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TY - JOUR AU - Barton, N H AU - Hewitt, G M PY - 1981 DA - 1981/12/01 TI - The genetic basis of hybrid inviability in the grasshopper Podisma pedestris JO - Heredity SP - 367 EP - 383 VL - 47 IS - 3 AB - 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 S∼2·5), 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. SN - 1365-2540 UR - https://doi.org/10.1038/hdy.1981.98 DO - 10.1038/hdy.1981.98 ID - Barton1981 ER -