Cristina Torti

Genetic Differentiation, Gene Flow and the Origin of Infestations of the Medfly, Ceratitis Capitata

The genetic structure of natural populations of the economically important dipteran species Ceratitis capitatawas analysed using both biochemical and molecular markers. This revealed considerable genetic variation in populations from different geographic regions. The nature of this variation suggests that the evolutionary history of the species involved the spread of individuals from the ancestral African populations through Europe and, more recently, to Latin America, Hawaii and Australia. The observed variation can be explained by various evolutionary forces acting differentially in the different geographic areas, including genetic drift, bottleneck effects, selection and gene flow. The analysis of the intrinsic variability of the medflys genome and the genetic relationships among populations of this pest is a prerequisite for any control programme.

A New Basal Subfamily of mariner Elements in Ceratitis rosa and Other Tephritid Flies

Several copies of highly related transposable elements, Crmar2, Almar1, and Asmar1, are described from the genomes of Ceratitis rosa, Anastrepha ludens, and A. suspensa, respectively. One copy from C. rosa, Crmar2.5, contains a full-length, uninterrupted ORF. All the other copies, from the three species contain a long deletion within the putative ORF. The consensus Crmar2 element has features typical of the mariner/Tc1 superfamily of transposable elements. In particular, the Crmar2 consensus encodes a D,D41D motif, a variant of the D,D34D catalytic domain of mariner elements. Phylogenetic analysis of the relationships of these three elements and other members of the mariner/Tc1 superfamily, based on their encoded amino acid sequences, suggests that they form a new basal subfamily of mariner elements, the rosa subfamily. BLAST analyses identified sequences from other diptera, including Drosophila melanogaster, which appear to be members of the rosa subfamily of mariner elements. Analyses of their molecular evolution suggests that Crmar2 entered the genome of C. rosa in the recent past, a consequence of horizontal transfer.

Ccmar1, a full-length mariner element from the Mediterranean fruit fly, Ceratitis capitata.

Using a PCR primer specific to the ITR sequence of a deleted mariner element we amplified a fragment of ∼1300 bp from the genome of Ceratitis capitata. Analysis of four clones showed that they differed by ∼4.6% in nucleotide sequence and exhibited high homology to mariner elements of the mellifera subfamily. One clone in particular, Ccmar1.18, was found to possess an ORF of 338 amino acids together with many of the features typical of mariner elements. The consensus sequence, Ccmar1, derived from these clones is presented. Maximum parsimony phylogenetic analysis of the Ccmar1 element confirms its position at the periphery of the mariner mellifera subfamily. The Ccmar1 element is estimated to be present in about 500 copies in the genome. The evolutionary history of the element in relation to the colonization history of the medfly is discussed.

Allozyme divergence and phylogenetic relationships among species of tephritid flies

Multilocus enzyme electrophoresis data from 24 orthologous loci (212 alleles) were used to infer the genetic similarities between 11 Tephritidae pest species from the Ceratitis, Trirhithrum, Capparimyia, Bactrocera, Anastrepha and Rhagoletis genera. Within some of the considered species, different degrees of genetic variability were demonstrated, which appear to be related to zoogeography and to the biological traits peculiar to each species. Nei (1978) and Cavalli-Sforza & Edwards (1967) genetic distances were used to express the genetic divergence and to infer phylogenetic relationships among the species. The upgma clustering algorithm and the optimality criteria of Fitch & Margoliash (1967), with (kitsch) and without (fitch) the tree constrained to have contemporary tips, were used. All the methods indicate the same clusters of species. One cluster is composed of Ceratitis capitata, Trirhithrum coffeae and Capparimyia savastanoi, another is composed of Rhagoletis cerasi, Bactrocera dorsalis and Bactrocera oleae. A further loose cluster is comprised of Ceratitis rosa and Anastrepha spp. The congruence between electrophoretic phylogeny and morphological classification is discussed. Our analysis also elucidated cases, within the Ceratitis and Bactrocera genera, of interest from the evolutionary point of view, where allozyme dendrograms do not correlate well with morphological taxonomic relationships.

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

Abstract.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 very different for these elements. Their abundance did not change significantly within the native, the ancient or the newly derived populations, indicating that the rapid colonization process of the medfly had not affected the copy number of mariner elements. The distribution of the mariner elements was analyzed using fluorescent in situ hybridization (FISH) with charge-coupled device (CCD) camera analysis. The pattern of distribution in euchromatin and heterochromatin varied greatly and was distinctive and specific for each element. The implications of these findings are discussed and it is concluded that they generally support the hypothesis of a transposition/selection model in which the abundance and distribution patterns of these elements are regulated primarily by selection against deleterious effects due to meiotic ectopic recombination, while genetic drift would have played a minor role.

