RESUMO
The adaptive value of chromosomal inversions continues raising relevant questions in evolutionary biology. In many species of the Drosophila genus, different inversions have been recognized to be related to thermal adaptation, but it is necessary to determine to which specific climatic variables the inversions are adaptive. With this aim, the behavior of thermal adapted inversions of Drosophila subobscura regarding climatic variables was studied in the natural population of Avala (Serbia) during the 2014-2017 period. The results obtained were compared with those previously reported in the Font Groga (Barcelona, Spain) population, which presents different climatic and environmental conditions. In both populations, it was observed that most thermal adapted inversions were significantly associated with the first, second or both principal components, which were related with maximum, minimum and mean temperatures. Moreover, a significant increase over years (2004-2017) for the minimum temperature was detected. In parallel, a significant variation over time in Avala was only observed for the frequencies of 'warm' and 'non-thermal' adapted inversions of the U chromosome. However, stability in the chromosomal inversion polymorphism was observed for the 2014-2017 period which might result from the temporal span of the study and/or selective process acting on the population.
Assuntos
Aclimatação , Inversão Cromossômica , Drosophila/genética , Animais , Cromossomos de Insetos/genética , Drosophila/fisiologia , Ecótipo , Polimorfismo GenéticoRESUMO
The changes of chromosomal inversion polymorphism composition of Drosophila subobscura in samples from Apatin (Serbia) were studied in a 24-years interval (1994-2018). The variation was significant for all autosomes and directional, increasing the inversions considered as 'warm', whereas those reported as 'cold' decreased. Furthermore, the Chromosomal Thermal Index (CTI), which allows studying the thermal adaptation of the whole karyotype increased significantly in that period of time. These results were in agreement with the indicators of global warming in Apatin: a trend to increase of the mean, maximum and minimum (this latter even significant) temperatures, and an erratic pattern of rainfall (also usual in global warming). The deviations from the Wright-Fisher model of genetic drift were used to consider the possible effect of migration or selection as evolutionary factors responsible for the change in inversion frequencies. To quantify approximately the rate of change in the frequencies, for each kind of inversions ('cold', 'warm' and 'non-thermal adapted'), the difference in frequency between the Apatin samples obtained in 1994 and 2018 was computed and then it was divided by the number of years elapsed. This rate was always higher (from twice as many as thirty times more depending on the autosome) for thermal adapted inversions ('cold' or 'warm') than the 'non-thermal' adapted. From this study, it could be concluded that the chromosomal inversions of D. subobscura could change (in composition and frequencies) in a predictable direction and a rather 'rapid' rhythm to adapt to the global warming scenario.
Assuntos
Inversão Cromossômica , Drosophila/genética , Taxa de Mutação , Termotolerância , Animais , Seleção GenéticaRESUMO
Drosophila subobscura is a species with a rich chromosomal polymorphism which is adaptive to different climatic conditions. Five samples of the Font Groga population (Barcelona, Spain) were sampled in autumn during 5 consecutive years (2011-2015) to obtain their inversion chromosomal polymorphism, and climatic data of several meteorological variables were also collected. The aim was to analyze the adaptive potential of inversions with regard to climatic variables, being the most relevant: mean temperature (Tmean), maximum temperature (Tmax), minimum temperature (Tmin), humidity (Hm) and rainfall (Rf). As expected, no significant variation in inversion frequencies were detected over this short period of time. However, from a climatic point of view it was possible to differentiate 'warm' and 'dry' from 'cold' and 'humid' samples. The joint study of maximum (Tmax) and minimum (Tmin) temperatures was a key element to understand the effect on adaptation of many inversions. It was also observed that temperature had to be considered in conjunction with humidity and rainfall. All these factors would condition the biota of D. subobscura habitat, and chromosomal inversions could provide an adaptive response to it.
