Phylogeography and species distribution modeling reveal a historic disjunction for the conifer Podocarpus lambertii

Abstract

Phylogeography and species distribution models (SDMs) were integrated to test the hypothesis that the current disjunct distribution of Podocarpus lambertii, a cold-tolerant species, preserves the signature of Quaternary climatic oscillations, revealing historical barriers to gene flow. Twenty-five populations (286 individuals) of P. lambertii were screened for sequence variation at three intergenic cpDNA loci. We characterized the genetic diversity, constructed a haplotype network, identified population groups based on genetic divergence among populations and putative refugial areas, and tested the association between genetic and geographic distances. For SDMs, we used an ensemble approach based on five algorithms to estimate climatically suitable areas for the species during the Last Glacial Maximum (LGM), Holocene (HOL), and the present-day (PD). For all populations, haplotype and nucleotide diversity were 0.676 and 4.8 × 10−4, respectively. Neutrality tests indicated a recent expansion for the species. Analysis of molecular variance revealed genetic divergence among populations (FST = 0.1385), significantly correlated with geographic distances (r = 0.524, p < 0.01). Bayesian analysis suggested the formation of a Southern Group (SG) and Northern Group (NG), separated by a barrier to gene flow, with high differentiation among groups (FCT = 0.6458). The SDMs showed temporal changes in an area suitable for P. lambertii, mainly present at high altitudes and cold temperatures. The main occurrence area of P. lambertii now resides in SG, owing to a colder climate when compared with NG and the expansion of Araucaria angustifolia, a nurse plant that may have created better microclimatic conditions for P. lambertii expansion.