Subobscura Populations Research Articles

Genetic loads and coadaptivity of chromosomal inversions I. Inversion polymorphism and genetic load on chromosome O in a Drosophila subobscura population from Petnica

Inversion polymorphism on chromosome O and polymorphism for the viability of determining genes have been studied in a natural population of Drosophila subobscura from Petnica (Serbia). The range of inversion polymorphism and the abundance of particular gene arrangements in the study population agree with a general pattern of inversion polymorphism of D. subobscura in Europe. The data obtained on the amount of genetic loads show that the D. subobscura population from Petnica displays a moderate degree of that polymorphism, compared to the other studied populations of these species. Therefore, the D. subobscura population from Petnica could be tentatively classified as an ecologically central population. Examination association of chromosomal, thus, inversion polymorphism with gene polymorphism, in the form of genetic loads show that differences exist in the mean viability among certain gene arrangements. The distribution of deleterious genes among chromosome O gene arrangements were non-random.

Chromosomal inversion polymorphism of Drosophila subobscura populations from Jastrebac Mountain shows temporal and habitat-related changes

Inversion polymorphism in populations of D. subobscura from a beech forest on Jastrebac mountain was studied in June 1990, 1993, and 1994, respectively. The same analysis was performed in 1990 for D. subobscura populations in a beech forest and an oak forest in the same region. Statistically significant differences in the frequencies of the gene arrangements of A1, J and U chromosome were observed during the period of investigation. A tendency towards a decrease in the frequency of the standard gene arrangements was found for all chromosomes, but was particularly evident with chromosomes A and J. The frequency of the gene arrangements A1 A2, J1 and U1–2+6 increased at the same time. Differences in the frequency of the gene arrangements of A, J and U chromosomes were also observed when the populations from two ecologically different habitats (beech and oak forest) were compared in 1990.

This month in Evolutionary Applications.

This third issue of Evolutionary Applications features a wide range of topics, including evolutionary causes of invasiveness (Lee and Gelembiuk 2008), human sexual dimorphism (Crespi 2008), estimation of effective population size (Nomura 2008), genetic connectivity and habitat restoration (Raeymaekers et al. 2008), maize adaptation (Mercer et al. 2008), fitness consequences of wild-farm salmon hybridization (Fraser et al. 2008), adaptation to environmental stress (Gilchrist et al. 2008), and Darwinian perspectives on fisheries management (Olsen et al. 2008). Similar to the first two issues in this inaugural year, once again we see that evolutionary biology greatly contributes to our understanding of a wide array of practical issues. Below we highlight just a few of the articles representing the breath of topics covered in this month’s issue.

HOW REPEATABLE IS ADAPTIVE EVOLUTION? THE ROLE OF GEOGRAPHICAL ORIGIN AND FOUNDER EFFECTS IN LABORATORY ADAPTATION

The importance of contingency versus predictability in evolution has been a long-standing issue, particularly the interaction between genetic background, founder effects, and selection. Here we address experimentally the effects of genetic background and founder events on the repeatability of laboratory adaptation in Drosophila subobscura populations for several functional traits. We found disparate starting points for adaptation among laboratory populations derived from independently sampled wild populations for all traits. With respect to the subsequent evolutionary rate during laboratory adaptation, starvation resistance varied considerably among foundations such that the outcome of laboratory evolution is rather unpredictable for this particular trait, even in direction. In contrast, the laboratory evolution of traits closely related to fitness was less contingent on the circumstances of foundation. These findings suggest that the initial laboratory evolution of weakly selected characters may be unpredictable, even when the key adaptations under evolutionary domestication are predictable with respect to their trajectories.

Evolutionary dynamics of molecular markers during local adaptation: a case study in Drosophila subobscura.

