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THE EFFECT OF A PARTIAL BARRIER ON THE MOVEMENT OF A HYBRID ZONE
Bert Kohlmann,
David Shaw,
Bert Kohlmann
Research School of Biological Sciences, Australian National University, Canberra, 2601 AUSTRALIA
Present address: Instituto de Biología, Universidad Nacional Autónoma de México, A. P. 7–153, México, D. F. 04510, México.Search for more papers by this authorDavid Shaw
Research School of Biological Sciences, Australian National University, Canberra, 2601 AUSTRALIA
Offprint requests to: Molecular and Population Genetics Group, RSBS. PO Box 475, Canberra, ACT 2601, Australia.Search for more papers by this authorBert Kohlmann,
David Shaw,
Bert Kohlmann
Research School of Biological Sciences, Australian National University, Canberra, 2601 AUSTRALIA
Present address: Instituto de Biología, Universidad Nacional Autónoma de México, A. P. 7–153, México, D. F. 04510, México.Search for more papers by this authorDavid Shaw
Research School of Biological Sciences, Australian National University, Canberra, 2601 AUSTRALIA
Offprint requests to: Molecular and Population Genetics Group, RSBS. PO Box 475, Canberra, ACT 2601, Australia.Search for more papers by this authorAbstract
Computer simulations of clines (Brues, 1972; Endler, 1977) as well as theoretical arguments (Nagylaki, 1975), have shown that steps in gene frequencies will be pulled to partial barriers (areas of reduced gene flow) if they form within approximately a cline width of the partial barrier.
The behavior of a hybrid zone between two chromosomal taxa (“Moreton” and “Torresian”) of the acridine grasshopper Caledia captiva in southeast Queensland has been analyzed and found to comform qualitatively with a model of altered gene flow patterns. Clines in four enzyme systems were analyzed for 1983 and 1986 along a transect across the hybrid zone. The clines have shifted towards an area of regenerating forest, while homozygote frequencies have increased at this point. This forest barrier has broken the continuity of the spatial distribution of C. captiva, forming population islands in part of the hybrid zone, and thus reducing the amount of gene flow. The distance between the barrier and the original cline is approximately of the order of a cline width, so that they would be expected to interact.
Historical information suggests that the secondary contact between the “Moreton” and “Torresian” taxa occurred very recently (1844–1940), due to the intensive land-clearing activities during the European settlement.
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