Repeated losses of TTAGG telomere repeats in evolution of beetles (Coleoptera)

Abstract

We studied the occurrence of (TTAGG)n telomere repeats in 12 species of beetles, representing main lineages of the Coleoptera phylogenetic tree, by Southern hybridization and fluorescence in situ hybridization (FISH). In contrast to other insect orders, beetles were heterogeneous with respect to the occurrence of TTAGG repeats. In addition, the presence or absence of (TTAGG)n motif was irrespective of phylogenetic relationships. In the suborder Polyphaga, six species displayed positive hybridization signals. These were Silpha obscura, Agrilus viridis, Ampedus sanguineus, Stegobium paniceum, Oryzaephilus surinamensis, and Leptinotarsa decemlineata. Whereas negative signals were obtained in three polyphagan species, Geotrupes stercorarius, Thanasimusformicarius, and Sitophilus granarius. In the suborder Adephaga, the TTAGG sequence was present in one species, Graphoderus cinereus, and absent in two species, Orectochilus villosus and Pterostichus oblongopunctatus. We concluded that the telomerase-dependent (TTAGG)n motif had been repeatedly lost in different phylogenetic branches of Coleoptera and probably replaced with another mechanism of telomere elongation. This had to happen at least 5-6 times. The results suggest a predisposition or a backup mechanism of telomere maintenance in the genome of beetles that enabled them to make frequent evolutionary changes in the telomere composition.