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It is generally accepted that chromosomal inversions have been key elements in adaptation and speciation processes. In this context, Drosophila subobscura has been, and still is, an excellent model species due to its rich chromosomal polymorphism. In this species, many analyses from natural populations have demonstrated the adaptive potential of individual inversions (and their overlapped combinations, the so-called arrangements). However, little information is available on the evolutionary role of combinations generated by inversions located in homologous and nonhomologous chromosomes. The aim of this research was to ascertain whether these combinations are also a target for natural selection. For this objective, we have studied the inversion composition of homologous and nonhomologous chromosomes from a D. subobscura sample collected in a well-studied population, Mount Avala (Serbia). No significant deviation from H-W expectations was detected, and when comparing particular karyotypic combinations, likelihood ratios close to 1 were obtained. Thus, it seems that for each pair of homologous chromosomes inversions no deviation from randomness was detected. Finally, no linkage disequilibrium was observed between inversions located in different chromosomes of the karyotype. For all these reasons, it can be assumed that, at the cytological level, the individual inversions rather than their combinations in different chromosomes are the main target of selection.

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To study whether inversions (or arrangements) by themselves or karyotypes are the main global warming adaptive target of natural selection, two Drosophila subobscura Serbian populations (Apatin and Petnica) were re-analyzed using different statistical approaches. Both populations were sampled in an approximately 15 years period: Apatin in 1994 and 2008 + 2009 and Petnica in 1995 and 2010. For all chromosomes, the four collections studied were in Hardy-Weinberg equilibrium. Thus, it seems that inversions (or arrangements) combined at random to constitute populations' karyotypes. However, there were differences in karyotypic frequencies along the years, although they were significant only for Apatin population. It is possible to conclude that inversions (or arrangements) are likely the target of natural selection, because they presented long-term changes, but combine at random to generate the corresponding karyotypic combinations. As a consequence, the frequencies of karyotypes also change along time.

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Gene flow (defined as allele exchange between populations) and gene flux (defined as allele exchange during meiosis in heterokaryotypic females) are important factors decreasing genetic differentiation between populations and inversions. Many chromosomal inversions are under strong selection and their role in recombination reduction enhances the maintenance of their genetic distinctness. Here we analyze levels and patterns of nucleotide diversity, selection and demographic history, using 37 individuals of Drosophila subobscura from Mount Parnes (Greece) and Barcelona (Spain). Our sampling focused on two frequent O-chromosome arrangements that differ by two overlapping inversions (OST and O(3+4)), which are differentially adapted to the environment as observed by their opposing latitudinal clines in inversion frequencies. The six analyzed genes (Pif1A, Abi, Sqd, Yrt, Atpα and Fmr1) were selected for their location across the O-chromosome and their implication in thermal adaptation. Despite the extensive gene flux detected outside the inverted region, significant genetic differentiation between both arrangements was found inside it. However, high levels of gene flow were detected for all six genes when comparing the same arrangement among populations. These results suggest that the adaptive value of inversions is maintained, regardless of the lack of genetic differentiation within arrangements from different populations, and thus favors the Local Adaptation hypothesis over the Coadapted Genome hypothesis as the basis of the selection acting on inversions in these populations.

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Lethal chromosomal frequencies were obtained from three Drosophila subobscura samples from the Mt. Avala (Serbia) population in September 2003 (0.218), June 2004 (0.204) and September 2004 (0.250). These values and those from other Balkan populations studied previously (Petnica, Kamariste, Zanjic and Djerdap) were used to analyze the possible effect of population, year, month and altitude above sea level on lethal chromosomal frequencies. According to ANOVAS no effect were observed. Furthermore, the lethal frequencies of the Balkan populations did not vary according to latitude. This is probably due to the relative proximity and high gene flow between these populations. From a joint study of all the Palearctic D. subobscura populations so far analyzed, it can be deduced that the Balkan populations are located in the central area of the species distribution. Finally, it seems that lethal chromosomal frequencies are a consequence of the genetic structure of the populations.

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A huge amount of data seem to confirm the adaptive value of inversions in Drosophila. The inhibition of recombination in heterokaryotypes mediated by inversions seems fundamental in maintaining their adaptive role. This study shows that recombination is highly suppressed in Drosophila subobscura because of chromosomal inversions, not only inside the inversions but also outside them. It seems that the region outside the inversion where recombination is inhibited is asymmetrical and independent of the inversion length. Despite the difficulty of crossovers taking place near inversion breakpoints, the only two recombination events detected inside inversions were located close to the breakpoint. Thus, selection could be largely responsible for the recombination reduction maintaining sets of adaptive alleles inside the inverted region. Heterokaryotype descendants were always in higher frequency than inbred or outbred homokaryotypes, regardless of the geographical origin of the chromosome, suggesting that chromosomes carrying the same arrangement, although with a different set of alleles for neutral markers, could be submitted to the same selection processes.

