1069 Conservation Biology, Pages 1069–1078 Volume 13, No. 5, October 1999 Genetic Diversity, Population Size, and Fitness in Central and Peripheral Populations of a Rare Plant Lychnis viscaria ANTTI LAMMI,* PIRKKO SIIKAMÄKI, AND KAISA MUSTAJÄRVI Department of Biological and Environmental Science, University of Jyväskylä, Konnevesi Research Station, P.O. Box 35, 40351 Jyväskylä, Finland Abstract: Genetic diversity is expected to decrease in small and isolated populations as a consequence of bot- tlenecks, founder effects, inbreeding, and genetic drift. The genetics and ecology of the rare perennial plant Lychnis viscaria (Caryophyllaceae) were studied in both peripheral and central populations within its distri- bution area. We aimed to investigate the overall level of genetic diversity, its spatial distribution, and possible differences between peripheral and central populations by examining several populations with electrophore- sis. Our results showed that the level of genetic diversity varied substantially among populations (H exp = 0.000–0.116) and that the total level of genetic diversity (mean H exp = 0.056) was low compared to that of other species with similar life-history attributes. The peripheral populations of L. viscaria had less genetic vari- ation (mean H exp = 0.034) than the central ones (0.114). Analysis of genetic structure suggested limited gene flow (mean F ST = 0.430) and high differentiation among populations, emphasizing the role of genetic drift ( N e m = 0.33). Isolation was even higher than expected based on the physical distance among populations. We also focused on the association between population size and genetic diversity and possible effects on fit- ness of these factors. Population size was positively correlated with genetic diversity. Population size and ge- netic diversity, however, were not associated with fitness components such as germination rate, seedling mass, or seed yield. There were no differences in the measured fitness components between peripheral and central populations. Even though small and peripheral populations had lower levels of genetic variation, they were as viable as larger populations, which emphasizes their potential value for conservation. Diversidad Genética, Tamaño Poblacional y Condición de Poblaciones Periféricas de la Planta Rara Lychnis viscaria Resumen: Se espera que la diversidad genética disminuya en poblaciones pequeñas y aisladas como con- secuencia de cuellos de botella, efecto fundador, intracruza y deriva génica. La genética y ecología de la planta perenne rara Lychnis viscaria (Caryophyllaceae) fueron estudiadas tanto en poblaciones periféricas como centrales dentro de su área de distribución. Investigamos el nivel total de diversidad genética, su dis- tribución espacial y posibles diferencias entre poblaciones. Nuestros resultados muestran que el nivel de di- versidad genética varía sustancialmente entre poblaciones ( H exp = 0.000–0.116) y que el nivel de diversidad genética total (media H exp = 0.056) fue bajo comparado con otras especies con atributos en la historia de vida similares. Las poblaciones periféricas de L. viscaria tienen una variación genética menor (media H exp = 0.034) que las centrales (0.114). El análisis de la estructura genética sugiere un flujo genético limitado (me- dia F ST = 0.430) y alta diferenciación entre poblaciones, haciendo énfasis en el papel de la deriva Génica ( N e m = 0.33). El aislamiento fue aún mayor que el esperado en base a la distancia física entre poblaciones. Adicionalmente, nos enfocamos en la asociación entre tamaño poblacional y diversidad genética y los posi- bles efectos de estos factores sobre la condición de las poblaciones. El tamaño poblacional estuvo positiva- *Current address: South West Finland Regional Environment Centre, P.O. Box 47, 20801 Turku, Finland, email antti. lammi@vyh.fi Paper submitted June 1, 1998; revised manuscript accepted January 13, 1999.