Phylogenetic relationships and horizontal gene transfer in panesthiine and geoscapheine cockroaches

Abstract

Cockroaches are a highly diverse and adaptable group. This thesis focuses on the wood- and soil-dwelling subfamilies Panesthiinae and Geoscapheinae, investigating their phylogeny, biogeography, morphological evolution, and horizontal gene transfer (HGT) from Blattabacterium symbionts using mitochondrial genomes, nuclear markers, high-quality genomes, and extensive species sampling.

The research confirmed seven independent transitions from wood-feeding to soil-burrowing lifestyles. It resolved the basal position of Geoscapheus with high support for the first time and clarified key sister-group relationships. Biogeographic reconstruction revealed that after colonizing Australia from Southeast Asia, lineage diversification was shaped by continental aridification and geographic isolation.

Phylogenomic analysis showed that Panesthiinae is paraphyletic. Ancestral state reconstruction revealed multiple independent reductions in wings, male genitalia, and oothecal membrane, correlated with shifts in substrate use and mating strategy.

Using long-read sequencing, we detected extensive HGT in non-coding regions. Panesthiinae and Geoscapheinae genomes contained significantly more insertions (1,543–5,037 per genome) than other cockroaches (0–647). Most inserts are short (<100 bp), non-coding, with some longer ones exhibiting a chimeric structure. These HGT events occurred within the last ~40 million years. No significant correlation was found between HGT accumulation and relaxed selection, nor between feeding habit and selective pressure.