Climatic niche differentiation among cryptic species of the Phyllotis xanthopygus complex (Rodentia: Cricetidae): insights into speciation patterns

Abstract

Abstract Cryptic species complexes provide a valuable framework for understanding how ecological divergence and niche conservatism interact during speciation. Here, we examined climatic niche differentiation within the Phyllotis xanthopygus complex, a group of Andean sigmodontine rodents characterized by recent diversification, cryptic diversity, and variable geographical overlap among lineages. We quantified climatic niche space using principal component analysis and estimated niche breadth for seven species across South America. Niche overlap and divergence were assessed for sister-species pairs and sympatric taxa using equivalency and background tests within the Humboldt framework. Species occupied distinct but partly overlapping regions of environmental space, with niche breadth varying by more than two orders of magnitude. Patterns of niche differentiation were highly heterogeneous: some sister-species pairs exhibited strong divergence associated with complete geographical isolation and limited shared environmental space, whereas others showed partial divergence or apparent conservatism associated with geographical overlap and low genetic differentiation. Isothermality and precipitation of the driest month emerged as the primary axes structuring ecological differentiation. Overall, niche evolution within the complex ranged from conservatism to strong divergence, shaped by evolutionary history, environmental heterogeneity, and the configuration of accessible environmental space.