The Origins and Conservation Genetics of Cirsium Scariosum in the Mingan Islands of Québec

Abstract

The Mingan Archipelago along the north shore of the Gulf of St. Lawrence is well known for the diversity and rarity of its vascular plants. This diversity is often explained by a combination of the islands’ temperate maritime climate and its unusual regional geology where the islands are formed of calcareous sedimentary rock. Among the 80 species of rare plants on the islands, one in particular stands out, Cirsium scariosum (Meadow thistle), a species native to western North America, but with a disjunct populations on the Mingan islands over 3500 km away. Initially recognized as a separate species, Cirsium minganense, when it was first discovered in 1924 by Marie-Victorin, recent authors believe these Mingan populations are either the result of eastern migration during the Pleistocene or a contemporary anthropogenic introduction. Nevertheless, the question of how these populations arrived on the islands or whether they should be treated as a separate species has not been resolved. The eastern populations of Cirsium scariosum are now endangered and conservation efforts have been made to save this emblematic plant. To determine whether the Mingan populations might represent a separate species and to better understand the plants’ breeding system and genetic diversity for conservation, a phylogeny of closely related species and a population genetic analysis using genotyping by sequencing (GBS) was conducted. Results suggest the Mingan island populations are not closely related to the western Cirsium scariosum and that outcrossing and dispersal between islands could be occurring.