IOPB Symposium: Plant Evolution in Mediterranean Climate Zones

Abstract

Mediterranean biodiversity richness is well recog nized and attributed to a combination of factors (M?dail 8c Qu?zel, 1997). Paleoclimatic changes have been doc umented for the last 5-10 million years including the establishment of a summer drought that represents the onset of a mediterranean climate (Sue, 1984). Two main climatic events have been invoked to explain almost every distribution pattern in the Mediterranean: the Mes sinian salinity crisis (Bocquet & al, 1978) and Pleisto cene glaciations (Hewitt, 1996; Peyron 8c al, 1998). Paleogeological events are determinant factors for diver sity in this region both through their influence on climate changes as well as by creating land-mass connections resulting from tectonic dynamics or sea-level oscillations due to eustatic changes (R?gl & Steininger, 1984). The patchy nature of the current landscape, which hosts a diversity of habitats in a limited space, has also played a role in Mediterranean diversity by providing an arena for differentiation in partially isolated niches and ecotones. Human influence during the Pleistocene could have also contributed to the floristic richness by generating dis turbed habitats suitable for hybridization. However, a negative effect is likely as well, although we lack precise data for estimating rates of species extinction in the Mediterranean due to anthropogenic causes (Greuter, 1994). Many data on Mediterranean plants exist that cover different aspects relating to plant evolution (Thompson, 2005). However, much more basic empirical work is needed to continue to understand how plant groups react ed to the climatic, geologic and ecological changes that occurred along the last few million years within this basin and how those changes affected their diversifica tion and evolution. These standing questions have stimu lated symposia (e.g., Phylogeography in Southern European Refugia, Vairao, Portugal, Mar 2002) as well as ongoing projects, focusing on areas and biotic con nections within the region such as the Tyrrhenian or the westernmost Europe-Africa bridge (Gibraltar). In May 2004, the IXth Meeting of the International Organization of Plant Biosystematists (IOPB) was held in Valencia organized by the authors of this introduction, and sponsored by the Universities of Valencia and Zara goza, the Consejo Superior de Investigaciones Cien t?ficas (CSIC), the Spanish Ministry of Science and Education, and the International Association for Plant Taxonomy (Comes, 2004; Stuessy, 2004; http://www. jardibotanic.org/iopb.html). The topic of the meeting was Plant Evolution in the Mediterranean Climate Zones, and it was addressed through several approaches, which the organizers arranged into the following symposia: bio geography and phylogeography, conservation and genet ic diversity, systematics and phylogeny, ecological fac tors in speciation, speciation models, and comparisons among the Mediterranean areas of the world. There were twelve invited lectures, plus 43 oral communications and some 91 posters. Although all five regions with Medi terranean climate (Australia, California, Cape Region, Chile, Mediterranean Basin) were considered, a majority of the papers were devoted to the Mediterranean Basin itself. A selection of eleven of the papers presented dur ing the meeting is published within this issue of Taxon. The first four papers are mostly devoted to phylo geographic and biogeographic topics. In searching for phylogeographic patterns along the Mediterranean, Kadereit & al. (p. 861) use a spatially simplified system, i.e., species restricted to coastal habitats and thus with linear ranges. They found similarities in the partitioning of genetic diversity across the five coastal species stud ied, including more consistency among Eastern patterns presumably due to a lesser impact of Pleistocene climat ic changes as well as to the occurrence of isolating sea currents in that area. Based on the large amount of data gathered by his team, Petit & al. (p. 877) provide an essay on tree and shrub diversity in the context of cli matic change. They discuss the currently rich genetic diversity of Mediterranean species as product of the bio geographic history of the area, and especially on climat ic changes. Diadema & al. (p. 887) use ITS sequence data, which reveal a geographical structure across the range of a maritime alpine endemic species, together with topography and paleoclimatic data to reconstruct