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      Two types of highly ordered micro- and macrochromosome arrangement in metaphase plates of butterflies (Lepidoptera)

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          Abstract

          Abstract

          In karyotype of many organisms, chromosomes form two distinct size groups: macrochromosomes and microchromosomes. During cell divisions, the position of the macro- and microchromosomes is often ordered within metaphase plate. In many reptiles, amphibians, birds, insects of the orthopteran family Tettigoniidae and in some plants, a so called “reptilian” type organization is found, with microchromosomes situated in the center of metaphase plate and with macrochromosomes situated at the periphery. An opposite, “lepidopteran” type is known in butterflies and moths (i.e. in the order Lepidoptera ) and is characterized by macrochromosomes situated in the center and by microchromosomes situated at the periphery. The anomalous arrangement found in Lepidoptera was previously explained by holocentric organization of their chromosomes. Here I analyse the structure of meiotic metaphase I plates in ithomiine butterfly, Forbestra olivencia (H. Bates, 1862) ( Nymphalidae , Danainae , Ithomiini ) which has a clear “reptilian” organization, contrary to previous observations in Lepidoptera . In this species large bivalents (i.e. macrochromosomes) form a regular peripheral circle, whereas the minute bivalents (i.e. microchromosomes) occupy the center of this circle. The reasons and possible mechanisms resulting in two drastically different spatial chromosome organization in butterflies are discussed.

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          An inexpensive, automation-friendly protocol for recovering high-quality DNA

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            Critical factors for assembling a high volume of DNA barcodes.

            Large-scale DNA barcoding projects are now moving toward activation while the creation of a comprehensive barcode library for eukaryotes will ultimately require the acquisition of some 100 million barcodes. To satisfy this need, analytical facilities must adopt protocols that can support the rapid, cost-effective assembly of barcodes. In this paper we discuss the prospects for establishing high volume DNA barcoding facilities by evaluating key steps in the analytical chain from specimens to barcodes. Alliances with members of the taxonomic community represent the most effective strategy for provisioning the analytical chain with specimens. The optimal protocols for DNA extraction and subsequent PCR amplification of the barcode region depend strongly on their condition, but production targets of 100K barcode records per year are now feasible for facilities working with compliant specimens. The analysis of museum collections is currently challenging, but PCR cocktails that combine polymerases with repair enzyme(s) promise future success. Barcode analysis is already a cost-effective option for species identification in some situations and this will increasingly be the case as reference libraries are assembled and analytical protocols are simplified.
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              Versatility of multivalent orientation, inverted meiosis, and rescued fitness in holocentric chromosomal hybrids

              Changes in the number and/or structure of chromosomes (i.e., chromosomal rearrangements) have the potential to drive speciation. However, their accumulation in a population is considered both difficult and unpredictable, because the greatly reduced reproductive fitness of chromosomal hybrids prevents fixation of novel karyotypes. Here, we provide evidence for a mechanism that rescues fertility of chromosomal hybrids in species with holocentric chromosomes. We demonstrate that chromosomal heterozygotes of Leptidea Wood White butterflies have a reverse order of main meiotic events in which the first and most critical stage of the chromosome number reduction is replaced by the less risky stage of sister chromatid separation. This may facilitate long-term persistence of chromosomal rearrangements, which is a major prerequisite for chromosomal speciation. Chromosomal rearrangements (e.g., fusions/fissions) have the potential to drive speciation. However, their accumulation in a population is generally viewed as unlikely, because chromosomal heterozygosity should lead to meiotic problems and aneuploid gametes. Canonical meiosis involves segregation of homologous chromosomes in meiosis I and sister chromatid segregation during meiosis II. In organisms with holocentric chromosomes, which are characterized by kinetic activity distributed along almost the entire chromosome length, this order may be inverted depending on their metaphase I orientation. Here we analyzed the evolutionary role of this intrinsic versatility of holocentric chromosomes, which is not available to monocentric ones, by studying F 1 to F 4 hybrids between two chromosomal races of the Wood White butterfly ( Leptidea sinapis ), separated by at least 24 chromosomal fusions/fissions. We found that these chromosomal rearrangements resulted in multiple meiotic multivalents, and, contrary to the theoretical prediction, the hybrids displayed relatively high reproductive fitness (42% of that of the control lines) and regular behavior of meiotic chromosomes. In the hybrids, we also discovered inverted meiosis, in which the first and critical stage of chromosome number reduction was replaced by the less risky stage of sister chromatid separation. We hypothesize that the ability to invert the order of the main meiotic events facilitates proper chromosome segregation and hence rescues fertility and viability in chromosomal hybrids, potentially promoting dynamic karyotype evolution and chromosomal speciation.
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                Author and article information

                Contributors
                Journal
                Comp Cytogenet
                Comp Cytogenet
                CompCytogen
                Comparative Cytogenetics
                Pensoft Publishers
                1993-0771
                1993-078X
                2019
                14 January 2019
                : 13
                : 1
                : 19-25
                Affiliations
                [1 ] Department of Karyosystematics, Zoological Institute of the Russian Academy of Sciences, Universitetskaya nab. 1, St. Petersburg 199034, Russia Zoological Institute of the Russian Academy of Sciences St. Petersburg Russia
                [2 ] Department of Entomology, St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg 199034, Russia St. Petersburg State University St. Petersburg Russia
                Author notes
                Corresponding author: Vladimir A. Lukhtanov ( lukhtanov@ 123456mail.ru )

                Academic editor: V.G. Kuznetsova

                Article
                10.3897/CompCytogen.v13i1.32614
                6341045
                4a0bba67-e8d2-4bcf-999a-824a066fcec7
                Vladimir A. Lukhtanov

                This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 21 December 2018
                : 23 December 2018
                Categories
                Short Communication
                Animalia
                Lycaenidae
                Nymphalidae
                Evolutionary Biology
                Genetics
                Systematics
                South America

                asymmetrical karyotype,dna barcoding,bivalent,coi,holocentric,holokinetic,kinetochore,meiosis,metaphase,spindle,spermatocyte, lepidoptera , nymphalidae , danainae , ithomiini ,peru

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