Comparative analysis of rDNA location in five Neotropical gomphocerine grasshopper species

Abstract

We report here, for the first time, the chromosome complement, number and location of the nucleolar organizer regions (NORs) revealed by silver staining (AgNO(3)) and fluorescent in situ hybridization (FISH) in five Neotropical gomphocerine species: Rhammatocerus brasiliensis, R. brunneri, R. palustris, R. pictus and Amblytropidia sp. The objective of this study was to summarize available data and propose a model of chromosome evolution in Neotropical gomphocerines. All five species studied showed chromosome numbers consisting of 2n = 23,X0 in males and 2n = 24,XX in females. Amblytropidia sp. was the only species showing a bivalent (M(8)) with megameric behavior during meiosis. The rDNA sites were restricted to autosomal pairs, i.e. the pericentromeric region of the S(9) chromosome, the consensus NOR location in all five species. R. brasiliensis was the only species showing additional NORs on M(4) and M(6) pairs which, likewise the S(9) NOR, were active in all cells analyzed. Comparison of these results with those reported previously in Palearctic gomphocerine species suggests higher resemblance of Neotropical species with the Old World species also possessing 23/24 chromosomes. Evolutionary mechanisms responsible for the observed interspecific variation in NOR location in this group are discussed.

Physical mapping of 18S and 5S rDNA loci and histone H3 gene in grasshopper species of the subfamily Gomphocerinae (Acrididae)

“…The chromosomes are acrocentric and divided into groups according to their size: large (L), medium (M) and small (S). The 18S rDNA site was located in the proximal region of chromosome S9 in Amblytropidia sp (Figure 1a), as previously reported by Loreto et al (2008), and in C. borelli (Figure 1b). In C. pulcher, the 18S rDNA site was detected in the interstitial region of pair M6 ( Figure 1c, g), but in O. punctata was located distally on chromosome pairs L1 and L2 (Figure 1d) (Table 2).…”

“…The position of the 18S rDNA site in the proximal region of chromosome pair 9 in C. borelli and Amblytropidia sp corresponds to that observed in five other gomphocerine species and in 16 species of the family Acrididae Loreto et al, 2008;Rocha et al, 2011;Bueno et al, 2013), all with a karyotype of 2n = 23,X0. This finding indicates that the ancestral site was located on S9 bivalent in of Neotropical gomphocerine grasshoppers (Loreto et al, 2008).…”

“…In contrast, studies of 5S rDNA sites in 14 species showed that they are present on more than one chromosome pair in 99.8% of cases; the only exceptions were Chorthippus apicalis and Stauroderus scalaris in which signals are limited to chromosome pairs 6 and 3, respectively (Loreto et al, 2008;Cabral-de-Mello et al, 2011a). These studies show the variation in dispersion of rDNA sequences, which in most species are present on two to five chromosome pairs.…”

“…This finding indicates that the ancestral site was located on S9 bivalent in of Neotropical gomphocerine grasshoppers (Loreto et al, 2008). However, 18S rDNA sites have been identified on large autosomes and the X chromosome in species with a derived karyotype (2n = 17,X0) .…”

“…Molecular cytogenetic studies using fluorescence in situ hybridization (FISH) with repetitive DNA probes, such as rDNA and histone genes, have been carried out on many grasshopper species, particularly of the family Acrididae Loreto et al, 2008;Cabrero et al, 2009;Cabral-de-Mello et al, 2011a;Oliveira et al, 2011;Rocha et al, 2011;Jetybayev et al, 2012;Bueno et al, 2013;Palacios-Gimenez et al, 2013). The objective of physical mapping of these and other repetitive DNA sequences is to provide information on chromosome structure and gene distributions in a range of species that would serve as a basis for phylogenetic studies Cabrero et al, 2009;Cabral-de-Mello et al, 2011a,b;Jetybayev et al, 2012).…”