BackgroundNatural selection and genetic drift are major forces responsible for temporal genetic changes in populations. Furthermore, these evolutionary forces may interact with each other. Here we study the impact of an ongoing adaptive process at the molecular genetic level by analyzing the temporal genetic changes throughout 40 generations of adaptation to a common laboratory environment. Specifically, genetic variability, population differentiation and demographic structure were compared in two replicated groups of Drosophila subobscura populations recently sampled from different wild sources.ResultsWe found evidence for a decline in genetic variability through time, along with an increase in genetic differentiation between all populations studied. The observed decline in genetic variability was higher during the first 14 generations of laboratory adaptation. The two groups of replicated populations showed overall similarity in variability patterns. Our results also revealed changing demographic structure of the populations during laboratory evolution, with lower effective population sizes in the early phase of the adaptive process. One of the ten microsatellites analyzed showed a clearly distinct temporal pattern of allele frequency change, suggesting the occurrence of positive selection affecting the region around that particular locus.ConclusionGenetic drift was responsible for most of the divergence and loss of variability between and within replicates, with most changes occurring during the first generations of laboratory adaptation. We also found evidence suggesting a selective sweep, despite the low number of molecular markers analyzed. Overall, there was a similarity of evolutionary dynamics at the molecular level in our laboratory populations, despite distinct genetic backgrounds and some differences in phenotypic evolution.

Monitoring of the genetic structure of natural populations: change of the effective population size and inversion polymorphism in Drosophila subobscura

We analyzed changes in the genetic structure and effective population size of two ecologically distinct populations of Drosophila subobscura over several years. Population sizes of D. subobscura in beech and oak wood habitats for a period of 6 years were estimated by the capture-mark-release-recapture method. Inversion polymorphism parameters were also assessed in the same populations for a period of 3 years. Significant differences in the numbers of individuals were observed between sexes. This affected the effective population sizes between particular years. The ratio of the effective size over the cenzus dropped significantly in beech wood in 2 years. Although overall heterozygosity remained unchanged during the years in both habitats, frequencies of gene arrangements on five chromosomes show variability. After the bottleneck, some complex chromosomal arrangements appeared for the first time in both populations. Standard gene arrangements of chromosome A increased in frequency over the years in each habitat, while the complex arrangements remain rather stable and specific for each population. The results obtained indicate that the population structure may significantly change if the effective size of D. subobscura population is reduced, which is mostly related to microclimatic changes in habitats. Based on the results to date, monitoring of microevolutionary changes by using D. subobscura and its relatives seems a promising way to study the effects of global climate changes.

Diurnal variability of gene arrangement frequencies in Drosophila subobscura populations from two habitats*

The rich inversion polymorphism of chromosomes of Drosophila subobscura varies in association with environmental changes at spatial and temporal level. Due to random factors this might become less regular and this might be the reason that there is little evidence of altitudinal and seasonal, microgeographic and habitat-related variability. The variability of gene arrangement frequencies over daytime period was investigated in populations of D. subobscura from two ecologically different habitats. According to gene arrangement frequencies and inversion polymorphism parameters populations fit into the existing patterns of regional polymorphism. Even though populations display daytime variability for the frequencies of arrangements of chromosomes U and J, the nonsignificant differences in other arrangement frequencies, as well as data obtained from genetic distances between samples from different times of day, rule out the existence of subpopulations distinguished from each other by diurnal activity within two habitats. Some particular arrangement frequencies vary according to temperature and humidity and some changes appear for different karyotypic combinations between beech and oak habitat, which suggests different adaptive advantages and selective mechanisms. Cluster analysis of gene arrangement frequencies indicates some importance of A chromosome arrangements for diurnal activity and show in dependence to other ecological data that internally fixed daily activity rhythm might exists in D. subobscura. Analysis of light, temperature and humidity factors in relation to the frequency data obtained indicate a choice of different ecological niche in a temporally structured habitat due to behavioural genetic information. Der starke Chromosomenpolymorphismen von D. subobscura variiert in Abhängigkeit von Umweltfaktoren auf räumlicher und zeitlicher Ebene. Durch den Effekt von Zufallsprozessen mag dies manchmal weniger regelhaft werden, was auch der Grund dafür sein mag, dass es wenige gute Beweise von altitudionalen und saisonalen wie auch mikrogeographischen und habitatsabhängigen Unterschieden gibt.In dieser Arbeit wurde die Frequenzvariabilität von chromosomalen Strukturtypen in Populationen von D. subobscura an zwei verschiedenen Habitaten in Serbien zu verschiedenen Tagesabschnitten untersucht. In Bezug auf die Strukturtypenhäufigkeiten und anderen populationsgenetischen Parametern sind die Populationen in ihrer Zusammensetzung den regionalen Mustern vergleichbar. Wenn die Populationen auch tageszeitliche Variabilitäten der Strukturtypenhäufigkeiten der Chromosomen U und J zeigen, so weisen die Daten von genetischen Distanzen jedoch darauf hin, dass es sich hier nicht um Subpopulationen handelt, die durch tageszeitliche Aktivitäten voneinander unterscheidbar sind. Einige Frequenzen besonderer Chromosomenstrukturen variieren in Abhängigkeit von Temperatur und Luftfeuchtigkeit und einige Unterschiede zwischen den Buchen- und Eichen-Habitaten treten für bestimmte Karyotypenkombinationen auf, was auf verschiedene Anpassungsvorteile und Selektionsmechanismen hinweist. Eine Clusteranalyse der Strukturtypenfrequenzen lässt die Bedeutung des Geschlechtschromosoms (Chromosom A) für die tageszeitlichen Aktivitäten erkennen und macht in Zusammenhang mit ökologischen Daten die Existenz eines innerlich fixierten Tagesrhythmus von D. subobscura wahrscheinlich. Analysen von Licht-, Temperatur- und Luftfeuchtigskeits-Faktoren zeigen in Zusammenhang mit den Strukturtypenhäufigkeiten darauf hin, dass es eine Wahl für die verschiedenen ökologischen Nischen aufgrund von verhaltensgenetischen Informationen geben mag.

