Further evidence for latitudinal inversion clines in natural populations of Drosophila melanogaster from India.

Chromosomal analysis of eight Indian natural populations (six from north India and two from south India) of Drosophila melanogaster revealed the presence of 13 paracentric inversions, including one in the X chromosome. All four types of inversions--common cosmopolitan (4), rare cosmopolitan (3), recurrent endemic (2), and unique endemic (4)--were detected. The frequency of commonly occurring inversions and the level of inversion heterozygosity were found to be higher in the two southern populations. The south Indian populations are genetically more differentiated than those from the north. Also, latitudinal clines in the frequencies of the four common cosmopolitan inversions were detected. These results provide further evidence for the existence of inversion clines in Indian populations of D. melanogaster.     

Chromosome Inversion Polymorphisms in DROSOPHILA MELANOGASTER. I. Latitudinal Clines and Associations between Inversions in Australasian Populations

Nineteen Australasian populations of Drosophila melanogaster have been screened for chromosome inversion polymorphisms. All 15 of the inversion types found are paracentric and autosomal, but only four of these, one on each of the major autosome arms, are common and cosmopolitan. North-south clines occur, with the frequencies of all four of the common cosmopolitan inversions increasing toward the equator. These clines in the Southern Hemisphere mirror north-south clines in the Northern Hemisphere, where the frequencies of all four of the common cosmopolitan inversions again increase towards the equator.-While few of the Australasian populations show significant disequilibrium between linked common cosmopolitan inversions, those that do invariably have excesses of coupling gametes, which is consistent with other reports. We also find nonrandom associations between the two major autosomes, with the northern populations in Australasia (those with high inversion frequencies) tending to be deficient in gametes with common cosmopolitan inversions on both major autosomes, while the southern populations in Australasia (low inversion frequencies) tend to have an excess of this class of gametes.-The clines and the nonrandom associations between the two major autosomes are best interpreted in terms of selection operating to maintain the common cosmopolitan inversion polymorphisms in natural populations of D. melanogaster.     

Inversion Clines in Populations of DROSOPHILA MELANOGASTER

Twenty different natural populations of Drosophila melanogaster were sampled to determine the frequencies of inversions. Based on their frequencies and geographical distributions, the inversions could be classified as follows: (1) Common cosmopolitan inversions that are present in many populations in frequencies exceeding five percent and that may exhibit frequency clines over large geographical regions; (2) Rare cosmopolitan inversions that occur throughout the species range but usually at frequencies below five percent and that may be absent in many populations; (3) Recurrent endemic inversions that are found in several adjacent populations in frequencies usually not exceeding one or two percent; and (4) Unique endemic inversions that are found only among the progeny of a single individual and that may represent one aspect of the syndrome termed "hybrid dysgenesis". Four common cosmopolitan inversions that exhibit highly significant clines in populations in the eastern United States are In(2L)t, In(2R)NS, In(3L)P and In(3R)P.     

Inversion polymorphism in Indian natural populations of Drosophila melanogaster

Six natural populations (three urban and three rural) of Drosophila melanogaster from India were analysed for chromosome inversions, revealing the presence of 19 different paracentric autosomal inversions. One new inversion has also been detected in a laboratory stock established from flies collected from Kerala. In total 20 different paracentric inversions in Indian D. melanogaster have been detected during the present study, and of these, 4 are common cosmopolitans; 2 are rare cosmopolitans; 7 are recurrent endemics; and 7 are unique endemics. The quantitative data clearly show that the urban populations are different from the rural ones with respect to inversion polymorphism.     

