Possible autosomal origin of macro B chromosomes in two grasshopper species

Abstract

The acrocentric macro B chromosomes of Rhammatocerus brasiliensis (Acrididae, Gomphocerinae) and Xyleus discoideus angulatus (Romaleidae, Romaleinae) are highly similar to the X chromosome in each species in terms of morphology, size, and pycnosis. However, the results of FISH experiments using 45S and 5S rDNA probes suggest that in both species the B chromosomes are most likely of autosomal origin. In R. brasiliensis, the B chromosome presented 5S rDNA but not 45S rDNA, in resemblance to the L(2), L(3), M(5) and S(11) autosomes, but the X chromosome lacks both rDNA families. In X. d. angulatus, 45S rDNAs is absent from the B chromosome, whereas the X chromosome contains one of the two 45S rDNA clusters in the genome. The occurrence of B chromosomes in all nine R. brasiliensis populations analyzed indicates that they are widely distributed in Northeastern Brazil, and the small amount of interpopulation variation found for B chromosome prevalence suggests the existence of high gene flow, presumably due to the abundance of this grasshopper species on several types of vegetation and its relatively high flight capability.

B chromosome prevalence and physical mapping of 18S rDNA and H4 histone sites in the grasshopper Xyleus discoideus angulatus (Romaleidae)

“…This is because both 18S rDNA and H4 histone are present in the pericentromeric region of X and absent in B chromosomes. Additionally, C-banding and fluorochrome staining with CMA 3 /DA/DAPI showed different patterns of heterochromatic block distribution and composition among these chromosomes (Souza et al, 1998;Loreto et al, 2008). Rebollo et al (1998) suggested another hypothesis to explain the similarities between X and B chromosomes.…”

“…Mechanisms, such as translocation and transposition, have been responsible for the dispersion of ribosomal sequences in the genomes and have been described for other grasshopper species Loreto et al, 2008). However, heteromorphism of the 18S rDNA is not uncommon in grasshoppers and variability in size, number, and location of sites has been described in several species (Souza and Moura, 2000;Cabral-de-Mello et al, 2010).…”

“…The karyotype of X. d. angulatus was first described by Mesa et al (1982), with diploid number of 2n = 23, X0/2n = 24, XX. Subsequently, conventional and molecular cytogenetic techniques, such as C-banding, base-specific fluorochromes [chromomycin A 3 /distamycin A/4,6-diamidino-2-phenylindole (CMA 3 /DA/DAPI)], silver nitrate (AgNO 3 ) impregnation, and fluorescent in situ hybridization (FISH) with 45S rDNA probe were used in karyotypic analyses of heterochromatin and nucleolar organizer regions (Souza and Silva-Filha, 1993;Souza and Kido, 1995;Souza et al, 1998;Loreto et al, 2008).…”

Short Communication A small B chromosome in the grasshopper Ommexecha virens (Ommexechidae)

“…In insects, occur mainly in Diptera, Coleoptera and Orthoptera (Loreto et al, 2008). They may have different origins, including the derivation of autosomal (Jamilena et al, 1995), sexual chromosomes (LopezLeon et al, 1994) and resulting from interspecies crosses (Mcallister and Werren, 1997).…”

“…This species has forty types of B variants along the populations found in the Mediterranean and Atlantic coasts of the Iberian Peninsula and North Africa (Cabrero et al, 1999). Loreto et al (2008) investigated the possible origin of macro B chromosome in Rhammatocerus brasiliensis and Xyleus discoideus angulatus populations originated in Northeastern region of Brazil. In these species, the B chromosome proved very similar to the X chromosome in morphology.…”