Abstract
Abstract. 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.
Highlights
On the 14th of November 1963, just 30 km off the southern coast of Iceland, the island of Surtsey was born
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
The highest genetic diversity found in the present study was from Surtsey
Summary
On the 14th of November 1963, just 30 km off the southern coast of Iceland, the island of Surtsey was born. During the first survey of the island on 21 May 1964, plant seeds were already documented having washed up on shore (Einarsson, 1965). It seems almost certain that the first plants to arrive on the island grew from seeds drifting with sea currents to the island, as seedlings of the first colonizers, i.e. Cakile edentula, Leymus arenarius, Honckenya peploides and Mertensia maritima, were found growing at the high tide line (Einarsson, 1968; Fridriksson and Johnsen, 1968; Fridriksson, 1970). The recent geologic origin and meticulously welldocumented history of colonization on Surtsey provide an unprecedented opportunity to study the birth, coming of age and decline of a small, relatively isolated oceanic volcanic island ecosystem by natural means, devoid of all human influence. The study species, Honckenya peploides, was first recorded on the island in 1967 with 26 individuals
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