Assuntos
Adaptação Biológica/genética , Drosophila/genética , Adaptação Fisiológica/genética , Animais , Animais Selvagens/genética , Inversão Cromossômica/genética , Mudança Climática , Proteínas de Drosophila/genética , Aquecimento Global , Polimorfismo Genético/genética , Chuva , TemperaturaRESUMO
Drosophila has demonstrated to be an excellent model to study the adaptation of organisms to global warming, with inversion chromosomal polymorphism having a key role in this adaptation. Here, we introduce a new index (Chromosomal Thermal Index or CTI) to quantify the thermal adaptation of a population according to its composition of "warm" and "cold" adapted inversions. This index is intuitive, has good statistical properties, and can be used to hypothesis on the effect of global warming on natural populations. We show the usefulness of CTI using data from European populations of D. subobscura, sampled in different years. Out of 15 comparisons over time, nine showed significant increase of CTI, in accordance with global warming expectations. Although large regions of the genome outside inversions contain thermal adaptation genes, our results show that the total amount of warm or cold inversions in populations seems to be directly involved in thermal adaptation, whereas the interactions between the inversions content of homologous and non-homologous chromosomes are not relevant.
Assuntos
Cromossomos de Insetos , Drosophila/genética , Aquecimento Global , Temperatura , Animais , Cariótipo , Polimorfismo GenéticoRESUMO
Using a well-adapted Drosophila subobscura population (Avala, Serbia), a drastic experiment of inbreeding was carried out to assess whether the expected level of homozygosity could be reached or if other evolutionary forces affected the process. In general, no significant changes of inversion (or arrangement) frequencies were detected after 12 brother-sister mating generations. Furthermore, no significant differences were obtained between observed and expected (under the inbreeding model) karyotypic frequencies. Thus, these results seemed to indicate that the main evolutionary factor in the experiment was inbreeding. However, in the G12 generation, complete chromosomal fixation was reached only in two out of the eight final inbred lines. In these lines, the chromosomal compositions were difficult to interpret, but they could be likely a consequence of adaptation to particular laboratory conditions (constant 18 °C, food, light period, etc.). Finally, in a second experiment, the inbred lines presented higher fertility at 18 °C than at 13 °C. Also, there was a significant line effect on fertility: inbred line number 6 (A1, J1, U1+2; U1+2+6, E8, and O3+4+7) presented the highest values, which maybe the result of an adaptation to laboratory conditions. Thus, the results obtained in our experiments reflect the adaptive potential of D. subobscura inversions.
Assuntos
Aclimatação/genética , Inversão Cromossômica , Drosophila/genética , Endogamia , Animais , Drosophila/fisiologia , Fertilidade , Polimorfismo Genético , TemperaturaRESUMO
The adaptive value of the Drosophila subobscura chromosomal inversion polymorphism with regard to environmental effects is well-known. However, the specific details of the inversion adaptations to the global warming scenario deserve to be analyzed. Toward this aim, polymorphism and karyotypes were studied in 574 individuals from Petnica (Serbia) in annual samples taken in June for the period 2019-2022. Comparing the results of Petnica (Cfa: humid subtropical climate) with those from Avala (Serbia: Cfb, temperate oceanic climate) and Font Groga (Barcelona, Spain; Csa: hot-summer Mediterranean climate), significant differences were observed for their chromosomal polymorphism. In Petnica, inversions from U and E chromosomes mainly reacted significantly with regard to temperature, humidity, and rainfall. Moreover, the inversion polymorphism from Petnica (2019-2022) was compared with that from 1995. In this period, a significant increase in mean and maximum temperature was observed. However, to properly explain the observed variations of inversions over time, it was necessary to carefully analyze annual seasonal changes and particular heat wave episodes. Interestingly, yearly fluctuations of U chromosome 'warm'-adapted inversions corresponded with opposite changes in 'non-thermal' inversions. Perhaps these types of inversions were not correctly defined with regard to thermal adaptation, or these fluctuations were also due to adaptations to other physical and/or biological variables. Finally, a joint study of chromosomal inversion polymorphism from many Balkan populations of D. subobscura indicated that different climatic regions presented distinct composition, including thermal-adapted inversions.