CONVERGENCE TO A NOVEL ENVIRONMENT: COMPARATIVE METHOD VERSUSEXPERIMENTAL EVOLUTION

Laboratory adaptation allows researchers to contrast temporal studies of experimental evolution with comparative studies. The comparative method is here taken to mean the inference of microevolutionary processes from comparisons among contemporaneous populations of diverse origins, from one or multiple species. The data contrasted here come from Drosophila subobscura populations that were introduced to the laboratory at several different times and from two different locations. Two questions were addressed. First, can we correctly infer evolutionary dynamics from comparative data collected simultaneously from disparate populations? In most cases, we could, except for the character of starvation resistance. Second, are the evolutionary dynamics inferred from the comparative approach similar to those revealed by temporal studies of experimental evolution? For fecundity characters, they were. Overall the results show that both comparative and temporal studies are useful, though the former can be uninformative for characters with complex evolutionary trajectories.

Genetic load in marginal populations of Drosophila subobscura.

HereditasVolume 129, Issue 3 p. 283-286 Open Access Genetic Load in Marginal Populations of Drosophila Subobscura* Anssi Saura, Anssi Saura Department of Genetics, Umeå University, S-901 87 Umeå, SwedenSearch for more papers by this authorBo Johansson, Bo Johansson Department of Genetics, Umeå University, S-901 87 Umeå, SwedenSearch for more papers by this authorJuhani Lokki, Juhani Lokki Zoological Museum, FIN–00014 University of Helsinki, FinlandSearch for more papers by this authorMaija Kohonen–corish, Maija Kohonen–corish Cancer Genetics Laboratory, John Curtin School of Medical Research, The Australian National University, GPO BOX 334, Canberra ACT 2601, AustraliaSearch for more papers by this author Anssi Saura, Anssi Saura Department of Genetics, Umeå University, S-901 87 Umeå, SwedenSearch for more papers by this authorBo Johansson, Bo Johansson Department of Genetics, Umeå University, S-901 87 Umeå, SwedenSearch for more papers by this authorJuhani Lokki, Juhani Lokki Zoological Museum, FIN–00014 University of Helsinki, FinlandSearch for more papers by this authorMaija Kohonen–corish, Maija Kohonen–corish Cancer Genetics Laboratory, John Curtin School of Medical Research, The Australian National University, GPO BOX 334, Canberra ACT 2601, AustraliaSearch for more papers by this author First published: 06 May 2004 https://doi.org/10.1111/j.1601-5223.1998.00283.xCitations: 6 † * We dedicate this paper to Prof. Dr. Diether Sperlich of the University of Tübingen, Germany, in recognition to his inspiring leadership in the study of D. subobscura populations. AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL References Ayala FJ, Serra L and Prevosti A, (1989). A grand experiment in evolution: the Drosophila subobscura colonization of the Americas. Genome 31: 246– 255. Begon M, Krimbas CB and Loukas M, (1980). The genetics of D. subobscura populations. XV. Effective size of a natural population estimated by three independent methods. Heredity 45: 335– 350. Brussard PF, (1984). Geographic patterns and environmental gradients: the central–marginal model in Drosophila revisited. Ann. Rev. Ecol. Syst. 15: 25– 64. Desmet G, Nassimbeni P and Belli M, (1990). 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Krimbas CB, (1992). Drosophila suboscura: Biology, genetics and inversion polymorphism. In: Inversion polymorphism in Drosophila (eds CB Krimbas and JR Powell) CRC Press, Boca Raton , p. 127– 220. Lakovaara S and Saura A, (1971). Genic variation in marginal populations of Drosophila subobscura. Hereditas 69: 77– 82. Latorre A, Hernandez C, Martinez D, Castro JA, Ramon M and Moya A, (1992). Population structure and mitochondrial DNA gene flow in Old World populations of Drosophila subobscura. Heredity 68: 15– 24. Loukas M, Krimbas CB and Sourdis J, (1979). The genetics of Drosophila subobscura populations. XII. A study of lethal allelism. Genetica 54: 197– 206. Mestres F, Pegueroles G, Prevosti A and Serra L, (1990). Colonization of America by D. subobscura: lethal genes and the problem of the 05 inversion. Evolution 44: 1564– 1568. Pfriem P and Sperlich D, (1982). Wild O chromosomes of Drosophila subobscura from different geographic regions have different effects on viability. 