1) 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.


Staff
Dr. Lluís Serra
Dr. Francesc Mestres
Dr. Marta Pascual
Dr. Joan Balanyà


Predocs
Pedro Arauz
Héctor Ruiz


Collaborators
Dr. Raymond  B. Huey (Department of Zoology, University of Washington, Seattle, USA)
Dr. George W. Gilchrist (Department of Biology, College of William & Mary, Williamsburg, VA, USA)
Dr. Concepció Arenas (Departament d’Estadística, Universitat de Barcelona)
Dr. Arnaud Estoup (Centre de Biologie et de Gestion des Populations, INRA, France)
Pedro Fernández Iriarte (Universidad Nacional de Mar del Plata, Argentina)




2) Chromosomal polymorphism of Drosophila subobscura and its relation with the global warming

We determined the magnitude and direction of shifts over time (24 years between samples on average) in chromosome inversion frequencies and in ambient temperature for populations of the fly Drosophila subobscura on three continents. In 22 of 26 populations, climates warmed over the intervals, and genotypes characteristic of low latitudes (warm climates) increased in frequency in 21 of those 22 populations. Thus, genetic change in this fly is tracking climate warming and is doing so globally. The putative role of temperature per se was investigated in the laboratory by using three sets of populations at each of three temperatures (13º, 18º and 22ºC) spanning much of the tolerable range for this species. We found a quick and consistent shift in gene arrangement frequencies in response to temperature, although the relationship between temperature and the frequencies of chromosomal arrangements is not straightforward. In nearly all the new populations the chromosomal variability has increased. This could suggest a best strategy for adaptation in the populations of these flies: to have not only those arrangements that better adapt the individuals to ever warming environments, but also to have other arrangements that permit the individuals to cope with the fluctuations in the environment.

Figure 1. Temporal shifts in temperature and in chromosome inversion frequencies at different latitudes on three continents. (A) A climate temperature index (TPC1) is inversely correlated with latitude for 26 sites on three continents and has increased from the historical (open symbols, dashed regression lines) to contemporary samples (filled symbols, solid regression lines). Black, European sites; red, North American sites; and blue, South American sites. Regression lines are for second-degree orthogonal polynomials. (B) A chromosome index (ChPC1) is inversely related to latitude and has increased from the historical to contemporary samples.


Staff
Dr. Lluís Serra
Dr. Joan Balanyà


Predocs
Héctor Ruiz


Collaborators
Dr. Antonio Fontdevila  (Departament de Genètica i Microbiologia, Universitat Autònoma de Barcelona, Bellaterra)
Dr. Raymond B. Huey (Department of Zoology, University of Washington, Seattle, EUA)
Dr. Josep M. Oller (Departament d’Estadística, Universitat de Barcelona)
Dr. Mauro Santos (Departament de Genètica i Microbiologia, Universitat Autònoma de Barcelona, Bellaterra)
Dr. Dieter Sperlich (Biologisches Institut, Universität Tübingen, Tübingen, Alemanya)




3) Evolutionary study of Mediterranean and American populations of D. subobscura

Two main hypotheses have been raised with regard to the origin of the American colonization by D. subobscura:  The origin could take place from a Western Mediterranean population or from an Eastern one. To 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.Francesc Mestres
Dr. Lluís Serra


Predocs
Pedro Arauz


Collaborators
Dr. Joan Balanyà
Héctor Ruiz
Cinta Pegueroles
Amparo Latorre