RESUMO
Drosophila subobscura is characterized by a rich chromosomal polymorphism for inversions. Many inversions are adaptive to global warming and can be classified as 'warm' or 'cold' adapted. However, most studies were carried out from European populations located in the central area of the species distribution or from American colonizing populations. For this reason, we aimed to analyse the isolated and marginal Rasht population, located in the Hyrcanian forests area (Iran). The chromosomal polymorphism for inversions was compared with the previous Rasht samples (Rasht I and II) obtained 57 years ago. This polymorphism has changed based on the inversion composition and frequencies. Interestingly, the polymorphism for inversions was scarce and similar to that of Madeira, an isolated Atlantic island. Likely, this similarity is a consequence of the marginal location and isolation of the Rasht population. Also, the chromosomal thermal index (CTI) was 0.445, showing a significant increase over those from Rasht I (0.184) and II (0.210). All these observations were in agreement with the global warming expectations. Moreover, the CTI was also computed for Russian Caucasus and Turkish populations collected more than 40 years ago to better understand the adaptive potential of D. subobscura and to study the similarity between populations of different geographic areas. In summary, the inversions of D. subobscura also changed in marginal and isolated populations in agreement with the global warming expectations, and an open question is to know where is the threshold for this evolutionary change.
Assuntos
Inversão Cromossômica , Drosophila , Animais , Drosophila/genética , Irã (Geográfico) , Inversão Cromossômica/genética , Polimorfismo Genético , CromossomosRESUMO
An interesting evolutionary question that still remains open is the connectivity between marine populations. Marine currents can favour the dispersal of larvae or adults, but they can also produce eddies and gyres generating oceanographic fronts, thus limiting gene flow. To address this subject, we selected the Atlantic-Mediterranean transition, where several fronts are located: Gibraltar Strait (GS), Almeria-Oran Front (AOF) and Ibiza Channel (IC). Seven populations of the marine crab Liocarcinus depurator (Cadiz, West and East Alboran, Alacant, Valencia, Ebro Delta and North Catalonia) located along this transition were analysed in six consecutive years (2014-2019) using a fragment of the COI (Cytochrome Oxidase subunit I) gene. All sequences (966) belonged to two well defined haplogroups: ATL (most abundant in Atlantic waters) and MED (predominant in Mediterranean waters). Following a geographic variation, the frequency of ATL decreased significantly from Cadiz to North Catalonia. However, this variation presented steps due to the effect of oceanographic restrictions/fronts. Significant effects were recorded for GS (2015, 2017, 2018 and 2019), AOF (all years except 2018) and IC (2016). The intensity and precise location of these fronts changed over time. Multivariate analyses distinguished three main population groups: Cadiz, Alboran Sea and the remaining Mediterranean populations. These findings could be relevant to properly define Marine Protected Areas and for conservation and fisheries policies.
Assuntos
Braquiúros/fisiologia , Animais , Oceano Atlântico , Evolução Biológica , Braquiúros/genética , Conservação dos Recursos Naturais , Complexo IV da Cadeia de Transporte de Elétrons/genética , Política Ambiental , Pesqueiros/normas , Fluxo Gênico , Variação Genética , Humanos , Mar Mediterrâneo , Formulação de Políticas , Movimentos da ÁguaRESUMO
The recent colonization of America by Drosophila subobscura represents a great opportunity for evolutionary biology studies. Knowledge of the populations from which the colonization started would provide an understanding of how genetic composition changed during adaptation to the new environment. Thus, a 793 nucleotide fragment of the Odh (Octanol dehydrogenase) gene was sequenced in 66 chromosomal lines from Barcelona (western Mediterranean) and in 66 from Mt. Parnes (Greece, eastern Mediterranean). No sequence of Odh fragment in Barcelona or Mt. Parnes was identical to any of those previously detected in America. However, an Odh sequence from Barcelona differed in only one nucleotide from another found in American populations. In both cases, the chromosomal lines presented the same inversion: O(7), and the Odh gene was located within this inversion. This evidence suggests a possible western Mediterranean origin for the colonization. Finally, the molecular and inversion data indicate that the colonization was not characterized by multiple reintroductions.
