Karyotypic Races Research Articles

Aphids, sex, chromosomes and molecular biology (Hemiptera: Aphidoidea).

In this paper, I summarise work at Macquarie University on aphid diversity in Australia, chromosome numbers, and chromosome behaviour during spermatogenesis and during sex determination in the aphid embryo. Much of this was inspired by Dr Roger Blackman, and some was done in direct collaboration with him. During the 1990s, the Macquarie group developed molecular techniques to investigate aphid population genetics and major questions such as the evolution of sex. These experiments built on the earlier work on aphid karyotypic races and the cytology of egg maturation and spermatogenesis. "From little things, big things grow".1 1 Title of song by Paul Kelly and Kev Carmody, first recorded in 1991.

Cryptic diversity and dynamic chromosome evolution in Alpine scorpions (Euscorpiidae: Euscorpius)

Over time, mountain biota has undergone complex evolutionary histories that have left imprints on its genomic arrangement, geographical distribution and diversity of contemporary lineages. Knowledge on these biogeographical aspects still lags behind for invertebrates inhabiting the Alpine region. In the present study, we examined three scorpion species of the subgenus Euscorpius (Alpiscorpius) from the European Alps using cytogenetic and molecular phylogenetic approaches to determine the variation and population structure of extant lineages at both chromosome and genetic level, and to provide an insight into the species diversification histories. We detected considerable intraspecific variability in chromosome complements and localization of the 18S rDNA loci in all studied species. Such chromosome differences were noticeable as the existence of three [in E. (A.) alpha and E. (A.) germanus] or four [in E. (A.) gamma] range-restricted karyotypic races. These races differed from one another either by 2n [in E. (A.) alpha 2n = 54, 60, 90; in E. (A.) gamma 2n = 58, 60, 88, 86–92], or by the karyotypic formula [in E. (A.) germanus 2n = 34m + 12sm; 36m + 10sm; 42m + 4sm]. Using mitochondrial (16S rRNA, COI) and nuclear (28S rDNA) genetic markers, we examined genetic variation and reconstructed phylogenetic relationships among the karyotypic races. Both approaches provided evidence for the existence of ten deeply divergent lineages exhibiting the features of local endemics and indicating the presence of cryptic species. Molecular dating analyses suggest that these lineages diversified during the Plio-Pleistocene and this process was presumably accompanied by dynamic structural changes in the genome organization.

Chromosomal polymorphism of populations of the common shrew, Sorex araneus L., in Belarus

The present paper reports karyotypic data for 76 individuals of the common shrew, Sorex araneus L., collected from 10 geographic sites in Belarus. We revealed two vast areas of polymorphism for diagnostic chromosomes of karyotypic races Białowieża (gr, hn, ik, mp) and Kiev (gm, hi, ko) with low frequency of metacentrics. The frequencies of the Białowieża diagnostic metacentrics decreased towards the east and the frequency of the Kiev metacentrics decreased towards the north. A high level of chromosomal variability was observed in the River Ptich basin. The contact zone of races Białowieża and Kiev was observed along the Ptich and Pripyat Rivers. The polymorphism and a low metacentric frequencies in the studied populations of the Białowieża and Kiev races from the Pripyat and Ptich basin may be associated either with selection against heterozygotes in the hybrid zone of these two races (“acrocentric peak”) or with the spread of the diagnostic metacentrics of the Białowieża and Kiev races in populations characterized by 10 pairs of acrocentric diagnostic chromosomes (g, h, i, k, m, n, o, p, q, r). Individuals with single diagnostic metacentric hk (such karyotype was previously attributed to new race Turov, Mishta et al. Acta Theriol 45 (Suppl 1):47–58, 2000) occurred in sites where the Białowieża and Kiev races cohabited. In accordance with these data, the previous description of the Turov race (Mishta et al. Acta Theriol 45 (Suppl 1):47–58, 2000) needs a revision.

Phenotypic variation across chromosomal hybrid zones of the common shrew (Sorex araneus) indicates reduced gene flow.

