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Premise of the Study: Seed banks may increase the effective population size (N-e) of plants as a result of elevated coalescence times for alleles residing in the populations. This has been empirically demonstrated in populations of the annual Arabidopsis thaliana, whereas comparable data for perennial species are currently lacking. We studied the contribution of seed banks to effective sizes of natural populations of the self-incompatible, perennial Arabidopsis lyrata subsp. petraea, a close relative of A. thaliana.

Methods: Fourteen populations of A. lyrata collected throughout the Norwegian distribution range were analyzed using micro-satellite markers.

Key Results: The genetic composition of seed-bank and aboveground cohorts was found to be highly similar, with little genetic differentiation between cohorts in most populations. However, the proportion of private alleles was higher in aboveground than in seed-bank cohorts. The presence of seed banks significantly increased total N-e, but the contribution from seed banks to overall N-e were lower than the contribution from aboveground cohorts in most populations. Estimated historical N-e values, reflecting the effective sizes of populations throughout the history of the species, were considerably higher than estimates of contemporary N-e, reflecting number of reproducing individuals within the past few generations.

Conclusions: The results show that the seed bank contributes to total N-e in the perennial herb A. lyrata. However, the contribution is similar to or lower than that of the above-ground fraction of the population and markedly weaker than that previously documented in the annual A. thaliana.