Statistical association of complete PYHIN gene family loss with flight and inverted roosting in bats

The PYHIN (pyrin and HIN domain-containing) gene family encodes central cytosolic DNA sensors, including AIM2 and IFI16, that activate inflammasome and type I interferon pathways during infection. While these pathways are critical for antiviral and antimicrobial defense, how ecological pressures shape their evolution remain unclear. The PYHIN gene family varies across mammals, and bats have completely lost all PYHIN genes. Here, we integrate phylogenomic, comparative genomic, and phylogenetically controlled analyses across more than 150 mammalian species to investigate PYHIN evolutionary dynamics. We show that PYHIN genes form a tightly linked genomic cassette within a conserved chromosomal interval flanked by SPTA1 and CADM3, a pattern we describe as an Anchored Gene Cluster Pulsation mechanism characterized by coordinated expansion, contraction, and loss. Across mammals, the genomic distance between these anchor genes correlates with PYHIN copy number. In bats, phylogenetic logistic regression identifies powered flight and inverted roosting as traits statistically associated with PYHIN loss, whereas echolocation and hibernation show no association. Olfactory receptor genes within the same region are retained, indicating targeted loss of DNA-sensing immune genes rather than generalized genome contraction. These findings support a model in which bat immunity is associated with ecological specialization favoring immune tolerance and provide a framework for understanding immune gene family evolution as integrated genomic modules.