Sorex araneus, the Common shrew, is a species with more than 70 karyotypic races, many of which form parapatric hybrid zones, making it a model for studying chromosomal speciation. Hybrids between races have reduced fitness, but microsatellite markers have demonstrated considerable gene flow between them, calling into question whether the chromosomal barriers actually do contribute to genetic divergence. We studied phenotypic clines across two hybrid zones with especially complex heterozygotes. Hybrids between the Novosibirsk and Tomsk races produce chains of nine and three chromosomes at meiosis, and hybrids between the Moscow and Seliger races produce chains of eleven. Our goal was to determine whether phenotypes show evidence of reduced gene flow at hybrid zones. We used maximum likelihood to fit tanh cline models to geometric shape data and found that phenotypic clines in skulls and mandibles across these zones had similar centers and widths as chromosomal clines. The amount of phenotypic differentiation across the zones is greater than expected if it were dissipating due to unrestricted gene flow given the amount of time since contact, but it is less than expected to have accumulated from drift during allopatric separation in glacial refugia. Only if heritability is very low, Ne very high, and the time spent in allopatry very short, will the differences we observe be large enough to match the expectation of drift. Our results therefore suggest that phenotypic differentiation has been lost through gene flow since post-glacial secondary contact, but not as quickly as would be expected if there was free gene flow across the hybrid zones. The chromosomal tension zones are confirmed to be partial barriers that prevent differentiated races from becoming phenotypically homogenous.

Craniometric differences between karyotypic races of the common shrew Sorex araneus (Mammalia) as a result of limited hybridization

Craniometric differences between karyotypic races of the common shrew Sorex araneus (Mammalia) as a result of limited hybridization

Краниометрические различия контактирующих хромосомных рас обыкновенной бурозубкиSorex araneus(Mammalia) как следствие их ограниченной гибридизации

The contact points of four karyotypic races (St. Petersburg, Moscow, Seliger and West Dvina) of the common shrew Sorex araneus L. were studied at the Valdai Hills (European Russia) in an area unimpeded by geographic barriers. The populations of the races are separated by narrow hybrid zones that represent the most complex heterozygous hybrid karyotypes. At these points of contact, the morphometric differentiation of karyotype races was examined in 12 cranial measurements in 190 shrews of a known karyotype. A. comparison of the mean values in studied samples of immature shrews revealed statistically significant differences and the correlation of some measurements in order to describe the level of musculus temporalis. It has been proposed that morphometric differences in the karyotypic races were preserved and accumulated because of a 50% reduction of the frequencies of hybrids. The deviation from the Hardy-Weinberg ration in the frequencies of the genotype and haploid sets of chromosomes in the hybrid zones can be attributed to a number of fatalities of hybrid embryos or the nonrandom mating of karyotypic races. The ethological isolation might arise in the evolution of some karyotypic races from the reduced fitness of the hybrids.

Distribution of two karyotypic races of Sorex araneus (Insectivora, Soricidae) in Switzerland and the post-glacial recolonization of the Valais: First results

Two chromosome races of Sorex araneus were found in southern and western Switzerland. It is suggested they were issued by introgression of different sets of metacentrics, coming respectively from north-east and south, into a primitive “acrocentric” population which recolonized the country from the west after the last glaciation.

Genetic differentiation in Sorex: Electrophoretic analysis of the karyotypic races of Sorex araneus in Sweden

The common shrew, Sorex araneus L., is in Sweden represented by animals of three karyotypic races. The chromosomal differences are due to Robertsonian changes and are not accompanied by any obvious morphological differences. Animals from six populations (two from each karyotypic race) were analyzed chromosomally and electrophoretically. A total number of 225 animals were used in the electrophoretic investigation. Of the 27 loci studied, 24 showed no or only little electrophoretic variation. Three loci were clearly polymorphic but showed no allele difference diagnostic for any of the karyotypic races. However, one of the alleles at the Mpi locus, with a frequency between 0.20 and 0.40 in the southern and central races, was not found in the northern race. At this locus, there was also a difference between the northern and the other two races for the most common allele. Comparison of this result with information from other chromosomally variable mammalian species shows that normally only small electrophoretic differences exist between karyotypic races belonging to the same species.

