A comparison of five hybrid zones of the weta Hemideina thoracica (Orthoptera: Anostostomatidae): degree of cytogenetic differentiation fails to predict zone width

Abstract Tension zones are maintained by the interaction between selection against hybrids and dispersal of individuals. Investigating multiple hybrid zones within a single species provides the opportunity to examine differences in zone structure on a background of differences in extrinsic factors (e.g., age of the zone, ecology) or intrinsic factors (e.g., chromosomes). The New Zealand tree weta Hemideina thoracica comprises at least eight distinct chromosomal races with diploid numbers ranging from 2n = 11 (XO) to 2n = 23 (XO). Five independent hybrid zones were located that involve races differing from one another by a variety of chromosomal rearrangements. The predicted negative correlation between extent of karyotypic differentiation (measured in terms of both percent of genome and number of rearrangements) and zone width was not found. Conversely, the widest zones were those characterized by two chromosome rearrangements involving up to 35% of the genome. The narrowest zone occurred where the two races differ by a single chromosome rearrangement involving approximately 2% of the genome. The five estimates of chromosomal cline width ranged from 0.5 km to 47 km. A comparative investigation of cline width for both chromosomal and mitochondrial markers revealed a complex pattern of zone characteristics. Three of the five zones in this study showed cline concordance for the nuclear and cytoplasmic markers, and at two of the zones the clines were also coincident. Zones with the widest chromosomal clines had the widest mitochondrial DNA clines. It appears that, even within a single species, the extent of karyotypic differentiation between pairs of races is not a good predictor of the level of disadvantage suffered by hybrids.     

Genetic variation,population structure and cryptic species within the black mudfish,Neochanna diversus,an endemic galaxiid from New Zealand

To investigate the phylogenetic relationships and geographical structure among landlocked populations of the black mudfish, Neochanna diversus, mitochondrial DNA nucleotide sequence data were sampled from seven populations from the Waikato and Northland regions of New Zealand. The complete D-loop region was sequenced from 70 individuals, with 913 bp from the tRNA-pro end used in population and phylogenetic analysis. A tandem repeat array, which ranged in size up to 200 bp, was found in most populations at the 3′ end of the D-loop that was not able to be aligned for analysis. Of the seven sites sampled, two from Northland exhibited significant sequence divergence from all other sites. There was also a clear distinction among remaining Northland sites and those from the Waikato. An additional 518 bp segment of the 16S region was sequenced from all sites and compared with the other New Zealand mudfish species, N. apoda, N. burrowsius and the Tasmanian mudfish Galaxias (Neochanna) cleaveri using Galaxias maculatus as an outgroup. Both D-loop and 16S sequence data provided strong evidence for a cryptic species of mudfish present in Northland. The significant genetic structure apparent in the black mudfish appears most probably to be attributed to geological conditions during the Pliocene, where peat wetlands became apparent in the Waikato while Northland consisted of disjunct ‘islands’. Conservation and management of these populations must take into account the historical processes that have shaped these patterns of genetic diversity.     

Low population differentiation and high genetic diversity in the invasive species Carduus acanthoides L. (Asteraceae) within its native range in the Czech Republic

Colonizing species are predicted to suffer from reductions in genetic diversity during founding events. Although there is no unique mode of reproduction that is characteristic of successful plant colonizers, many of them are predominantly self-fertilizing or apomictic species, and almost all outcrossing colonizers are self-compatible. Carduus acanthoides comprises a species of disturbed habitats with wind-dispersed seeds that colonizes open spaces of various sizes. Population genetic diversity was expressed by assessing patterns of variation at nine putatively neutral allozyme loci within and among 20 natural populations in its native distribution range in the Czech Republic. Overall, C. acanthoides displayed high levels of genetic diversity compared to other herbaceous plants. The percentage of polymorphic loci was 84.5, with values of 2.37, 0.330, and 0.364 for the mean number of alleles per polymorphic locus ( A ), observed heterozygosity ( H _o), and expected heterozygosity ( H _e), respectively. There was only weak evidence of inbreeding within populations ( f  = 0.097) and very low genetic differentiation among populations ( θ  = 0.085). Analyses of the data provide strong evidence for isolation-by-distance for the whole study area. Even the colonizing species, C. acanthoides , currently supports a substantial amount of allozyme variation at both the species and population levels.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 596–607.     

