A comparative analysis of the mole vole sibling species Ellobius tancrei and E. talpinus (Cricetidae, Rodentia) through chromosome painting and examination of synaptonemal complex structures in hybrids

A comparative genomic analysis was carried out in the mole vole sibling species Ellobius tancrei and E. talpinus. Performing fluorescent in situ hybridisation (Zoo-FISH) using chromosome paints from the field vole Microtus agrestis showed no differences in the allocation of syntenic groups in the karyotypes of these sibling species. The only difference between their karyotypes was the position of the centromere in one pair of chromosomes, which is assumed to be the result of an inversion. To verify this hypothesis, we analysed chromosome synapsis in prophase I of meiosis. We utilised a synaptonemal complex (SC) surface-spreading technique to visualise the process of chromosome synapsis in the spermatocytes and oocytes of first-generation hybrids and back-crosses of these sibling species. In prophase I of meiosis, immunocytochemical and electron microscopy analyses revealed that all bivalents had been fully adjusted. Even in the case of a submetacentric-acrocentric bivalent with different centromere locations, synapsis of SC lateral elements was fulfilled along the entire length of the chromosomes and the formation of an inversion loop was not observed. We hypothesise that a possible mechanism leading to the change in centromere position is the repositioning and/or generation of a neocentromere. Despite the great similarity in the karyotypes of these sibling species, they exhibited significant genomic diversification, which manifested as hybrid sterility and parous female death.     

云南省库态按蚊复合体的亲缘种型研究(双翅目,蚊科)(英文)

库态按蚊是1个由5种亲缘种型组成的按蚊复合体,这些种型分别被命名为A、B、C、D 和 E 型。在使用PCR 检测还没有条件的地区,鉴定库态按蚊亲缘种型的一个重要方法是作染色体组型分析。使用库态按蚊幼虫作染色体涂片,对云南地区的库态按蚊种型作了初步研究,并首次报道了该地区存在的亲缘种型成员,认为在云南省库态按蚊 A型和 B 型在同一个地区并存。同时,还展示了库态按蚊复合体的染色体组型、核型模式图及种型在中国毗邻国家的分布地图。     

Salivary polytene chromosome mapping of Anopheles (Cellia) subpictus Grassi (Culicidae: Diptera).

With the introduction of molecular taxonomy of mosquitoes, polytene chromosome maps have become indispensable as standard references for locating genes, puffs, and inversion breakpoints of unique DNA sequences. We present a line map and a photomap of the salivary polytene chromosomes of Anopheles (Cellia) subpictus Grassi, an important emerging vector of malaria in India. In addition, we discuss the nature of this species complex consisting of sibling species A, B, C, and D. The comparative study is in relevance to the X chromosome heterozygous inversion differences between 2 allopatric populations of the species and the recognition of 4 X-chromosome inversion genotypes viz: species A-X(+a+b), B-X(ab), C-X(a+b) and D-X(+ab).     

Divergence of karyofunds in sibling species of the plumosus group (Diptera: Chironomidae)

Cytogenetic differentiation of eight sibling species of the plumosus group was examined. The karyofunds of these sibling species were shown to diverge incompletely. In each species karyofund, the banding sequences homologous to those of the remaining species of this group were revealed. The number of banding sequences that displayed interspecific homology varied from 3 to 13 per species karyofund. In a species karyotype, the homologous sequences were localized to chromosome arms 1-6. Both similar and contrasting frequencies of homologous banding sequences were observed in karyofunds of different sibling species. The average cytogenetic distance between sibling species of the plumosus group was 2.618 +/- 0.400. The presence of species-specific banding sequences, the absence of homologous banding sequences in some chromosome arms of the karyotype, and different frequencies of the homologous banding sequences determined the cytogenetic divergence of the sibling species.     