Assuntos
Drosophila/genética , América , Substituição de Aminoácidos , Animais , Evolução Biológica , Inversão Cromossômica , Drosophila/classificação , Feminino , Fluxo Gênico , Genes de Insetos , Grécia , Haplótipos , Masculino , Filogenia , Polimorfismo Genético , Dinâmica Populacional , EspanhaRESUMO
In the context of the COVID-19 pandemic, this paper provides recommendations for medical eye care during the easing of control measures after lockdown. The guidelines presented are based on a literature review and consensus among all Spanish Ophthalmology Societies regarding protection measures recommended for the ophthalmologic care of patients with or without confirmed COVID-19 in outpatient, inpatient, emergency and surgery settings. We recommend that all measures be adapted to the circumstances and availability of personal protective equipment at each centre and also highlight the need to periodically update recommendations as we may need to readopt more restrictive measures depending on the local epidemiology of the virus. These guidelines are designed to avoid the transmission of SARS-CoV-2 among both patients and healthcare staff as we gradually return to normal medical practice, to prevent postoperative complications and try to reduce possible deficiencies in the diagnosis, treatment and follow-up of the ophthalmic diseases. With this update (5th ) the Spanish Society of Ophthalmology is placed as one of the major ophthalmology societies providing periodic and systematized recommendations for ophthalmic care during the COVID-19 pandemic.
Assuntos
COVID-19/transmissão , Controle de Doenças Transmissíveis/métodos , Oftalmologia/normas , Equipamento de Proteção Individual/normas , COVID-19/epidemiologia , Consenso , Oftalmopatias/terapia , Humanos , Pandemias/prevenção & controle , Guias de Prática Clínica como Assunto , SARS-CoV-2 , Espanha , Telemedicina/métodosRESUMO
Recombination plays an important role in species adaptation since it acts as an evolutionary force that can influence genome pattern organization. However, recombination can be detrimental in some situations, causing the breakdown of some adaptive gene combinations such as coadapted gene complexes. Genetic and cytological chromosome maps allow recombination throughout the genome to be analyzed. In this study we compare the recombination rate of two types of homokaryotypic lines of D. subobscura (O(ST) and O( 3+4 )) using a set of at least 13 microsatellite loci. The genetic maps obtained present similar lengths: 184 and 196 cM for O(ST) and O( 3+4 ) chromosomes, respectively. For most pairs of markers analyzed, a sample size of about 150 individuals appeared sufficient to obtain appropriate recombination values, with the exception of markers located in the same cytological band. Recombination rates seemed to be fairly uniform along the O chromosome, but some regional differences were observed. Several recombination hot and coldspots were detected, and their numbers were different in the homokaryotypic line types (O(ST) and O( 3+4 )). This variability could be attributed to differences between the genetic content of the two arrangements or to differences between the lines.
Assuntos
Cromossomos de Insetos/genética , Drosophila/genética , Repetições de Microssatélites/genética , Recombinação Genética/genética , Animais , Distribuição de Qui-Quadrado , Mapeamento Cromossômico , Escore LodRESUMO
The interactions of lethal and non-lethal genes and their contributions to the viability of Drosophila inversion karyotypes are not well understood. This is especially true under variable environmental conditions. Here we examine the viability of natural chromosomal O-inversion homo- and heterokaryotypes in a D. subobscura population from Avala Mountain, Serbia. The observations we report were performed at a range of temperatures over several years. The heterotic effect of O-lethal heterozygotes on viability was found to be independent of the effects of inversion backgrounds and temperature. Positive epistatic interactions of lethal, mildly deleterious (subvital) and quasinormal (normal) genes were found in O-inversions in heterokaryotypes but not in homokaryotypes. These interactions were independent of temperature. This finding could explain the limitation of the genetic load in D. subobscura populations. In the population analyzed, annual fluctuations in the frequencies of certain chromosomal arrangements, karyotypes and non-lethal chromosomes under cold-stress temperatures seemed to indicate a correlation between these polymorphisms and environmental conditions. Our results indicate that there is a response in tolerance to extreme temperatures that may be due to natural selection. The differences in mean viability between some O-inversion karyotypic combinations indicate that there are differences in their tolerance to variable temperatures. All our results suggest that both frequency-dependent and supergene selection are mechanisms that protect O-chromosomal inversions. Chromosomal inversions may be genetically differentiated and coadapted complexes in D. subobscura populations.
