Spreading of heterochromatin and karyotype differentiation in two Tropidacris Scudder, 1869 species (Orthoptera, Romaleidae)

Abstract

Tropidacris Scudder, 1869 is a genus widely distributed throughout the Neotropical region where speciation was probably promoted by forest reduction during the glacial and interglacial periods. There are no cytogenetic studies of Tropidacris, and information allowing inference or confirmation of the evolutionary events involved in speciation within the group is insufficient. In this paper, we used cytogenetic markers in two species, Tropidacris collaris (Stoll, 1813) and Tropidacris cristata grandis (Thunberg, 1824), collected in different Brazilian biomes. Both species exhibited 2n=24,XX for females and 2n=23,X0 for males. All chromosomes were acrocentric. There were some differences in the karyotype macrostructure, e.g. in the chromosome size. A wide interspecific variation in the chromosome banding (C-banding and CMA3/DAPI staining) indicated strong differences in the distribution of repetitive DNA sequences. Specifically, Tropidacris cristata grandis had a higher number of bands in relation to Tropidacris collaris. FISH with 18S rDNA revealed two markings coinciding with the NORs in both species. However, two analyzed samples of Tropidacris collaris revealed a heterozygous condition for the rDNA site of S10 pair. In Tropidacris collaris, the histone H3 genes were distributed on three chromosome pairs, whereas in Tropidacris cristata grandis, these genes were observed on 14 autosomes and on the X chromosome, always in terminal regions. Our results demonstrate that, although the chromosome number and morphology are conserved in the genus, Tropidacris cristata grandis substantially differs from Tropidacris collaris in terms of the distribution of repetitive sequences. The devastation and fragmentation of the Brazilian rainforest may have led to isolation between these species, and the spreading of these repetitive sequences could contribute to speciation within the genus.

Cytogenetic analysis of five Ctenidae species (Araneae): detection of heterochromatin and 18S rDNA sites

“…The first pattern could arise by dispersion of heterochromatin due to contact of chromosomes during their polarization of Rabl in mitosis or during bouquet orientation at the early prophase I as described by Schweizer and Loidl (1987). The second pattern could arise by occurrence of chromosomal rearrangements (Schweizer and Loidl 1987) or by spreading of the heterochromatin by transposable elements, as proposed for grasshopper (Rocha et al 2015). Furthermore, despite the few species studied, GC-rich blocks seem to be common in entelegyne spiders (Araujo et al 2005; Ramalho et al 2008, Chemisquy et al 2008).…”

Chromosome mapping in Abracris flavolineata (De Geer, 1773) (Orthoptera) from the Iguaçu National Park – Foz do Iguaçu, Paraná, Brazil

“…In Abracris flavolineata , studies show that most heterochromatin is GC-rich and there are no AT-rich blocks (Bueno et al 2013). Thus, the pattern observed in specimens of A. flavolineata in this study shows a considerable karyotypic differentiation, where heterochromatinization processes, such as heterochromatin spreading, can be responsible for the differentiation of the Iguaçu National Park population, as in the grasshopper of the genus Tropidacris Scudder, 1869 (Rocha et al 2015). Moreover, this differentiation of heterochromatin may be related to action of transposable elements (Grewal and Jia 2007).…”