Colonization of an empty island: how does a plant with a plastic gender system respond?

Honckenya peploides is the most common plant species on the island of Surtsey. It arrived in 1967 and after a juvenile period of 4 years it produced seeds and had increased its number from below 100 to several millions. Most populations had the individuals distributed in a regular or random pattern, suggesting that intraspecific competition is important. H. peploides has a subdioecious reproductive system consisting of pistillate plants producing capsules, and staminate plants delivering pollen. Some of the latter are in addition producing capsules and are denoted hermaphrodites. Populations at the south coast of Iceland had around equal numbers of pistillate and staminate plants. At Surtsey we found more pistillate plants, probably due to their higher water stress tolerance. We also found a tendency to a higher frequency of hermaphrodite plants with a higher number of seeds per capsule compared to populations at the south coast of Iceland and the nearby island of Heimaey. We suggest that this arises from the time right after the colonization of Surtsey where population size was small and the small generalist pollinators were not able to deposit sufficient pollen on pistillate plants, causing the hermaphrodites to have an advantage by being able to set seed after selfing. The result of this initial advantage of the hermaphrodites in combination with the inheritance of the sexes can still be seen due to the longevity of individuals. A generalized account of the colonization history of H. peploides is given.