Cytogenetic Features of Blackfly Wilhelmia paraequina Puri (Diptera: Simuliidae) from Armenia

Three blackfly Wilhelmia paraequina populations of Armenia (rivers Debet and Megriget, channel Megri) were studied. 2n = 6: IS + IIL, IIS + IL, IIIS + IIIL. Cytological maps of polytene chromosomes were constructed. High inversion polymorphism (95.63%) was observed, with 2.6 inversions per individual. Three inversions proved to be associated with male development: Y₁ was characterized by a combination of two heterozygous inversions, IIL-3 + IIL-1, while Y₂ had another combination of heterozygous inversions, IIL-5 + IIL-3. The X chromosome had a standard homozygous IIL band pattern. The populations were shown to be similar in autosomal polymorphism. A tendency for differentiation was observed with respect to frequencies and types of sex-linked inversions: the sex determination system was Y₁X–XX in the Debet and Megriget populations and Y₂X–XX in the channel (Megri) population. On the strength of these findings, one W. paraequina morphotype was assumed to involve two cytotypes, A (Debet and Megriget populations) and B (Megri population).     

Population cytogenetics of <Emphasis Type="Italic">Chironomus circumdatus</Emphasis> Kieffer, 1921 (Diptera,Chironomidae) from Thailand

The objectives of this study were to explore cytogenetic variation and the role of chromosomal change on local adaptation and genetic differentiation of Chironomus circumdatus Kieffer from Thailand. A total of 1,505 larvae from 24 populations were examined cytologically. Twelve chromosomal inversions were found and most of these (9 of 12) were rare inversions. All populations were in Hardy–Weinberg equilibrium. Significant association (P < 0.001) between the A2 and B5 inversions was detected in one population. Population genetic structure analysis indicated significant genetic differentiation between populations (F _ST = 0.037, P < 0.001). Geographic distance was the principal factor limiting gene flow between populations. Nei’s modified genetic distance (D _A) between populations ranged from 0.001 to 0.011 with an average of 0.003. An UPGMA population phenogram depicting relationship between populations based on D _A values revealed three groups of populations, group I, II and III each characterized by different inversions/inversion frequencies. Significant correlation of inversion C3 and water temperature suggested that this inversion might have a role to play on adaptation to high temperature habitat. However, if detection of significant population subdivision and relationship between genetic and geographic distance are taken into account, relationship between C3 and water temperature will also be due to the effect of migration/drift alone without the effect of selection.     

Molecular characterization,relatedness of <Emphasis Type="Italic">Haematobia irritans</Emphasis> (horn fly) populations,by RAPD-PCR

Haematobia irritans is a hematophagous parasite of cattle that causes significant economic losses in many parts of the world, including Brazil. In the present work, one American, four Brazilian populations of this species were studied by Random Amplified Polymorpht DNA (RAPD) to assess basically genetic variability within and between populations. Ten different decamer random primers were employed in the genomic DNA amplification, yielding 117 fragments in the five H. irritans populations. In Drosophila prosaltans, used as an outgroup, 81 fragments were produced. Forty-three of these fragments were shared by both species. Among the H. irritans samples, that from Rio Branco (Acre State, Brazil) produced the smallest numbers of fragments, polymorphic bands. This high genetic homogenity may be ascribed to its geographic origin (in the Northwest of Brazil), which causes high isolation, low gene flow, unlike the other Brazilian populations, from the South Central region, in which cattle trade is very intensive. Marker fragments (exclusive bands) detected in every sample enabled the population origin to be characterized, but they are also potentially useful for further approaches such as the putative origin of Brazilian populations from North America. Similarity indices [Nei & Li, 1979, Proc. Natl. Acad. Sci. USA 76: 5269–5273], phylogenetic trees, rooted by using the outgroup, produced by the Phylogenetic Analysis using Parsimony (PAUP 4.0-Swofford, 2001) program showed the closest relationships between flies from São José do Rio Preto, Turiúba (both from São Paulo State, Brazil) while flies from the geographically distant Rio Branco showed the greatest differentiation relative to the others.     