Assuntos
Drosophila/fisiologia , Animais , Drosophila/genética , Epistasia Genética , Cariotipagem , Estresse Fisiológico , TemperaturaRESUMO
Here we report the viability of natural chromosomal O-inversion structural homo- and heterokaryotypes in a population of D. subobscura from Avala Mountain, Serbia, subjected to cold and heat stress during spring 2004. These results were compared with those observed in the same population in September 2004. We detected protection of a great number of lethal genes in O-chromosome lethal heterozygous combinations, independently of inversion backgrounds and temperature stress. The positive epistatic interactions of mildly-deleterious genes observed only in O-inversion heterokaryotypes (at distinct temperatures) and lethal genes in O-inversion homokaryotypes (under temperature stress only) could be responsible for reducing the genetic load. The seasonal fluctuations in frequencies of several chromosomal arrangements and karyotypes indicate a seasonal adaptation to changeable environmental conditions. The sample of D. subobscura collected in spring 2004 was tolerant to cold but not to heat, and these results point to tolerance to extreme low temperatures, possibly as a result of natural selection. Also, a non-random distribution of distinct combinations of viability classes among several O-inversion karyotypes (under both optimal conditions and heat stress) was observed. This observation could be taken as evidence of co-adaptation: different capacities of several O-inversion karyotypes with different combinations of genes to tolerate a range of temperatures. We conclude that frequency-dependent and supergene selection are balancing selection mechanisms and are responsible for the protection of chromosomal inversions in natural populations of D. subobscura.
Assuntos
Drosophila/fisiologia , Estações do Ano , Animais , Drosophila/genética , Cariotipagem , TemperaturaRESUMO
Drosophila suzukii is native to East and Southeast Asia and spread very fast around the world being considered an invasive pest species. Many demographic, population genetics and genomic studies have been recently developed, but so far no analysis has been carried out regarding the presence of chromosomal inversions in D. suzukii natural populations. In this research, we studied polytene chromosomes of flies collected from the Font Groga (Barcelona) population. The chromosomes and many of their segments were characterized for their similarity with those from D. melanogaster. This is the report of one paracentric inversion (in heterozygous condition) in the right arm of the third chromosome (3R). As far as we know, it is the first time that an inversion has been observed in a D. suzukii natural population. Finally, the evolutionary significance of the finding of inversions in this species is discussed.
Assuntos
Inversão Cromossômica , Drosophila/genética , Espécies Introduzidas , Cromossomos Politênicos/genética , Animais , Centrômero/genética , Genética Populacional/métodos , Cariótipo , Espanha , Telômero/genéticaRESUMO
Knowledge of the frequency, distribution, and fate of lethal genes in chromosomal inversions helps to illuminate the evolution of recently founded populations. We analyze the relationship between lethal genes and inversions in two colonizing populations of D. subobscura in Chile. In the ancestral Palearctic populations of this species, lethal genes seem distributed at random on chromosomes. But in colonizing American populations, some lethal genes are associated with specific chromosomal arrangements. Some of these associated lethals were detected only during the first stages of the colonization (O( 3+4+2 )), and never thereafter, whereas others have persisted (O( 3+4+7 ) and O(5)). However, most lethal genes in American populations have been observed only once: they have arisen by novel mutation and soon disappear. Finally, recombination between different inversions has been observed in America. However, the persistence of lethal genes associated with the heterotic inversions O( 3+4+7 ) and O(5) could indicate that recombination inside these inversions is rare.
