Highly repeated DNA and allozyme variation between sibling species: evidence for introgression

The Caledia captiva complex of grasshoppers includes two sibling species along with two subspecies. Two populations (Papuan Torresian and Daintree) representing the two sibling species were found to share six allozyme characters and a highly repeated DNA family not found in any of the other Caledia taxa. These two populations showed genic divergence that was equivalent to comparisons between the two subspecies from the complex. Sequenced, cloned repeats from the Papuan Torresian and Daintree taxa showed equivalent variation for both intra- and inter-specific comparisons. A phenetic clustering analysis did not separate the repeats from these two taxa into different clades. Furthermore, the overall genomic organization of the sequence family in the two species is very similar, although the repeats are cytologically dispersed in one form (Papuan Torresian) and clustered in the other form (Daintree). It is argued that the most likely evolutionary explanation for the observed pattern of variation in the allozymes and highly repeated DNA sequences between these types is introgressive hybridization. The possible consequences of such an event are discussed in light of the population genetics and distribution of the present day Caledia taxa. Key words: highly repeated DNA, Caledia, grasshopper, allozymes.