends in Ecology & Evolution. - : Elsevier. - 1872-8383 .- 0169-5347. ; 30:10, s. 581-589
  • Tidskriftsartikel (refereegranskat)abstract
    • The recent trend for journals to require open access to primary data included in publications has been embraced by many biologists, but has caused apprehension amongst researchers engaged in long-term ecological and evolutionary studies. A worldwide survey of 73 principal investigators (Pls) with long-term studies revealed positive attitudes towards sharing data with the agreement or involvement of the PI, and 93% of PIs have historically shared data. Only 8% were in favor of uncontrolled, open access to primary data while 63% expressed serious concern. We present here their viewpoint on an issue that can have non-trivial scientific consequences. We discuss potential costs of public data archiving and provide possible solutions to meet the needs of journals and researchers.
  • Ekblom, Robert, et al. (författare)
  • Genetic mapping of the major histocompatibility complex in the zebra finch (Taeniopygia guttata)
  • 2011
  • Ingår i: Immunogenetics. - 0093-7711 .- 1432-1211. ; 63:8, s. 523-530
  • Tidskriftsartikel (refereegranskat)abstract
    • Genes of the major histocompatibility complex (MHC) have received much attention in immunology, genetics, and ecology because they are highly polymorphic and play important roles in parasite resistance and mate choice. Until recently, the MHC of passerine birds was not well-described. However, the genome sequencing of the zebra finch (Taeniopygia guttata) has partially redressed this gap in our knowledge of avian MHC genes. Here, we contribute further to the understanding of the zebra finch MHC organization by mapping SNPs within or close to known MHC genes in the zebra finch genome. MHC class I and IIB genes were both mapped to zebra finch chromosome 16, and there was no evidence that MHC class I genes are located on chromosome 22 (as suggested by the genome assembly). We confirm the location in the MHC region on chromosome 16 for several other genes (BRD2, FLOT1, TRIM7.2, GNB2L1, and CSNK2B). Two of these (CSNK2B and FLOT1) have not previously been mapped in any other bird species. In line with previous results, we also find that orthologs to the immune-related genes B-NK and CLEC2D, which are part of the MHC region in chicken, are situated on zebra finch chromosome Z and not among other MHC genes in the zebra finch.
  • Immler, Simone, et al. (författare)
  • Distinct evolutionary patterns of morphometric sperm traits in passerine birds
  • 2012
  • Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - 0962-8452 .- 1471-2954. ; 279:1745, s. 4174-4182
  • Tidskriftsartikel (refereegranskat)abstract
    • The striking diversity of sperm shape across the animal kingdom is still poorly understood. Postcopulatory sexual selection is an important factor driving the evolution of sperm size and shape. Interestingly, morphometric sperm traits, such as the length of the head, midpiece and flagellum, exhibit a strong positive phenotypic correlation across species. Here we used recently developed comparative methods to investigate how such phenotypic correlations between morphometric sperm traits may evolve. We compare allometric relationships and evolutionary trajectories of three morphometric sperm traits (length of head, midpiece and flagellum) in passerine birds. We show that these traits exhibit strong phenotypic correlations but that allometry varies across families. In addition, the evolutionary trajectories of the midpiece and flagellum are similar while the trajectory for head length differs. We discuss our findings in the light of three scenarios accounting for correlated trait evolution: (i) genetic correlation; (ii) concerted response to selection acting simultaneously on different traits; and (iii) phenotypic correlation between traits driven by mechanistic constraints owing to selection on sperm performance. Our results suggest that concerted response to selection is the most likely explanation for the phenotypic correlation between morphometric sperm traits.
  • Immler, Simone, et al. (författare)
  • Resolving variation in the reproductive tradeoff between sperm size and number
  • 2011
  • Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - 0027-8424 .- 1091-6490. ; 108:13, s. 5325-5330
  • Tidskriftsartikel (refereegranskat)abstract
    • Spermatozoa are amongst the most variable cells, and three factors are thought to account for this variation in design: fertilization mode, phylogeny, and postcopulatory sexual selection. In addition, it has long been assumed that a tradeoff exists between sperm size and number, and although postcopulatory sexual selection affects both traits, empirical evidence for a tradeoff has so far been elusive. Our recent theoretical model predicts that the nature of a direct tradeoff between sperm size and number varies with sperm competition mechanism and sperm competition risk. We test these predictions using a comparative approach in two very different taxa with different sperm competition mechanisms: passerine birds (mechanism: simple raffle) and Drosophila fruit flies (sperm displacement). We show that in both groups, males increase their total ejaculate investment with increasing sperm competition risk, but whereas passerine birds allocate disproportionately to sperm number, drosophilids allocate disproportionately to sperm size. This striking difference between the two groups can be at least partly explained by sperm competition mechanisms depending on sperm size relative to the size of the female reproductive tract: in large animals (passerines), sperm numbers are advantageous in sperm competition owing to dilution inside the female tract, whereas in small animals (drosophilids), large spermare advantageous for physical competition (sperm displacement). Our study provides two important results. First, we provide convincing evidence for the existence of a sperm size-number tradeoff. Second, we show that by considering both sperm competition mechanism and dilution, can we account for variation in sperm size between different taxa.
