The canonical model of sex-chromosome evolution predicts that, as recombination is suppressed along sex chromosomes, gametologs will progressively differentiate, eventually becoming heteromorphic. ...However, there are numerous examples of homomorphic sex chromosomes across the tree of life. This homomorphy has been suggested to result from frequent sex-chromosome turnovers, yet we know little about which forces drive them. Here, we describe an extremely fast rate of turnover among 28 species of Ranidae. Transitions are not random, but converge on several chromosomes, potentially due to genes they harbour. Transitions also preserve the ancestral pattern of male heterogamety, in line with the 'hot-potato' model of sex-chromosome transitions, suggesting a key role for mutation-load accumulation in non-recombining genomic regions. The importance of mutation-load selection in frogs might result from the extreme heterochiasmy they exhibit, making frog sex chromosomes differentiate immediately from emergence and across their entire length.
Darevskia rock lizards is a unique complex taxa, including more than thirty species, seven of which are parthenogenetic. In mixed populations of Darevskia lizards, tri- and tetraploid forms can be ...found. The most important issues in the theory of reticulate evolution of Darevskia lizards are the origin of parthenogenetic species and their taxonomic position. However, there is little data on how meiosis proceeds in these species. The present work reports the complex results of cytogenetics in a diploid parthenogenetic species - D. unisexualis. Here we detail the meiotic prophase I progression and the specific features оf mitotic chromosomes organization. The stages of meiosis prophase I were investigated by immunocytochemical analysis of preparations obtained from isolated primary oocytes of D. unisexualis in comparison with maternal species D. raddei nairensis. It has been shown that in D. unisexualis at the leptotene-zygotene stages the axial elements and the synaptonemal complex (SC) form typical "bouquets". At the pachytene-diplotene stage, 18 autosomal SC-bivalents and thickened asynapted sex Z and w univalents were observed. The presence of SYCP1 protein between the lateral elements of autosomal chromosomes proved the formation of assembled SCs. Comparative genomic hybridization (CGH) on the mitotic metaphase chromosomes of D. unisexualis was carried out using the genomic DNA isolated from the parental species D. raddei nairensis and D. valentini. In the pericentromeric regions of half of the mitotic chromosomes of D. unisexualis, specific regions inherited from maternal species have been found. Following our results, we suggest a model for diploid germ cells formation from diploid oocytes without premeiotic duplication of chromosomes in the oogenesis of diploid parthenogenetic lizards D. unisexualis. Taken as a whole, our findings confirm the hybrid nature of D. unisexualis and shed light on heterozygosity and automixis in diploid parthenogenetic forms.
Once introduced into new area, invasive species can be expected to have low genetic diversity due to the founder effect. Here we tested this prediction using cytogenetic and molecular analysis of ...Armenian and Belarusian populations of Colorado potato beetle Leptinotarsa decemlineata (Say, 1824) and by comparing the results with those of native (North America) and those introduced into Europe. This revealed that the karyotype of males from Armenia and Belarus is remarkably conserved with 2n = 35 (34 + X0), n = 17AA + X0; and includes a pair of large acrocentric chromosomes. Thus, these populations belong to the so-called acrocentric chromosome race of the Colorado potato beetle. At diakinesis there are clearly visible argentophilic signals, probably NORs (the nucleolus organizer regions) present on some autosomal bivalents, while the X chromosome was homogenously argentophilic during different stages of meiosis. C-banding revealed a small amount of constitutive heterochromatin weakly visible in the pericentromeric regions of some chromosomes. Analysis of the DNA-barcode fragment of the gene cytochrome c oxidase subunit I (COI) revealed a single haplotype (we call it "the European haplotype") and lack of inter-population variability in all the samples collected from different locations in Armenia and Belarus. The comparison of our karyological and molecular data with that available in the literature and GenBank shows that all the populations studied from the Old World are monomorphic with respect to karyotype and the mitochondrial DNA-barcode. We assume that (1) the presence of acrocentric chromosomes in the karyotype and (2) the European haplotype of mitochondrial genome are the ancestral states for all populations in the Old World and inherited from the New World invaders who colonized Europe 100 years ago. New World populations are polymorphic with respect to karyotype and mitochondrial genes; however, the European haplotype has not yet been found in America. We believe that in the future it will be found in North America, which will shed light on the origin of populations of this dangerous pest in Eurasia.
Darevskia rostombekowi
, the most outstanding of the seven known parthenogenetic species in the genus
Darevskia
, is the result of an ancestral cross between two bisexual species
Darevskia raddei
and
...Darevskia portschinskii
. The chromosomal set of this species includes a unique submetacentric autosomal chromosome; the origin of this chromosome was unresolved as only acrocentric chromosomes are described in the karyotypes of
Darevskia
genus normally. Here, we applied a suite of molecular cytogenetic techniques, including the mapping of telomeric (TTAGGG) n repeats using fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH), and whole-chromosome painting (WCP) in both
D. rostombekowi
and parental (
D. portschinskii
and
D. raddei
) species. The obtained results in total suggest that a de novo chromosomal rearrangement via Robertsonian translocation (centric fusion) between two maternal (
D. raddei
) acrocentric chromosomes of different size was involved in the formation of this unique submetacentric chromosome present in the parthenogenetic species
D. rostombekowi
. Our findings provide new data in specific and rapid evolutional processes of a unisexual reptile species karyotype.
