The origin of the American colonization by D. subobscura is a very interesting topic and there are two hypotheses:  the origin could take place from a Western Mediterranean population or from an Eastern one. For ascertain which of both is more likely we are analyzing a couple of populations, one from each region, with regard to lethal genes, Odh  gene nucleotide sequences and chromosomal inversions. The lethal genes associated with chromosomal inversions found in both Paleractic populations and in America will be analyzed using the lethal allelism tests. Furthermore, the presence of common Odh gene haplotypes in Europe and America will be studied. Outstanding information on the differentiation of both Mediterranean regions and on the origin of the American colonization by the species is expected.

Diagram showing the sequenced fragment of the Odh gene, which includes part of exon 2, intron 2, exon 3, intron 3 and part of exon 4. The sequenced fragment of the gene is 793 b.p. long. There are also indicated the locations of the primers used both, for amplifying and sequencing the gene fragment.


Staff
Dr. F. Mestres
Dr. L. Serra


Predocs
Pedro Arauz


Collaborators
Dr. Joan Balanyà
Dra. Amparo Latorre (Institut Cavanilles de Biodiversitat i Biologia Evolutiva, València)
Héctor Ruiz
Cinta Pegueroles





2) Colonization of America by Drosophila subobscura

D. subobscura was introduced into both North and South America just over two decades ago and then spread rapidly. Just a few years after the introduction clines for chromosomal inversion frequencies were detected in both North and South America that almost always had the same sign with latitude as in the Old World, providing experimental support for the adaptive value of this polymorphism. Two decades after the introduction wing length clines had also evolved, which largely converged on the ancestral cline in Europe, showing that the rate of morphological evolution on a continental scale is very fast. Recessive lethal genes are not randomly distributed among the chromosomal arrangements in colonizing populations. The persistence of the allelism over several years suggests that some lethal-carrying chromosomes may be heterotic. Data on microsatellite variation are consistent with a rather strong founder effect and also with the two-phase microsatellite mutational model .

Microsatellite loci can be used as molecular markers to study processes of genomic reorganization, rates of recombination in different genomic regions and for detecting areas under selection in processes of adaptation to the laboratory conditions and to nature. In order to carry out these studies we have localized by fluorescent in-situ hybridization on polytene chromosomes the microsatellite loci isolated from a genomic library of Drosophila subobscura. The cytological positions in D. subobscura have been compared with the whole genomic sequence of other two drosophilid species, D. pseudoobscura and D. melanogaster available in GenBank. The mapping has allowed using some loci in studies on laboratory adaptation analyzing the role of drift and selection in the change of allele frequencies through time. A genetic map is currently being under construction and will be compared to the cytological map which will allow to empirically detecting high and low recombination areas. The localized microsatellite loci are also being used to study the role of inversions in preventing recombination as well as to analyze the associations between these loci and chromosomal rearrangements that will allow inferring the effect of selection.