A new approach to chromosomal evolution in the giant water bug (Heteroptera: Belostomatidae) (original) (raw)
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Comparative Cytogenetics, 2013
Male meiosis behaviour and heterochromatin characterization of three big water bug species were studied. Belostoma dentatum (Mayr, 1863), B. elongatum Montandon, 1908 and B. gestroi Montandon, 1903 possess 2n = 26 + X 1 X 2 Y (male). In these species, male meiosis is similar to that previously observed in Belostoma Latreille, 1807. In general, autosomal bivalents show a single chiasma terminally located and divide reductionally at anaphase I. On the other hand, sex chromosomes are achiasmatic, behave as univalents and segregate their chromatids equationally at anaphase I. The analysis of heterochromatin distribution and composition revealed a C-positive block at the terminal region of all autosomes in B. dentatum, a Cpositive block at the terminal region and C-positive interstitial dots on all autosomes in B. elongatum, and a little C-positive band at the terminal region of autosomes in B. gestroi. A C-positive band on one bivalent was DAPI negative/CMA 3 positive in the three species. The CMA 3-bright band, enriched in GC base pairs, was coincident with a NOR detected by FISH. The results obtained support the hypothesis that all species of Belostoma with multiple sex chromosome systems preserve NORs in autosomal bivalents. The karyotype analyses allow the cytogenetic characterization and identification of these species belonging to a difficult taxonomic group. Besides, the cytogenetic characterization will be useful in discussions about evolutionary trends of the genome organization and karyotype evolution in this genus.
Genes
The Lygaeoidea comprise about 4660 species in 790 genera and 16 families. Using standard chromosome staining and FISH with 18S rDNA and telomeric (TTAGG)n probes, we studied male karyotypes and meiosis in 10 species of Lygaeoidea belonging to eight genera of the families Blissidae, Cymidae, Heterogastridae, Lygaeidae, and Rhyparochromidae. Chromosome numbers were shown to range from 12 to 28, with 2n = 14 being predominant. All species have an XY system and all but one have a pair of m-chromosomes. The exception is Spilostethus saxatilis (Lygaeidae: Lygaeinae); in another species of Lygaeinae, Thunbergia floridulus, m-chromosomes were present, which represents the first finding for this subfamily. All species have an inverted sequence of sex chromosome divisions (“post-reduction”). The 18S rDNA loci were observed on one or both sex chromosomes in Kleidocerys resedae and Th. floridulus, respectively (Lygaeidae), while on an autosomal bivalent in all other species. The rDNA loci tende...
European Journal of Entomology, 2014
A novel chromosome complement (2n = 14 = 12 + XY/XX; male/female sex chromosomes), male meiosis behaviour, het erochromatin characterization, and frequency and distribution of chiasmata are described for the first time in specimens from a natural population of the giant water bug, Belostoma candidulum Montandon, 1903 (Heteroptera: Belostomatidae) from Argentina. To date, specimens of B. candidulum have been reported by other authors in a sample from a natural population from Brazil. Our results dem onstrate that Argentinean and Brazilian populations have different diploid numbers and chromosomal features. During male meiosis, autosomal bivalents generally show a single chiasma, behave as telokinetic chromosomes (i.e. kinetic activity is restricted to terminal regions), and divide reductionally at anaphase I; in contrast, the sex chromosomes are achiasmatic, behave as univalents and segregate equationally at anaphase I. Among autosomal bivalents of B. candidulum, one is remarkably larger and may present one or two termi nal chiasmata, showing rod, V-shaped and ring configurations. Here we propose a new mode of segregation for ring bivalents, since it is not essential that one of the chiasmata is released during anaphase I because alternative sites for microtubule attachment become functional for the normal chromosome segregation to the poles. Heterochromatin content is very scarce in specimens from Argentinean B. candidulum populations, revealing Cpositive interstitial and terminal dots in three pairs of autosomes and Cblocks at both ends of X chromosome, whereas the Y chromosome is mainly Cpositive. One of the Cpositive bands from X and Y chromosomes is DAPI dull/CMA-bright, which could represent the nucleolus organizing region (NOR) detected by fluorescent in situ hybridization (FISH). The location of the NORs in both sex chromosomes allowed us to use them as a cytological marker to describe their behaviour during meiosis. Despite the fact that specimens from the Argentinean and Brazilian populations have been classified as a single species due to their morphological similarity, our results suggest that both populations are chromosomal races or even morphologicallyidentical cryptic species. The results obtained support the hypothesis that karyotype of B. candidulum originated through autosomal fusions and the fusion of the X and Y chromosomes with the ancestral NORautosomal pair. Lastly, the genus Belostoma represents an excellent model for assessing the main mechanisms involved in the karyotype evolution in organisms with holokinetic chromosomes, from which inferences may be made concerning its broader ecology and evolution.