Speciation and chromosomal evolution of the palaearctic species of chironomids of the genus Sergentia Kieffer (Diptera, Chironomidae): Chromosome polymorphism in the populations of S. baueri Wülker et al., 1999, S. prima Proviz et al., 1997, and S. electa Proviz et al., 1999 from the Irkutsk reservoir

Chromosome polymorphism was studied in populations of three Palaearctic species of chironomids of the genus Sergentia Kieffer (Diptera, Chironomidae) from the Irkutsk reservoir: S. baueri Wülker et al., 1999, S. prima Proviz et al., 1997, and S. electa Proviz et al., 1999. It was found that in S. baueri heterozygous individuals constitute 72% of the population with 0.8 of inversion per individual. In total, three inversion sequences were detected. The most widespread was the inversion in regions 7–12 of the arm IIIR with the borders similar to those of the inversion in the Far East S. baueri populations and in populations of other species of the genus. In S. prima, heterozygotes constituted 60%, with the number of inversions per individual was 1.3. Seven inversion sequences were revealed, of which three were found in chromosome IV. In the S. electa population, only one inversion sequence was observed in chromosome III in 36% of larvae (0.4 of inversion per individual). The level of chromosome polymorphism in the populations of the Palaearctic species is comparable with that in the populations of endemic Sergentia from the Baikal Lake. Ten rearrangements were revealed in each of the two groups, but similar borders of chromosome regions were established only for two inversions. In the studied Sergentia species, chromosome IV has the most variable structure.     

Comparative polytene chromosome maps of <Emphasis Type="Italic">D. montana</Emphasis> and <Emphasis Type="Italic">D. virilis</Emphasis>

Chromosomal inversion polymorphism was characterized in Finnish Drosophila montana populations. A total of 14 polymorphic inversions were observed in Finnish D. montana of which nine had not been described before. The number of polymorphic inversions in each chromosome was not significantly different from that expected, assuming equal chance of occurrence in the euchromatic genome. There was, however, no correlation between the number of polymorphic inversions and that of fixed inversions in each chromosome. Therefore, a simple neutral model does not explain the evolutionary dynamics of inversions. Furthermore, in contrast to results obtained by others, no significant correlation was found between the two transposable elements (TEs) Penelope and Ulysses and inversion breakpoints in D. montana. This result suggests that these TEs were not involved in the creation of the polymorphic inversions seen in D. montana. A comparative analysis of D. montana and Drosophila virilis polytene chromosomes 4 and 5 was performed with D. virilis bacteriophage P1 clones, thus completing the comparative studies of the two species.     

Chromosomal evolution of the Hawaiian Telmatogeton (Chironomidae,Diptera)

It is only in the Hawaiian Islands that species of the otherwise marine genus Telmatogeton have evolved into freshwater. An analysis of polytene chromosomes and karyotypes of two marine species and five freshwater species revealed that paracentric inversions and centric fusions were important in chromosomal evolution. The sequence of polytene chromosome bands common to most species, established as the Telmatogeton standard sequence, is found in a population of T. torrenticola from West Maui. Most species and other populations of T. torrenticola may be derived from the standard sequence by paracentric inversions. Similarities with the standard band sequence places T. japonicus (n=7) rather than T. pacificus (n=4) in the proposed phylogeny as the species closest to the marine ancestor of the freshwater species. One of three species (T. fluviatilis from Oahu, T. torrenticola from West Maui, or an undescribed species from East Maui), each with seven pairs of chromosomes is considered to be closest to the original freshwater species. T. torrenticola is a complex species in which there is an accumulation of fixed inversions and centric fusions in stepwise fashion in populations from west to east (West Maui n=7; East Maui n=6; Kohala Mountains n=5 and Mauna Kea n=4 both from the island of Hawaii). The population of T. torrenticola from Molokai has a reduced chromosome number (n=4) and fixed inversions. T. abnormis and T. hirtus, the only species which exhibit differentiated sex chromosomes, may be derived from the standard sequency by paracentric inversions. T. abnormis (n=4) has a simple XY system and T. hirtus (n=3/4) has a complex XY₁Y₂ system. Unique sequences of bands, differences in staining intensity of puffs and bands, and an inversion form the basis for the differentiation of the various Y-chromosomes in these species.     

