Genetic variability and gene flow in geographical populations of Ceratitis capitata (Wied.) (medfly).

TwoAfrican populations of Ceratitis capitata (Kenya and Reunion IsL) and two Mediterranean ones (Sardinia and Procida IsI.) have been studied for genetic variability at 25 foci by electro- phoresis. Wright's F5 Slatkin's Nm gene flow estimator, Nei's distance (D) together with measures of variability such as 1-1, P, A have been used to compare the population from Kenya with the other three. Parameters using gene frequencies (F51, D, Nm) indicate the presence of substantial geographic heterogeneity, largely attributable to genetic drift and correlated with dispersion of the medfly from its source area (Subsaharan Africa) to the periphery. The Kenyan population has high genetic variability (assessed by H, P and A), as might be expected given its native status. Significant gene flow estimates between Kenya and the derived Mediterranean populations supports the hypothesis of recent colonization. Part of the geographic heterogeneity is related to the presence of fixed alleles in the more differentiated Reunion population although it maintains the genetic attributes of the ancestral population. Selection or other forces may have played an important role in the differentiation of this population

A biochemical genetic study of alcohol dehydrogenase isozymes of the medfly, Ceratitis capitata Wied.

A concerted effort is under way to analyze, at the genetic, biochemical, and molecular level, the Adh gene system in the medfly Ceratitis capitata, an important agricultural pest. The isoelectric focusing (IEF) pattern of alcohol dehydrogenase (ADH) of the medfly demonstrates the presence of two well-differentiated, genetically independent dimeric proteins, called ADH-1 and ADH-2. These proteins do not exhibit interlocus heterodimeric isozymes, and the genes are not controlled coordinately during development, Adh1 and Adh2 being expressed mainly in muscle or in fat body and ovary, respectively. From the intensity of the IEF isozyme patterns, primary alcohols are judged to be better substrates than secondary alcohols, in contrast with Drosophila melanogaster ADH, and ethanol is probably the most efficient substrate for both sets of isozymes. The isoelectric points of ADH-1 (pI = 5.4) and ADH-2 (pI = 8.6) are different from D. melanogaster ADH (pI = 7.6), but the medfly ADH-1 has a native molecular weight (approx. 58 kD) close to that of D. melanogaster. A population survey of samples both from laboratory strains and from wild geographically different populations showed that the Adh1 locus is more polymorphic than Adh2. The most variable populations are from Africa, the supposed source area of the species. Further, a case of selection at the Adh1 locus under laboratory conditions is reported. The hypothesis of Adh gene duplication and the degree of similarity between medfly and Drosophila ADH are also discussed

Spatial and temporal differentiation in colonizing populations of Ceratitis capitata

Twoancestral populations (Kenya and Reunion), two Mediterranean (Procida and Sardinia) and one new American population (Guatemala) of Ceratitis capitata were examined by electrophoresis for genetic variability at 27 enzyme loci. Two ordination approaches (principal component analysis and a tree representation) and F-statistical analysis have been used to distinguish the various patterns of genetic variations and to infer the underline causes and their relative contribution to the total variation. Three main patterns of variation emerge from the data: geographical, annual and seasonal differentiation. A main part of intraspecific variability involves the differentiation of central (Kenya and Reunion) versus peripheral populations (the Meditterranean and the American populations). The analysis suggests that the genetic structure of these populations is correlated with the historical events of their colonization. The affinity of the Guatemalan population with the Kenyan one could be the result of a recent founding of this population from the source area (Africa). More ancient historical events of colonization characterize the two Mediterranean populations. Seasonal variation has been found in the Procida population and chiefly involves the Mpi locus. In the same population the genetic variation across years has a minimum in 1986 due to the release of sterile T- 101 males