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Organisationseinheit der BAM
Horizontal gene transfer (HGT), the transmission of genetic material across species, is an important innovation source in prokaryotes. In contrast, its significance is unclear in many eukaryotes, including insects. Here, we used high-quality genomes of 45 termites and two cockroaches to investigate HGTs from non-metazoan organisms across blattodean genomes. We identified 289 genes and 2,494 pseudogenes classified into 168 orthologous groups originating from an estimated 281 HGT events. Wolbachia represented the primary HGT source, while termite gut bacteria and the cockroach endosymbiont Blattabacterium did not contribute meaningfully to HGTs. Most horizontally acquired genes descended from recent and species-specific HGTs, experienced frequent duplications and pseudogenizations, and accumulated substitutions faster than synonymous sites of native protein-coding genes. Genes frequently transferred horizontally to termite genomes included mobile genetic elements and genetic information processing genes. Our results indicate that termites continuously acquired genes through HGT, and that most horizontally acquired genes are specific to restricted lineages. Overall, genes acquired by HGT by termites and cockroaches seemed generally non-functional and bound to be lost.
Unravelling the evolution of wood-feeding in termites with 47 high-resolution genome assemblies
(2025)
Termites are a lineage of social cockroaches abundant in tropical ecosystems where they are key decomposers of organic matter. Despite their ecological significance, only a handful of reference-quality termite genomes have been sequenced, which is insufficient to unravel the genetic mechanisms that have contributed to their ecological success. Here, we perform sequencing and hybrid assembly of 45 taxonomically and ecologically diverse termites and two cockroaches, resulting in haplotype-merged genome assemblies of 47 species, 22 of which were near-chromosome level. Next, we examine the link between termite dietary evolution and major genomic events. We find that Termitidae, which include ~80% of described termite species, have larger genomes with more genes and a higher proportion of transposons than other termites. Our analyses identify a gene number expansion early in the evolution of Termitidae, including an expansion of the repertoire of CAZymes, the genes involved in lignocellulose degradation. Notably, this expansion of genomes and gene repertoires coincided with the origin of soil-feeding in Termitidae and remained unchanged in lineages that secondarily reverted to a wood-based diet. Overall, our sequencing effort multiplies the number of available termite genomes by six and provides insights into the genome evolution of an ancient lineage of social insects.
Phylogenetic trees are typically reconstructed using conserved sequence alignments. Other genomic elements, such as transposable elements (TEs), make up a large fraction of eukaryotic genomes but are ignored for phylogenetic reconstruction, despite potentially containing phylogenetic information, which could be used to resolve nodes that remain contentious. Here, we reconstructed accurate phylogenetic trees of 45 termites and two cockroaches using two types of characters derived from the TE landscape: (1) genome-wide presence and absence of 37,966 TE families and (2) presence/absence data of 37,966 TE families in the flanking regions of orthologous ultraconserved elements (UCEs), which was a proxy for TE insertions. The topologies of our TE-based phylogenetic trees were largely congruent with phylogenetic trees inferred from alignments of UCEs and single-copy orthologous genes, only differing for a few nodes variably reconstructed in other phylogenetic analyses. Notably, trees based on genome-wide TE family composition were more accurate than trees inferred from mitochondrial genome alignments, and trees based on TE family composition in regions flanking UCEs achieved comparable accuracy with trees inferred from single-copy orthologous gene alignments. Our results demonstrate that the TE landscape is phylogenetically informative, representing an additional set of markers for robust phylogenetic reconstructions, with potential use to resolve ambiguous nodes in the tree of life.