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Viabilities of originally natural O-chromosomal inversion homo- and heterokaryotypes in Drosophila subobscura.

The influence of epistatic interactions of lethal and non-lethal genes upon viability of Drosophila inversion karyotypes is poorly known. In this paper we present comparative results for viabilities of 21 originally natural O-inversion homo- and 38 heterokaryotypes in a D. subobscura population. We observed strong heterotic effect in viability of O-lethal heterozygotes irrespective of different inversion backgrounds, which indicates a mechanism for protection of a great number of lethal genes. In O-non-lethal heterozygotes the heterotic effect in viability was absent irrespective of different inversion backgrounds. Our results showed a great extent of genetic load and high abundance of O-chromosomal arrangements in the population analyzed. It belongs to the set of central European populations. An epistasis of lethal genes present in O-inversion hetero- and not present in O-inversion homokaryotypes of moderate or low frequencies could be good example for co-adaptation of chromosomal inversions with regard to the genetic load. This represents a more efficient mechanism for limitation of genetic load than alternative mechanisms for protection of lethals. Except for lethal genes, possible epistatic interactions of mildly deleterious (subvital) genes, could also be responsible for limiting the extent of genetic load in natural D. subobscura populations. We demonstrated a non-random distribution of several combinations of viability classes among different O-inversion homo- and heterokaryotypes. As a consequence of that, the viabilities of the O-inversion homokaryotypes compared to heterokaryotypes were significantly higher at low frequencies than in moderate or high frequencies. This shows frequency-dependence as a mechanism of balancing selection for protection of O-chromosomal inversions in natural D. subobscura populations. In addition, the viabilities of the O-inversion homokaryotypes of lower frequency, compared to homokaryotypes of moderate or high frequency, were significantly higher. This again indicates the existence of supergene selection as another mechanism for protection of chromosomal inversions, as co-adapted complexes in natural D. subobscura populations.

CONVERGENCE TO A NOVEL ENVIRONMENT: COMPARATIVE METHOD VERSUS EXPERIMENTAL EVOLUTION

Laboratory adaptation allows researchers to contrast temporal studies of experimental evolution with comparative studies. The comparative method is here taken to mean the inference of microevolutionary processes from comparisons among contemporaneous populations of diverse origins, from one or multiple species. The data contrasted here come from Drosophila subobscura populations that were introduced to the laboratory at several different times and from two different locations. Two questions were addressed. First, can we correctly infer evolutionary dynamics from comparative data collected simultaneously from disparate populations? In most cases, we could, except for the character of starvation resistance. Second, are the evolutionary dynamics inferred from the comparative approach similar to those revealed by temporal studies of experimental evolution? For fecundity characters, they were. Overall the results show that both comparative and temporal studies are useful, though the former can be uninformative for characters with complex evolutionary trajectories.

