Living at the edge: population differentiation in endangered Arnica montana from NW Iberian Peninsula

Abstract

Arnica montana (Asteraceae) is a herbaceous species with high interest for pharmaceutical industry due its anti-inflammatory properties. However, commercial collection in wild, habitat loss, abandonment of land, reforestation and the ongoing climate change threaten the conservation of the species throughout its natural distribution. Galicia (north-western Spain) is one of the main flower suppliers, but no legislation on A. montana exploitation is currently applied. In order to assess the genetic status and population structure in this region, 27 locations were genotyped for 14 microsatellite loci and sequenced for 2 plastid DNA (cpDNA) markers. The relationship of environmental, biochemical and morphological variables with genetic differentiation was also evaluated. Two different cpDNA groups previously described were found. One of them was widely distributed while the other was restricted to heathlands of the O Courel Mountains. The percentage of clonality was low (< 10%). Genetic diversity based on microsatellites (He = 0.245) was lower than in Central European populations, with high levels of population differentiation (FST = 0.441), suggesting strong effects of genetic drift. Bayesian clustering methods revealed the presence of four genetically distinct population units, one of them corresponding to the O Courel Mountains group described by cpDNA analysis. Environmental and biochemical factors were related to genetic differentiation, suggesting local adaptation. Necessary conservation measures include the overdue implementation of the Habitats Directive by the Galician Regional Administration, establishing sustainable harvesting regimes, and aim to conserve genetic variation in these endangered populations at the southern range edge.