Additional notes on Anisopteromalus sp. (Hymenoptera: Pteromalidae), the sibling species of a parasitic wasp of stored‐product pests,Anisopteromalus calandrae (Howard): A new alternative host,an eye color mutant and DNA barcodes

A parasitic wasp of stored‐product pests, Anisopteromalus calandrae (Howard), is known to have a sibling species with a different chromosome number. Here, we report establishment and characterization of an eye color mutant in this sibling species. The phenotype of the mutant is red eye in adults, and crossing experiments revealed that the mutant phenotype is recessive to wild type (brown eye color). We also report DNA barcode sequences (a partial sequence of mitochondrial cytochrome‐c oxidase subunit I) of A. calandrae and the sibling species to enable accurate identification of these morphologically similar species. Analyses of our laboratory strains showed that 12.6% of the analyzed sequences (82 of 652 bp) differed between the two species. Finally, we note that the seed beetle Callosobruchus chinensis (Linné) (family Bruchidae), host of our laboratory strains of the sibling species, is a new record of alternative host at the family‐level for the wasp (known hosts: Anobiidae (natural host) and Curculionidae (alternative host)).     

A Genetic Basis for the Inviability of Hybrids between Sibling Species of Drosophila

A mutation of Drosophila melanogaster whose only known effect is the rescue of otherwise lethal interspecific hybrids has been characterized. This mutation, Hmr, maps to 1-31.84 (9D1-9E4). Hmr may be the consequence of a P element insertion. It rescues hybrid males from the cross of D. melanogaster females to males of its three sibling species, D. simulans, D. mauritiana and D. sechellia. This rescue is recessive, since hybrid males that carry both Hmr and a duplication expected to be Hmr+ are not rescued. Hmr also rescues the otherwise inviable female hybrids from the cross of compound-X D. melanogaster females to males of its sibling species. This rescue is also recessive, since a compound-X heterozygous for Hmr does not rescue. Another mutation, discovered on the In(1)AB chromosome of D. melanogaster, is also found to rescue normally inviable species hybrids: unlike Hmr, however, In(1)AB rescues hybrid females from the cross of In(1)AB/Y males to sibling females, as well as hybrid males from the cross of In(1)AB females to sibling males. These data are interpreted on the basis of a model for the genetic basis of hybrid inviability of complementary genes.     

Lactate dehydrogenase allozyme differentiation of species in the Anopheles culicifacies complex

Abstract Genetically controlled enzyme variation exists within and between four sibling species of the Anopheles culicifacies complex of malaria vectors in India. A study on electrophoretic variation of nine enzymes in An.culicifacies sibling species revealed that the lactate dehydrogenase ( Ldh ) locus has Fast (F) and Slow (S) allozymes distinguishing species A+D from species B+C with a probability of c . 95%.     

Sex-linked differentiation between incipient species of Anopheles gambiae

Emerging species within the primary malaria vector Anopheles gambiae show different ecological preferences and significant prezygotic reproductive isolation. They are defined by fixed sequence differences in X-linked rDNA, but most previous studies have failed to detect large and significant differentiation between these taxa elsewhere in the genome, except at two other loci on the X chromosome near the rDNA locus. Hypothesizing that this pericentromeric region of the X chromosome may be accumulating differences faster than other regions of the genome, we explored the pattern and extent of differentiation between A. gambiae incipient species and a sibling species, A. arabiensis, from Burkina Faso, West Africa, at 17 microsatellite loci spanning the X chromosome. Interspecific differentiation was large and significant across the entire X chromosome. Among A. gambiae incipient species, we found some of the highest levels of differentiation recorded in a large region including eight independent loci near the centromere of the X chromosome. Outside of this region, no significant differentiation was detected. This pattern suggests that selection is playing a role in the emergence of A. gambiae incipient species. This process, associated with efficient exploitation of anthropogenic modifications to the environment, has public health implications as it fosters the spread of malaria transmission both spatially and temporally.     

