Growth form and population genetic structure ofAzorella selagoon sub-Antarctic Marion Island

Abstract

AbstractSeven community complexes have been described across sub-Antarctic Marion Island, amongst these fellfield that comprise low plant cover dominated byAzorella selagoHook. f.Azorellais considered a keystone species since it forms nutrient rich environments for microarthropod communities and epiphytic plants. Two distinct growth forms typifyAzorella, namely discrete cushions and continuous mats. Whether these continuous mats normally consist of a single large cushion individual, or whether several individual plants merge, interdigitating to form a continuous area, remains unclear. As such, it is important to obtain some measure ofAzorellagrowth dynamics before embarking on phylogeographic studies. Previous genetic studies indicated that several microarthropod species are significantly substructured across Marion Island, but it remains unclear whether similar subdivisions characterizeAzorella. We used chloroplast sequence data (trnH-psbA) and amplified fragment length polymorphism (AFLP) to investigate these questions. No sequence variation characterized thetrnH-psbA region inAzorellaacross Marion Island. In contrast, the AFLP results indicated that anA. selagomat comprises multiple individuals. We argue that mats can be formed through at least two processes namely fragmentation, where parts of the cushion plant die off creating open areas for the establishment of different individuals and/or high density of interdigitating individuals merging to form the mat. Fragment data further indicated significant substructure forAzorellaacross Marion Island (FST = 0.101,P = 0.01) and we attribute this to past vicariance.