Evolution of different subfamilies of mariner elements within the medfly genome inferred from abundance and chromosomal distribution

The abundance and distribution pattern of eight mariner elements from three different subfamilies in the genome of the medfly Ceratitis capitata were determined. The copy numbers, as determined by slot-blot analysis, were ver y different for these elements. Their abundance did not change significantl y within the native, the ancient or the newly derived populations, indicati ng that the rapid colonization process of the medfly had not affected the c opy number of mariner elements. The distribution of the mariner elements wa s analyzed using fluorescent in situ hybridization (FISH) with charge-coupl ed device (CCD) camera analysis. The pat tern of distribution in euchromati n and heterochromatin varied greatly and was distinctive and specific for e ach element. The implications of these findings are discussed and it is con cluded that they generally support the hypothesis of a transposition/select ion model in which the abundance and distribution patterns of these element s are regulated primarily by selection against deleterious effects due to m eiotic ectopic recombination, while genetic drift would have played a minor role.