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.

A revision of the Solanum elaeagnifolium clade (Elaeagnifolium clade; subgenus Leptostemonum, Solanaceae)

“…In Argentina, polyploid populations of S. elaeagnifolium are generally found in wetter parts of the species range (Scaldaferro et al 2012). Chiarini et al (2016) have shown that tetraploid populations have arisen repeatedly from both diploid and hexaploid progenitors, but also show that using plastid markers, all populations at particular ploidy levels cluster together (see discussion of S. elaeagnifolium ).…”

“…This latter event may be more recent, such as has been observed for some species of Tiquilia (Moore et al 2006b). Studies of chloroplast haplotypes suggest S. elaeagnifolium has a long history in southern South America (Chiarini et al 2016) and is not a recent introduction.…”

“…Populations of S. elaeagnifolium in North America are diploid, with n=12 (Powell and Weedin 2005; Chiarini et al 2016), while those in Argentina are diploid, tetraploid or hexaploid (Scaldaferro et al 2012). Morphological differentiation between ploidy levels has not been found (Nilda Dottori, pers.…”

“…), but hexaploid populations appear to possess a number of differences in plastid haplotypes. Chiarini et al (2016) suggest this might indicate presence of a cryptic species, but data from the entire genome is needed to test this hypothesis. Tetraploids appear to have arisen multiple times from either diploid or hexaploid populations (Chiarini et al 2016).…”

“…Chiarini et al (2016) suggest this might indicate presence of a cryptic species, but data from the entire genome is needed to test this hypothesis. Tetraploids appear to have arisen multiple times from either diploid or hexaploid populations (Chiarini et al 2016). All plants tested outside of the native range (e.g., South Africa, Australia, the Mediterranean) are diploid, and in Australia, genetic variation as measured using AFLP markers suggests that populations in southern Australia are the result of several introductions (Zhu et al 2013a).…”