松属植物遗传多样性研究进展

研究松属遗传多样性的方法涉及表型、同工酶、染色体、DNA等多层面。 松树表型性状变异广泛,其不同树种不同性状的遗传力（或遗传率）均存在差异。到目前为止,同工酶仍是检测松树遗传多样性的最常用方法,一般而言,松属树种群体内等位酶多样性程度高,群体间分化较低,但各树种的情形也不尽相同。松属树种染色体水平的变异很低,其核型高度一致。核DNA组较一般阔叶树大,遗传多样性丰富,但叶绿体等质体DNA则多样性较低。影响遗传多样性的因素很多,其中自身的交配系统和外部的生长环境是影响它的两个主要因素。最后,回顾了松树的起源及其遗传多样性保护策略等方面的研究。 Abstract:The ways of probing genetic diversity of pines involve many aspects,such as morphology,chromosome,isozyme,DNA,etc.The phenotypic characteristics in pines vary widely and the differences of inheritability(h2) are obvious among characteristics and among species.Up to now,isozyme is still the most common means to measure genetic diversity of pines.Generally,there are high allozyme diversity within populations and low differentiation coefficient among populations,but differences exist between species in Pinus.The variations of chromosome among pines are very low and the karyotypes of pines are consentaneous,but the genomes of pines in cell nucleus are much larger than that of broadleaves.Diversity of pines are abundant at nucleus DNA level but are poor at plastid DNA level,such as ctDNA.There are many factors that will affect genetic diversity of pines,in which mating system and environment are two main factors.Finally,we reviewed the research on origin of Pinus and conservation strategy of genetic diversity,etc.     

Microsatellite variation and population structure in a declining Australian Hylid Litoria aurea

The green and golden bell frog (Litoria aurea) was once a common Australian Hylid. Today, many populations are small and fragmented as a result of dramatic declines in distribution and abundance. We undertook a large-scale assessment of genetic structure and diversity in L. aurea using four species-specific microsatellite markers. Twenty-one locations were sampled from throughout the species range covering 1000 km of the east coast of Australia. Levels of allelic diversity and heterozygosity were high (uncorrected mean alleles/locus and H(E) were 4.8-8.8 and 0.43-0.8, respectively) compared to other amphibian species and significant differences among sampled sites were recorded. Despite recent population declines, no sites displayed a genetic signature indicative of a population bottleneck. Significant genetic structuring (overall F(ST) 0.172) was detected throughout the species range, but was relatively low compared to previous amphibian studies employing microsatellites. In addition we found that some areas sampled within continuous habitat showed evidence of weak genetic structuring (data subset F(ST) 0.034). We conclude that maintaining areas of continuous habitat is critical to the conservation of the species and argue that population recovery and/or persistence in all areas sampled is possible if appropriate protection and management are afforded.     

Allozyme variation within and divergence between Lemna gibba and L. disperma: Systematic and biogeographic implications

Enzyme electrophoresis was employed to assess genetic diversity within and divergence between Lemna disperma and Lemna gibba, sister species that have often been considered conspecific because of the few technical morphological characters distinguishing them. L. gibba is distributed widely except in Australia and New Zealand, where it is replaced by L. disperma. Allozyme data were employed to examine: (1) whether species recognition is supported by genetic divergence between accessions assigned to the two taxa, (2) whether the level of diversity in the two species supports the hypothesis that L. gibba–L. disperma are related as a progenitor–derivative species pair, and (3) whether estimates of divergence times obtained from allozymes are in general agreement with those from plastid sequences. Accessions of the two species are highly divergent at allozyme loci, with a genetic identity of 0.404, and the putative derivative species (L. disperma) has only one-third the diversity of its proposed ancestor, L. gibba. Therefore, allozyme data support the continued recognition of the two species and are concordant with the hypothesis that the species are related as progenitor and derivative. The reduced morphology of L. disperma and the allozyme data indicate that this species originated via dispersal of L. gibba or of a common ancestor of the two species. Estimated divergence times from allozymes and plastid sequences vary widely, but assuming that actual divergence was within the broad range of estimates, long distance dispersal is required to explain the present distribution of the two species.     

Allozyme variation in endangered Castanea pumila var. pumila

Allozyme genetic variation in 12 populations of the endangered Castanea pumila var. pumila (Allegheny chinkapin), sampled across the natural range of the species in the United States, was evaluated using 11 loci from seven enzyme systems. At the species level, the percentage of polymorphic loci (Ps) was 72.7 %, the mean number of alleles per locus (As) was 1.9, the mean number of alleles per polymorphic locus (APs) was 2.3, the effective number of alleles per locus (Aes) was 1.5 and the genetic diversity (Hes) was 0.296. At the population level, Pp = 49.2 %, Ap = 1.5, Aep = 1.4, APp = 2.1 and Hep = 0.21. Most of the allozyme variation (70 %) in C. pumila var. pumila occurred within populations. Wright's gene flow rate [Nm(W)] was as low as 0.57. Population differentiation along the species range was not detected. Populations of C. pumila var. pumila in Florida had the most variable levels of genetic diversity, but populations in Virginia and Mississippi also showed high levels. Based on the results of this study, conservation management strategies are discussed.     