A cytogenetical analysis of reproduction in common shrews (Sorex araneus) from a karyotypic hybrid zone

Searle, J. B. 1990. A cytogenetic analysis of reproduction in common shrews (Sorex araneus) from a karyotypic hybrid zone. —Hereditas 113: 121–132. Lund, Sweden. ISSN 0018–0661. Received May 21, 1990. Accepted June 25, 1990 Sixteen pregnant female common shrews were collected near Oxford (U.K.) from a hybrid zone between two karyotypic races which differ by Robertsonian rearrangements. Some females were homozygotes and others were ‘simple’ or ‘complex’ Robertsonian heterozygotes. The females and their fetuses were karyotyped and number of ovulations and regressing implants scored. Prenatal losses were noted in female simple Robertsonian heterozygotes. Some losses, including two trisomics, were likely to be due to anaphase I nondisjunction of the maternal autosomal trivalent. However, numbers of ovulations were found to be higher in these heterozygotes than in the homozygotes, and this could compensate for prenatal losses due to nondisjunction. Overall, fertility of females from the hybrid zone did not differ substantially from that of females from other areas of karyotypic polymorphism or monomorphism. There was no evidence for assonative mating or assortative fertilisation within the hybrid zone. On chromosomal grounds, the hybrid zone is unlikely to be a major barrier to gene flow.

Karyotypic Variation in the Australian Gecko Diplodactylus Tessellatus, with the Description of a New Karyotypic Complement for Diplodactyline Geckos

Abstract We report the discovery of a 2n = 30 karyotype race in the Australian diplodactyline gecko Diplodactylus tessellatus. The new chromosome race has four large metacentric pairs and 11 acrocentric pairs, a unique complement among diplodactyline geckos. Three karyotypic races are now known from D. tessellatus. One retains the ancestral Diplodactylus 2n = 38 all-acrocentric karyotype, whereas the 2n = 30 and the 2n = 28 races appear to have been derived from a 2n = 38 karyotype via fusion of four or five pairs of acrocentrics. Diplodactylus tessellatus and its relatives in the Diplodactylus vittatus species complex are now known to possess five different diploid number complements; 2n = 38, 36, 34, 30, and 28, more variation than any other diplodactyline gecko genus or species group for which data are available.

Karyotypic Races of the Common Shrew (Sorex Araneus) with Exceptionally Large Ranges: The Novosibirsk and Tomsk Races of Siberia

Altogether 419 common shrews comprising 38 samples from 36 geographically-distinct sites in Siberia have been categorised as belonging to either the Novosibirsk karyotypic race (XX/XY1Y2af, bc, g/o, hn, ik, j/l, m/p, q/r, tu) or the neighbouring Tomsk karyotypic race (XX/XY1Y2af, bc, g/k, hi, j/l, mn, o, p, q/r, tu). The most notable Robertsonian polymorphism was that for arm combination qr present in both races that may reflect introgression after contact of the ancestral Novosibirsk race (fixed for metacentric qr) and the ancestral Tomsk race (fixed for acrocentrics q, r) at the end of the last glaciation. The Novosibirsk race occurs over a huge area (estimated at 700,000 km2) and is one of the most widespread karyotypic forms in S. aruneus. Together with rather less extensive Tomsk race, these two races occupy much of the range of the species to the east of the Ural Mts. We discuss how the distributions of the Novosibirsk and Tomsk races were attained, in the context of the Pleistocene-Holocene transition.

A hybrid zone between the chromosomal races Łęgucki Młyn and Popielno of the common shrew in north-eastern Poland: preliminary results

A newly discovered hybrid zone between two karyotypic races, Łęgucki Młyn (g/r, h/k, i/o, j/l, m/n, p, q) and Popielno (g/r, h/q, i/k, j/l, m/n, o, p), of the common shrewSorex araneus Linnaeus, 1758 has been studied in north-eastern Poland. In the Łęgucki Młyn/Popielno hybrid zone the complex heterozygotes form theoretically only short meiotic chain configurations, consisting of four or five elements. In all hybrid populations a high frequency of complex heterozygotes was observed, varying from 0.30 to 0.43 between localities. In the centre of the hybrid zone the frequencies of telocentricsh andk increased. In two individuals of the hybrid populations (Krutyń I and Krutyń II), homozygous telocentric for chromosome armsh, i, k, o andq were observed.

Evolution of the common shrewSorex araneus:

We review data on the chromosomal variation in the common shrewSorex araneus Linnaeus, 1758 in the context of recent molecular findings. The article considers all aspects of chromosomal variation in this species: within-population polymorphism, karyotypic races, hybrid zones between karyotypic races, chromosomal evolution, and speciation. The recent molecular data provide vital information on different evolutionary processes such as inbreeding, genetic drift, population expansion, and selective forces. In particular, the molecular data challenge traditional models for the fixation of chromosomal variants, provide new insights into the manner of spread of such variants once they are formed and allow in-depth analysis of gene exchange between karyotypic races.