GENETIC VARIATION IN THE SPREAD OF DROSOPHILA SUBOBSCURA FROM A NONEQUILIBRIUM POPULATION

Drosophila subobscura was first identified in North America in the early 1980s, and a newer D. subobscura population in Utah appears to have been established more than 10 years later. In this study, we use nuclear microsatellite allele frequencies, mitochondrial restriction fragment length polymorphism (RFLP) allele frequencies, and computer simulations to investigate possible scenarios of how this species has spread across North America. Our method develops a 95% confidence interval for the maximum and minimum number of founders that could have colonized the new population given various scenarios for spread. Unlike many other methods, it may be applied to nonequilibrium source populations given certain conditions. We find that observed allele frequency differences between newer and older D. subobscura populations are consistent with very few inseminated females being transported east from the coast in a single step or with larger numbers of colonizers invading after several intermediate steps. They are not consistent with a large, panmictic population of D. subobscura colonizing Utah in a single step.

GENETIC VARIATION IN THE SPREAD OF DROSOPHILA SUBOBSCURA FROM A NONEQUILIBRIUM POPULATION

Drosophila subobscura was first identified in North America in the early 1980s, and a newer D. subobscura population in Utah appears to have been established more than 10 years later. In this study, we use nuclear microsatellite allele frequencies, mitochondrial restriction fragment length polymorphism (RFLP) allele frequencies, and computer simulations to investigate possible scenarios of how this species has spread across North America. Our method develops a 95% confidence interval for the maximum and minimum number of founders that could have colonized the new population given various scenarios for spread. Unlike many other methods, it may be applied to nonequilibrium source populations given certain conditions. We find that observed allele frequency differences between newer and older D. subobscura populations are consistent with very few inseminated females being transported east from the coast in a single step or with larger numbers of colonizers invading after several intermediate steps. They are not consistent with a large, panmictic population of D. subobscura colonizing Utah in a single step.Corresponding Editor: K. Ross

The genetic structure of Drosophila subobscura populations from the Islands of Majorca and Minorca (Balearic Islands, Spain) based on allozymes and mitochondrial DNA.

The genetic structure of seven populations of Drosophila subobscura from different locations on Majorca and Minorca (Balearic Islands, Spain) was studied using two types of markers: allozyme and mitochondrial DNA restriction analyses. Both markers showed congruent results. In the allozyme data, when the Acph-1 locus was excluded from the joint FST statistics, only three out of 21 comparisons were statistically significant, lending support to the hypothesis of low genetic differentiation. The mtDNA restriction analyses showed two haplotypes at a high frequency (more than 40% each), irrespective of the location considered, and a number of endemic haplotypes at very low frequencies (not higher than 2% each). The analyses of the genetic structure yielded a pattern similar to the allozymes. The cytonuclear disequilibrium analyses showed the difficulty of detecting cytonuclear associations in natural populations because they are mainly transient.

Adaptation to the laboratory environment in Drosophila subobscura

Abstract Adaptation to a novel environment is expected to have a number of features. Among these is a temporal increase in fitness and some or all of its components. It is also expected that additive genetic variances for these fitness characters will fall. Finally, it is expected that at least some additive genetic correlations will decrease, from positive toward negative values. In a study of several life-history variables in a Drosophila subobscura population sampled from the wild and then cultured in the laboratory, we did not find any such longitudinal trends over the first 29 generations. However, a temporal comparison (over 14 generations) of the later generations of this laboratory-adapted population with a new population, derived from a more recent wild-caught sample, indicated clearly that laboratory adaptation was nonetheless occurring. This study suggests the need for extensive replication and control in studies of the features of adaptation to a novel environment.

