@article{3670, abstract = {The grasshopper Podisma pedestris includes two chromosomal races, which differ by a Robertsonian fusion involving the sex chromosome. The two races meet in a cline which runs for 100 km across the Alpes Maritimes in south-eastern France. An intensive study of the easternmost end of this cline shows that it is about 800 m wide; the cline is not smooth, containing substantial spikes in chromosome frequency which might be due to sampling drift. Though the cline seems narrow, it is wide compared with the dispersal rate of the insect; a selective force of only 0.5% would be enough to maintain the cline. It is difficult to determine the nature of this force, but some evidence comes from the position of the cline, and from the presence of coincident clines at other loci. An estimate of the distribution of Podisma has been made, and the cline seems to follow, for the most part, a region of low population density, suggesting that it is maintained by hybrid unfitness. However, in the one region where the cline is relatively free to move, the XY race bulges forwards more than would be expected if hybrids are unfit. The observation of severe inviability in crosses between the races, though it is not associated with the chromosomal difference, also indicates that this cline is the result of some sort of genetic incompatibility.}, author = {Barton, Nicholas H and Hewitt, Godfrey}, issn = {1558-5646}, journal = {Evolution; International Journal of Organic Evolution}, number = {5}, pages = {1008 -- 1018}, publisher = {Wiley-Blackwell}, title = {{A chromosomal cline in the grasshopper Podisma pedestris}}, doi = { 10.1111/j.1558-5646.1981.tb04966.x}, volume = {35}, year = {1981}, } @article{3671, author = {Barton, Nicholas H}, issn = {1365-2540}, journal = {Heredity}, pages = {279 -- 282}, publisher = {Nature Publishing Group}, title = {{The width of the hybrid zone in Caledia captiva}}, doi = {10.1038/hdy.1981.86}, volume = {47}, year = {1981}, } @article{4133, abstract = {In 1979 Kirpatrick obtained a practically feasible algorithm for planar regionlocation working in linear space and logarithmic time, provided the regions are bounded by straight line segments. No algorithm requiring only linear space and log-polynomial time was known, so far, for general planar regionlocation, i.e. for the case where regions are bounded by curves more complicated than straight line segments. As main result of this paper such an algorithm is presented.}, author = {Edelsbrunner, Herbert and Maurer, Hermann}, issn = {0304-3975}, journal = {Theoretical Computer Science}, number = {3}, pages = {329 -- 336}, publisher = {Elsevier}, title = {{A space-optimal solution of general region location}}, doi = {10.1016/0304-3975(81)90103-1}, volume = {16}, year = {1981}, } @article{4132, author = {Edelsbrunner, Herbert and Maurer, Hermann}, issn = {0020-0190}, journal = {Information Processing Letters}, number = {4-5}, pages = {177 -- 181}, publisher = {Elsevier}, title = {{On the intersection of Orthogonal objects}}, doi = {10.1016/0020-0190(81)90053-3}, volume = {13}, year = {1981}, } @inbook{4332, author = {Barton, Nicholas H and Hewitt, Godfrey}, booktitle = {Evolution and Speciation}, editor = {Atchley, William and Woodruff, David}, isbn = {9-780-5212-3823-6}, pages = {109 -- 145}, publisher = {Cambridge University Press}, title = {{Hybrid zones and speciation}}, year = {1981}, } @article{4333, abstract = {Samples were taken from five sites in a transect across the hybrid zone between two chromosomal races of the grasshopper Podisma pedestris. Crosses were set up between insects from the same population, and between populations spanning the zone, and the early viability of the offspring was measured. Hybrids between pure populations had reduced viability, and the viability of insects from the middle of the zone was still lower, showing that most (87 per cent) of the inviability was due to the breakup of coadapated gene complexes. Although the total selection acting was strong (log. fitness reduced by S25), it was spread over a region wider than the dispersal range (350 m vs. 20 m). Hence, the selection on each locus contributing towards the inviability is weak (3 per cent). Many (150) independent chromosome segments act cumulatively to produce inviability at this stage in the life history. The implications of these findings for models of divergence are discussed.}, author = {Barton, Nicholas H and Hewitt, Godfrey}, issn = {1365-2540}, journal = {Heredity}, number = {3}, pages = {367 -- 383}, publisher = {Springer Nature}, title = {{The genetic basis of hybrid inviability between two chromosomal races of the grasshopper Podisma pedestris}}, doi = {10.1038/hdy.1981.98}, volume = {47}, year = {1981}, }