Cryptic genetic diversity in Solanum elaeagnifolium (Solanaceae) from South America

Abstract

Solanum elaeagnifolium is a global invasive weed that is polyploid in the South American range. Our aim was to establish the origin and distribution of these polyploid lineages, together with their relationship with the invasion of new habitats. Ploidy level was determined in 26 natural populations using chromosomal counts, and two non-coding plastid regions trnL-trnF and rpl32F-trnL were sequenced. Relationships among haplotypes were examined by a median-joining network, and groups of populations were identified by employing a spatial analysis of molecular variance. Phylogenetic relationships among haplotypes were reconstructed using Bayesian inference, and divergence times were estimated using BEAST. We found 21 haplotypes structured into three lineages: one with diploids in North America and invaded areas, and two in South America that developed independent polyploidisation events. The separation of lineages took place during the Pliocene with more recent divergences in the Early Pleistocene. The existence of three lineages can be attributed to the uplift of the Andes and the emergence of the Isthmus of Panama. Diversification within each lineage may be related to the recent cyclical glacial variation throughout the Pleistocene creating haplotype diversity and recurrent polyploidy. Thus, the South American populations of S. elaeagnifolium did not originate from a recent colonisation but are established ancient lineages.