Quantitative genetics of life-history and morphology in a rare plant, Senecio integrifolius

Abstract

A paternal half-sib analysis was performed to estimate the narrow-sense heritability for 35 morphological and life-history characters in two populations of Senecio integrifolius, a rare and threatened plant in Sweden. The two populations differed greatly in size, the small one consisting of separate patches and the large one having a more or less continuous distribution. In addition to significant population differences in the mean of 26 characters, we found slightly higher heritabilities in the small and patchy population (average 0.49) than in the large and continuous population (average 0.43). Overall, the small population displayed significant additive genetic variation for a larger number of characters than the large population (19 vs. 14). Paternal (genetic) effects were consistent in two different environments; the ranking of sire means was similar despite a drastic reduction in light intensity, and few characters had a significant sire × environment interaction. Genetic correlations were also found between different characters measured in the same environment, although most of these were in the 'favourable' direction. Population differences in genetic parameters may reflect contrasting selection regimens at the two sites, although genetic drift may also be important. That more genetic variability was detected in the small population where plants occur in small and isolated patches indicates that the spatial structure has great effects on the retention of heritable variation, and that demographic and environmental factors are more important in the long-term survival of S. integrifolius. This is the first study that relates quantitative genetic variation to population size in a rare and threatened plant.