  • Pizzari, Tommaso, et al. (författare)
  • Sophisticated sperm allocation in male fowl
  • 2003
  • Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 426:6962, s. 70-74
  • Tidskriftsartikel (refereegranskat)abstract
    • When a female is sexually promiscuous, the ejaculates of different males compete for the fertilization of her eggs; the more sperm a male inseminates into a female, the more likely he is to fertilize her eggs. Because sperm production is limited and costly, theory predicts that males will strategically allocate sperm (1) according to female promiscuity, (2) saving some for copulations with new females, and (3) to females producing more and/or better offspring. Whether males allocate sperm in all of these ways is not known, particularly in birds where the collection of natural ejaculates only recently became possible. Here we demonstrate male sperm allocation of unprecedented sophistication in the fowl Gallus gallus. Males show status-dependent sperm investment in females according to the level of female promiscuity; they progressively reduce sperm investment in a particular female but, on encountering a new female, instantaneously increase their sperm investment; and they preferentially allocate sperm to females with large sexual ornaments signalling superior maternal investment. Our results indicate that female promiscuity leads to the evolution of sophisticated male sexual behaviour.
  • Svensson, Magnus, et al. (författare)
  • Impaired hatching success and male-biased embryo mortality in Tree Sparrows
  • 2007
  • Ingår i: Journal of Ornithology = Journal fur Ornithologie. - 0021-8375 .- 1439-0361. ; 148:1, s. 117-122
  • Tidskriftsartikel (refereegranskat)abstract
    • During the past 30 years, many species of farmland birds have declined dramatically in numbers in Northern Europe, a trend coinciding with a tremendous intensification of agriculture, although the exact causes of these declines remain unclear. One of the worst affected species is the Tree Sparrow (Passer montanus). We studied two Swedish Tree Sparrow populations during the years 1996–2004 and found that in both populations, almost half of all laid eggs remained unhatched. This led us to investigate whether the eggs failed to hatch because of: (1) eggs not being fertilised or (2) embryo mortality. Our analyses showed that all of the eggs investigated contained sufficient number of sperm for fertilisation and that they also had other visible signs indicating that fertilisation had occurred. Hatching failure was instead shown to result from embryo mortality. Using molecular techniques, we were able to determine that embryo mortality is more likely to affect male embryos than females and that the fledgling sex ratio was consequently highly female biased. The cause of this sex-biased embryo mortality remains unknown, but various potential explanations are discussed.
  • Warren, Wesley C, et al. (författare)
  • The genome of a songbird
  • 2010
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 464:7289, s. 757-762
  • Tidskriftsartikel (refereegranskat)abstract
    • The zebra finch is an important model organism in several fields with unique relevance to human neuroscience. Like other songbirds, the zebra finch communicates through learned vocalizations, an ability otherwise documented only in humans and a few other animals and lacking in the chicken-the only bird with a sequenced genome until now. Here we present a structural, functional and comparative analysis of the genome sequence of the zebra finch (Taeniopygia guttata), which is a songbird belonging to the large avian order Passeriformes. We find that the overall structures of the genomes are similar in zebra finch and chicken, but they differ in many intrachromosomal rearrangements, lineage-specific gene family expansions, the number of long-terminal-repeat-based retrotransposons, and mechanisms of sex chromosome dosage compensation. We show that song behaviour engages gene regulatory networks in the zebra finch brain, altering the expression of long non-coding RNAs, microRNAs, transcription factors and their targets. We also show evidence for rapid molecular evolution in the songbird lineage of genes that are regulated during song experience. These results indicate an active involvement of the genome in neural processes underlying vocal communication and identify potential genetic substrates for the evolution and regulation of this behaviour.
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  • Resultat 1-9 av 9

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