REPRODUCTIVE-SYSTEM AND POPULATION-STRUCTURE IN 3 ARCTIC SAXIFRAGA SPECIES

1. Manipulative field experiments were used to investigate the reproductive system of individuals and populations of Saxifraga cespitosa, S. tenuis and S. cernua in the Abisko area of northern Sweden. 2. Populations of S. cespitosa were gynodioecious. Hermaphrodite individuals showed a high selfing efficiency and low pollen:ovule ratios - consistent with a low outbreeding rate. 3. Saxifraga tenuis was hermaphrodite with some indication of sexual asymmetry. Pollen:ovule ratios were low, as in S. cespitosa, but the ability to set seed by autodeposition was lower in S. tenuis than in S. cespitosa. 4. Saxifraga cernua was androdioecious in the study area, with some populations that contained only female-sterile individuals and other populations with both female-sterile and hermaphrodite individuals. The higher production of bulbils by female-sterile individuals, coupled with self-incompatibility in hermaphrodites, suggests a means by which androdioecy may be maintained in S. cernua, in the absence of differences in male reproductive success between gender classes. 5. Population structure and the hierarchical partitioning of morphometric diversity within and between populations and individuals in the three species were investigated using image analysis of leaf shape. Although all three species showed significant inter-population differentiation, the morphometric distances between populations were not related to the geographic distances between populations. The majority of the total diversity in leaf shape was accounted for by inter-population differentiation in all three species, with <1% of the diversity due to variation within individuals. 6. The mosaic pattern of variation in the three saxifrages is consistent with a scenario of localized founder effect and may still reflect patterns of recruitment after the deglaciation of the study area c. 8200 BP.