Chromosomal distribution of interstitial telomeric sequences as signs of evolution through chromosome fusion in six species of the giant water bugs (Hemiptera, Belostoma)

BRESSA, M. J.; CHIRINO, M. G.; DALÍKOVÁ, M.; DALÍKOVÁ, M.; MAREC, F.; MAREC, F.; BRESSA, M. J.; CHIRINO, M. G.

Ecology and Evolution

John Wiley & Sons Ltd

Año: 2017 vol. 7 p. 5227 - 5235

2045-7758

Tandem arrays of TTAGG repeats show a highly conserved location at thetelomeres, across the phylogenetic tree of arthropods. In giant water bugs Belostoma, the chromosome number changedduring speciation by fragmentation of the single ancestral X chromosome,resulting in a multiple sex chromosome system. Several autosome-autosomefusions and a fusion between the sex chromosome pair and an autosome pair resultedin the reduced number in several species. We mapped the distribution oftelomeric sequences and interstitial telomeric sequences (ITS) in Belostoma candidulum (2n= 12 + XY/XX; male/female), B. dentatum (2n= 26 +  X1X2Y/X1X1X2X2),B. elegans (2n= 26 + X1X2Y/X1X1X2X2),B. elongatum (2n= 26 + X1X2Y/X1X1X2X2),B. micantulum (2n= 14 + XY/XX), and B. oxyurum (2n= 6 + XY/XX) by FISH with the(TTAGG)n probes. Hybridizationsignals confirmed the presence of TTAGG repeats in the telomeres of all speciesexamined. The three species with reduced chromosome numbers showed additionalhybridization signals in interstitial positions, indicating the occurrence ofITS. From the comparison of all species here analysed, we observed an inverserelationships between chromosome number and chromosome size, and between thepresence/absence of ITS and chromosome number. The ITS distribution betweenthese closely related species supports the hypothesis that several telomere-telomerefusions of the chromosomes from an ancestral diploid chromosome number of2n=26+XY/XX played a major role in the karyotype evolution of Belostoma. Consequently, our studyprovides valuable features that can be used to understand the karyotypeevolution, may contribute to a better understanding of taxonomic relationshipsand also elucidate the high plasticity of nuclear genomes at the chromosomallevel during the speciation processes.