22 research outputs found
Colonization of an empty island:how does a plant with a plastic gender system respond?
<i>Honckenya peploides</i> 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. <i>H. peploides</i> 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 <i>H. peploides</i> is given
Spatial genetic structure of the sea sandwort (<i>Honckenya peploides</i>) on Surtsey:an immigrant's journey
Sea sandwort (Honckenya peploides) was one of the first plants to successfully colonize and
reproduce on the volcanic island Surtsey, formed in 1963 off the southern
coast of Iceland. Using amplified fragment length polymorphic (AFLP) markers,
we examined levels of genetic variation and differentiation among
populations of H. peploides on Surtsey in relation to populations on the nearby island
Heimaey and from the southern coast of Iceland. Selected populations from
Denmark and Greenland were used for comparison. In addition, we tested
whether the effects of isolation by distance could be seen in the Surtsey
populations. Using two primer combinations, we obtained 173 AFLP markers
from a total of 347 plant samples. The resulting binary matrix was then
analysed statistically. The main results include the following: (i) Surtsey had
the highest proportion of polymorphic markers as well as a comparatively
high genetic diversity (55.5% proportion of polymorphic loci, PLP; 0.1974 HE) and Denmark the lowest
(31.8% PLP; 0.132 HE), indicating rapid expansion during an early
stage of population establishment on Surtsey and/or multiple origins of
immigrants; (ii) the total genetic differentiation (FST) among Surtsey
(0.0714) and Heimaey (0.055) populations was less than half of that found
among the mainland populations in Iceland (0.1747), indicating substantial
gene flow on the islands; (iii) most of the genetic variation (79%, p < 0.001) was found within localities, possibly due to the
outcrossing and subdioecious nature of the species; (iv) a significant genetic
distance was found within Surtsey, among sites, and this appeared to
correlate with the age of plant colonization; and (v) the genetic structure
analysis indicated multiple colonization episodes on Surtsey, whereby H. peploides most
likely immigrated from the nearby island of Heimaey and directly from the
southern coast of Iceland