View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by idUS. Depósito de Investigación Universidad de Sevilla 58 INFORMATORE BOTANICO ITALIANO , 44 SUPPL. 2, 2012 Atti Riunione Scientifica Sezione Piemonte - Valle d’Aosta Extreme phylogeography in Carex (Cyperaceae) T. VILLAVERDE, S. MARTÍN-BRAVO, M. ESCUDERO and M. LUCEÑO RIASSUNTO - Filogeografia di estremità di areale in Carex (Cyperaceae) - Le disgiunzioni negli areali di distribuzione dei taxa hanno suscitato l’interesse dei naturalisti sin dall’inizio del XIX secolo. Sono note solo trenta specie aventi distribu- zione bipolare e Carex risulta il genere con il maggior numero di specie bipolari. Una disciplina emergente, la filogeogra- fia, dovrebbe essere usata per testare le ipotesi sulle specie bipolari poiché tenta di spiegare le cause e i processi di evolu- zione relativi alla distribuzione delle specie e alle loro relazioni genetiche. Sono proposte diverse ipotesi per spiegare le dis- giunzioni bipolari: vicarianza, parallelismo, convergenza, dispersione a lunga distanza e spostamento a balzi sui rilievi. Key words: bipolar disjunctions, Carex, long distance dispersal, mountain hopping, parallelism, phylogeography, vicariance INTRODUCTION DARWIN committed two chapters of The Origin of these hypotheses without even knowing the existence the Species (1872) to explain the past and present dis- of the genetic material. tribution of the species. He stated that patterns of Phylogeography is a rising discipline that tries to species distribution may often be seen as clear foot- understand the reasons for the distribution of species steps of their evolution and diversification. Thus, and closely related genetic lineages, over time and the present-day taxa distribution may be frequently evolutionary processes involved (A VISE et al. , 1987; explained by a combination of historical events (cli- AVISE, 2000). This discipline emerged in a multidis- matic oscillations like aridifications or glaciations; ciplinary context and it integrates methods and con- geological movements like plate tectonics or oroge- cepts from population genetics (microevolution) and nies) and evolutionary processes (extinction, vicari- from systematics (macroevolution). ance, dispersal...). Bipolar biogeography is still the focus of numerous One of the most fascinating distribution patterns is studies after Darwin’s first approach based on organ- range disjunction. The largest and most challenging ism migrations (D U RIETZ, 1940; W ILSON, 1986; disjunction for biologists, the bipolar distribution, MOORE, C HATER , 1971; M OORE, 1972; S MITH, already captivated HUMBOLDT (1817) and DARWIN 1986; BALL, 1990 ). Researchers have proposed dif- (1859) who realized the existence of common plant ferent hypotheses to unravel the evolutionary history species in the flora of remotely distant areas (Tierra of bipolar taxa based on molecular and morphologi- del Fuego in the southern hemisphere and Northern cal data (E SCUDERO et al., 2010; P OPP et al., 2011). Europe/North America in the northern). D ARWIN The objective of this work is to briefly review the (1872) tried to explain this disjunction as a forced hypotheses suggested to explain bipolar disjunctions migration of species due to climate change. During and how to test them with molecular techniques. glacial periods, the advance of the ice-sheet in the northern hemisphere might have pushed arctic species towards lower latitudes; then, a remigration BIPOLAR DISTRIBUTIONS IN CAREX would have occurred on the returning warmth, since MOORE, CHATER (1971) termed bipolar species fol- those lowland areas are too warm for their existence. lowing a single and simple criterion: such species Some species might have found a refugium in moun- must reach latitudes as high as the European Arctic tain summits in southern latitudes in stead of mov- or Alaska (c. 55º N. lat.) in the northern hemisphere ing northward. DARWIN (1859) then thought that and the Straight of Magellan (c. 52º S. lat.) in the there were few species identically the same in both southern hemisphere, regardless of their occurrences hemispheres and on the mountains of intermediate elsewhere. Under this criterion, they pointed 30 tropical regions, whose mutual relations will not species belonging to 12 families (Tab. 1) and 23 gen- have been much disturbed. Admirably, he stated all era, 6 of them (20%) corresponding to the genus Atti Riunione Scientifica Sezione Piemonte - Valle d’Aosta 59 Carex L. (Cyperaceae ). Although Poaceae family has 8 HYPOTHESES TO TEST bipolar species, they are belonging to three different Once the taxonomy of the bipolar species has been genera (Phleum , Poa and Deschampsia ). Then, Carex clearly solved, it is possible to study their biogeogra- is