Habitat heterogeneity drives niche partitioning and morphological divergence in two sympatric Diploderma lizard species

Understanding how closely related taxa diverge and persist in spatial contact zones is central to explaining biodiversity dynamics. Habitat heterogeneity can promote lineage divergence through disruptive ecological pressures that favor differentiation in morphology, behavior, and ecological traits. This study focused on two closely related parapatric species, Diploderma yangi and D. slowinskii, which occupy contrasting microhabitats across the Nujiang River Basin in western China. The analysis integrated environmental, morphological, and dietary datasets to elucidate how niche partitioning stabilizes species boundaries in a landscape characterized by pronounced heterogeneity. Altitudinal gradients and microhabitat features, including substrate composition and stone size, clearly delineated their distributions. The arboreal species, D. slowinskii, exhibited a larger overall body size, elongated limbs, and an extended tail relative to the saxicolous-terrestrial taxon D. yangi, consistent with biomechanical demands of climbing rather than ground‑based movement. Despite both taxa functioning as arthropod generalists, trophic profiles diverged markedly: D. yangi predominantly consumed smaller prey items, whereas D. slowinskii targeted larger arthropods, reflecting differentiation in trophic niche breadth driven by habitat-specific prey structure. These results suggest that strong environmental gradients within a narrow contact zone generate persistent ecological divergence, with coordinated shifts in habitat use, morphology, and diet. Collectively, this study supports a mechanistic model of parapatric diversification and underscores the role of fine‑scale habitat complexity in sustaining high species richness across the Hengduan Mountains.