@article{3672,
  author       = {Barton, Nicholas H},
  issn         = {1365-2540},
  journal      = {Heredity},
  pages        = {277 -- 278},
  publisher    = {Springer Nature},
  title        = {{The hybrid sink effect}},
  doi          = {10.1038/hdy.1980.23},
  volume       = {44},
  year         = {1980},
}

@inbook{4334,
  author       = {Hewitt, Godfrey and Barton, Nicholas H},
  booktitle    = {Insect Cytogenetics},
  editor       = {Blackman, Roger and Ashburner, Michael},
  isbn         = {9-780-6320-0552-9},
  pages        = {149 -- 170},
  publisher    = {Wiley-Blackwell},
  title        = {{The structure and maintenance of hybrid zones as exemplified by Podisma pedestris}},
  volume       = {10},
  year         = {1980},
}

@article{4335,
  abstract     = {Genetic incompatibilities between two races of the grasshopper Podisma pedestris, which differ by a Robertsonian fusion involving the sex chromosome, have been investigated. Crosses were made between four populations spanning the chromosomal cline; F1 hybrids between the races, though not between separated populations of the same race, showed markedly reduced hatching success. Observations of the fate of chromosomes transplanted across the cline supported this finding. Crosses between grasshoppers from a mixed population in the cline showed a lower average hatching success, but no correlation of this inviability with the chromosomal polymorphism. The karyotypes of pre-diapause embryos from both types of cross gave no evidence for non-disjunction of the sex chromosome trivalent in heterozygous females; an upper limit of 16 per cent can be set on the non-disjunction rate. These findings suggest that the karyotypic difference is only a weakly selected marker for more fundamental changes in genotype.},
  author       = {Barton, Nicholas H},
  issn         = {1365-2540},
  journal      = {Heredity},
  pages        = {47 -- 59},
  publisher    = {Springer Nature},
  title        = {{The fitness of hybrids between two chromosomal races of the grasshopper Podisma pedestris}},
  doi          = {10.1038/hdy.1980.49},
  volume       = {45},
  year         = {1980},
}

@article{3673,
  abstract     = {The effect of a cline as a barrier to gene flow at closely linked, weakly selected loci is investigated using a continuous diffusion model. It is shown that a linked cline induces a step in the frequency of a neutral allele, which is proportional to the gradient in neutral allele frequency and to the inverse of the recombination rate. A barrier to dispersal or a local region of low abundance has a similar effect (Nagylaki, 1976). The cline will block the flow of neutral alleles over a region of chromosome roughly 2s/t map units long. However, a slightly advantageous allele will be little affected, and must be very tightly linked to be delayed for long.},
  author       = {Barton, Nicholas H},
  issn         = {1365-2540},
  journal      = {Heredity},
  number       = {3},
  pages        = {333 -- 339},
  publisher    = {Springer Nature},
  title        = {{Gene flow past a cline}},
  doi          = {10.1038/hdy.1979.86},
  volume       = {43},
  year         = {1979},
}

@article{4336,
  abstract     = {This paper investigates the dynamic behaviour of hybrid zones which are maintained by a balance between dispersal and selection against hybrids. In the first section it is shown that a hybrid zone involving a single locus can move in response to a selective imbalance between the two homozygotes, and also to variation in population density and dispersal rate. It can be trapped by natural barriers, and so an allele which is selected against when rare cannot advance, even if it is advantageous when common. The continuous model used in deriving these results is shown to be a good approximation to the stepping-stone model, provided that the cline contains several demes.

The effect of stochastic forces on multi-locus hybrid zones is then considered. An expression giving the shift in position after an arbitrary perturbation in gamete frequency is derived. Using this formula, it is found that sampling drift is negligible unless the zone includes few organisms and involves few loci. Random variations in population structure are the dominant force, and could allow considerable movement in an even environment. However, natural barriers can still trap hybrid zones, and so it is likely that they will remain roughly where they first formed.},
  author       = {Barton, Nicholas H},
  issn         = {1365-2540},
  journal      = {Heredity},
  number       = {3},
  pages        = {341 -- 359},
  publisher    = {Springer Nature},
  title        = {{The dynamics of hybrid zones}},
  doi          = {10.1038/hdy.1979.87},
  volume       = {43},
  year         = {1979},
}

@phdthesis{4337,
  author       = {Barton, Nicholas H},
  publisher    = {University of East Anglia},
  title        = {{A hybrid zone in the alpine grasshopper Podisma pedestris}},
  year         = {1979},
}