Dynamic karyotype evolution and unique sex determination systems in Leptidea wood white butterflies

[Background] Chromosomal rearrangements have the potential to limit the rate and pattern of gene flow within and between species and thus play a direct role in promoting and maintaining speciation. Wood white butterflies of the genus Leptidea are excellent models to study the role of chromosome rearrangements in speciation because they show karyotype variability not only among but also within species. In this work, we investigated genome architecture of three cryptic Leptidea species (L. juvernica, L. sinapis and L. reali) by standard and molecular cytogenetic techniques in order to reveal causes of the karyotype variability.[Results] Chromosome numbers ranged from 2n = 85 to 91 in L. juvernica and 2n = 69 to 73 in L. sinapis (both from Czech populations) to 2n = 51 to 55 in L. reali (Spanish population). We observed significant differences in chromosome numbers and localization of cytogenetic markers (rDNA and H3 histone genes) within the offspring of individual females. Using FISH with the (TTAGG) n telomeric probe we also documented the presence of multiple chromosome fusions and/or fissions and other complex rearrangements. Thus, the intraspecific karyotype variability is likely due to irregular chromosome segregation of multivalent meiotic configurations. The analysis of female meiotic chromosomes by GISH and CGH revealed multiple sex chromosomes: W1W2W3Z1Z2Z3Z4 in L. juvernica, W1W2W3Z1Z2Z3 in L. sinapis and W1W2W3W4Z1Z2Z3Z4 in L. reali.[Conclusions] Our results suggest a dynamic karyotype evolution and point to the role of chromosomal rearrangements in the speciation of Leptidea butterflies. Moreover, our study revealed a curious sex determination system with 3–4 W and 3–4 Z chromosomes, which is unique in the Lepidoptera and which could also have played a role in the speciation process of the three Leptidea species.This research was funded by Grant 14-22765S of the Czech Science Foundation, Grant IAA600960925 of the Grant Agency of The Czech Academy of Sciences, Grant 063/2012/P of the Grant Agency of the University of South Bohemia and Grant CGL2013-48277-P from the Spanish Ministerio de Economía y Competitividad. JŠ and AV were supported by Grant 052/2013/P of the Grant Agency of the University of South Bohemia, VD by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme (project no. 625997), PN by Grant 14-35819P of the Czech Science Foundation and KS by JSPS 23380030 grant and JSPS Excellent Young Researchers Overseas Visit Program (21–7147).Peer reviewe

Rapid turnover of the W chromosome in geographical populations of wild silkmoths, Samia cynthia ssp.

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

Contrasting patterns of karyotype and sex chromosome evolution in Lepidoptera

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

Analysis of the codling moth (\kur{Cydia pomonella}) Z chromosome by means of laser microdissection.

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

Molecular divergence of sex chromosomes compared to autosomes in related species of tortricids

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

Dynamic karyotype evolution and multiple sex chromosomes in wood white butterflies

Trabajo presentado en la 19th International Chromosome Conference (ICC), celebrado en Bologna del 2 al 6 de septiembre de 2013.Lepidopteran genomes consist of small-sized holokinetic chromosomes with an ancestral chromosome number of n=31, and a prevalent WZ/ZZ sex chromosome system with female heterogamety. Although the holokinetic nature of lepidopteran chromosomes is supposed to facilitate karyotype evolution mainly due to chromosomal fusions and fissions, recent studies revealed a highly conserved synteny of genes between chromosomes of distantly related taxa and evolutionary stability of karyotypes. The high degree of conservation at the chromosomal level across the phylogenetic tree of Lepidoptera contrasts with exceptional diversity found in some taxa. A typical example is the butterfly genus Leptidea, which shows karyotype variability not only between but also within species. In this work we studied karyotypes of three cryptic Leptidea species (L. juvernica, L. sinapis, and L. reali) by means of standard and molecular cytogenetic techniques.This research was funded by GAAV IAA600960925, GAJU 052/2013/P, and 063/2012/P grants.N

Evolution of multiple sex-chromosomes associated with dynamic genome reshuffling in Leptidea wood-white butterflies