Population and behaviour genetics of Drosophila ananassae

Drosophila ananassae is a cosmopolitan and domestic species. It occupies a nuique status among the Drosophila species due to certain peculiarities in its genetic behaviour. The most unusual feature of this species is spontaneous male recombination in appreciable frequency. The present review summarises the work done on population and behaviour genetics of D. ananassae from India. Population dynamics of three cosmopolitan inversions has been studied in Indian population of D. ananassae and it is evident from the results that there is a considerable degree of genetic divergence at the level of inversion polymorphism. In general, the populations from south India show more differentiation than those from the north. These three cosmopolitan inversions, which are coextensive with the species, exhibit heterosis. Interracial hybridization does not lead to beaakdown of heterosis, which suggests that evidence for coadaptation is lacking in geographic populations of D. ananassae. Heterosis appears to be simple luxuriance rather than populational heterosis (coadaptation). Unlinked inversions occur in random associations, indicating no interchromosomal interactions. However, two inversions of the third chromosome often show strong linkage disequilibrium in laboratory populations, which is due to epistatic gene interaction and suppression of crossing-over. Genetic variations for certain allozyme polymorphism and sternoleural bristle phenotypes in Indian populations of D. ananassae have also been observed.A number of investigations have also been carried out on certain aspects of behaviour genetics of Indian D. ananassae. There is evidence for sexual isolation within D. ananassae. Significant variations in mating propensity of several isofemale strains, inversion karyotypes, the diminishing effects of certain mutations on sexual activity of males and positive response to selection for high and low mating propensity provide evidence for genetic control of sexual behaviour in D. ananassae. Males contribute more to variation and thus are more subject to intra-sexual selection than females. Evidence for rare male mating advantage has also been presented. Geographic strains of D. ananassae show variation with respect to oviposition site preference. The results of studies on pupation site preference, which is an important component of larval behaviour, suggest that larval pupation behaviour in D. ananassae is under polygenic control with a substantial amount of additive genetic variation.     

Continuing studies on chromosomal polymorphism in a Korean natural population of Drosophila melanogaster

Investigations on the chromosomal inversion polymorphism were conducted on a Korean (Taenung) natural population of D. melanogaster during the period 1978 to 1992. A total of 66 different endemic and cosmopolitan inversions were found on both major chromosome pairs II and III. Some of them proved to be rare cosmopolitan types (2LKA, 2LNS, 2LF, 2RCy, 3LM, 3RKI, and 3RK), while others were endemics. The distribution of breakpoints for endemic and rare cosmopolitan inversions are not random along the two autosome arms.With respect to frequency changes, the 15-year survey revealed that five of the cosmopolitan types (2Lt, 2RNS, 3LP, 3RC, and 3RMo) exhibit cyclical frequency changes, whereas gene arrangement 3RP shows relatively stable frequencies. Tests for correlations between gene arrangement frequencies and several climatic variables gave no clear evidence for such relationships. Only one correlation coefficient out of 64 was statistically significant. This revised version was published online in July 2006 with corrections to the Cover Date.     

Patterns of inversion polymorphism in three species of the Drosophila melanogaster species group

In Drosophila, chromosomal polymorphism due to paracentric inversions is very common and constitutes an adaptive character. The degree of chromosomal variability varies in different species and also in different populations of the same species. Chromosomal polymorphism in Indian natural populations of three species, D. melaonogaster, D. ananassae and D. bipectinata which belong to the melanogaster species group has been studied and the quantitative data on frequency of inversions have been reported. Behaviour of chromosome inversions has also been studied in laboratory conditions. The present review summarises the work done on inversion polymorphism in Indian populations of three species which clearly demonstrates that these three species vary in their patterns of inversion polymorphism and have evolved different mechanisms for adjustment to their environments although they belong to the same species group.     

Latitudinal clines in<Emphasis Type="Italic">Drosophila melanogaster</Emphasis>: Body size,allozyme frequencies,inversion frequencies,and the insulin-signalling pathway

Many latitudinal clines exist inDrosophila melanogaster: in adult body size, in allele frequency at allozyme loci, and in frequencies of common cosmopolitan inversions. The question is raised whether these latitudinal clines are causally related. This review aims to connect data from two very different fields of study, evolutionary biology and cell biology, in explaining such natural genetic variation inD. melanogaster body size and development time. It is argued that adult body size clines, inversion frequency clines, and clines in allele frequency at loci involved in glycolysis and glycogen storage are part of the same adaptive strategy. Selection pressure is expected to differ at opposite ends of the clines. At high latitudes, selection onD. melanogaster would favour high larval growth rate at low temperatures, and resource storage in adults to survive winter. At low latitudes selection would favour lower larval critical size to survive crowding, and increased male activity leading to high male reproductive success. Studies of the insulin-signalling pathway inD. melanogaster point to the involvement of this pathway in metabolism and adult body size. The genes involved in the insulin-signalling pathway are associated with common cosmopolitan inversions that show latitudinal clines. Each chromosome region connected with a large common cosmopolitan inversion possesses a gene of the insulin transmembrane complex, a gene of the intermediate pathway and a gene of the TOR branch. The hypothesis is presented that temperateD. melanogaster populations have a higher frequency of a ’thrifty’ genotype corresponding to high insulin level or high signal level, while tropical populations possess a more ’spendthrift’ genotype corresponding to low insulin or low signal level.     

