Conserved gene content and unique phylogenetic history characterize the 'bloopergene' underlying Triturus' balanced lethal system

In a balanced lethal system, half the reproductive output succumbs. Triturus newts are the best-known example. Their chromosome 1 comes in two distinct versions and embryos carrying the same version twice experience developmental arrest. Those possessing two different versions survive, suggesting that each version carries something uniquely vital. With target capture we obtain over 7,000 nuclear DNA markers across the genus Triturus and all main lineages of Salamandridae (the family to which Triturus belongs) to investigate the evolutionary history of Triturus chromosome 1 versus other chromosomes. Dozens of genes are completely missing from either one or the other version of chromosome 1 in Triturus. Furthermore, the unique gene content of 1A versus 1B is remarkably similar across Triturus species, suggesting that the balanced lethal system evolved before Triturus radiated. The tree topology of chromosome 1 differs from the rest of the genome, presumably due to pervasive, ancient hybridization between Triturus ancestor and other newt lineages. Our findings accentuate the complex nature of Triturus chromosome 1 - the bloopergene driving the evolutionarily enigmatic balanced lethal system.