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Biological invasions are excellent opportunities to study the evolutionary forces leading to the adaptation of a species to a new habitat. Knowledge of the introduction history of colonizing species helps tracking colonizing routes and assists in defining management strategies for invasive species. The Palearctic species Drosophila subobscura is a good model organism for tracking colonizations since it was detected in Chile and western North America three decades ago and later on in the Atlantic coast of Argentina. To unravel the origin of the Argentinean colonizers two populations have been analysed with several genetic markers. Chromosomal arrangements and microsatellite alleles found in Argentina are almost similar to those observed in Chile and USA. The lethal allelism test demonstrates that the lethal gene associated with the O(5) inversions in Argentina is identical to that found in Chile and USA, strongly supporting the hypothesis that all the American colonizing populations originated from the same colonization event. A secondary bottleneck is detected in the Argentinean populations and the genetic markers suggest that these populations originated from the invasion of 80-150 founding individuals from Chile.

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Drosophila subobscura is a Palearctic species that was first observed in South and North America in the early 1980s, and that rapidly invaded broad latitudinal ranges on both continents. To trace the source and history of this invasion, we obtained genotypic data on nine microsatellite loci from two South American, two North American and five European populations of D. subobscura. We analysed these data with traditional statistics as well as with an approximate Bayesian computation (ABC) framework. ABC methods yielded the strongest support for the scenario involving a serial introduction with founder events from Europe into South America, and then from South America into North America. Stable effective population size of the source population was very large (around one million individuals), and the propagule size was notably smaller for the introduction into South America (i.e. high bottleneck severity index with only a few effective founders) but considerably larger for the subsequent introduction into North America (i.e. low bottleneck severity index with around 100-150 effective founders). Finally, the Mediterranean region of Europe (and most likely Barcelona from the localities so far analysed) is proposed as the source of the New World flies, based on mean individual assignment statistics.

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PURPOSE: To study the ocular surface changes following laser assisted in situ keratomileusis (LASIK). METHODS: Prospective study of pre and post-LASIK impression cytology in two sites of the conjunctival epithelium of 12 eyes from 6 patients. The samples were studied for changes in cellularity, cell size, nucleus size, nucleus-cytoplasm ratio, number of goblet cells, PAS positivity and number of inflammatory cells. RESULTS: All the samples except two, showed pathological changes like a decrease in nuclear size, increase in cytoplasm, change in nucleus-cytoplasm ratio, a significant decrease in goblet cell density and certain degree of squamous metaplasia. CONCLUSIONS: One month following LASIK we observed histopathologic changes in the perilimbal conjunctiva, mainly a decrease in the number of goblet cells and different grades of squamous metaplasia.

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Objetivo: Estudiar los cambios anatomopatológicos de superficie que aparecen en ojos sometidos a queratomileusis asistida por laser excimer (LASIK).Métodos: Se realizó un estudio prospectivo de citología de impresión conjuntival antes y un mes post-LASIK en 2 localizaciones de12 ojos de 6 pacientes. Se evaluaron los cambios en celularidad, tamaño celular, relación núcleo-citoplasma, células caliciformes, PAS positividad y células inflamatorias. Resultados: No aparecen cambios en una impronta de un ojo de dos pacientes. Todas las demás muestras presentan cambios anatomopatológicos como disminución en el tamaño nuclear, aumento del tamaño citoplasmático. Aparece una disminución de densidad de células entre el número de células caliciformes y diverso grado de metaplasia escamosa posterior a la cirugía. Conclusiones: Existe un cambio anatomopatológico en las células de la conjuntiva perilímbica al primer mes de cirugía refractiva por LASIK, con disminución de células caliciformes y diverso grado de queratinización (AU)

Purpose: To study the ocular surface changes following laser assisted in situ keratomileusis (LASIK). Methods: Prospective study of pre and post-LASIK impression cytology in two sites of the conjunctival epithelium of 12 eyes from 6 patients. The samples were studied for changes in cellularity, cell size, nucleus size, nucleus-cytoplasm ratio, number of goblet cells, PAS positivity and number of inflammatory cells. Results: All the samples except two, showed pathological changes like a decrease in nuclear size, increase in cytoplasm, change in nucleus-cytoplasm ratio, a significant decrease in goblet cell density and certain degree of squamous metaplasia. Conclusions: One month following LASIK we observed histopathologic changes in the perilimbal conjunctiva, mainly a decrease in the number of goblet cells and different grades of squamous metaplasia (AU)

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Substitutions rates are expected to be rather constant when a gene is compared between species. To analyze this feature, Ka/Ks ratios have been studied for Alcohol dehydrogenase (Adh) and Alcohol dehydrogenase duplication (Adh-dup) genes in Drosophila species. Adh Ka/Ks values are lower in intrasubgenus comparisons involving species of the Sophophora group than when these species are compared to the D. immigrans and S. lebanonensis, and this difference does not occur in the Adh-dup comparisons.

