Landscape genetics of the copal tree, Bursera cuneata (Burseraceae): the key role of the tropical dry forest in shaping connectivity at the regional scale.

Land-use changes in tropical dry forests (TDF) have rapidly reduced native vegetation, disrupting gene flow dynamics of tree species. Bursera cuneata is a co-dominant TDF tree in central Mexico, which is threatened by habitat loss and overexploitation. We investigated landscape drivers of functional connectivity of B. cuneata across scales to inform species conservation efforts. We genotyped 227 B. cuneata individuals from 33 populations across five hydrological basins: covering western, central, and southern Mexico, at 10,499 single-nucleotide polymorphism (SNP) loci. We examined spatial patterns of genetic structure among hydrological basins and the landscape correlates of gene flow. We applied gravity models that incorporated within-site (i.e., local conditions within populations; slope and east aspect) and between-site (terrain roughness, habitat suitability, and habitat cover) factors associated with B. cuneata gene flow. Clustering analyses showed genetic structure among basins, with higher differentiation in more isolated regions. Gravity models revealed that functional connectivity is a scale-dependent process. Specifically, terrain roughness was the primary factor of connectivity at finer scales (1000-3000 m), while TDF cover became the main driver at regional scales (>4000 m). We recommend protecting and prioritizing crucial TDF remnants to maintain large-scale gene flow by integrating urban natural parks as important links to prevent genetic isolation between urban and rural populations.