Anopheles culicifacies Y-chromosome dimorphism indicates sibling species (B and E) with different malaria vector potential in Sri Lanka

In Sri Lanka, malaria is transmitted mainly by Anopheles culicifacies Giles sensu lato (Diptera: Culicidae). In India, this nominal taxon comprises sibling species A, B, C, D and E, distinguished by their chromosome morphology. Species B (identified by polytene chromosome sequence Xab, 2g1 + h1) is not such an efficient vector of malaria as other members of the An. culicifacies complex in India. All specimens of An. culicifacies s.l. examined from Sri Lanka possess Xab, 2g1 + h1 polytenes, previously interpreted as species B, despite their important vector status. Recently, species E was described from Rameshwaram Island (Tamil Nadu, India) between Sri Lanka and the Indian mainland, where both species B and E are sympatric. Species B and E share polytene sequence Xab, 2g1 + h1 but differ by the mitotic Y-chromosome being acrocentric in species B, submetacentric in species E, the latter implicated as vector of vivax malaria. From May 1999 to January 2000, we surveyed Y-chromosomes of male progeny from An. culicifacies Xab, 2g1 + h1 females collected from cattle bait in diverse malarious districts of Sri Lanka: Badulla, Monaragala, Puttalam and Trincomalee. Karyotypes of readable quality were obtained from 42/83 families examined, with overall proportions 24% acrocentric and 76% submetacentric Y-chromosome carriers, both types being sympatric in at least 3/4 localities sampled. By analogy with the situation on Rameshwaram Island, we interpret these observations to demonstrate widespread presence of two members of the An. culicifacies complex in Sri Lanka, their karyotypes being compatible with species B and E, the latter predominant and having greater vector potential.     

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.     

Identification and comparisons of the yolk polypeptides and the genes which code for them in D. melanogaster sibling species

Summary The yolk proteins stored in Drosophila, oocytes for utilisation during embryogenesis are an ideal system for studying the regulation of gene expression during development. The 3 major polypeptides found in yolk in D. melanogaster are synthesised in the fat body and ovarian follicle cells and selectively accumulated by the oocyte during vitellogenesis. In order to understand more about their regulation and the mechanism of uptake, studies on other species are necessary.Three yolk polypeptides have previously been identified in the D. melanogaster sibling species (D. melanogaster, D. simulans, D. mauritiana, D. erecta, D. teissieri, D. orena and D. yakuba). In D. melanogaster three genes located on the X chromosome are known to code for these yolk polypeptides. in this study genomic Southern transfers and in situ hybridisation experiments were carried out on the sibling species. Using the three cloned yolk protein genes from D. melanogaster, homologous sequences could be detected in the sibling species. It is suggested that three yolk protein genes occur in each of these species, all being located on the X chromosome, and that two of the genes are very closely linked in these same species. Yolk protein gene-homologous DNA sequences have also been identified in two more distantly related species D. funebris and D. virilis.     

Localization of the Dras1 sequence to polytene chromosomes in sibling species of the Drosophila virilis group

Drasl gene was mapped by in situ hybridization to polytene chromosomes of several sibling species of the Drosophila virilis group and hybrids between them. A 1037 bp fragment of the Drasl gene of the D. virilis genome was used as a probe. The gene sequence is localized to the region of the disk 25 A-B on the chromosome 2 of the polytene chromosome map of D. virilis.     

Cytotaxonomy of the Simulium damnosum complex from central and northeastern Tanzania.

A cytotaxonomic study of the medically important insect vector, Simulium damnosum s.l., revealed the presence of seven and possibly eight distinct taxa from central and northeastern Tanzania. Larval salivary gland polytene chromosome maps are presented for the first time for five cytotypes and one sibling species, which include the Nkusi form, the Sanje form, the Kisiwani form, Ketaketa C1 and C2, and the Kibwezi form. Inversion disequilibrium in males of the Kibwezi form indicate population substructuring is occurring and that this population may be in the early stages of speciation. Adults of the sibling species S. damnosum Kibwezi form and cytotype of the S. damnosum Nkusi form were identified using Malpighian tubule polytene chromosomes. The taxonomic status of the populations under study are discussed in relation to previously published papers and unpublished reports. Dimorphisms for centromere band enhancement occur on all three polytene chromosomes of the complement. The same centromere band can be polymorphic, sex linked, fixed, or lost in various cytotypes. In constructing a partial phylogeny, a hypothetical intermediate is proposed to account for the diverse fate of these centromere band dimorphisms and other inversion polymorphisms in different members of this nearly pan African complex. This pattern of chromosome restructuring is consistent with that seen for other species complexes within the Simuliidae.     

