| 1. |
- Lukhtanov, Vladimir A., et al.
(författare)
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Incomplete Sterility of Chromosomal Hybrids : Implications for Karyotype Evolution and Homoploid Hybrid Speciation
- 2020
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Ingår i: Frontiers in Genetics. - : Frontiers Media SA. - 1664-8021. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Heterozygotes for major chromosomal rearrangements such as fusions and fissions are expected to display a high level of sterility due to problems during meiosis. However, some species, especially plants and animals with holocentric chromosomes, are known to tolerate chromosomal heterozygosity even for multiple rearrangements. Here, we studied male meiotic chromosome behavior in four hybrid generations (F1-F4) between two chromosomal races of the Wood White butterfly Leptidea sinapis differentiated by at least 24 chromosomal fusions/fissions. Previous work showed that these hybrids were fertile, although their fertility was reduced as compared to crosses within chromosomal races. We demonstrate that (i) F1 hybrids are highly heterozygous with nearly all chromosomes participating in the formation of trivalents at the first meiotic division, and (ii) that from F1 to F4 the number of trivalents decreases and the number of bivalents increases. We argue that the observed process of chromosome sorting would, if continued, result in a new homozygous chromosomal race, i.e., in a new karyotype with intermediate chromosome number and, possibly, in a new incipient homoploid hybrid species. We also discuss the segregational model of karyotype evolution and the chromosomal model of homoploid hybrid speciation.
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| 2. |
- Lukhtanov, Vladimir A., et al.
(författare)
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Versatility of multivalent orientation, inverted meiosis, and rescued fitness in holocentric chromosomal hybrids
- 2018
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 115:41, s. E9610-E9619
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 3. |
- Sahoo, Ranjit Kumar, et al.
(författare)
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Ten genes and two topologies : An exploration of higher relationships in skipper butterflies (Hesperiidae)
- 2016
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Ingår i: PeerJ. - : PeerJ. - 2167-8359. ; 2016:12
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Tidskriftsartikel (refereegranskat)abstract
- Despite multiple attempts to infer the higher-level phylogenetic relationships of skipper butterflies (Family Hesperiidae), uncertainties in the deep clade relationships persist. The most recent phylogenetic analysis included fewer than 30% of known genera and data from three gene markers. Here we reconstruct the higher-level relationships with a rich sampling of ten nuclear and mitochondrial markers (7,726 bp) from 270 genera and find two distinct but equally plausible topologies among subfamilies at the base of the tree. In one set of analyses, the nuclear markers suggest two contrasting topologies, one of which is supported by the mitochondrial dataset. However, another set of analyses suggests mito-nuclear conflict as the reason for topological incongruence. Neither topology is strongly supported, and we conclude that there is insufficient phylogenetic evidence in the molecular dataset to resolve these relationships. Nevertheless, taking morphological characters into consideration, we suggest that one of the topologies is more likely.
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