Estimating the genic and chromosomal components of reproductive isolation within and between subspecies of the grasshopper Caledia captiva

Abstract

Previous studies have indicated that the Moreton and Torresian subspecies of the grasshopper Caledia captiva are distinguished by a series of pericentric rearrangements involving 8 of the 12 members of the genome. In addition, they show distinctive allozyme patterns with. The two taxa meet in southeast Queensland where they form a narrow hybrid zone. Experimental hybridization between the taxa reveals that the F2 generation is totally inviable and backcrosses are 53–64% inviable.A major component of inviability is correlated with the redistribution of chiasmata which occurs in F1 heterozygotes and leads to the production of novel recombinant chromosomes. However, the relative contributions of the effects of chromosomal heterozygosity versus those effects because of genic divergence could not be distinguished. The discovery that the metacentric Moreton subspecies represents the northerly limit of a continuous chromosomal cline has resolved this problem. At the southern end of the cline (Lakes Entrance), th...