Intraspecific Phylogenetic Relationships in Sorex araneus L.: The Southern Baltic Subgroup of Chromosome Races

Results of chromosome G-banding were used to identify two new karyotypic races of the common shrew (Sorex araneus L.) in the European part of Russia. The chromosomal diagnosis of race St. Petersburg included five metacentrics (hk, ip, jl, mq, and nr) and two acrocentrics (g and o) (2Na = 20); the diagnosis of race West Dvina included six metacentrics (gm, hk, ip, jl, no, and qr) (2Na = 18). The phylogenetic significance of the chromosomal markers gm, hk, and ip is considered and the possibility of reticulate evolution in the species S. araneus is discussed.

Alps, genes, and chromosomes: their role in the formation of species in the Sorex araneus group (Mammalia, Insectivora), as inferred from two hybrid zones

During the Pleistocene glaciations, the Alps were an efficient barrier to gene flow between isolated populations, often leading to allopatric speciation. Afterwards, the Alps strongly influenced the post-glacial recolonization of Europe and represent a major suture zone between differentiated populations. Two hybrid zones in the Swiss and French Alps between genetically and chromosomally well-differentiated species—the Valais shrew, Sorex antinorii, and the common shrew, S. araneus—were studied karyotypically and by analyzing the distribution of seven microsatellite loci. In the center of the Haslital hybrid zone the two species coexist over a distance of 900 m. Hybrid karyotypes, among them the most complex known in Sorex, are rare. F-statistics based on microsatellite data revealed a strong heterozygote deficit only in the center of the zone, due to the sympatric distribution of the two species with little hybridization between them. Structuring within the species (both F_IS and F_ST) was low. An hierarchical analysis showed a high level of interspecific differentiation. Results were compared with those previously reported in another hybrid zone located at Les Houches in the French Alps. Genetic structuring within and between species was comparable in both hybrid zones, although chromosomal incompatibilities are more important in Haslital, where a linkage block of the race-specific chromosomes should additionally impede gene flow. Evidence for a more restricted gene flow in Haslital comes from the genetically intermediate hybrid karyotypes, whereas in Les Houches, hybrid karyotypes are genetically identical to individuals of the pure karyotypic races. Genic and chromosomal introgression was observed in Les Houches, but not in Haslital. The possible influence of a river, separating the two species at Les Houches, on gene flow is discussed.

Geographical Variations in Chromosomes of the Greater Japanese Shrew-Mole, Urotrichus talpoides (Mammalia: Insectivora)

Karyotypes of the greater Japanese shrew-mole, Urotrichus talpoides (Talpidae), collected from 57 localities in Japan were studied by conventional, G- and C-band staining techniques to elucidate geographical chromosomal variations, the mechanism of changes in chromosomes, and the distribution patterns of karyotypic races. Shrew-mole samples examined could be divided geographically into two slightly divergent chromosomal forms designated as the western and eastern races. These two karyotypic races had the same diploid number (34) and fundamental number (64), but they had autosomes with different makeups. A comparison of conventional karyotypes showed a distinct intraspecific variation in shape of autosomal pair no. 14 which was classified as subtelocentric in the western race and as metacentric in the eastern race. G- and C-banding analyses revealed that karyotypic variation found in no. 14 pair was involved in pericentric inversion and quantitative changes in constitutive heterochromatin. Intraspecific and geographical variation in chromosomes caused by such karyological events is rare and unique among members of the family Talpidae examined so far. Furthermore, our results demonstrated that the clear boundary between the two parapatric karyotypic races was actually located along the Kurobe-Fuji line in the central part of Honshu, but not along the Owari-Tsuruga isthmian line previously postulated by Tsuchiya (1987, 1988). Zoogeographical implications of the boundary of parapatric distribution in U. talpoides are also discussed.

Raciation and speciation in house mice from the Alps: the role of chromosomes.