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About 20 years ago Drosophila subobscura, a native Palearctic species, colonized both North and South America. In Palearctic populations lethal genes are not associated in general with particular chromosomal arrangements. In colonizing populations they are not randomly distributed and usually are associated to a different degree with chromosomal arrangements caused by the founder event. The persistence of two lethal genes in the colonizing populations, one completely associated with the O(5) inversion and the other partially associated with the O(3+4+7) arrangement, has been analyzed. In all populations studied (five North American and six South American) the observed frequency of the lethal gene completely associated with the O(5) inversion is higher than expected, the difference being statistically significant in all South American and one North American populations. The observed frequency of the lethal gene partially associated with the O(3+4+7) arrangement is also significantly higher than expected. Taking into account that the O(5) inversion exhibits significant latitudinal clines both in North and South America, an overdominant model favoring the heterokaryotypes seems to be in operation. From this model, a polynomial expression has been developed that allows us to estimate the relative fitness and the coefficient of selection against all karyotypes not carrying the O(5) inversion. The relative fitness of the O(5) heterokaryotypes is higher in South American than in North American populations. Furthermore, the observed frequencies of the lethal genes studied are in general very close to those of the equilibrium. This case is an outstanding demonstration in nature of an heterotic effect of chromosomal segments associated with lethal genes on a large geographic scale.

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About twenty years ago Drosophila subobscura, a western Palearctic species, colonized both North and South America. Lethal genes in the O chromosome has been subject to much research. Lethal gene allelisms between American populations far away have been studied. These allelisms were not negligible, but all cases were due to the lethal gene completely associated to the O5 chromosomal inversion. Here we analyze the lethal genes in a new American population of D. subobscura (Centralia, Washington), located fairly close to a previously studied population (Bellingham, Washington) and separated in space and time with other American populations (Gilroy I and II in California and Santiago de Chile). The frequencies of lethal and semilethal genes of Centralia were 16.9+/-4.6 and 6.2+/-3.0, respectively. The intrapopulational allelism of Centralia was 0.122+/-0.036. Interpopulational allelisms were studied using the lethal genes from the populations separated in space and time from Centralia. The interpopulational allelisms between Centralia and Gilroy I (California) and between Centralia and Bellingham (Washington) were higher than the intrapopulational allelism (0.155+/-0.032 and 0.153+/-0.024, respectively). In all these cases allelism was due to a complete association between a lethal gene and the O5 chromosomal inversion. Accordingly, no other lethal genes are shared in these populations.

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Drosophila subobscura is a species with rich chromosomal polymorphism. More than 45 arrangements have been described in the O chromosome. The recombination between them is an interesting topic, because many nonoverlapping arrangements are inherited together. In the analysis of recombination between the arrangements O7 and O3 + 4 + 8, out of 415 individuals observed none was found to be recombinant. The same result was obtained in the study of the recombination between the inversions O5 and O3 + 4, in which 437 individuals were analyzed. In this case a significant non equivalent segregation was found, the O5 chromosomes being more frequent than expected. This phenomenon could be explained by three hypotheses: a meiotic drive, a greater fitness of the individuals carrying this inversion and heterotic effect of a wild chromosome in combination with a chromosome from an inbred laboratory strain. If the second hypothesis is correct, it could explain why an inversion always associated with a lethal gene in American populations is not infrequent and presents a clinal distribution in the colonized areas. Furthermore, another inversion, O22, is very similar to O5. These two inversions can be distinguished only by careful observation. Although O22 and O5 are very similar they show different behavior in the wild, probably due to the combinations of genes included in them.

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PURPOSE: To compare the intraoperative complications of planned extracapsular cataract extraction (ECCE) with those of manual nucleofragmentation. SETTING: Hospital de la Esperanza, Universitat Autónoma de Barcelona, Spain. METHODS: This retrospective study comprised 567 eyes; 444 had planned ECCE and 123, manual nucleofragmentation through a scleral tunnel incision. RESULTS: No significant differences between techniques were found in terms of intraoperative complications (P < .05). Manual nucleofragmentation did not increase the risk of intraoperative complications (P < .05). CONCLUSIONS: Although phacoemulsification is the procedure of choice in many cases, manual nucleofragmentation is a safe and valid alternative that achieves the goals of small incision cataract surgery.

