Genetic diversity of an invasive tree across time and contrasting landscape conditions

Current biodiversity changes mostly result from human land-use changes and terrestrial biological invasions. These disturbances are often intermingled as invasive species often colonize fragmented habitats. No research has yet assessed fragmentation effects on the genetic diversity of invasive plant populations, incorporating both the relative onset of the invasion and habitat fragmentation processes. Here, we estimated the age of all sampled adult tree individuals of Glossy privet (Ligustrum lucidum) and assessed the genetic diversity of invasive populations established before and after the major events of habitat loss and fragmentation in the late 1980′s in Sierras Chicas, central Argentina. When considering all the individuals together within each forest condition, regardless of their relative age, we observed a mild but significant lower allelic richness and percent polymorphic loci in populations growing in fragmented conditions. However, when incorporating the relative age of individuals in the model, fragmentation effects are overridden and become non-significant; that is, both pre- and post-fragmentation individual cohorts show similar levels of genetic diversity in both landscape conditions. Interestingly, younger trees showed higher genetic diversity than older cohorts regardless of landscape condition, implying the occurrence of multiple introduction events since its initial spreading. Our results suggest that bird seed dispersal of this invasive tree species provides high connectivity across the landscape, maintaining and even increasing genetic diversity across time and space.