Systematic and conservation implications of geographic variation in pipits (Anthus: Motacillidae) in New Zealand and some offshore islands

The New Zealand Pipit Anthus novaeseelandiae occurs as a single species in Europe (as Richard's Pipit), Asia, Africa, New Guinea, Australia and New Zealand. In the New Zealand region, subspecific status has been accorded to allopatric populations on the mainland (A. n. novaeseelandiae) , on the Auckland and Campbell Islands (A. n. aucklandicus) , on the Antipodes Islands (A. n. steindachneri) and on the Chatham Islands (A. n. chathamensis) . Analyses of 23 allozyme loci and morphometric variation of populations on mainland New Zealand and on the Auckland, Campbell, Antipodes and Chatham Islands showed an appreciable and significant divergence between mainland and island populations. The magnitude of the allozyme difference is sufficient to suggest full species designation for the island birds, a conclusion supported by morphometric analyses and in sharp contrast to current taxonomy. However, formal taxonomic change will not be undertaken until the two New Zealand groups have been compared with more distant populations of this wideranging genus. The cryptic variation found in this species has conservation management implications for the small offshore populations.     

High levels of allozyme variation within populations and low allozyme divergence within and among species of Hemerocallis (Liliaceae)

Thirty populations from five species of Hemerocallis in Korea were analyzed by starch gel electrophoresis to measure genetic diversity and to determine genetic population structure and the amount of genetic divergence within and between species at 12 isozyme loci. In addition, Moran's I spatial autocorrelation statistics were used to examine the spatial distribution of allozyme polymorphisms in populations of H. thunbergii and H. hakuunensis. Populations of five Korean species maintain high levels of genetic variation and little differentiation among populations and species. Mean expected heterozygosities range from 0.165 in H. hongdoensis, an island endemic, to 0.265 in H. taeanensis, and a total of 81 alleles across the 12 loci were detected in the five species. G(ST) values for each of the five species were low, ranging from 0.051 in H. taeanensis to 0.078 in H. hakuunensis. Mean intraspecific Nei's genetic identities (I) between populations of the five species were all above 0.97. However, a considerable level of heterozygote deficiencies within populations was detected, ranging from 0.242 to 0.411 measured as F(IS) statistics. This deficiencies may be due to inbreeding, limited pollen and seed dispersal, or from the pooling of subpopulations that differ in allele frequencies. A small spatial scale population substructuring (<12 m) was found in H. thunbergii and H. hakuunensis. A group of populations from each of the five previously designated Hemerocallis species (based on their morphology, ecology, and phenology) agrees with our allozyme data, though pairwise comparisons among species had high I values (from 0.862, H. middendorffii vs. H. hongdoensis, to 0.969, H. thunbergii vs. H. taeanensis). This is attributed to the presence of the same high-frequency alleles in different species at seven loci. In addition, no "diagnostic allele" that appears in all populations of one species, but is absent in other species, was detected at the 12 isozyme loci. These all suggest that species of Hemerocallis in Korea may have recently derived from an ancestor or progenitor harboring high levels of genetic diversity.     

Speciation and adaptive radiation of subterranean mole rats, Spalax ehrenbergi superspecies, in Jordan

The major initial mechanism of speciation in subterranean blind mole rats, Spalacidae, is chromosomal, primarily through Robertsonian rearrangements. Here we highlight another scenario of chromosomal rearrangement leading to ecological speciation and adaptive radiation apparently initiated by pericentric inversions and genie divergence to different ecologies in mole rats in Jordan. We analysed karyotype, allozyme, size and ecological diversity across the range of mole rats in Jordan from mesic Irbid in the north to xeric Wadi Musa (Petra region) in the south, a transect of 250 km. We examined mole rats for chromosome ( N =71), size ( N =76), and allozyme ( N =67) diversities, encoded by 32 loci, in 12 populations of the Spalax ehrenbetgi superspecies in Jordan. By a combination of chromosome morphology, genetic distance, body size and ecogeography, we identified four new putative biological species. All species (except two animals in Madaba) share 2 n = 60 but vary in chromosome morphology, caused by pericentric inversions and/or centromeric shifts. The 'north Moav' species is karyotypically polymorphic for 2 n (2 n = 60; including locally also two animals with 2 n = 62). The distribution of the four species is associated with ecogeographical different domains and climatic diversity. Genetic diversity indices were low, but like chromosome arms (NFa) were positively correlated with aridity stress. Discriminant analysis correctly classified 91% of the individuals into the four species utilizing combinatorially chromosome, allozyme and size diversities. It is hypothesized that mole rat evolution underground is intimately associated with climatic diversity stress above ground.     