The Drosophila Serido Speciation Puzzle: Putting New Pieces Together

The D. seridosuperspecies is a complex mosaic of populations distributed over a vast part of South America and showing various degrees of genetical divergence. We have analyzed its chromosomal constitution in 16 new localities of southeastern and southern Brazil. Both the metaphase and salivary gland chromosomes show a sharp split of these populations in two groups. Four populations, fixed for inversion 2e ⁸and showing the type I karyotype, represent the southwestern limit of D. seridotype B, which inhabits the Cerrado in central-western Brazil. The remaining populations are homozygous for 2x ⁷, an inversion also fixed in the Caatinga populations of northeastern Brazil. However, their karyotype, in those populations analyzed, belong to a different type (V) from that of the Caatinga populations. Populations in this second group are polymorphic for five inversions on chromosome 2 plus another on chromosome 5 and show considerable interpopulation differentiation. The breakpoints of chromosome 2 inversions are described and the inversion loops of several heterokaryotypes are presented. Biogeographical information suggests that there are clear ecological differences between the two groups of populations as well as among the populations within the second group. The possible role of host plants in promoting the genetic divergence among the D. seridopopulations is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Speciation and chromosomal evolution of the Baikalian endemic chironomids of the genus Sergentia Kief. (Diptera, Chironomidae): Karyotype divergence and chromosomal polymorphism in the populations of deep-water species Sergentia nebulosa Linevitsh et al. and Sergentia assimilis Proviz V. et Proviz L.

Specific karyotype structure and chromosomal polymorphism was investigated in the populations of Sergentia nebulosa Linevitsh et al., 1984 and Sergentia assimilis Proviz V. et Proviz L., 1999, the deep-water endemic chironomid species (Diptera, Chironomidae) from the Baikal Lake. The distinguishing feature of the karyotypes of these species, compared to the other Baikalian Sergentia, is well-developed nucleolus in region 6 of arm C. Both species display the presence of interspecific population polymorphism, determined by the structure of this arm. In some populations, chromosome regions from 4 to 6 contain a homozygous inversion, which is absent in the other populations. The distinguishing karyotype feature of S. assimilis, which shares fluctuating homozygous inversions with the other species, is the presence of two species-specific homozygous inversions. These are the secondary overlapping inversion in arm A, regions 2 to 7, and the inversion in regions 4 to 10 of arm G. Both species of interest contain nucleolus organizer in region 10 of arm G. In populations of S. nebulosa, six heterozygous inversions localized in arms A, B, C, F, and G were discovered. The highest number of heterozygotes for inversions (71%) was observed in the population from Southern Baikal. In arm B of S. assimilis, one heterozygous inversion and heterozygosity for nucleolus organizer in the chromosome region 16 was detected. Chromosomal evolution of Baikalian Sergentia, and the role of inversion polymorphism in the population adaptation is discussed. Original Russian Text ? V.I. Proviz, 2008, published in Genetika, 2008, Vol. 44, No. 12, pp. 1627–1637.     

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 Differentiated Populations of Cruzii: Evidence for a Third Sibling Species

Anopheles cruziiis the most common species of mosquito in Southeast Brazil and a vector of human and monkey malaria. The banding pattern of the ovarian polytene chromosomes and the frequencies of paracentric inversions of individuals from two populations were studied. A new sequence of bands on the sex chromosome, defined as form C, was disclosed. In both populations where forms A (considered as standard) and C are sympatric no heterozygotes were detected. A sequence of events that could account for the observed changes in the banding sequences of the X chromosome forms was proposed. The frequencies of 22 paracentric inversions were used to assess panmixia and the results indicated the presence of two distinct genetic pools in each population. We consider these results as evidence of another sibling species in the taxon cruzii, characterized by a distinctive form of the X chromosome and provisionally designated Anopheles cruziispecies C.     

Breakdown of distyly and pin‐monomorphism in Psychotria carthagenensis Jacq. (Rubiaceae)

Rubiaceae contains the largest number of distylous species in the Angiosperms, but the evolution and control of distyly is poorly understood in this group. Atypical distylous populations and species have been described in this family and associated with disturbance, pollination failure and impaired reproductive success. Some of these atypical taxa belong to Psychotria, the largest genus in the family. In the present study, we investigate the pollination and breeding biology of Psychotria carthagenensis Jacq., a widely distributed species that has been described as typically distylous. Fieldwork was carried out mainly at the Panga Ecological Station, in Uberlândia, MG, Brazil. We carried out phenological observations, floral biology studies and hand pollination experiments within the Panga Ecological Station population. We complemented these data with herbarium and field surveys from elsewhere in Brazil. The studied population bloomed at the beginning of the rains (September–December). The main pollinators were Bombus and small Halictidae bees. The Panga Ecological Station population presented pin‐monomorphism with only two thrum individuals in more than 100 flowering individuals surveyed. Hand pollinations at the Panga Ecological Station showed self‐compatibility and intramorph compatibility. Typical distyly and isoplethy were found in other areas and both morphs appeared in herbarium material. However, pin‐monomorphism was also observed elsewhere in Brazil. Typical distyly, pin‐monomorphism and homostyly observed concurrently in Brazilian populations of P. carthagenensis indicate that alternative reproductive strategies, probably favoring selfing, appear to have developed independently in this species.     