The role of the transposable element hobo in the origin of endemic inversions in wild populations of Drosophila melanogaster

Evidence from in situ hybridizations of DNA from the transposable element hobo to polytene salivary gland chromosome squashes reveals that hobo occupies both cytological breakpoints of three of four endemic inversions sampled from natural populations of Drosophila melanogaster in the Hawaiian islands. The fourth endemic inversion has a single hobo insert at one breakpoint. Cosmopolitan inversions on the same chromosomes do not show this association. Frequencies of both endemic and cosmopolitan inversions in Hawaiian populations fall in ranges typical for natural populations of D. melanogaster sampled worldwide, suggesting that these results may be typical of other regions besides Hawaii. This appears to be the first direct demonstration that transposable elements are responsible for causing specific rearrangements found in nature; consequently, it is also the first direct demonstration that chromosome rearrangements can arise in nature in a manner predicted by results of hybrid dysgenic crosses in the laboratory. Possible population genetic and evolutionary consequences are discussed.     

Inherited and somatic cytogenetic variability in Palearctic populations of Chironomus riparius Meigen 1804 (Diptera, Chironomidae).

Inter- and intracytogenetic variability was analyzed in 13 natural Palearctic populations of Chironomus riparius Meigen 1804 (syn. Chironomus thummi) by examining hereditary and somatic aberrations (mainly inversions) of the salivary gland polytene chromosomes. In total, 77 different types of inherited inversion sequences and 184 different types of somatic inversions were found. The median percent frequency of inherited inversions was 1.4% and karyotypic divergence between populations was very low. Most hereditary inversions were endemic and always in a heterozygous state. Only six inversion sequences, each of them shared by two very distant populations, may be considered a relic of very ancient ancestral inversions. Unlike inherited inversions, occurrence of somatic aberrations seems to increase with the overall rise in the level of heavy metal pollution of the sediments from which larvae were sampled. In contrast with what occurs in populations of other chironomid species, populations of C. riparius do not seem to undergo a process of cytogenetic differentiation.     

Population genetics of Drosophila ananassae: genetic differentiation among Indian natural populations at the level of inversion polymorphism

The present study, which is one of the longest temporal (two decades) and largest spatial (different parts of India covered) investigations on inversion polymorphism in natural populations of D. ananassae, was undertaken to understand the dynamics of inversion polymorphism in a broad and comprehensive manner. Forty-five natural populations from different ecogeographic regions of the country (covering the regions from Kashmir to Kanniyakumari and Gujarat to Nagaland) were analysed for chromosomal inversions. All the populations show the presence of the three cosmopolitan inversions, frequencies of which vary among the populations analysed. Simple correlations between frequencies of different inversions and regression analysis of inversion frequencies with latitude, longitude and altitude were insignificant. This reinforces the concept of rigid polymorphism in D. ananassae. Genetic divergence (spatial and temporal) at the level of chromosomal polymorphism among natural populations was calculated. Results show spatial divergence but no temporal divergence. Rigid polymorphic systems of D. ananassae did not show long-term directional trends. On the basis of the present study, and after including comparisons with the studies conducted more than two decades ago, the most important conclusion to be drawn is that the three cosmopolitan inversions in D. ananassae segregate within populations at fairly similar frequencies, and the general geographic pattern has remained constant.     

Genetic differentiation in natural populations of Drosophila ananassae

Inversion polymorphism has been studied in three natural populations of Drosophila ananassae. The three cosmopolitan inversions have been detected in all the three populations analysed. Some quantitative variations in the inversion frequencies seem to exist and the level of inversion heterozygosity varies between the different populations.     