Assuntos
Cromossomos/genética , Drosophila/genética , Evolução Molecular , Genes Letais , Alelos , Animais , Chile , Inversão Cromossômica , Genética PopulacionalRESUMO
Although Drosophila subobscura has been a model organism for European and American population geneticists, little information is available on the genetic structure of its natural populations. In this paper we report the estimates of some population parameters. We have used data from lethal allelism tests in four Balkan populations (Kamariste, Djerdap and Petnica in Serbia and Zanjic in Montenegro). In all populations, lethal genes were found to have a deleterious effect on heterozygotes. The N(e) values varied greatly from 370 (Petnica) to 19413 (Kamariste), depending on the habitat conditions and some environmental factors. Finally, gene flow between the Balkan populations was detected by the estimates of N(m) (from 4.68 in Petnica to 106.2 in Kamariste) and m (from 0.0041 in Djerdap to 0.0126 in Petnica). These results agree with those obtained in a previous study where the frequencies of allelism between populations were greater than predicted by independently arising lethal genes.
Assuntos
Drosophila/genética , Genética Populacional , Alelos , Animais , Genes Letais , Modelos Genéticos , IugosláviaRESUMO
Adaptation is defined as an evolutionary process allowing organisms to succeed in certain habitats or conditions. Chromosomal inversions have the potential to be key in the adaptation processes, since they can contribute to the maintenance of favoured combinations of adaptive alleles through reduced recombination between individuals carrying different inversions. We have analysed six genes (Pif1A, Abi, Sqd, Yrt, Atpα and Fmr1), located inside and outside three inversions of the O chromosome in European populations of Drosophila subobscura. Genetic differentiation was significant between inversions despite extensive recombination inside inverted regions, irrespective of gene distance to the inversion breakpoints. Surprisingly, the highest level of genetic differentiation between arrangements was found for the Atpα gene, which is located outside the O1 and O7 inversions. Two derived unrelated arrangements (O3+4+1 and O3+4+7) are nearly fixed for several amino acid substitutions at the Atpα gene that have been described to confer resistance in other species to the cardenolide ouabain, a plant toxin capable of blocking ATPases. Similarities in the Atpα variants, conferring ouabain resistance in both arrangements, may be the result of convergent substitution and be favoured in response to selective pressures presumably related to the presence of plants containing ouabain in the geographic locations where both inversions are present.
Assuntos
Adaptação Fisiológica/genética , Cromossomos de Insetos/efeitos dos fármacos , Drosophila/efeitos dos fármacos , Ouabaína/toxicidade , Toxinas Biológicas/toxicidade , Sequência de Aminoácidos , Substituição de Aminoácidos , Animais , Proteínas de Transporte/genética , Proteínas de Transporte/metabolismo , Inversão Cromossômica/efeitos dos fármacos , Cromossomos de Insetos/química , Drosophila/genética , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Proteína do X Frágil da Deficiência Intelectual/genética , Proteína do X Frágil da Deficiência Intelectual/metabolismo , Modelos Moleculares , Ouabaína/metabolismo , Plantas/química , Plantas/metabolismo , Polimorfismo Genético , Proteínas de Ligação a RNA/genética , Proteínas de Ligação a RNA/metabolismo , ATPase Trocadora de Sódio-Potássio/genética , ATPase Trocadora de Sódio-Potássio/metabolismo , Toxinas Biológicas/biossíntese , Toxinas Biológicas/metabolismoRESUMO
Spatial genetic studies often require sampling broadly separated areas, difficult to access simultaneously. Although comparing localities surveyed at different time periods might result in spurious genetic differentiation, there is a general believe on the stability of genetic structure through time, particularly if sampled localities are isolated or very distant. By analysing spatial and temporal genetic differentiation of the portunid crab Liocarcinus depurator we assessed the contribution of historical and contemporary processes on population connectivity patterns across three main oceanographic discontinuities along the Atlantic-Mediterranean transition: Gibraltar Strait, Almeria-Oran Front and Ibiza Channel. A partial fragment of the cytochrome oxidase I gene was sequenced in 366 individuals collected from localities at both sides of each discontinuity during three time periods. Although localities showed genetic fluctuations through time, a significant gradient was detected along the coast for all sampling periods. Significant inter-annual differences identified within the Alicante area, north of the Almeria-Oran Front, were associated with shifts in the relative contribution of Atlantic and Mediterranean water masses. The persistence of a clinal pattern in the Atlantic-Mediterranean transition area together with local fluctuations suggests a complex balance of dispersal and selection.
