Intron size polymorphism of the Adh₁ gene parallels the worldwide colonization history of the Mediterranean fruit fly, Ceratitis capitata

Abstract

The exon‐primed intron‐crossing (EPIC) PCR technique was used to analyse the size variation at the first intron of the Ceratitis capitata Adh1 gene. A total of 27 samples from 16 natural populations was analysed from five geographical regions in the species range: Africa, Mediterranean Basin, Latin America, Hawaii and Australia. The Adh1 first intron varies extensively in length with at least 18 size variants ranging from 1400 bp to 3450 bp. These variants can be grouped into four distinct size categories: short, medium, 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 process. The medfly population structure inferred from the intron size polymorphism is congruent with that observed from the analysis of allozyme variation. The geographical dispersal of the medfly from its source area is associated with a gradual and great reduction in intron variability which parallels 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 forces such as drift, bottleneck effects and migration seem to have played the major roles in the dispersion pattern of Adh1 intron variation during the colonization of the medfly.

Globalization and fruitfly invasion and expansion: the medfly paradigm

“…2) (Gasperi et al 1991Sheppard et al 1992;Gomulski et al 1998;Bonizzoni et al 2000). Furthermore, when compared with all other geographic populations, those from Kenya have the highest average number of alleles per locus many of which are at low frequency and most are private.…”

“…The genetic differentiation between these populations is significantly correlated with geographic distance indicative of a hierarchical migration structure through Spain and subsequently along the Mediterranean Basin to the East (Malacrida et al 1998;Gomulski et al 1998). Drift has probably played the major role in the dispersion pattern from Africa to the Mediterranean area.…”

Microsatellite analysis of medfly bioinfestations in California

“…1995; Gasparich et al . 1997; Gomulski et al . 1998) have been used to study the genetic aspects of the medfly worldwide colonization process.…”

“…2000), and their variability paralleled that derived from allozymes (Malacrida et al . 1992, 1998) and single copy DNA (ScDNA) markers (Gomulski et al . 1998) in reflecting the medfly colonization history.…”

Medfly transposable elements: diversity, evolution, genomic impact and possible applications

“…Comparison of native and derived medfly populations suggests that the rapid colonization process of this species had little or no significant effect on the copy numbers of mariner, Tc1-like or Cchobo elements Torti et al, 2000;Gomulski et al, unpublished;Torti et al, unpublished). Drift, which appears to have been the most important evolutionary force in the reduction of genetic variability, both at coding and non-coding sequences, during the colonization process (Baruffi et al, 1995;Gomulski et al, 1998;Malacrida et al, 1998;Bonizzoni et al, 2000) has had little effect on transposable element abundance. However, given that the derived populations of C. capitata have been separated from the ancestral African populations by a matter of only a century or so, it may be too early to detect any changes in copy number due to stochastic loss.…”