Extensive amino acid polymorphism at the pgm locus is consistent with adaptive protein evolution in Drosophila melanogaster

PGM plays a central role in the glycolytic pathway at the branch point leading to glycogen metabolism and is highly polymorphic in allozyme studies of many species. We have characterized the nucleotide diversity across the Pgm gene in Drosophila melanogaster and D. simulans to investigate the role that protein polymorphism plays at this crucial metabolic branch point shared with several other enzymes. Although D. melanogaster and D. simulans share common allozyme mobility alleles, we find these allozymes are the result of many different amino acid changes at the nucleotide level. In addition, specific allozyme classes within species contain several amino acid changes, which may explain the absence of latitudinal clines for PGM allozyme alleles, the lack of association of PGM allozymes with the cosmopolitan In(3L)P inversion, and the failure to detect differences between PGM allozymes in functional studies. We find a significant excess of amino acid polymorphisms within D. melanogaster when compared to the complete absence of fixed replacements with D. simulans. There is also strong linkage disequilibrium across the 2354 bp of the Pgm locus, which may be explained by a specific amino acid haplotype that is high in frequency yet contains an excess of singleton polymorphisms. Like G6pd, Pgm shows strong evidence for a branch point enzyme that exhibits adaptive protein evolution.     

Mammalian karyotype evolution

The chromosome complements (karyotypes) of animals display a great diversity in number and morphology. Against this background, the genomes of all species are remarkably conserved, not only in transcribed sequences, but also in some chromosome-specific non-coding sequences and in gene order. A close examination with chromosome painting shows that this conservation can be resolved into small numbers of large chromosomal segments. Rearrangement of these segments into different combinations explains much of the observed diversity in species karyotypes. Here we discuss how these rearrangements come about, and show how their analysis can determine the evolutionary relationships of all mammals and their descent from a common ancestor.     

Comparative phylogeography of three skink species (Oligosoma moco, O. smithi, O. suteri; Reptilia: Scincidae) in northeastern New Zealand

Sea-level fluctuations during the Pliocene and Pleistocene have shaped the landscape of the Northland region of New Zealand. We examined the comparative phylogeography of three skink species (Oligosoma moco, O. smithi, O. suteri) in northeastern New Zealand in order to investigate the impact of the historical processes that have prevailed since the Pliocene on the Northland fauna. O. moco, O. smithi and O. suteri have similar distributions across northeastern New Zealand, frequently occurring in sympatry. We obtained sequence data from across the entire range of each species, targeting the ND2 mitochondrial gene. Using Neighbor-Joining, Maximum likelihood and Bayesian methods, our analysis revealed contrasting phylogeographic patterns in each species. We found substantial phylogeographic structure within O. moco, with three distinct clades identified. Similarly, deep phylogeographic divergence was evident within O. smithi, with three distinct clades present. Clade 1 included O. smithi populations from the Three Kings Islands and the western coastline of Northland, while Clade 2 encompassed the remainder of the range. However, since Clade 3 corresponded to a described species (O. microlepis), O. smithi might represent a species complex. In both O. moco and O. smithi, divergences among clades are estimated to have occurred in the Pliocene, with divergences within clades occurring during the Pleistocene. In contrast, genetic divergence among O. suteri populations was extremely limited and indicative of more recent divergences during the Pleistocene. The lack of phylogeographic structure in O. suteri might be a consequence of its oviparous reproductive mode, which restricted its distribution to warm northern refugia during glacial maxima. Differences in the ecology and biology of each species might have produced contrasting responses to the same historical processes, and ultimately diverse phylogeographic patterns. Our study reveals an absence of consistent and concordant phylogeographic patterns in the Northland biota, even within the same taxonomic group.     

