Genetic Population Structure and Reproductive Fitness in the PlantSanguisorba officinalisin Populations Supporting Colonies of an EndangeredMaculineaButterfly

Abstract

The loss of genetic variation in small populations through drift and inbreeding is thought to decrease fitness and population viability. In order to evaluate the suitability of small Sanguisorba officinalis populations for the long‐term conservation of an endangered Maculinea butterfly species, we investigated the plant's genetic population structure using amplified fragment length polymorphism (AFLP) and measured life‐history traits related to reproduction. Genetic distances between populations were low (mean $$F_{\mathrm{ST}\,}=0.008$$) and not correlated with geographic distances, indicating that substantial gene flow compensates for the effects of genetic drift. Analysis of molecular variance indicated the absence of genetic differentiation among different habitat types and low differentiation among populations. High outcrossing rates ($$t_{\mathrm{m}\,}=0.856$$ and $$t_{\mathrm{m}\,}=0.972$$) obtained in two populations suggest that gene flow is promoted by the mating system. Populations differed in the level of intrapopulation genetic variation. These differences were not related to habitat type, population size, or plant density. Mean seed mass and the percentage of germination decreased in small and low‐density populations. However, reduced fitness was not related to lower levels of genetic variation. Thus, the observed fitness decline was presumably due to lower habitat quality associated with small populations and low plant densities. The relevance of the results for the conservation of Maculinea butterflies is discussed.