Chromosomal inversion polymorphism in Afrotropical populations of Drosophila melanogaster

When 41 populations from Africa (south of the Sahara) and Indian Ocean islands were analysed for their chromosomal inversion polymorphism, 34 rearrangements were found, including the four common cosmopolitans (In(2L)t, In(2R)NS, In(3L)P and In(3R)P), four rare cosmopolitans (In(2L)NS, In(3R)C, In(3R)Mo and In(3R)K) and six African polymorphic ('recurrent') endemics. Mean inversion frequencies per major autosome arm were positively and, generally, highly correlated to each other. There was no altitudinal nor latitudinal cline of inversion frequency, except for one African polymorphic endemic. Significant longitudinal clines were detected for In(2L)t, In(3L)P and In(3R)K; in all cases, inversion frequencies decreased eastward. Principal components analysis and ANOVA made it possible to distinguish three groups of populations. A high level of polymorphism was found in populations from west tropical Africa. The other low altitude populations from the mainland were moderately polymorphic, whereas the lowest levels of polymorphism were those of high altitude populations and of Indian Ocean islands. Moreover, some regional and local differentiation was also found. The frequency of unique autosomal inversions was not different from those found in Asia, Australia and America, but was significantly higher than that in Europe and North Africa. A West-East differentiation was also observed for the African polymorphic endemics. The present geographic pattern suggests a long, patchy evolution with restricted gene flow, followed by the modern period with numerous recent migrations linked to human transportation.     

The effect of developmental temperature on the genetic architecture underlying size and thermal clines in Drosophila melanogaster and D. simulans from the east coast of Australia

Body size and thermal tolerance clines in Drosophila melanogaster occur along the east coast of Australia. However the extent to which temperature affects the genetic architecture underlying the observed clinal divergence remains unknown. Clinal variation in these traits is associated with cosmopolitan chromosome inversions that cline in D. melanogaster. Whether this association influences the genetic architecture for these traits in D. melanogaster is unclear. Drosophila simulans shows linear clines in body size, but nonlinear clines in cold resistance. Clinally varying inversions are absent in D. simulans. Line-cross and clinal analyses were performed between tropical and temperate populations of D. melanogaster and D. simulans from the east coast of Australia to investigate whether clinal patterns and genetic effects contributing to clinal divergence in wing centroid size, thorax length, wing-to-thorax ratio, cold and heat resistance differed under different developmental temperatures (18 °C, 25 °C, and 29 °C). Developmental temperature influenced the genetic architecture in both species. Similarities between D. melanogaster and D. simulans suggest clinally varying inversion polymorphisms have little influence on the genetic architecture underlying clinal divergence in size in D. melanogaster. Differing genetic architectures across different temperatures highlight the need to consider different environments in future evolutionary and molecular studies of phenotypic divergence.     

Maintenance of a large pericentric inversion generated by the hobo transposable element in a transgenic line of Drosophila melanogaster

The impact of the hobo transposable element in the global reorganization of the Drosophila melanogaster genome has been investigated in transgenic lines generated by the injection of hobo elements into the Hikone strain, which lacked them previously. Extensive surveys of transgenic lines followed for 250 generations have identified 13 inversions with hobo inserts at most breakpoints. One of these inversions is pericentric on chromosome 2. It has been maintained in the line where it was discovered and in several sublines at frequencies from 0.19 to 0.45, generating stable chromosomal polymorphisms, similar to cosmopolitan paracentric inversions in natural populations. Individuals homozygous for this inversion were viable and fertile, allowing the creation of a new homozygous strain.     