Evidence for a genetic duplication involving alcohol dehydrogenase genes inCeratitis capitata

AnAdh duplication is described in the medflyCeratitis capitata. Evidence is presented for two separateAdh1 andAdh2 structural loci mapping at a distance of 0.49 recombination unit from each other. By deletion mapping theAdh region has been cytologically located near the free end of the left arm of the second chromosome within an area between 2C;3A segments of the polytene chromosome. The genetic analysis of the region aroundAdh has identified seven neighboring genes (Acon1,Mpi, Est6,Aox, Xdh, Mdh2,LspI) which identify the linkage group D. The orientation of loci with regard to the centromere sets the origin of the map of the left arm of the second chromosome close to the twoAdh loci.

Characterization and Evolution of mariner Elements from Closely Related Species of Fruit Flies (Diptera: Tephritidae)

Abstract.Mariner elements were amplified using the polymerase chain reaction from two species of tephritid flies, Ceratitis rosa and Trirhithrum coffeae. The sequences were ∼1.3 kb in length. None of these elements appeared to be functional, as in every case the open reading frame (ORF) was disrupted by the presence of frameshifts or stop codons. These elements, Crmar1 and Tcmar1, are very similar to the Ccmar1 element previously amplified from the closely related tephritid species C. capitata and are members of the mellifera subfamily of mariner elements. The phylogeny and pattern of divergence of these elements were examined in relation to the phylogeny of the host species. It is highly probable that the elements were present in the ancestral lineage prior to the divergence of the three species. The copy numbers of the elements within each species are very different, ranging from about 10 in T. coffeae to 5,000 in C. rosa. The possible mechanisms which determine the copy number of an element in the host genome are discussed.

Cchobo, a hobo-related sequence in Ceratitis capitata

A hobo-related sequence, Cchobo, with high similarity to the Drosophila melanogaster HFL1 and hobo108 elements was isolated from the medfly. Thirteen PCR-derived clones, which share 97.9–100% DNA identity, were sequenced, seven of which do not show frame-shift or stop codon mutations in their conceptual translations. The consensus sequence has 99.7% DNA identity with the D. melanogaster hobo element HFL1. In a phylogenetic analysis with other hobo-related elements, Cchobo clusters with the HFL1 and hobo108 elements from D. melanogaster and hobo-related elements from D. simulans, D. mauritiana and Mamestra brassicae. These elements may have undergone horizontal transfer in the recent past. The genomic distribution of Cchobo was studied by FISH to mitotic and polytene chromosomes, which revealed that Cchobo is distributed within both the heterochromatin and euchromatin. Intra- and interstrain polymorphisms were detected both at euchromatic and heterochromatic sites. These findings suggest that active copies of the element may be present in the medfly genome.

Mature and developing visual system of Ceratitis capitata (Diptera, Tephritidae): histochemical evidence of nitric oxide synthase in the wild type and the white eye mutant strains

Nitric oxide (NO) is acknowledged as a messenger molecule in the nervous system. It has a role in the modulation of the chemosensory information and seems implicated also in visual processes and visually guided behaviour of some insects. In the present study, we used two different strains of the medfly Ceratitis capitata (Diptera, Tephritidae), a wild type eye colour and a white eye mutant line, as models to clarify the involvement of NO in the mature and developing visual system. The comparison between the pattern of enzyme histochemical localization of NO synthase (NOS), through NADPH diaphorase (NADPHd) staining, in the optic lobes of the two strains revealed for adults a stronger intensity of reaction in all the neuropiles and the sub-retinic monopolar cell layer of the wild type flies, with respect to the white eye mutant correspondent areas. Anti-NOS immunocytochemistry correlated with these results, underlying reactivity both in fine fibres and varicosities and in cell bodies and supporting the idea of presence of NOS also in the retina of the medfly optic lobes. NADPHd reactivity was present in the first developmental stages of the white eye mutant also, but at lower intensity than wild type, and it decreased in some areas during the transition to adult fly stage both in the wild type and in the white eye mutant. All these observations together indicate that changes in the NO system of C. capitata could be related to the visual information processing, when the visual response or discrimination are altered. Furthermore, NO may be involved in the establishment of the retinal projection pattern and in the control of optic lobes morphogenesis.

Genetic and molecular investigations on the endogenous mobile elements of non-drosophilid fruitflies

A syndrome of abnormal genetic effects, resembling Drosophila hybrid dysgenesis, occurs in Ceratitis capitata when strains of different origin are mated. The pattern of abnormal traits observed appears to be the phenotypic expression of a complex interacting dysgenic system of inducer and suppressor effects; probably more than one system is activated in the crosses. This suggests that different systems of mobile elements occur in different strains and populations of C. capitata. Using a PCR primer specific to the ITR sequence of a deleted element, full length mariner elements were isolated from C. capitata, Ceratitis rosa, and Trirhithrum coffeae. Very high similarities were found in inter- and intraspecific comparisons of the elements. The majority of these elements contained deletions and frame-shifts. However, one clone Ccmar1.18, from C. capitata, was found to possess an uninterrupted ORF coding for 338 amino acids with ∼60% similarity to the Mos1 element of Drosophila mauritiana. Database searches and phylogenetic analyses showed that the mariner elements isolated in the present study are representatives of Robertsons mellifera mariner subfamily. The copy numbers of the elements within each species are very different, ranging from about 10 in T. coffeae to 5000 in C. rosa.