Ommexecha virens (Thunberg, 1824) and Descampsacris serrulatum (Serville, 1831) (Orthoptera, Ommexechidae): karyotypes, constitutive heterochromatin and nucleolar organizing regions

Abstract

Chromosomes of Ommexecha virens and Descampsacris serrulatum (Ommexechidae) were analyzed through conventional staining, C-banding, base specific fluorochromes, silver nitrate impregnation (AgNO3), and fluorescent in situ hybridization (FISH) with probe for 45S rDNA. The two species presented diploid number 2n= 23,X0 in males and acrocentric autosomes, except the pair one that presented submetacentric morphology. The X chromosome has distinct morphology in the two analyzed species, being a medium acrocentric in Ommexecha virens and large submetacentric in Descampsacris serrulatum. The C-banding revealed pericentromeric blocks of constitutive heterochromatin (CH) in all the chromosomes of Descampsacris serrulatum. For Ommexecha virens it was evidenced that the blocks of CH are preferentially located in the pericentromeric area (however some bivalents presents additional blocks) or in different positions. The staining with CMA3/DA/DAPI showed GC rich CH blocks (CMA3+) in some chromosomes of the two species. The nucleolar organizer regions (NORs) were located in the bivalents L2, S9, S10 of Ommexecha virens and M5, M6, M7, S11 of Descampsacris serrulatum. The FISH for rDNA showed coincident results with the pattern of active NORs revealed by AgNO3. This work presents the first chromosomal data, obtained through differential cytogenetics techniques in Ommexechidae, contributing to a better characterization of karyotypic evolution for this grasshopper family.

Chromosomal evolution of rDNA and H3 histone genes in representative Romaleidae grasshoppers from northeast Brazil

“…Data may be most plentiful for the Acrididae family [10,15,16,24]. The 18S rDNA clusters are restricted to a single medium-sized autosomal pair in C. nuptialis , C. speciosa , and X. robustus , corroborating previous studies from Loreto et al [23] and Souza et al [22], which suggests that it may be the ancestral bearer of 18S rDNA.…”

“…Two species of Ommexechidae, Ommexecha virens and Descampsacris serrulatum had three and four 45S rDNA sites, respectively. These data show a possible spread of this cluster in these two species [15]. However, in four Proscopiidae grasshoppers there was a consensus location in the seventh chromosome pair, indicating an ancestral condition with this single pair as the original bearer of the 18S rDNA cluster and the extra sites present in two species as a derived pattern [16].…”

“…In 47 Old World grasshoppers, the 126 rDNA sites detected by FISH showed that 52.4% were located in the proximal region, 34.9% were interstitial, and only 12.7% were distal [10]. The majority of sites mapped to date in grasshoppers were located in the proximal or pericentromeric regions in acrocentric chromosomes [10,15,16]. …”

“…The distributions of rDNA and histone genes have been studied in some groups of grasshoppers, such as the Acrididae, Ommexechidae, and Proscopiidae families [10,15,16]. Different groups show large variation in the location of ribosomal genes.…”