Seed traits, terminal velocity and germination in sexual diploid and apomictic triploid Hieracium alpinum (Asteraceae): Are apomicts better dispersers?

Abstract

In this study, we examined the effect of seed characteristics (seed weight, seed length, seed width, pappus length and pappus width) and ploidy level on seed terminal velocity and germination in Hieracium alpinum, an arcto-alpine anemochorous species with vicariant diploid sexual and triploid apomictic populations producing diploid and triploid seeds, respectively. Importantly, triploids occupy a considerably larger range than diploids, suggesting that they have better colonization abilities putatively mediated by increased dispersal potential of the former. In total, 970 seeds collected from 228 mother plants from 30 populations across the distribution range were analysed. Diploid and triploid seeds did not differ significantly in most morphological traits, except for triploid seeds being wider. Terminal velocity was greater in diploid seeds compared to triploid seeds. This difference was not significant if a nested design (ploidy, population, mother plant) was used but significant if the population level was not considered, indicating high interpopulation variation in this trait. Terminal velocity was positively and significantly correlated with seed mass, length and width and negatively correlated with pappus length and width. Germination probability was positively associated with seed mass and negatively with ploidy (higher in diploids, compared to triploids). Our results thus indicate partly opposite dispersal-establishment strategies of diploid sexual and triploid apomictic biotypes of H. alpinum. One the one hand, the slightly greater values of terminal velocity of diploid seeds might reduce their dispersal potential, but on the other, their significantly greater germination rates, when compared to triploid seeds are likely to allow their more successful establisment. To sum up, our result do not support the hypothesis of heavier seeds with higher terminal velocity and higher germination rates in autopolyploids compared to their diploid progenitors.