Inversion polymorphism in malarial mosquito <Emphasis Type="Italic">Anopheles messeae</Emphasis> natural populations from the north-eastern region of the range

A cytogenetic study of eight natural populations of Anopheles messeae from the north-eastern part of the species areal was conducted. Complete predominance of homozygotes XL₁₁ and 3R₁₁ in the northern populations was observed. Change in the chromosome 2 inversion frequencies from south northwards was shown. The 2R₁₁ variant, which was not observed in the southern region, was found in the northern populations. These results indicate the maintenance of chromosome frequency of the distribution of inversions XL₁ and 3R₁ (in longitude) and 2R₁ (in latitude). The inversion frequency distribution in the examined part of the areal have been preserved for a long time.     

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.     

Population genetics and gene variation in screwworms (Diptera: Calliphoridae) from Brazil

Allozyme variation in New World screwworm,Cochliomyia hominivorax (Coquerel), populations from Brazil was examined. Variability was observed in 8 of 13 enzyme loci and the frequency of the most common allele was <0.95 for seven loci. Observed and expected heterozygosities were 0.159 and 0.165, respectively. Comparisons of the Brazilian populations with previously studied populations from Costa Rica resulted in Nei's genetic distances of between 0.000 and 0.006, with the greatest distance being between populations within Brazil. Comparisons with Mexican populations using only three loci resulted in genetic distances ≤0.031. Goodness-of-fit statistics for Hardy-Weinberg equilibrium and Wright'sF statistics indicated small deviations from expected equilibrium genotype frequencies and low levels of differentiation between populations within Brazil. Differentiation among screwworm populations from Brazil, Costa Rica, and Mexico was minimal.     

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.     

Allozyme variability in an invasive drosophilid,Zaprionus indianus (Diptera: Drosophilidae): comparison of a recently introduced Brazilian population with Old World populations

Colonizing species often go through genetic bottlenecks when new territories are invaded. The South American continent has been recently colonized by a generalist African drosophilid, Zaprionus indianus, which has become an agricultural pest in Brazil in the last five years. In this paper we used allozyme electrophoresis to estimate levels of genetic differentiation of Z. indianus collected from sites 4 300 km apart in Brazil. We also compared the level of polymorphism of the Brazilian populations with that found in laboratory strains from Africa and Asia, to verify if a significant decrease in gene variability has taken place during the invasion process. The populations were polymorphic for three out of the 11 loci investigated. Genetic distances and F_ST indices among Brazilian populations were small and generally non significant, suggesting a colonization from one single propagule followed by a rapid demographic expansion. Ancestral and old populations from Africa and Asia were slightly more heterozygous than those from Brazil. Compared to other drosophilids, Z. indianus appears to be characterized by a low proportion (25%) of polymorphic loci. We suggest that the propagule introduced to Brazil had a sufficient size to carry almost all the polymorphism from the (unknown) origin population, although not the precise allelic frequencies.     

Chromosome Inversion Polymorphisms Influence Morphological Traits in <Emphasis Type="Italic">Trimerotropis Pallidipennis</Emphasis> (Orthoptera)

Trimerotropis pallidipennis is a New World grasshopper whose South-American populations are polymorphic for six pericentric inversions. Previous work has demonstrated that the frequences of these inversions correlate with climatic variables, and hence a possible adaptive pattern was put forward. In the present work we analysed a sample of a natural population of T. pallidipennis to ascertain whether the chromosomal inversions have effects on exophenotypes. Two hundred and sixty-eight males coming from a natural population at Uspallata, Mendoza Province, Argentina were analysed, and it was observed that most inversions had significant effects on phenotypes. Furthermore, some body size-related characteristics (such as tegmina length) were correlated with the number of inversions. Individuals from populations at higher altitude or latitude (i.e., at lower minimum temperatures), along with higher frequencies of standard sequences, were significantly smaller, and this coherence between interpopulational with intrapopulational results may indicate that the diminished body size of the standard sequence-carrying individuals may be caused by an effect of the inversions, or genes within the inversions, on body size. We finally put forward the hypothesis that reduced body size in a context of reduced minimum temperature may be a response to shortened development season, and so smaller individuals may be advantageous.     

