Population Size, Genetic Variation, and Reproductive Success in a Rapidly Declining, Self-Incompatible Perennial (Arnica montana) in The Netherlands

Abstract

Arnica montana is a rare and rapidly declining, self-incompatible plant species. In 26 populations in The Netherlands we investigated the relationship between population size and genetic variation using allozyme markers. Genetic variation was low in A. montana ( H e ϭ 0.088). There were positive correlations between population size and the proportion of polymorphic loci, the number of effective alleles, and expected heterozygosity, but not with observed heterozygosity. There was a significantly positive correlation between population size and the inbreeding coefficient. Generally, small populations showed heterozygote excess, which decreased with increasing population size. Possibly, the heterozygous individuals in small populations are survivors from the formerly larger populations with relatively high fitness. The F statistics showed a moderately high level of differentiation among populations ( F ST ϭ 0.140 Ϯ 0.02), implying a low level of gene flow. For three out of four allozyme loci, we found significant inbreeding ( F IS ϭ 0.104 Ϯ 0.03). Only 14 of 26 populations were in Hardy-Weinberg equilibrium at all four polymorphic loci. In a subset of 14 populations of various size, we investigated natural seed production and offspring fitness. Population size was positively correlated with seed set, seedling size, number of flowering stems and flowerheads, adult survival, and total relative fitness, but not with the number of florets per flowerhead, germination rate, or the proportion of germination. Offspring performance in the greenhouse was not associated with genetic diversity measured on their mothers in the field. We conclude that the fitness of small populations is significantly reduced, but that there is as yet no evidence that this was caused by inbreeding. Possibly, the self-incompatibility system of A . montana has been effective in reducing selfing rates and inbreeding depression.

Isozyme variability of the wetland specialistSwertia perennis(Gentianaceae) in relation to habitat size, isolation, and plant fitness

“…Reports of positive correlations between population size and heterozygosity (H e or H o ) are much rarer than those for A or P p (Ellstrand and Elam, 1993;Frankham, 1996; but see Godt, Johnson, andHamrick, 1996 andLuijten et al, 2000). In our study, observed heterozygosity (H o ) was also nearly significantly reduced on Distant islands, which indicates relatively pronounced effects of habitat fragmentation on the genetic variability of individual plants.…”

“…Because reduced leaf size or vegetative plant mass can lead to reduced reproductive success (e.g., Calvo, 1990;Schmid et al, 1994), long-term viability of populations with reduced genetic variability could become destabilized. Indications for positive relationships between population size and genetic variability on the one hand and/or between genetic variability and fitness on the other were found in Gentiana pneumonanthe (Oostermeijer, van Eijck, and den Nijs, 1994;Oostermeijer et al, 1995), Gentianella germanica (Willdenow) Börner (Fischer and Matthies, 1998), Pedicularis palustris L. (Schmidt and Jensen, 2000), Rutidosis leptorrhynchoides (Young et al, 2000), and Ranunculus reptans L. (Fischer, van Kleunen, and Schmid, 2000), but not in Salvia pratensis (Ouborg and van Treuren, 1994), Lychnis flos-cuculi L. (Hauser and Loeschcke, 1994), and Arnica montana L. (Luijten et al, 2000). In L. flos-cuculi only one of four examined populations was small (300 ramets; Hauser and Loeschcke, 1994), and the self-incompatibility system of A. montana may have reduced the importance of inbreeding depression (Luijten et al, 2000).…”

Genetic rescue in interconnected populations of small and large size of the self-incompatible Ranunculus reptans

“…Increased genetic load through drift in small populations is predicted by theory (Wright, 1931;Kimura et al, 1963;Lynch et al, 1995) and was recently affirmed in two studies of natural plant populations (Paland and Schmid, 2003;Willi et al, 2005). Reduced seed set in small populations of selfincompatible species has been recorded in several studies (Widén, 1993;Luijten et al, 2000;Fischer et al, 2003), probably because of a lack of compatible partners.…”

“…Numerous studies of plants (and animals) have recorded reduced fitness in small populations in nature and when individuals from small populations are raised in a common environment (Menges, 1991;Oostermeijer et al, 1994;Heschel and Paige, 1995;Fischer and Matthies, 1998;Morgan, 1999;Fischer et al, 2000a;Kéry et al, 2000;Luijten et al, 2000;Schmidt and Jensen, 2000;Mavraganis and Eckert, 2001;Jacquemyn et al, 2002;Paschke et al, 2002;Severns, 2003;Vergeer et al, 2003;Brys et al, 2004). There are three likely genetic causes for reduced fitness of plants from smaller populations.…”

Embryological features, pollen and seed viability of Arnica montana (Asteraceae) – a threatened endemic species in Europe

“…It is a diploid species with 2n = 38 (Ekenäs 2008), highly self-incompatible with entomophily (Luijten et al 1996(Luijten et al , 2000. Arnica montana has been used for medical purposes since the 1500s because of the contents of various active compounds with antiseptic, antifungal, antimicrobial and antibiotic activities.…”