There are at least 24 different karyotypic races of house mouse in the central Alps, each characterized by a different complement of ancestral acrocentric and derived metacentric chromosomes; altogether 55 different metacentric chromosomes have been described from the region. We argue that this chromosome variation largely arose in situ. If these races were to make contact, in most cases they would produce F1 hybrids with substantial infertility (sometimes complete sterility), due to nondisjunction and germ cell death associated with the formation of long-chain and/or ring configurations at meiosis. We present fertility estimates to confirm this for two particular hybrid types, one of which demonstrates male-limited sterility (in accordance with Haldane's Rule). As well as a model for speciation in allopatry, the Alpine mouse populations are of interest with regards speciation in parapatry: we discuss a possible reinforcement event. Raciation of house mice appears to have happened on numerous occasions within the central Alps. To investigate one possible source of new karyotypic races, we use a two-dimensional stepping stone model to examine the generation of recombinant races within chromosomal hybrid zones. Using field-derived ecological data and laboratory-derived fertility estimates, we show that hybrid karyotypic races can be generated at a reasonable frequency in simulations. Our model complements others developed for flowering plants that also emphasize the potential of chromosomal hybrid zones in generating new stable karyotypic forms.

Clinal analysis of a chromosomal hybrid zone in the house mouse.

These studies centre on the 'Barcelona' karyotypic race of the western house mouse (Mus musculus domesticus), first described by Adolph & Klein (1981). This is one of many races within M. m. domesticus characterized by metacentric chromosomes that have originated by repeated Robertsonian fusions, with perhaps further modification by whole-arm reciprocal translocations. Data on 111 mice from 20 sites show that the race is centred 24 km to the west of Barcelona city and has a homozygous metacentric karyotype of 2n = 28 (3.8, 4.14, 5.15, 6.10, 9.11, 12.13). The race has a small range, and mice with the standard 40-acrocentric karyotype were caught only 30 km from the race centre. Throughout the area of occurrence of metacentrics there is polymorphism (i.e. presence of acrocentrics in the population), although all six metacentrics approach fixation close to the race centre. Thus, there is a hybrid zone between the Barcelona and standard races. The centres and widths of all clines (except 3.8) were determined. Likelihood ratio tests showed that most of the cline centres differed significantly in position (i.e. the clines were staggered) and the clines for metacentrics 6.10 and 9.11 were significantly narrower than those for 4.14, 5.15 and 12.13. Overall, the clines tended to be wider the further they were from the race centre. There are various possible explanations for this hybrid zone structure and further data are needed to distinguish between them.

Mitochondrial DNA and chromosomal studies of wild mice (Mus) from Turkey and Iran.

Complete D-loop sequences of 20 Mus from three localities in Turkey and seven in Iran were characterized. These countries are thought to be close to the place of origin of the subspecies Mus musculus domesticus. Five new M. m. domesticus haplotypes were added to the nine already known for the region. Four of these 14 haplotypes were very similar to the consensus D-loop sequence for western Europe defined by Nachman et al. (1994), which may represent the ancestral condition for M. m. domesticus. A divergent mtDNA lineage is found in various parts of Turkey and northern Iran; it has spread into western Europe, but other European lineages were not found in either Turkey or Iran. The other Mus D-loop sequences were of M. m. castaneus and Mus macedonicus and confirmed M. macedonicus as a monotypic species with low nucleotide diversity. The prevalence of the standard 40-chromosome complement in this region is particularly interesting with regards M. m. domesticus, as it is consistent with the in situ origin of Robertsonian karyotypic races (2n < 40) in western Europe.

Chromosomal segregation and fertility in Robertsonian chromosomal heterozygotes of the house musk shrew (Suncus murinus, Insectivora, Soricidae).

Crucial to our understanding of chromosomal variation and evolution in mammals are detailed studies of chromosomal heterozygotes, with analyses of chromosomal segregation and chromosome-derived infertility. We studied segregation and fertility in hybrids between karyotypic races of the house musk shrew Suncus murinus. These individuals were heterozygous for up to five Robertsonian fusions (Rbs) and an insertion of heterochromatin in an autosome. All variant chromosomes showed Mendelian segregation and all Rbs segregated independently of each other in the progeny of double heterozygotes. Litter size in single and even multiple Rb heterozygotes was no smaller than that in the less fertile parental strain. The effects of genetic background were more important in determining litter size than Rb heterozygosity for the shrews that we examined.