Presentation on theme: "Evolution and biogeography of Pleurophyllum (Asteraceae), a small genus of megaherbs endemic to the Subantarctic Islands Steven J. Wagstaff 1, Ilse Breitwieser."— Presentation transcript:
Evolution and biogeography of Pleurophyllum (Asteraceae), a small genus of megaherbs endemic to the Subantarctic Islands Steven J. Wagstaff 1, Ilse Breitwieser 1, & Motomi Ito 2 1 Allan Herbarium, Landcare Research, Lincoln 7640, New Zealand. 2 Department of Systems Sciences (Biology), University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan.
Premise of the study : The abundance of fossils in Antarctica suggests this continent was a center of diversification and corridor for migration for many austral plant groups until the late Tertiary and may have played a pivotal role in shaping plant distributions in the Southern Hemisphere. While the Antarctic flora was largely erased by glaciation during the Pleistocene, at least some Antarctic plant species found refuge on the subantarctic islands. BARREDA, V. D., L. PALAZZESI, M. C. TELLERIA, L. KATINAS, J. V. CRISCI, K. BREMER, M. G. PASSALIA, R. CORSOLINI, R. R. BRIZUELA, AND F. BECHIS. 2010. Eocene Patagonia Fossils of the Daisy Family. Science 329: 1621-. Distribution of Pleurophyllum. The insert shows a polar view of Antarctica with the relative positions of the Southern Hemisphere continents Microfossil localities of Asteraceae are indicated with +, and a recent macrofossil locality with *. Habitat and morphology of Pleurophyllum. A. Panoramic view of Campbell Island. B. P. speciosum habit associated with Bulbinella rossii. C. P. speciosum close-up of the capitula. D. P. hookerii habit. E. P. hookerii close-up of the capitula. F. P. criniferum habit. Photo A by Colin Meurk and B– F by David Norton.
Methods : We used independent and combined analysis of ITS, ETS, trnK and trnL sequences to infer phylogenetic relationships in Pleurophyllum, a small genus of three species that are endemic to the subantarctic islands of Australia and New Zealand. Bayesian approaches were used to infer ancestral distribution patterns and divergence times. Topological constraints were applied to well-supported clades and posterior probabilities of the ancestral character states were estimated at each of these node Based upon fossil evidence we applied an exponential prior distribution with an offset of 47.5 million years, and a mean of 6. These settings give a median probability distribution around 51 million years ago (Ma) that tails off with 95% probability to 65 Ma for the most recent common ancestor (mrca) of Dasyphyllum diacanthoides and the members of Asteroideae.. A uniform prior, with a lower bound of 1.0 and an upper bound of 3.0, was placed on the split between the Chatham Island endemics, Olearia chathamica and O. semidentata.
Key results : Pleurophyllum survived episodes of Pleistocene glaciation in the subantarctic islands, and its sisters dispersed northward in response to glacial advance. A single tree −ln= 15179.1062 recovered from a maximum likelihood analysis of the combined data partitions. Bootstrap values (bs) > 50% are provided above the branches. Clades labelled A–C were well supported by the combined data analysis. A proposed reconstruction of ancestral distribution patterns is illustrated by the inset. Posterior probabilities (pp) for the ancestral state reconstruction are shown above the nodes. Equivocal reconstructions are shown with hatched lines. Aus = Australian, SA= South American, NZ = New Zealand distribution. Bayesian chronogram illustrating divergence times. Posterior probabilities (pp) > 0.95 are provided above the branches. The crown radiation in Pleurophyllum occurred at the boundary between the Pliocene and Pleistocene about 4.1 million years ago. Comparison of strict consensus parsimony trees recovered from independent analyses of ITS, ETS, trnK and trnL. Bootstrap values > 50% are provided above the branches. Conflicting relationships were not well supported, and the tree topologies are largely congruent. Summary statistics and the results from Incongruence Length Difference (ILD) tests are presented in Table 1. Clades labelled A–C are discussed in the text.
Conclusions : The distinctive flora of the subantarctic islands include some of the last remnants of a once diverse Antarctic flora. These plants may still retain distinctive features of their ancestors. Studies of endemic plants such as Pleurophyllum are key to resolving this puzzle. WAGSTAFF, S. J., I. BREITWIESER, AND M. ITO. 2011. Evolution and biogeography of Pleurophyllum (Astereae, Asteraceae), a small genus of megaherbs endemic to the subantarctic islands. Am. J. Bot. 98: 62-75. http://www.amjbot.org/content/98/1/62.abstracthttp://www.amjbot.org/content/98/1/62.abstract
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