The aphid Myzus persicae is a destructive agricultural pest that displays an exceptional ability to develop resistance to both natural and synthetic insecticides. To investigate the evolution of ...resistance in this species we generated a chromosome-scale genome assembly and living panel of >110 fully sequenced globally sampled clonal lines. Our analyses reveal a remarkable diversity of resistance mutations segregating in global populations of M. persicae. We show that the emergence and spread of these mechanisms is influenced by host–plant associations, uncovering the widespread co‐option of a host-plant adaptation that also offers resistance against synthetic insecticides. We identify both the repeated evolution of independent resistance mutations at the same locus, and multiple instances of the evolution of novel resistance mechanisms against key insecticides. Our findings provide fundamental insights into the genomic responses of global insect populations to strong selective forces, and hold practical relevance for the control of pests and parasites.Singh, Bass and colleagues generate new genomic resources for the aphid crop pest, Myzus persicae, comprising a chromosome-scale genome assembly and resequenced genomes of >100 globally sampled clonal lines. Using this dataset, they uncover both mechanisms underpinning the evolution of insecticide resistance and ecological factors that influence its emergence and spread.
According to the synthesis of 30 years of multidisciplinary studies, parthenogenetic species of rock lizards of genus
were formed as a result of different combination patterns of interspecific ...hybridization of the four bisexual parental species:
,
,
, and
. In particular,
and
are considered as the parental species for the parthenogenetic species
. Here for the first time, we present the result of comparative immunocytochemical study of primary spermatocyte nuclei spreads from the leptotene to diplotene stages of meiotic prophase I in two species:
and
. We observed similar chromosome lengths for both synaptonemal complex (SC) karyotypes as well as a similar number of crossing over sites. However, unexpected differences in the number and distribution of anti-centromere antibody (ACA) foci were detected in the SC structure of bivalents of the two species. In all examined
spermatocyte nuclei, one immunostained centromere focus was detected per SC bivalent. In contrast, in almost every studied
nuclei we identified three to nine SCs with additional immunostained ACA foci per SC bivalent. Thus, the obtained results allow us to identify species-specific karyotype features, previously not been detected using conventional mitotic chromosome analysis. Presumably the additional centromere foci are result of epigenetic chromatin modifications. We assume that this characteristic of the
karyotype could represent useful marker for the future studies of parthenogenetic species hybrid karyotypes related to
.
This paper presents a checklist of aphids of Armenia. Nowadays, 203 species of aphids belonging to 83 genera, 10 subfamilies, two families and two superfamilies are known, of which nine species are ...recognized in Armenia for the first time: Aphis cephalariae Barjadze, A. chloris Koch, A. solanella Theobald, A. urticata Gmelin, A. wellensteini (Brner), Brachyunguis harmalae Das, Macrosiphoniella millefolii (De Geer), Microlophium carnosum (Buckton), and Metopeurum buryatica (Pashtshenko). Twelve alien aphid species are cited in the paper.
Eight aphid species - Aphis hederae Kaltenbach, 1843, A. mirifica (Börner, 1950), A. origani Passerini, 1860, A. umbrella (Börner, 1950), Chaitophorus horii Takahashi, 1939, Hyadaphis coriandri (Das, ...1918), Uroleucon jaceae (Linnaeus, 1758) and U. inulicola (Hille Ris Lambers, 1939) are recorded for the first time from Armenia. Additionally, Aphis mirifica and Chaitophorus horii are newly recorded species for the Caucasian aphid fauna. Sampling data, biology, and distribution for each species are provided. Key Words: Aphis, Chaitophorus, Hyadaphis, Uroleucon, Host plant, Caucasus
Сhromosomal complements of Pelophylax ridibundus Pallas, 1771 from 9 localities (Northern, Central and South Armenia) and Rana macrocnemis Boulenger, 1885 from one locality (NorthWest Armenia) have ...been analyzed. The chromosome sets of P. ridibundus collected from 8 localities showed 2n=26, (10m+12sm+4st; NF=52). A secondary constriction has been observed in all studied individuals on the 10th chromosome pair showing NORpositive reaction. Cpositive heterochromatin blocks have been observed on long arms of the 2nd and 10th pairs of chromosomes (7 localities). In addition, Cheterochromatin blocks have been found on interstitial regions of short arms of the 12th pairs, as well as in telomeric regions of long arms of the 9th pairs and on short arms of the 5th pair in the frogs from 2 localities. The karyotype of P. ridibundus from populations near Ejmiatsin differs from other populations (2n=26, 12m+10sm+4st). Diploid number of chromosomes of R. macrocnemis was also 26 (8m+12sm+6st, NF=52). Blocks of Cpositive heterochromatin have been revealed in telomeric parts of the 1st, 2nd (p), 3rd (q), 4th (q), 6th, 9th (p), 10th (p,q) and 13th (q) pairs, as well as in interstitial regions of the 1st and 2nd pairs of chromosomes. Intrapopulation and interpopulation geographic variations of karyotypes and Cheterochromatin banding patterns of P. ridibundus have been revealed. Karyotypically, morphotypes “macrocnemis” and “camerani” are closely related.
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