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Rapid turnover of the W chromosome in geographical populations of wild silkmoths, Samia cynthia ssp.
ŠÍCHOVÁ, Jindra
Geographical subspecies of wild silkmoths, Samia cynthia ssp. (Lepidoptera: Saturniidae) exhibit a unique polymorphism in chromosome numbers, resulting from variations in the sex chromosome systems. Three different sex chromosome constitutions were identified: Z0/ZZ in S. c. ricini (2n=27/28), neo-Wneo-Z/neo-Zneo-Z in S. c. walkeri (2n=26/26), and neo-WZ1Z2/Z1Z1Z2Z2 in S. cynthia subsp. indet. (2n=25/26). It has been proposed, that the common ancestor of S. cynthia subspecies had a classical WZ/ZZ constitution with diploid chromosome number of 2n=28/28 and the neo-sex chromosomes in S. c. walkeri and S. cynthia subsp. indet. arose by repeated sex chromosome-autosome fusions. Our sampling effort enabled us to examine five populations of S. cynthia with an ancestral-like karyotype with the aim to verify a hypothesis about sex chromosome evolution in this species complex. Obtained results suggest that the curious WZ system of S. cynthia pryeri may represent an ancestral state of the Samia species complex. However, they do not exclude an alternative hypothesis of its derived origine.
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Contrasting patterns of karyotype and sex chromosome evolution in Lepidoptera
ŠÍCHOVÁ, Jindra
It is known that chromosomal rearrangements play an important role in speciation by limiting gene flow within and between species. Furthermore, this effect may be enhanced by involvement of sex chromosomes that are known to undergo fast evolution compared to autosomes and play a special role in speciation due to their engagement in postzygotic reproductive isolation. The work presented in this study uses various molecular-genetic and cytogenetic techniques to describe karyotype and sex chromosome evolution of two groups of Lepidoptera, namely selected representatives of the family Tortricidae and Leptidea wood white butterflies of the family Pieridae. The acquired knowledge points to unexpected evolutionary dynamics of lepidopteran karyotypes including the presence of derived neo-sex chromosome systems that originated as a result of chromosomal rearrangements. We discuss the significance of these findings for radiation and subsequent speciation of both lepidopteran groups.
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Srovnání molekulární divergence pohlavních chromosomů a autosomů u příbuzných druhů obalečů (Tortricidae)
ŠÍCHOVÁ, Jindra
In systems with female heterogamety (e.g. WZ/ZZ; female/male), the Z chromosome has several characteristics that distinguish it from autosomes, such as different effective population size (Ne) and hemizygosity in the heterogametic sex. These characteristics may lead to an accelerated rate of adaptive changes for the Z-linked genes compared to autosomal coding sequences, often referred to as the Fast-Z effect. This work is the first attempt to test the Fast Z effect in Lepidoptera by using two methodological approaches. These included comparative fluorescence in situ hybridizations and comparisons of substitution rates in coding sequences.
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Analýza pohlavního chromosomu Z obaleče jablečného(\kur{Cydia pomonella}) pomocí laserové mikrodisekce
ŠÍCHOVÁ, Jindra
This study uses a new methodical approach for the molecular analysis of the lepidopteran Z chromosome. The Z-chromosome DNA was collected from male mitotic spermatogonial cells of the codling moth (Cydia pomonella) by laser microdissection and then amplified by degenerate oligonucleotide-primed polymerase chain reaction (DOP-PCR). Products of DOP-PCR were used to prepare painting probes and create a Z-chromosome DNA sequence library. Specificity of painting probes was tested on spread chromosomal preparations from testes and ovaries of the codling moth larvae using fluorescence in situ hybridization (FISH). However, all painting probes made exhibited a low specificity for the Z chromosome: they hybridized evenly to all chromosomes in male preparations, whereas in female preparations highlighted almost the entire W chromosome. For construction of the Z-chromosome DNA library, DOP-PCR-generated DNA fragments were cloned, sequenced and further analyzed. A total of 30 different sequences were obtained. Only four of the sequences exhibited a significant homology to sequences in GenBank, all other represent unknown sequences. Five sequences were characterized by Southern hybridization. The results correlated with hybridization signals from FISH; we recovered highly repetitive sequences, either ubiquitous(i.e. occurring in all chromosomes) and/or accumulated on the W chromosome. Only a few copies were located on Z chromosome.
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