Relatedness structure in Rhododendron metternichii var. hondoense revealed by microsatellite analysis.

The relatedness structure of Rhododendron metternichii Sieb. et Zucc. var. hondoense Nakai was analysed in a 150 x 70-m quadrat in Hiroshima Prefecture, western Japan. The population of R. metternichii occurred as three subpopulations at the study site (A1-A3). Pairwise relatedness based on microsatellite genotypes at eight loci and Mantel tests revealed a hierarchical structure of relatedness within and among subpopulations: (i) relatedness between individuals within 10 m of one another was significantly positive; (ii) relatedness between individuals in the same subpopulation was significantly positive, but negative between individuals in distant subpopulations; and (iii) relatedness was not significantly different from zero among neighbouring subpopulations. In detail, however, relatedness within each subpopulation was significantly positive in subpopulation A1, relatively weak but significantly positive in subpopulation A2, and not significantly different from zero in subpopulation A3. Relatedness within each subpopulation was inversely related to correlations between interindividual distance and relatedness. The aggregation of related individuals at short distances from one another may lead to decreasing relatedness within subpopulations as a whole. Moreover, negative correlations between interindividual distance and relatedness corresponded to high flowering densities at less than 10-m distance, implying that high flowering densities reduce pollinator foraging distance and lead to stronger genetic structure within subpopulations. Small individuals (< 2.0 m in height) showed stronger genetic structure compared with that of large individuals (> or = 2.0 m in height). The different relatedness structure within and among subpopulations may be caused by various degrees of gene flow affected by distribution patterns of individuals and population density.