Evolutionary cytogenetics in Heteroptera
Journal of Biological Research
INTRODUCTION Cytogenetic studies in Heteroptera date from 1891 with Henking's morphological study on the sper-matogenesis of the bug Pyrrhocoris apterus Linnaeus (Pyrrhocoridae). He described the presence of a chromatin body (the "X chromosome") that showed an unusual staining during meiotic prophase and a peculiar behaviour during meiosis. The observations of Henking and other cytologists, together with their own observations in males and females of different Heteroptera species, were finally interpreted by Mc Clung (1901) and Wilson (1909b). They suggested a direct relationship between sex determination and presence of either one or two "X chromosomes" in X0/XX systems, or an XY or XX chromosome pair in species with XY/XX systems. Through a series of publications that appeared between 1897 and 1932, Wilson and Montgomery settled the foundations on Heteroptera cytogenetics. Some years later, between the 1930s and the 1960s, Schrader and Hughes-Schrader contr...
Biological Journal of the Linnean Society, 2020
The Polyommatus butterflies have holocentric chromosomes, which are characterized by kinetic activity distributed along the entire chromosome length, and the highest range of haploid chromosome numbers (n) known within a single eukaryotic genus (from n = 10 to n = 226). Previous analyses have shown that these numbers most likely evolved gradually from an ancestral karyotype, in accordance with the Brownian motion model of chromosome change accumulation. Here we studied chromosome sets within a monophyletic group of previously non-karyotyped Polyommatus species. We demonstrate that these species have a limited interspecific chromosome number variation from n = 16 to n = 25, which is consistent with the Brownian motion model prediction. We also found intra- and interpopulation variation in the chromosome numbers. These findings support the model of karyotype evolution through the gradual accumulation of neutral or weakly underdominant rearrangements that can persist in the heterozygou...
2020
The structure of a genome can be described at its simplest by the number of chromosomes and the sex chromosome system it contains. Despite over a century of study, the evolution of genome structure on this scale remains recalcitrant to broad generalizations that can be applied across clades. To address this issue, we have assembled a dataset of 823 karyotypes from the insect group Polyneoptera. This group contains orders with a range of variations in chromosome number, and offer the opportunity to explore the possible causes of these differences. We have analysed this data using both phylogenetic and taxonomic approaches. Our analysis allows us to assess the importance of rates of evolution, phylogenetic history, sex chromosome systems, parthenogenesis and genome size on variation in chromosome number within clades. We find that fusions play a key role in the origin of new sex chromosomes, and that orders exhibit striking differences in rates of fusions, fissions and polyploidy. Our...
Comparative cytogenetics, 2015
The karyotypes of Luciliacluvia (Walker, 1849) and Luciliasericata (Meigen, 1826) from Argentina were characterized using conventional staining and the C- and G-like banding techniques. Besides, nucleolus organizer regions (NORs) were detected by fluorescent in situ hybridization (FISH) and silver staining technique. The chromosome complement of these species comprises five pairs of autosomes and a pair of sex chromosomes (XX/XY, female/male). The autosomes of both species have the same size and morphology, as well as C- and G-like banding patterns. The X and Y chromosomes of Luciliacluvia are subtelocentric and easily identified due to their very small size. In Luciliasericata, the X chromosome is metacentric and the largest of the complement, showing a secondary constriction in its short arm, whereas the Y is submetacentric and smaller than the X. The C-banding patterns reflect differences in chromatin structure and composition between the subtelocentric X and Y chromosomes of Luc...