RAPD marker diversity within and divergence among species of Dendroseris (Asteraceae: Lactuceae)

Random Amplified Polymorphic DNA (RAPD) markers were used to measure genetic diversity within and divergence among species of Dendroseris (Asteraceae: Lactuceae), a genus endemic to the Juan Fernandez Islands, Chile. Results were compared to previous studies employing allozymes. For five of the species, RAPD banding patterns distinguished all individuals examined, and different mutilocus genotypes were found even in species exhibiting no allozyme diversity. RAPD band diversities ranged from 0.003 to 0.022 within species; >90% of total diversity was among species and <10% within them. Relative levels of allozyme and RAPD diversity were similar for some species, particularly those with highest and lowest diversities, but overall there was no significant correlation. Relationships inferred from a neighbor-joining tree generated from RAPD bands were similar to results obtained from morphology, chloroplast DNA (cpDNA) restriction site mutations, and sequences from the internal transcribed spacer regions of nuclear ribosomal DNA (ITS), but somewhat better resolution was achieved. Relationships shown by allozymes differed from trees based on other data; this ostensibly is a result of the sharing of ancestral alleles and the absence of alleles generated subsequent to speciation. Dendroseris represents an example where RAPD markers, because of their greater variability, provide a useful alternative to allozymes for assessing diversity in rare species endemic to oceanic islands and for resolving relationships among the species.     

Genetic evidence for population expansion in Hydrotaea irritans (Fallèn) (Diptera: Muscidae)

Allozyme variation in the sheep headfly Hydrotaea irritans was studied on two spatial scales. Geographic variation among seven Danish and one Dutch population revealed significant but rather low genetic differentiation with F _ST = 0.01 over all loci. The Dutch population was on average not more different from the Danish populations than the Danish populations from each other. Allele frequencies were very skewed with the most common allele always exceeding 0.85 and usually 0.9 in frequency, but with many rare alleles at some loci. Tests for neutrality of the variation at the nine polymorphic loci revealed highly significant deviations from expected homozygosity in this species, which was not found in a comparative analysis of allozyme variation at similar loci of seven other Hydrotaea species. To explain the peculiar observed pattern of allozyme variation in H. irritans , it is suggested that this species has successfully expanded its range and spread through northern and central Europe in the recent past. Alternatively, H. irritans may have recently invaded a new niche, resulting in increased abundance of the species and subsequent dispersal to former areas of the species distribution.     

Chloroplast DNA variation inCoreopsis nuecensoides andC. nuecensis (Asteraceae), a presumed progenitor-derivative species pair

Coreopsis nuecensoides andC. nuecensis are narrowly distributed endemics of southeastern Texas. While they overlap in range, they differ in chromosome number, and F₁ hybrids exhibit strong sterility barriers. Previous morphological, cytogenetic, and allozyme studies suggested thatC. nuecensoides andC. nuecensis are very closely related members of a progenitor-derivative species pair. The two species differ substantially in terms of their leaf flavonoid chemistry, but the flavonoid data do not address the exact nature of the relationship between them. We have further examined the relationship between the species by analyzing genetic diversity within both species using chloroplast DNA (cpDNA) restriction site data. Sixteen restriction site changes were used to define thirteen distinct cpDNA haplotypes. The pattern of relationships among haplotypes provides some support for the presumed ancestor-descendent relationship, but other interpretations are possible. Only one cpDNA haplotype was shared by the two species; of the remaining twelve, seven were unique to one species and five to the other. This result is consistent with results of flavonoid studies, in which each species exhibited flavonoid compounds not seen in the other, but differs from the allozyme results, in which the vast majority of alleles were shared by both species and only the presumed progenitor exhibited unique alleles. Taken together, the data support a very close relationship between the species, but are equivocal with regard to a progenitor-derivative relationship.     

Microgeographic variation in allozyme frequencies in relation to the degree of exposure to wave action in the dogwhelk Nucella lapillus (L.) (Prosobranchia: Muricacea)

