Similar degenerative patterns of olfactory receptor genes in the giant panda and marine carnivores

Olfactory receptor (OR) genes constitute the largest mammalian gene family and are critical for olfactory perception and ecological adaptation. OR gene variation is associated with interspecific differences in habitat, diet, and sensory reliance, yet the relative contributions of these ecological factors to OR evolution remain unclear. Here, we systematically analyzed OR repertoires across 25 carnivoran species occupying diverse niches. Marine carnivorans exhibit convergent OR degeneration, with fewer intact genes and ancestral orthologs, higher pseudogene ratios, and relaxed purifying selection compared with terrestrial species. Notably, bamboo-specialized giant pandas display identical degenerative signatures, possessing the smallest intact OR repertoire and most lost ancestral OR groups among terrestrial carnivorans. Our models show habitat primarily shapes intact OR quantity, while dietary specialization governs pseudogenization and selective constraints. These findings reveal convergent OR functional decay under aquatic adaptation and extreme dietary specialization, illustrating complex links between lifestyle and chemosensory genome evolution in mammals.