Assuntos
Braquiúros/genética , Especiação Genética , Genética Populacional , Filogenia , Animais , Fluxo Gênico , Deriva Genética , Geografia , Repetições de Microssatélites/genéticaRESUMO
Biologists have long debated the speed, uniformity, and predictability of evolutionary change. However, evaluating such patterns on a geographic scale requires time-series data on replicate sets of natural populations. Drosophila subobscura has proven an ideal model system for such studies. This fly is broadly distributed in the Old World, but was introduced into both North and South America just over two decades ago and then spread rapidly. Rapid, uniform, and predictable evolution would be demonstrated if the invading flies evolved latitudinal clines that progressively converged on those of the native populations. Evolutionary geneticists quickly capitalized on this opportunity to monitor evolutionary dynamics. Just a few years after the introduction, they surveyed chromosomal inversion frequencies in both North and South America. On both continents they detected incipient latitudinal clines in chromosome inversion frequencies that almost always had the same sign with latitude as in the Old World. Thus the initial evolution of chromosomal polymorphisms on a continental scale was remarkably rapid and consistent. Here we report newer samples of inversion frequencies for the colonizing populations: the time series now spans almost one decade for North America and almost two decades for South America. Almost all inversions in the New World continue to show the same sign of frequency with latitude as in the Old World. Nevertheless, inversion clines have not consistently increased in steepness over time; nor have they consistently continued to converge on the Old World baseline. However, five arrangements in South America show directional, continentwide shifts in frequency. Overall, the initial consistency of clinal evolutionary trajectories seen in the first surveys seems not to have been maintained.
Assuntos
Evolução Biológica , Inversão Cromossômica , Drosophila/genética , Geografia , Movimento/fisiologia , Polimorfismo Genético , Animais , Drosophila/fisiologia , Fatores de TempoRESUMO
The colonization of America by Drosophila subobscura has been a unique exper iment in nature that has allowed us to explore the effects of evolution on a continental scale. To analyze this evolutionary event, nucleotide sequences of the Odh (Octanol dehydrogenase) gene were obtained for 43 lethal chromosomal lines from colonizing populations of North America and 5 from South America, in addition to 5 chromosomal lines from Europe with different viabilities and 2 from laboratory marker stocks. Since 10 different Odh haplotypes were found in America, the minimum number of colonizers would be 5 (or 3 mated females). Only one Odh haplotype was found in American O(5) inversions confirming that only one copy of this inversion was included among the sample of colonizers. The same Odh haplotypes were detected in association with the same chromosomal arrangements and with identical lethal genes in both North and South America indicating that exactly the same chromosome types reached both hemispheres. These observations indicate that the two continental colonizations are not independent. They are derived from the same colonization event. The population from which the colonization started should contain the O(5) inversion, a non-negligible frequency of the O(3+4+7) arrangement and all other arrangements found in America. So far the only populations that fulfill all these requirements are those from Greece, indicating that these populations can be considered good candidates as a starting point for an in depth analysis of the origin of the American colonization by D. subobscura.