Phylogenomic insights into the taxonomy and evolutionary relationships of penduline tits (Remiz spp.)

Penduline tits (genus Remiz) are small passerines distributed across Europe, Central and East Asia, and North Africa, renowned for their elaborate nests and unusually diverse mating systems. However, the taxonomy and evolutionary relationships within this genus have remained contentious due to overlapping breeding distributions and extensive hybridization. Using broad-range geographic sampling and whole-genome sequencing, here we report the phylogenetic relationships within this genus. Our results from maximum likelihood trees, species trees, population structure, and PCA analyses consistently identify four distinct, well-supported monophyletic clades. Based on these robust results, we support dividing Remiz into four species: the Eurasian Penduline Tit (R. pendulinus), Black-headed Penduline Tit (R. macronyx), White-crowned Penduline Tit (R. coronatus), and Chinese Penduline Tit (R. consobrinus). Among these species, R. consobrinus diverged earlier from other species, followed by R. coronatus, and then, R. pendulinus and R. macronyx. R. pendulinus and R. macronyx showed shallow genetic differentiation with recent divergence (~87,000 years ago) and ongoing gene flow. Our findings demonstrate the effectiveness of phylogenomic approaches in resolving taxonomic ambiguities and provide a robust evolutionary framework for tracing the diversification of life history traits, particularly nest structures and mating systems, across the genus.