What Impact Do New Homologs Have on Detecting Interdomain Horizontal Gene Transfer in Eukaryotes? A Reassessment of Katz (2015)

The role of interdomain horizontal gene transfer (HGT) in eukaryotic genome evolution remains a topic of active debate. The numerous reported cases of prokaryote-to-eukaryote gene transfer suggest that this process may be widespread in the natural world. However, a critical reassessment of available data is essential to determine the true extent of interdomain HGT in eukaryotic evolution. In this study, we revisit the findings of Katz (2015), which evaluated the impact of interdomain lateral gene transfer in eukaryotes, using newly available data a decade after its publication. We retrieved updated homologs for the originally proposed HGT candidates and reconstructed phylogenetic trees to assess their topological consistency with an HGT scenario. Our results indicate that only 12% of the original candidates remain congruent with interdomain HGT. We argue that the inclusion of new homologs reveals phylogenetic patterns that, in their absence, may have been misinterpreted as evidence of HGT. Beyond biological and systematic biases associated with HGT detection through phylogenetic analyses, this study highlights the importance of considering database completeness before attributing gene origins to horizontal transfer events.