Intraspecific polymorphism of sex chromosome heterochromatin in two species of the Anopheles gambiae complex

The Hoechst 33258 banding pattern of the mitotic chromosomes of several laboratory and natural populations of the sibling species A. gambiae and A. arabiensis has been analyzed. A clear intraspecific polymorphism of sex chromosome heterochromatin has been observed. Nevertheless in each species heterochromatic variations fall within a characteristic species-specific pattern. Moreover, while laboratory populations tend to be monomorphic for a given heterochromatic variant, natural populations exhibit a high degree of intrapopulation polymorphism. The possible role of sex chromosome heterochromatin in controlling fertility and mating behaviour of Anopheles mosquitoes is discussed.     

Electrophoretic Characterization of Members of the Crypthecodinium cohnii (Dinophyceae) Species Complex1

Eighty-seven axenic clones of the colorless inshore dinoflagellate Crypthecodinium cohnii were found by mating experiments to fall into 52 sibling species, seven wide ranging (two possibly global)—called major sibling species—and 45 found only once—minor sibling species. Electrophoretic analysis of three soluble enzymes from these strains revealed the following: 1) Despite some polymorphism most members of major sibling species closely resemble one another electrophoretically. 2) Major sibling species and most minor ones are electrophoretically distinct. 3) Sharing of electromorphs is sufficiently extensive, however, that no major sibling species is totally unrelated to all others. 4) Some minor sibling species are electrophoretically indistinguishable from a member of a major sibling species or from one another, suggesting recent origin by sexual isolation in situ. 5) Other minor sibling species differ from majors by one, two, or all three of the enzymes studied. A “model” of sexual isolation and diversification is offered.     

The polytene chromosomes of Drosophila triauraria and D. quadraria, sibling species of D. auraria.

The polytene chromosomes of Drosophila triauraria and D. quadraria, two of the sibling species of D. auraria, were examined. The polytene chromosomes of all three species exhibit very clear homology. Unlike the stock of D. auraria that we studied, D. triauraria and D. quadraria carry heterozygous paracentric inversions. In both species, 2R and 3R are the arms where these inversions are concentrated. In addition, in D. quadraria, the 3L chromosome arm is very complicated because of heterozygous inversions. The mode of inheritance of these rearrangements was studied. A homozygous strain for all chromosome arms of D. triauraria was isolated, while a homozygous strain was obtained only for the arms X, 2L, 3L, and 4 of D. quadraria. Like D. auraria, both species show a large number of inverted tandem duplications in the paired condition, even in the chromosomes of their hybrids. Small deletions were also detected, one of which, in D. triauraria, is homozygous terminal. Hypotheses are discussed concerning the relationships of the species and the existence of inverted tandem duplications.     

A cytogenetic analysis of the Simulium ochraceum species complex (Diptera: Simuliidae) in Central America.

