Prevalence of B chromosomes in Orthoptera is associated with shape and number of A chromosomes

Abstract

We analyze the prevalence of B chromosomes in 1,601 species of orthopteran insects where chromosome number and shape are known. B chromosomes have been reported in 191 of these species. Bs are not uniformly distributed among orthopteran superfamilies, with evident hotspots in the Pyrgomorphoidea (32.3% of species carrying Bs), Grylloidea (14.9%), Acridoidea (14.6%) and Tetrigoidea (14.3%). As expected under the theory of centromeric drive, we found a correlation between B chromosome presence and A chromosome shape-Bs are more frequent in karyotypes with more acrocentric A chromosomes. We also found that Bs are less common in species with high chromosome numbers and appear to be most common at the modal chromosome number (2n = 24). Study effort, measured for each genus, was not associated with B prevalence, A chromosome shape or A chromosome number. Our results thus provide support for centromeric drive as an important and prevalent force in the karyotypic evolution of Orthoptera, just as it appears to be in mammals. We suggest that centromeric drive may provide a mechanistic explanation for White's principle of karyotypic orthoselection.

Comment on Schielzeth et al. (2014): “Genome size variation affects song attractiveness in grasshoppers: Evidence for sexual selection against large genomes”

“…In reality, B chromosomes are not especially frequent in grasshoppers as they have been found in about 17% of the Acridid species cytologically analyzed (see Palestis et al. ), a figure being very similar to the 15% average reported in animals and plants (see Jones ; Camacho ). Furthermore, B chromosomes are especially rare in species of the genus Chorthippus , and have been reported only in Chorthippus vagans (Cabrero and Camacho ), a genus of the Acrididae where many species have been cytologically analyzed (see Hewitt ).…”

Comparative analysis of chromosomes in the Palaearctic bush-crickets of tribe Pholidopterini (Orthoptera, Tettigoniinae)

“…Palestis et al 2010) while rare and often unstable in Tettigonioidea, (e.g. Warchałowska-Śliwa et al 2005, 2008, Hemp et al 2010a, 2015b).…”

B Chromosomes in Grasshoppers: Different Origins and Pathways to the Modern Bs

“…The number of eukaryotic species with B s were estimated from 1685 [ 2 ] in 1980 to more than 2828 [ 3 ] in 2017. Among Orthopteran species, B s were described in 191 species, which constitutes 11,9% of studied species [ 4 ]. Often B s are enriched with repetitive sequences and are highly heterochromatic.…”