High Genetic Diversity and Differentiation in Relict Lowland Populations of Gentianella austriaca (A. and J. Kern.) Holub (Gentianaceae)

Abstract: The biennial Gentianella austriaca (A. & J. Kern.) Holub, representing a nutrient-poor grassland taxon of low competition power, is becoming rare in the lowlands of eastern Austria due to changes in land use. To estimate effects of isolation and decreasing population sizes, as well as evolutionary relationships, we investigated variation in isozymes and morphological characters within and between seven populations from the mountains, foothills, and lowlands. Additionally, data on reproduction, habitat, germination and population sizes were collected to examine possible causes of variation and differentiation. We found highest genetic diversity (v_a, v_go) in the lowland and foothill populations, and highest genetic differentiation (D_ja, D_jgo) (i.e., lowest genetic identity: Nei's I) in the lowland populations. The low diversity of the mountain populations might indicate that they are derived from lowland populations. Surprisingly, highest genetic diversity was found in the smallest population. This indicates that in small remnant populations of taxa with a mixed mating system, genetic diversity might be maintained even after many generations after reducing population size dramatically. We found some relationship between genetic diversity and high fitness (germination success) and (inversely) with seed size. Plant size and reproductive success are negatively correlated with altitude, whereas flower size and seed size seem to be subject to other forces of selection. Combining all morphometric, reproductive and genetic traits, the lowland populations are most strongly differentiated and therefore of highest conservation priority.