Intron size polymorphism of the Adh(1) gene parallels the worldwide colonization history of the Mediterranean fruit fly, Ceratitis capitata

The exon-primed intron-crossing (EPIC) PCR technique was used to analyse th e size variation at the first intron of the Ceratitis capitata Adh, gene. A total of 27 samples from 16 natural populations was analysed from five geo graphical regions in the species range: Africa, Mediterranean Basin, Latin America, Hawaii and Australia. The Adh(1) first intron varies extensively i n length with at least 18 size variants ranging from 1400 bp to 3450 bp. Th ese variants can be grouped into four distinct size categories: short, medi um, long and very long. The majority of these variants are present only in the African populations. Only a subset of the ancestral variants appear to have succeeded in migrating from Africa during the medfly colonization proc ess. The medfly population structure inferred from the intron size polymorp hism is congruent with that observed from the analysis of allozyme variatio n. The geographical dispersal of the medfly from its source area is associa ted with a gradual and great reduction in intron variability which parallel s the trend of decreasing variability evaluated at 26 biochemical loci. The intron phylogenetic tree is in agreement with allozyme data in portraying the dynamic population history of the medfly. Stochastic evolutionary force s such as drift, bottleneck effects and migration seem to have played the m ajor roles in the dispersion pattern of Adh, intron variation during the co lonization of the medfly.