Frequency distribution of XbaIG > T and HaeIIIT > C <Emphasis Type="Italic">GLUT1</Emphasis> polymorphisms among different Brazilian ethnic groups

GLUT is the major glucose transporter in mammalian cells. Single nucleotide polymorphisms (SNP) at GLUT1 promoter and regulatory regions have been associated to the risk of developing nephropathy in different type 1 and type 2 diabetic populations. It has been demonstrated that differences in allelic and genotypic frequencies of GLUT1 gene (SLC2A1) polymorphisms occur among different populations. Therefore, ethnic differences in distribution of GLUT1 gene polymorphisms may be an important factor in determining gene-disease association. In this study, we investigated the XbaIG > T and HaeIIIT > C polymorphisms in six different Brazilian populations: 102 individuals from Salvador population (Northern Brazil), 56 European descendants from Joinville (South Brazil), 85 Indians from Tiryió tribe (North Brazil) and 127 samples from Southern Brazil: 44 from European descendants, 42 from African descendants and 41 from Japanese descendants. Genotype frequencies from both sites did not differ significantly from those expected under the Hardy–Weinberg equilibrium. We verified that the allele frequencies of both polymorphisms were heterogeneous in these six Brazilian ethnic groups.     

Chromosomal variation in natural populations of Drosophila guaramunu

Summary Brazilian populations of D. guaramunu (Dobzhansky and Pavan, 1943) exhibit a high degree of chromosomal polymorphism. At least 19 inversions are known.These inversions have been found in the four long autosomes, while the X chromosome and the dot-shaped chromosomes do not show any variation in the gene sequences. Among the autosomes, the fourth chromosome seems to be the most variable one, 13 out of 19 inversions here reported being localized in it.With the aid of crosses to a homozygous Standard strain, it has been possible to establish schematically the phylogenetic relationships between the different gene arrangements.With 7 figures in the text and 1 plate.Research Fellow of the University of São Paulo, Brazil, in 1951.     

Cytogenetics of the Anopheles gambiae complex in Sudan, with special reference to An. arabiensis: relationships with East and West African populations

The species composition of malaria vector mosquitoes belonging to the Anopheles gambiae complex (Diptera: Culicidae) from >40 localities in Sudan, representing most ecological situations, was determined by analysis of ovarian polytene chromosomes. Of 2162 females, 93% were identified as An. arabiensis Patton and 7% were An. gambiae Giles sensu stricto. No hybrids were found between the two species. Anopheles arabiensis occurred in all but two sites, whereas An. gambiae s.s. was effectively limited to the southernmost, more humid localities. For chromosomal paracentric inversions, the degree of polymorphism was low in An. gambiae s.s. (inversions 2La, 2Rb and 2Rd), higher in An. arabiensis (inversions Xe, 2Ra, b, bc, d1, s; 3Ra, d). Anopheles gambiae samples from Sudan were all apparently panmictic, i.e. they did not show restricted gene flow such as observed among West African populations (interpreted as incipient speciation). Chromosomal inversion patterns of An. gambiae in southern Sudan showed characteristics of intergrading Savanna/Forest populations similar to those observed in comparable eco-climatic situations of West Africa. Anopheles arabiensis was polymorphic for inversion systems recorded in West Africa (2Ra, 2Rb, 2Rdl, 3Ra) and for a novel 2Rs polymorphism, overlapping with inversion systems 2Rb and 2Rd1. Samples carrying the 2Rs inversion were mostly from Khashm-el-Girba area in central-eastern Sudan. In the great majority of the samples all polymorphic inversions were found to be in Hardy-Weinberg equilibrium. Sudan populations of An. arabiensis should therefore be considered as generally panmictic. Anopheles arabiensis shows more inversion polymorphism in west than in east African populations. Sudan populations have more evident similarities with those from westwards than those from eastwards of the Great Rift Valley. The possible influence of the Rift on evolution of An. arabiensis is discussed.