Nucella lapillus from 15 sites 50 m to 21 km apart in S. Devon, S. W. England were analysed for allozyme variation at eight soluble enzyme loci. Sites were classified as either Exposed or Sheltered and a hierarchical analysis of allozyme variation carried out using Wright's Fixation Index, F_ST. Whelks from Sheltered sites segregated for alleles at the Est-3, Lap-2, Pep-2 and Mdh-1 loci which were virtually absent from exposed sites resulting in high F_ST values (0.289–0.506) when all samples were included. Consequently mean heterozygosity of the Sheltered samples was roughly twice that of the Exposed. Between Sheltered sites the frequencies of these 'additional' alleles varied substantially, even on a microgeographic scale and were found to be highly correlated with exposure. Within individuals the presence of the 'sheltered' alleles was correlated with the possession of the 'sheltered' shell shape as indicated by length divided by aperture height. This must necessarily be the case, however, if both are related independently to exposure. Although these correlations imply the action of selection there is evidence within the data for stochastic factors affecting the pattern observed. Complicating the picture further is the correspondence observed in the distribution of the 'sheltered' alleles with the known distribution of chromosomal translocations. Phenotypic associations within individuals also support the hypothesis that variation at the Est-3, Lap-2, Mdh-1 and Pet-2 loci is related to variation in chromosome number. However, the nature of the relations of karyotype and allozyme variation with shell shape and exposure remain speculative.     

Allozyme variation in the three extant populations of the narrowly endemic cycad Dioon angustifolium Miq. (Zamiaceae) from North-eastern Mexico

BACKGROUND AND AIMS: Dioon angustifolium was considered within D. edule. Recent morphometric and allozyme studies on D. edule have shown that D. angustifolium has originated from geographic isolation and is therefore considered to be a separate species. This cycad is endemic to north-eastern Mexico and is known only from three populations in the Sierra Madre Oriental mountain chain. Its populations are small when compared with its southern relative D. edule. In this study, genetic variation was determined within and between populations of D. angustifolium and the genetic consequences of habitat fragmentation and isolation of populations of this species were assessed. METHODS: Allozyme electrophoresis of 14 presumptive loci was used. The data were analysed with statistical approximations for estimating genetic diversity, structure, gene flow and recent genetic bottlenecks. KEY RESULTS: Means and standard deviations of genetic diversity estimators were: number of alleles per locus (A = 1.67 +/- 0.23), percentage of polymorphic loci (P = 52.4 +/- 23 %) and expected heterozygosity (H(E) = 0.218 +/- 0.093). The genetic variation attributable to differences among populations was 16.7 %. Mean gene flow between paired populations was Nm = 1.55 +/- 0.67, which is similar to that reported for endemic plant species of narrow geographical distribution and species with gravity-dispersed seed. A recent bottleneck is detected in the populations studied. CONCLUSIONS: Dioon angustifolium presents high levels of genetic diversity compared with other cycad species, in spite of small population sizes. The recent bottleneck effect did not effectively reduce the genetic variation to the extent of eliminating these populations. The distribution of D. angustifolium appears to be the result of historical biogeographical effects related to the Pleistocene glaciations. It is recommended that this species be catalogued in the IUCN Red List of Threatened Species and conservation efforts be made to preserve it.     

Diagrammatic representation for chromosomal mutagenesis studies. I. Karyotypes most similar to that of man

In an attempt to discover which primate species have the karyotypes most similar to that of man, the chromosome numbers, the Nombre Fondamental and the numbers of chromosomal rearrangements separating the karyotypes of many species were considered. In addition to man, 6 species were selected for their karyotypic similarities and 1 for its dissimilarity. A model representing the karyotypes, by 2 diagrams, is proposed for these 8 species. These diagrams characterize each karyotype, as well as the theoretical random distribution of break-points, after the effect of a clastogenic agent. This allows one to make quantitative analyses of any type of chromosomal rearrangement, with objective criteria, and should improve the study of chromosomal mutagenesis, and particularly interspecies comparisons.     

The role of chromosomal polymorphism in divergence of populations and species of the genus Chironomus (Diptera)

The data on the structure and level of chromosomal polymorphism in natural populations of species of the genus Chironomus are summarized. A very high level of chromosomal polymorphism was noted for most species. Paracentric inversions prevailed among the chromosomal rearrangements found in natural populations. Changes in the set and frequency of inversion sequences are the most important factor of cytogenetic divergence of populations. Several cytogenetic types of populations were distinguished. The Palaearctic and Nearctic populations of Holarctic species diverged to a greater extent due to the formation of endemic Palearctic and Nearctic inversion sequences. The sequences common for both regions indicated a common ancestry of the populations. The cytogenetic distances between the Palearctic and Nearctic populations are greater by an order of magnitude than those between populations within each zoogeographic region. Divergence of species karyotypes was found to result from fixation of different inversion sequences in the course of evolution. The karyotypes of Palearctic and Nearctic species mainly differ by the presence of endemic Palearctic and Nearctic banding sequences. Several basic sequences common for some species allow the cytogenetic history of their origin to be revealed. A NJ phylogenetic tree was built for the genus Chironomus, demonstrating chromosomal evolution of its species.