Sex-chromosome systems tend to be highly conserved and knowledge about their evolution typically comes from macroevolutionary inference. Rapidly evolving complex sex-chromosome systems represent a rare opportunity to study the mechanisms of sex-chromosome evolution at unprecedented resolution. Three cryptic species of wood-white butterflies—Leptidea juvernica, L. sinapis and L. reali—have each a unique set of multiple sex-chromosomes with 3–4 W and 3–4 Z chromosomes. Using a transcriptome-based microarray for comparative genomic hybridisation (CGH) and a library of bacterial artificial chromosome (BAC) clones, both developed in L. juvernica, we identified Z-linked Leptidea orthologs of Bombyx mori genes and mapped them by fluorescence in situ hybridisation (FISH) with BAC probes on multiple Z chromosomes. In all three species, we determined synteny blocks of autosomal origin and reconstructed the evolution of multiple sex-chromosomes. In addition, we identified W homologues of Z-linked orthologs and characterised their molecular differentiation. Our results suggest that the multiple sex-chromosome system evolved in a common ancestor as a result of dynamic genome reshuffling through repeated rearrangements between the sex chromosomes and autosomes, including translocations, fusions and fissions. Thus, the initial formation of neo-sex chromosomes could not have played a role in reproductive isolation between these Leptidea species. However, the subsequent species-specific fissions of several neo-sex chromosomes could have contributed to their reproductive isolation. Then, significantly increased numbers of Z-linked genes and independent neo-W chromosome degeneration could accelerate the accumulation of genetic incompatibilities between populations and promote their divergence resulting in speciation.This research was funded by grant 14-22765S and follow-up grant 17-13713S of the Czech Science Foundation (CSF). Publishing was supported by CSF grant 20-13784S given to FM. PN was supported by CSF grants 17-17211S and 20-20650Y. RV acknowledges support from project CGL2016-76322-P (AEI/FEDER, UE).Peer reviewe

Identification of WZ bivalents in orcein-stained preparations of pachytene oocytes of three tortricid species.

<p><b>a</b> – pachytene complement of <i>Grapholita molesta</i>; the WZ bivalent is indistinguishable. <b>b</b> – incomplete pachytene nucleus of <i>Lobesia botrana</i>; note a WZ bivalent (arrow) identified according to W-chromosome heterochromatin. <b>c</b> – a WZ bivalent of <i>L. botrana</i>; note the deeply stained W-chromosome thread while the Z-chromosome thread shows a chromomere pattern (see arrowheads pointing to deeply stained chromatin beads). <b>d</b> – a part of pachytene nucleus of <i>Eupoecilia ambiguella</i> with a WZ bivalent (arrow) anchored by one end in the nucleolus (N); note that most of the W chromosome is formed by a continuous thread except the end opposite to the nucleolar end, which shows a chromomere pattern similar to the Z chromosome (arrowheads). <b>e</b> – a part of zygotene/early pachytene nucleus of <i>E. ambiguella</i> with not yet paired sex chromosomes; note W and Z univalents (arrows) anchored by one end in the nucleolus (N); also note a deeply stained Z-end (arrowhead) inbuilt in the nucleolus. Bar = 10 µm; <b>b–e</b> have the same scale.</p

Karyotype numbers (2n) in Tortricidae.

a<p>Species names are used according to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0064520#pone.0064520-Gilligan1" target="_blank">[19]</a>;</p>b<p>syn. <i>Choristoneura cerasivorana;</i></p>c<p>syn. <i>Homona menciana;</i></p>d<p>syn. <i>Pseudococcyx tessulatana;</i></p>e<p>syn. <i>Epinotia (Griselda) radicana;</i></p>f<p>syn. <i>Petrova albicapitana;</i></p>g<p><i>Zeiraphera diniana;</i></p>h<p><i>Sciaphila duplex;</i></p>i<p>species with multiple sex chromosomes W₁W₂Z/ZZ (female/male).</p

Chromosome preparations of wing discs in four members of the family Tortricidae.

<p>Spread mitotic chromosomes were stained with DAPI. White lines point to the largest chromosomes in the karyotype, the W and Z sex chromosomes. <i>Grapholita molesta</i> (<b>a</b>, <b>b</b>): <b>a</b> – male mitotic metaphase (2n = 56); <b>b</b> – female mitotic metaphase (2n = 56). <i>Grapholita funebrana</i> (<b>c</b>, <b>d</b>): <b>c</b> – male mitotic complement (2n = 56); <b>d</b> – female mitotic complement (2n = 56). <i>Lobesia botrana</i> (<b>e</b>, <b>f</b>): <b>e</b> – male mitotic nucleus (2n = 56); <b>f</b> – female mitotic nucleus (2n = 56) with indiscernible sex chromosome pair (arrows); the inset in the bottom left corner shows a detail of another mitotic nucleus with differentiated W and Z chromosomes. <i>Eupoecilia ambiguella</i> (<b>g</b>, <b>h</b>): <b>g</b> – spread male mitotic metaphase (2n = 60); <b>h</b> – spread female mitotic metaphase (2n = 60). Bar = 5 µm.</p