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An analysis of the effects of inbreeding on the genetic structure of a colonizing population of Drosophila subobscura has been carried out. Species of Drosophila, particularly D. subobscura, may have lethal alleles associated with chromosomal inversions and our aim was to assess the extent to which the genome is balanced in this way. The frequencies of chromosomal inversions were compared between a large population and a set of 72 lines that were maintained by brother-sister mating for 10 generations. Fisher's matrix method was used to calculate the expected homozygosity in these inbred lines for 5 allozyme loci (Aph, Hk-1, Lap, Odh, and Pept-1) used as markers of large chromosomal segments. Furthermore, the expected rates of fixation corresponding to these allozyme loci were also calculated. The results show that the amount of homozygosis observed did not differ significantly from expectations (with the corresponding loss of lines as a consequence of the reduction in viability). However, two deviations from strict neutrality were observed: there was a heterozygote excess at the Lap locus, and the frequency of the O5 inversion (always associated with a lethal gene in colonizing populations) was higher than expected.

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Drosophila subobscura is a Palearctic species that has recently colonized the Americas. It was first found in 1978 in Puerto Montt, Chile, and in 1982 in Port Townsend, WA. The colonization and rapid expansion of the species in western South and North America provides distinctive opportunities for investigating the process of evolution in action. The inversion polymorphism in the O chromosome from populations of central California and northern Washington, separated by 1300 km, corresponds to a previously observed latitudinal cline, also observed in Europe. Recessive lethal genes are not randomly distributed among the chromosomal arrangements. The incidence of lethal allelism is high, yielding unrealistically low estimates of the effective size of these populations (on the order of 1000 individuals). The high incidence of lethal allelism is likely to be a consequence of the low number of the American colonizers (on the order of 10-100 individuals), but the persistence of the allelism over several years suggests that some lethal-carrying chromosomes may be heterotic owing to shared associations between lethal and other genes.

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D. subobscura, a typically Palearctic species, has recently colonized the American continent. The population from which the colonization started is still unknown. A complete association between a lethal gene and the O5 chromosomal inversion has been detected in the colonizing populations; this association could be used to ascertain the origin of the colonization. In the present study, three hypotheses on the origin of this association are analyzed and their probabilities are calculated. According to the first hypothesis an O5 chromosome carrying a lethal gene would have been included in the sample from which the colonization started, thus originating the association found in the American populations. The second hypothesis assumes that, at the beginning of the colonization, the association between the O5 inversion and a lethal gene would have been formed from an Ost chromosome carrying a lethal gene, on which a new O5 (or similar) inversion arose. In the last hypothesis, the association between the O5 inversion and the lethal gene would have originated at the beginning of the colonization from a lethal-free O5 chromosome, in which a lethal gene arose due to mutation.

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In this work, the process of colonization of North and South America by the species Drosophila subobscura has been studied by analyzing the variability of lethal genes. The genetic structures of a Palearctic natural central population (Bordils, Spain) and a colonizer population from America (Gilroy, California) have been compared. The frequencies of lethal chromosomes and their allelism are 29.007% and 0.0069 in the first population and 14.414% and 0.0526 in the American population. A founder effect is detected after the computation of some population parameters (Ne , h, he and the lethal load). Furthermore, the allelism of lethal chromosomes has revealed a strong association between a lethal gene and the O5 inversion both in Gilroy and in the population of Puerto Montt (Chile). The interpopulation allelism shows that the O5 arrangement from the USA and Chile is the same, confirming that the colonizing processes of North and South America are correlated. The O5 arrangement can also be useful as a genetic marker to trace the origin of the colonization. The frequency of the O5 arrangement in the original population of the colonization could be used to estimate the number of colonizers. This population is still unknown, but taking the extreme values of the frequency of the O5 inversion in natural Palearctic populations (1-15%), the number of colonizers could vary between 9 and 149 individuals.

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North America and South America have recently been colonized by the Palearctic species Drosophila subobscura. This double colonization offers a rare opportunity for evolutionary studies. Correlations between chromosomal arrangement frequencies and latitude were calculated for the colonizing populations. Signs of these correlations are highly coincident with those found in the Old World. These results provide experimental support for the adaptive value of the chromosomal-inversion polymorphism; historical and other nonadaptive explanations are thus excluded or relegated to a secondary role.