the genus with more bipolar species. Why such a phy and evolutionary relationships. The geographi- striking pattern is so commonly found within Carex ? cal separation found in bipolar species might be con- This is not only the largest genus within the sidered as a major factor disrupting the pattern of Cyperaceae family, with more than 2.000 species gene flow. If genetic isolation allows northern and (K ÜKENTHAL, 1909) distributed across all floristic southern populations to diverge separately, it may regions (R EZNICEK, 1990), but also the most diverse lead to the accumulation of molecular and morpho- angiosperm genus of the northern temperate zone logical differences to clearly distinguish them. (E SCUDERO et al., 2012). It contains many cold- Different degrees of differentiation may account for adapted species that are eligible to have reached different hypotheses. extreme latitudes in both hemispheres and, therefore, the bipolar distribution. Amphitropical species of lower latitudes might not be considered as bipolar VICARIANCE, PARALLELISM AND CONVERGENCE because their environmental and biological histories Molecular differences between Northern and are likely to separate them from the arctic-alpine Southern Hemisphere populations might be due to flora when investigating the factors involved in the their dissimilar evolution. Populations might have patterns of their distributions (R AVEN , 1963). rested genetically isolated or fragmented, allowing a distinct molecular divergence but not a morphologi- cal one. TABLE 1 To reject vicariance hypothesis, estimation of diver- Number of bipolar species in vascular plants families gence times may help to test the congruence between (M OORE, C HATER , 1971). phylogenetic splits and ecological requirements. The Numero delle specie bipolari nell’ambito delle famiglie di relative age of this disjunction was evaluated through piante vascolari (M OORE , C HATER , 1971). estimation of divergence times and fossil evidences. Family Number Parallelism or convergence hypotheses imply the accumulation of evolutionary steps in the same fash- Lycopodiaceae P. Beauv. ex Mirb. 1 ion in northern and southern populations of distant- Plumbaginaceae Juss. 1 ly related lineages, in this case populations would Gentianaceae Juss. 1 belong to polyphyletic groups. Therefore, to reject Scrophulariaceae Juss. 1 these hypotheses, extreme edges populations must be Juncaginaceae Rich. 1 shown as together monophyletic. Hymenophyllaceae Mart. 2 Polygonaceae Juss. 2 DIRECT LONG DISTANCE DISPERSAL Ranunculaceae Juss. 2 If there are no observed molecular differences Plantaginaceae Juss. 2 between populations, it might be possible to consid- Caryophyllaceae Juss. 3 er a long distance dispersal hypothesis, occurred in Cyperaceae Juss. 6 recent times. To reject this hypothesis, populations at Poaceae Barnhart 8 the extremes of the distribution must belong to ancient monophyletic divergent groups. ESCUDERO et al. (2010) sampled five of the six bipo- lar Carex species (C. arctogena was not included) for Carex is divided in four sub-genera based on morpho- a molecular approach and suggested long-distant dis- logical and molecular data (S TARR , F ORD , 2009). persal, sensu lato, as the most plausible cause of bipo- Three of them have at least one bipolar species: C. lar disjunction for C. canescens, C. macloviana, C. arctogena H.Sm. and C. microglochin Wahlenb. in magellanica and C. maritima. Although alternative subgenus Psyllophora (Degl.) Peterm .; C. canescens L., dispersal hypotheses (e.g. direct long-distant disper- C. macloviana D’Urv. and C. maritima Gunn. in sub- sal) could not be tested due to their sampling genus Vignea (P. Beauv. ex Lestib.f.) Peterm.; C. mag- mrthod, genealogical relationships of chloroplast ellanica Lam. in subgenus Carex L. All these species haplotypes indicated a southwards direction of dis- are present in Tierra del Fuego (Patagonia, Argentina) persal for C. canescens, C. macloviana and C. magel- and in arctic-alpine areas of Eurasia and North lanica (E SCUDERO et al., 2010). America. Carex canescens is also present in Australia. A detailed taxonomic study of each bipolar species MOUNTAIN HOPPING encompassing populations across its range should be The mountain-hopping hypothesis (B ALL, 1990) mandatory before further steps towards elucidating relies on the idea that species have progressively the origin of such disjunctions. For example, some migrated from one mountain chain to the next (as populations of C. microglochin in South America were stepping-stones) through the low latitude regions to found to belong to a different species, C. camp- achieve such distribution (M OORE, C HATER , 1971; toglochin (W HEELER , G UAGLIANONE , 2003). VOLLAN et al., 2006).