A cytobiotaxonomic study of the medically important insect vector Simulium ochraceum s.l. revealed two sibling species and one cytotype from various endemic and nonendemic zones of human onchocerciasis in Guatemala and Mexico. Polytene chromosome maps and idiograms as well as notes on the biology of the three taxa designated S. ochraceum A, S. ochraceum B, and S. ochraceum C within the subgenus Psilopelmia are presented. All three taxa exhibit distinct sex chromosomes and taxon-specific suites of autosomal inversion polymorphisms. Simulium ochraceum C differs from both S. ochraceum A and S. ochraceum B by five interspecific inversions designated IIS-7,8 and IIIL-12, 13 + 14, 15. The three taxa exhibit niche and biting preferences, with S. ochraceum A being highly anthropophilic. Analysis of autosomal inversion polymorphism profiles indicates S. ochraceum A has long-range dispersal capability. Our results are consistent with the general findings that in the Simuliidae, sibling speciation may be suspected wherever a morphospecies occupies different niches in a stream continuum. We find for the first time an apparent partitioning of taxa by altitude. Simulium ochraceum A may be a primary vector of human onchocerciasis in Guatemala, as its vertical distribution is coincident with that of the highest areas of nodule prevalence in the human population. A genotypic component of variation in vectorial capacity of S. ochraceum A populations seems to occur, since the Y4 chromosome and its X chromosome counterpart are associated with hyperendemic areas of human onchocerciasis. Our observation that a supernumerary band, 37B1Hb, is associated with sex determination in two of the taxa may be of significance for the elucidation of the molecular basis of sex determination and possible resolution of issues pertinent to the general model of sympatric speciation in the Simuliidae.     

The speciation continuum: ecological and chromosomal divergence in the Simulium arcticum complex (Diptera: Simuliidae)

Chromosome inversions may be involved in adaptation and speciation. We investigate ecological diversification among members of the Simulium arcticum species complex at different stages of chromosome divergence. Our analyses focus on two geographical scales. First, we assess ecological divergence of sibling species throughout North America using niche modelling methods. Then, using canonical correspondence analysis, we investigate habitat associations of sibling species and cytotypes in the northern Rocky Mountains ecoregion, where cytotypes tend to occur. Despite significant overlap in predicted distributions, all sibling species are ecologically unique. On the other hand, we discover various degrees of ecological divergence for cytotypes. Some cytotypes are ecologically distinct and perhaps are in their initial stages of incipient speciation. Other cytotypes are ecologically associated with one another or with particular sibling species. Thus, for members of the S. arcticum complex, ecological and chromosomal differences tend to develop early in lineage formation. Ecological distinctiveness of sibling species and cytotypes suggests that local adaptation may be involved in diversification of these chromosomal forms. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 13–27.     

Genetics of speciation in the Aedes (Stegomyia) scutellaris subgroup (Diptera:Culicidae). 4. Chromosomal relationships of Aedes cooki with four sibling species

Morphology and behavior of chromosomes and development of testes and sperm were examined in hybrids from interspecific crosses involving Aedes cooki and four sibling species of the Aedes (Stegomyia) scutellaris subgroup of mosquitoes. The degree of abnormality in hybrid spermatogenesis in interspecific crosses involving Aedes cooki males and females of four sibling species paralleled the geographic distributions of these species and the genetic divergence indicated by other genetic studies. Hybrids from crosses involving Aedes malayensis females and Aedes cooki males were characterized by atrophied testes and extensive chromosome breakage. Hybrids from crosses involving Aedes alcasidi females and Aedes cooki males suggested a possible pericentric inversion distinguishing the largest autosome of Aedes alcasidi from that of Aedes cooki. Hybrids from interspecific crosses involving females of Aedes polynesiensis and Aedes pseudoscutellaris and males of Aedes cooki showed high percentages of univalents of the smallest chromosome pair. Hybrid spermatogenesis in two interspecific crosses involving Aedes cooki females differed from results of reciprocal crosses. Data were scant, however, and interpretation was difficult in view of negligible hatch in all interspecific crosses involving Aedes cooki females.     

Isolation and characterization of microsatellite markers from malaria vector,Anopheles culicifacies

Anopheles culicifacies, an important vector in the Indian subcontinent is a complex of five sibling species of which four are vectors. We describe the isolation of 31 microsatellite markers from the recently recognized isomorphic species A of which 13 were characterized in sympatric populations of Anopheles culicifacies isomorphic species A and B. The allele frequencies ranges from two to 12 in species A and two to seven in species B. Species A being a vector, and that these markers can be used in closely related species, makes the isolation of these markers important to study population structure of all sibling species in this complex.