Tracing the colonization of Madeira and the Canary Islands by Drosophila subobscura through the study of the rp49 gene region

AbstractNucleotide variation at the nuclear ribosomal protein 49 (rp49) gene region has been analysed by fine restriction mapping in a sample of 47 lines from a population from Madeira. Five restriction‐site (out of 37 sites scored) and 3 length polymorphisms have been detected, resulting in 14 different haplotypes. This population shows less variation than both continental and Canary Island populations. The population from Madeira shows some differentiation from mainland populations, which does not favor the idea of extensive migration between the continent and Madeira. Chromosomal and restriction‐map variation of the rp49 region in D. subobscura populations, together with data on sequence comparison of this nuclear region in D. guanche and D. madeirensis clearly indicate that the Canary Islands underwent at least two colonization events from the nearby continent. Although the data for Madeira are compatible with a single colonization event by a continental sample polymorphic for gene arrangements O3 and O3 + 4, an alternative scenario with at least two colonization events seems more likely.

Lack of seasonal changes in mitochondrial DNA variability of a Drosophila subobscura population

AbstractRestriction site analysis of mtDNA of 550 isofemale lines corresponding to different seasonal samples of a single geographic population of Drosophila subobscura was carried out. The distribution pattern of haplotypes was similar to that observed for the entire range of the species on the European continent: two haplotypes were equally and highly frequent, and a set of sporadic haplotypes were almost never present in more than one seasonal sampling. No statistically significant evidence was found for between‐population heterogeneity across time, and the mean within‐population variation was similar to other mtDNA restriction site analyses previously reported for D. subobscura populations. These observations could be interpreted in terms of the neutral mutation hypothesis where the entire population has not yet reached an equilibrium. The causes of this non‐equilibrium are most likely periodic winter bottlenecks, phenomena that particularly affect the distribution of mtDNA haplotypes across time.

Molecular characterization and cytonuclear disequilibria of two Drosophila subobscura mitochondrial haplotypes

According to restriction site analyses of mitochondrial DNA, Drosophila subobscura shows a polymorphism that consists of two frequent haplotypes that are evenly distributed all over the Old World and several rare haplotypes never present in more than one locality. To ascertain the causes responsible for such distribution, three different mtDNA fragments from haplotypes I and II sampled in a population from Zürich have been partially sequenced. Only three silent nucleotide changes have been detected in the ND5 gene. One of them implies the loss of the HaeIII restriction site, which differentiates haplotype I from haplotype II. On the basis of these results as well as on others involving the geographic distribution of haplotypes I and II, they can be considered phenotypically equivalent. The sequencing study has been complemented with the analysis of cytonuclear disequilibria between mitochondrial haplotypes and different nuclear loci in four D. subobscura populations. As expected, no significant cytonuclear disequilibria have been found between haplotypes I and II. Moreover, when haplotypes I and II were pooled and compared with the rare, endemic haplotypes similar results were obtained.

Differential flight activity among karyotypes: daily and weather-induced changes in chromosomal inversion polymorphism in natural populations of Drosophila subobscura

The question is posed whether karyotype frequencies in the active fraction of Drosophila subobscura populations vary consistently in the course of a day, or in accordance with weather changes. Significant daily variation occurred in all chromosomes with the exception of the sex chromosome. The proportions of the karyotypes Ust/1+2 and Ist/st decreased from early to late morning and increased during the evening. Ist/1 displayed a complementary behaviour. The homokaryotypes Ost/st and Est/st decreased both during the morning and the evening. Weather disturbances caused a remarkable variation in the frequencies of the standard gene arrangements.

Open ground individuals and population structure in Drosophila subobscura Collin

The distribution of Drosophila subobscura adults within, and their movement through, open ground habitats has been investigated, along with the status of such individuals within populations as a whole. Movement occurs between open ground and woodland, to some extent as a result of passive transport by air currents, but flies can remain in open ground for at least several days at a time. There are no detectable differences in either the reproductive age-structure or the body-size distributions of flies collected from woodland and open ground habitats, although a significantly higher proportion of females are found in open ground than in woodland. The large number of gravid females in open ground provide the potential for breeding there, but circumstantial evidence suggests that this is unlikely to occur. Rather, their presence appears to reflect the foraging strategy adopted by females in response to their high nutritional requirements. The flux of flies through open ground between woodlands suggests that previous estimates of the genetically-important parameter, effective population size, have been seriously underestimated for natural D. subobscura populations.