Cytogenetics of four Omophoita species (Coleoptera, Chrysomelidae, Alticinae): A comparative analysis using mitotic and meiotic cells submitted to the standard staining and C-banding technique

Checklist of Omophoita Chevrolat, 1836 (Coleoptera: Chrysomelidae: Galerucinae: Alticini) and diagnoses for some species from southern Brazil: notes on the taxonomic history, redescriptions and new records

Morphological descriptions, taxonomic history and distribution data of Omophoita species recorded for southern Brazil (states of Paran, Santa Catarina and Rio Grande do Sul) are presented. Through the analysis of the existing literature, databases, loaned material, and specimen collecting, we studied seven species of Omophoita recorded for southern Brazil: O. communis (Bechyn 1959), O. equestris (Fabricius 1787), O. magniguttis (Bechyn 1955), O. octoguttata (Fabricius 1775), O. personata (Illiger 1807), O. sesquilunata (Klug 1829), and O. sexnotata (Harold 1876). We report O. sesquilunata for this region for the first time. Updated morphological descriptions, including novel information for male and female genitalia are presented for those taxa with dissected specimens.

Giant Sex Chromosomes in Omophoita Species (Coleoptera, Chrysomelidae): Structural and Evolutionary Relationships Revealed by Zoo-FISH and Comparative Genomic Hybridization (CGH)

The beetles of the subtribe Oedionychina (Chrysomelidae, Alticinae) are the only ones that have the atypical giant and achiasmatic sex chromosomes, which are substantially larger than the autosomes. Previous cytogenetic analyses suggest a large accumulation of repetitive DNA in the sex chromosomes. In this study, we examined the similarity of X and Y chromosomes in four Omophoita species and compared genomic differentiation to better understand the evolutionary process and the giant sex chromosomes origin. Intraspecific genomic comparation using male and female genomes of O. octoguttata and interespecific analyses using genomic DNA of O. octoguttata, O. sexnotata, O. magniguttis, and O. personata were performed. In addition, whole chromosome painting (WCP) experiments were performed with X and Y chromosome probes of O. octogutatta. CGH analysis revealed great genomic similarity between the sexes and a sex-specific region on the Y chromosome, and interspecific analysis revealed a genomic divergence between species. In contrast, WCP results revealed that the sex chromosomes of O. octoguttata have high intra- and interspecific similarity with the studied species. Our data support a common origin under the canonical evolution of the sex chromosomes in this group, as they have high genomic similarity between them.

Cytogenetic and Molecular Characterization of Three Mimetic Species of the Genus Alagoasa Bechyné 1955 (Coleoptera: Alticinae) from the Neotropical Region

Coleoptera is a mega-diverse order, but only about 1% of its species have been analyzed cytogenetically. In this order, the subfamily Alticinae presents many identification problems, mainly due to the occurrence of mimicry. The objective of this work was to cytogenetically characterize 3 very similar species of the genus Alagoasa (A. pantina, A.areata, and A.scissa). We used classical and molecular cytogenetic as well as molecular genetic techniques. All 3 species showed a diploid chromosome number of 2n = 22 (20+X+y), but differences in the morphology of the chromosomes. All had a meiotic formula of 2n = 10II+X+y and an X+y sex determination system with giant, fully asynaptic sex chromosomes, concordant characteristics observed in the subtribe Oedionychina. FISH demonstrated the presence of 18S and 5S rDNA clusters in 1 pair of autosomes, syntenic and colocalizing in the 3 analyzed species. However, in A. areata, heteromorphism between the cistrons was observed. The telomeric (TTAGG)n probe showed signals in all 3 species, with proximal signals in the X and dispersed signals in the y chromosome of A. areata, and 2 proximal signals in the X chromosome of A. scissa. Molecular analysis of the COI gene indicated that they are 3 distinct species, corroborating the observed cytogenetic characteristics.

Accumulation of Transposable Elements in Autosomes and Giant Sex Chromosomes of Omophoita (Chrysomelidae: Alticinae)

Coleoptera is the most diverse order among insects, and comparative molecular cytogenetic studies in this group are lacking. The species of Omophoita (Oedionychina) possess a karyotype of 2n = 22 = 10II+X+Y. They are interesting models for evolutionary cytogenetic studies due to giant sex chromosomes which are asynaptic during meiosis. Transposable elements (TEs) confer plasticity and mobility to genomes and are considered hotspots for DNA double-strand breaks and chromosomal rearrangements. The objective of the present study was to verify the role of TEs in the karyotype and in the size expansion of the giant sex chromosomes in Omophoita. Thus, different TEs were characterized in the Omophoita genome and localized in the chromosomes by fluorescence in situ hybridization (FISH). The DNA sequencing data revealed identity with TE families Tc1/Mariner and RTE/L1-56_XT. FISH showed signals of all TEs in the karyotypes and a high accumulation in the sex chromosomes of the 3 Omophoita species analyzed. These data suggest that the genome size expansion and the origin of the giant sex chromosomes of Omophoita are due to an intensive genomic invasion of TEs, as those characterized here as Tc1/Mariner-Ooc and RTE-Ooc. Differences in the chromosomal location of the TEs among the 3 species indicate that they have participated in the karyotype differentiation in Omophoita.

