Are hermaphrodites better adapted to the colonization process in trioecious populations of Salix myrsinifolia?

In trioecious plant populations, the role of hermaphroditism is often uncertain. We investigated the advantages of hermaphroditism in the dioecious shrub Salix myrsinifolia. The sex ratio of 30 S. myrsinifolia populations in northeastern Poland (secondary range) and Lithuania (primary range) was investigated in 2010-2011. Measures of reproductive (number of catkins, number of flowers in catkins) and vegetative traits (height, diameter, number of shoots, vitality) were taken and compared among sexual morphs. In two populations, measurements collected 14 years prior on marked individuals were used to determine the rate of changes in height, crown diameter and survivorship rates. We found trioecy mostly in the secondary part of the range with an average share of hermaphrodites reaching 21% in the trioecious populations. The sex ratio varied between populations, but tended mostly towards female domination. Several traits differed significantly among sexes. The characteristics of hermaphrodites were often intermediate between males and females and provided no evidence for the higher competitive abilities of hermaphrodites. We concluded that the possible gain of hermaphroditism in the colonization process is restricted to reproduction. We consider hermaphroditism in S. myrsinifolia as an equilibrium between the allocation of resources for growth and reproduction in unstable conditions on the margins of the range.