Increase in the degree of inversion polymorphism in Drosophila bipectinata populations transfereed to laboratory conditions

Thirteen laboratory populations (six mass cultures and seven isofemale lines) of Drosophila bipectinata were established from files collected from six different geographic localities (four in the north and two in the south) in India. These mass cultures and isofemale lines were maintained in food bottles in the laboratory for varying number of generations by transferring about 50 files (females and males in equal number) in each generation. After several generations, all the laboratory populations were analysed chromosomally to determine the frequency of different inversions. The results indicate that all the laboratory populations remained chromosomally polymorphic due to the persistence of inversions which were originally present ion the populations. The quantitative data on the frequency of inverted gene orders and the level of inversions heterozygosity in laboratory populations are compared with those in corresponding natural populations. This comparison clearly shows that there is a considerable increase in the frequency of inverted gene orders and the level of inversion heterozygosity in laboratory populations when compared with corresponding natural populations. This is most likely to be due to selective advantage of inversion heterozygotes under stringent competition in laboratory populations. Thus heterotic buffering is associated with chromosome inversion of Drosophila bipectinata.     

Lack of Underdominance in a Naturally Occurring Pericentric Inversion in Drosophila Melanogaster and Its Implications for Chromosome Evolution

In(2LR)PL is a large pericentric inversion polymorphic in populations of Drosophila melanogaster on two Indian Ocean islands. This polymorphism is puzzling: because crossing over in female heterokaryotypes produces inviable zygotes, such inversions are thought to be underdominant and should be quickly eliminated from populations. The observed fixation for such inversions among related species has led to the idea that genetic drift can cause chromosome evolution in opposition to natural selection. We found, however, that In(2LR)PL is not underdominant for fertility, as heterokaryotypic females produce perfectly viable eggs. Genetic analysis shows that the lack of underdominance results from the nearly complete absence of crossing over in the inverted region. This phenomenon is probably caused by mechanical and not genetic factors, because crossing over is not suppressed in In(2LR)PL homokaryotypes. Our observations do not support the idea that the fixation of pericentric inversions among closely related species implies the action of genetic drift overcoming strong natural selection in very small populations. If chromosome arrangements vary in their underdominance, it is those with the least disadvantage as heterozygotes, like In(2LR)PL, that will be polymorphic or fixed in natural populations.     

Very low genetic variability in the Indian queenless ant Diacamma indicum

Abstract We developed microsatellite markers and combined them with mitochondrial markers to analyse the population genetic structure of the queenless ant Diacamma indicum. This species, lacking winged queens, is likely to have a restricted female dispersal but exhibits various life history traits suggesting higher dispersal abilities than the other Diacamma species. Only 4 of 11 microsatellites were polymorphic and only 1 had more than 4 alleles over 166 individuals originating from 7 populations from the south of India. Only one mitochondrial DNA (mtDNA) haplotype was detected throughout India (including one population in the north) and Sri Lanka. Such a level of polymorphism is particularly low compared with other Diacamma species having much smaller ranges in the south of India. A strong genetic differentiation was observed between populations separated by more than a few kilometres. We also analysed the genetic differentiation between the Indian populations and two populations from the Japanese island of Okinawa, which are morphologically similar and might belong to the same species. The genetic differentiation was high for both markers, suggesting an absence of ongoing gene flow between these populations.     

Inversions fail to account for allozyme clines

Allozyme and inversion data from natural populations of Drosophila melanogaster from the eastern United States were analyzed to determine whether the clines at allozyme loci are due to nonrandom associations with common cosmopolitan inversions. All inversions show strong clines. Clines were large and significant for half of the eight allozyme loci. An analysis of the contribution of inversions to clines of allozyme genes revealed three outcomes: the inversion cline (1) enhanced the allozyme cline, but was only partly responsible, (2) reduced the allozyme cline, and (3) had no effect. The allozyme clines were mainly determined by the pattern of allele frequencies within the chromosomal arrangements. Consequently, it was concluded that allozyme clines would exist in the absence of inversion clines.     

Patterns of diversity and linkage disequilibrium within the cosmopolitan inversion In(3R)Payne in Drosophila melanogaster are indicative of coadaptation

The cosmopolitan inversion In(3R)Payne in Drosophila melanogaster decreases in frequency with increasing distance from the equator on three continents, indicating it is subject to strong natural selection. We investigated patterns of genetic variation and linkage disequilibrium (LD) in 24 molecular markers located within and near In(3R)Payne to determine if different parts of the inversion responded to selection the same way. We found reduced variation in the markers we used compared to others distributed throughout the genome, consistent with the inversion having a relatively recent origin (相似文献