Nearly Synchronous Speciation in the Mexican Highlands: Did the <scp> <i>Juniperus deppeana</i> </scp> Complex Diverge Under Peripatry?

Speciation is a central focus in evolutionary biology, yet the processes driving diversification in montane regions remain incompletely understood. The Mexican highlands, a hotspot of conifer diversity characterised by complex topography and pronounced climatic heterogeneity, offer a unique setting to study these dynamics. Here, we investigated the genetic and taxonomic diversity within the Juniperus deppeana species complex, a group that exhibits notable cryptic variation. Using multiple species delimitation methods and Approximate Bayesian Computation, we identified at least four distinct evolutionary lineages that diverged largely without gene flow, likely influenced by geographic barriers and climatic differences. Our study enhances the understanding of how environmental heterogeneity and historical factors contribute to lineage diversification in montane conifers, offering new insights into the remarkable origins and resilience of biodiversity in the Mexican highlands. We present the J. deppeana complex as a compelling example of peripatric speciation and a valuable model system for understanding conifer diversification.