Comparative Cytogenetics of Omophoita abbreviata and O. aequinoctialis (Coleoptera, Chrysomelidae, Alticini) from the Adolpho Ducke Forest Reserve in Brazilian Amazonia: Intrapopulation Variation in Karyotypes

The chromosomes of 2 flea beetle species from central Amazonia, Omophoita abbreviata and O. aequinoctialis (Alticini), were investigated through analysis of meiotic and mitotic cells. These species belong to the subtribe Oedionychina, a taxon that has unique cytogenetic features, such as giant sex chromosomes which are aligned at a distance during meiosis I (asynaptic). O. abbreviata and O. aequinoctialis have a meiotic formula of 10II + X + y, which is predominant in this subtribe. While the species of the genus Omophoita possess a relatively stable karyotype, a typical feature for Oedionychina, the present study identified inter- and intrapopulational variation in chromosome morphology, constitutive heterochromatin, and the presence and number of B chromosomes in O. aequinoctialis. In addition, FISH mapping of telomeric sequences revealed signals in the collochores, raising several questions on the chromosomal evolution in this group.

Karyotype diversity of pseudoscorpions of the genus Chthonius (Pseudoscorpiones, Chthoniidae) in the Alps

Pseudoscorpions are found in almost all terrestrial habitats. However, their uniform appearance presents a challenge for morphology-based taxonomy, which may underestimate the diversity of this order. We performed cytogenetic analyses on 11 pseudoscorpion species of the genus Chthonius C. L. Koch, 1843 from the Alps, including three subgenera: Chthonius (Chthonius) C. L. Koch, 1843, Chthonius (Ephippiochthonius) Beier, 1930 and Chthonius (Globochthonius) Beier, 1931 inhabiting this region. The results show that the male diploid number of chromosomes ranges from 21-35. The sex chromosome system X0 has been detected in all male specimens. The X sex chromosome is always metacentric and represents the largest chromosome in the nucleus. Achiasmatic meiosis, already known from the family Chthoniidae, was further confirmed in males of Chthonius. C-banding corroborated the localization of constitutive heterochromatin in the centromere region, which corresponds to heteropycnotic knobs on the standard chromosome preparations. Morphological types and size differentiation of chromosomes in the karyotype suggest that the main chromosomal rearrangements in the evolution of Chthonius are centric or tandem fusions resulting in a decrease in the number of chromosomes. Pericentric inversions, inducing the change of acrocentric chromosomes into biarmed chromosomes, could also be expected. Variability in chromosome morphology and number was detected in several species: Chthonius (Chthonius) ischnocheles (Hermann, 1804), Chthonius (Chthonius) raridentatus, Chthonius (Chthonius) rhodochelatus Hadži, 1930, and Chthonius (Chthonius) tenuis L. Koch, 1873. We discuss the intraspecific variability within these species and the potential existence of cryptic species.

Physical mapping of 18S rDNA cistron in species of the Omophoita genus (Coleoptera, Alticinae) using fluorescent in situ hybridization

Alticinae has the greatest amount of biodiversity among the Chrysomelidae, with 40,000 described species, only 290 of which have been analyzed cytogenetically. The majority of studies refer to conventional staining and few species have been analyzed or have responded to differential staining methods. The aim of the present study was to describe an 18S rDNA probe for Alticinae and the location of this cluster in species of the Omophoita genus. The fragment of approximately 750bp obtained through a PCR (Polymerase Chain Reaction) amplification reaction with specific oligonucleotides to 18S rDNA was cloned and denominated pTZ_Ooct_18Sp and then submitted to automatic sequencing. The alignment of the sequences obtained through the sequencing of the clones generated a consensus sequence of 722bp for Omophoita octoguttata with 98% homology with other species of Alticinae. The analysis of mitotic cells of O. octoguttata and Omophoita magniguttis submitted to fluorescent in situ hybridization (FISH) with the 18S rDNA probe revealed that the ribosomal genes are located in 6th pair. O. magniguttis also has a second labeled pair. Omophoita personata exhibited nucleolar organizer regions associated to one autosome pair. The analysis of meiotic cells submitted to FISH revealed one labeled bivalent in metaphase I in O. octoguttata and O. personata and in one chromosome in metaphase II in O. octoguttata. FISH data suggest a conserved pattern in the species analyzed and an apomorphy of O. magniguttis karyotype. The rDNA 18S probe could be considered an important marker to evidence the karyotypic differentiation, not observed with conventional methodologies, in species considered karyotypically conserved and uniform.