Molecular and Chromosomal Evolution of DsTc1_5 and DsPogo_8 Elements (Tc1-Mariner) in Species of the Dichotomius Genus (Coleoptera: Scarabaeidae): Contributions to the Speciation Process.

In Dichotomius genus, transposable elements (TE) have been related to chromosome remodeling, genomic evolution, and, possibly, to the speciation process. The objective of this study was to verify the interpopulational and interspecific conservation/variation of Tc1-Mariner elements (possibly autonomous) in Dichotomius species, aiming to identify possible contributions in the speciation process of this group. The analysis was performed on four species of Dichotomius, belonging to the Selenocopris subgenus. We verified the presence of the DsPogo_8 and DsTc1_5 elements by PCR and sequencing. We also isolated and sequenced the 28S and 16S rRNA genes aiming at the phylogenetic reconstruction of the analyzed species. Chromosomal mapping of TEs DsTc1_5 and DsPogo_8 was performed by fluorescent in situ hybridization. The results revealed the presence of the elements in the different species analyzed, except for DsTc1_5 in D. (S.) geminatus. These results suggest a vertical inheritance, with the presence of these elements in the common ancestor of these species. In the analyzed species, the nucleotide similarity of DsTc1_5 was higher than that of the 28S and 16S rRNA genes, suggesting the occurrence of horizontal transfer. The phylogenetic tree indicated that the absence of DsTc1_5 in D. (S.) geminatus is related to stochastic loss of this TE. Chromosomal mapping revealed dispersed signals, with predominance in euchromatic regions and wide variation in the chromosomal localization pattern of DsTc1_5 and DsPogo_8, both interpopulational and interspecific. This variation indicates that DsTc1_5 and DsPogo_8 may have contributed to prezygotic and postzygotic isolation, thus contributing to the speciation of these species.

Mobilome characterization of the beetle Euchroma gigantea (Buprestidae) uncovers multiple long range Tc1-Mariner horizontal transfer events.

Transposable elements (TEs) are mobile repetitive DNA sequences that can transfer horizontally between species. Due to their mutagenic characteristics, TEs are associated with different evolutionary events, including chromosomal rearrangements that are abundant in the beetle Euchroma gigantea. In order to understand more in depth the impact of TEs on the genomic evolution of E. gigantea, we characterized the E. gigantea mobilome and evaluated the horizontal transfer of Tc1-Mariner elements. Genomic sequencing data was generated on the Illumina Hiseq plataform, from a specimen (Northeast lineage) collected in Recife, Pernambuco - Brazil. The TEs were characterized by two independent approaches based on the clustering and assembly of highly repetitive sequences, the RepeatExplorer and dnaPipeTE. The sequences obtained were further characterized using ORFfinder and CD-Search, to obtain the TEs' potential coding proteins and verify the presence and integrity of known TE domains. Evidence for horizontal transfer was evaluated by nucleotide and protein genetic distance between TEs from E. gigantea and other species and phylogenetic incongruences detected between TEs and hosts phylogenetic trees. The mobilome of E. gigantea represents about 21 to 26% of its genome. This mobilome is composed of TEs from 31 superfamilies, belonging to different classes and most known orders of TEs. Several types of TEs with intact domains were observed with emphasis on Tc1-Mariner suggesting the presence of potentially autonomous elements. This superfamily also stands out for having the greatest abundance and diversity, with TEs being classified into four families. When compared to TEs deposited in databases, Mariner TEs stood out as having the highest nucleotide identity (above 90%) with TEs from phylogenetically distant species, such as ants and bees. Altogether these results suggest that E. gigantea Mariner TEs underwent multiple horizontal transfer events to other insect species.