North and South Dispersals and Climatic Change in the Biogegraphic History of Chuquiraga (Asteraceae, Barnadesioideae) in the Andes

EZCURRA, C.; VIDAL-RUSSELL, R.

San Isidro, Buenos Aires, Argentina

Congreso; 7 Reunión de Cladística y Biogeografía; 2007

Instituto de Botánica Darwinion

The Andes have served both as a bridge and as a barrier in the evolution of the flora of South America by isolating organisms on either side of the mountains and by producing new high-elevation habitats that could be colonized. Chuquiraga is a genus of evergreen shrubs distributed from Colombia to Chile and Argentina that is especially diversified in the Andes and in the deserts of southern South America (Ezcurra, 1985, Ezcura, 2002). In this study, we investigate the biogeographic history of the group by analyzing events of dispersal and vicariance on a phylogeny of Chuquiraga and allied genera of Barnadesioideae constructed with parsimony cladistic analysis of morphological characters. Our goal is to examine the role of Andean orogeny and climatic change in South America in the diversification history of this mostly southern group. To achieve this, we performed dispersal - vicariance analyses (DIVA) (Ronquist, 1997) of (1) a two-state latitudinal distribution character (southern, tropical Andean), and (2) a two-state temperature region character (higher or lower than 20ºC mean annual temperature). Both DIVA analyses optimized the latitudinal and temperature distribution characters of each terminal taxa by using the optimization command and default options settings onto a simplified, fully resolved phylogeny from morphological data (Ezcurra 2002). The analysis of latitudinal distribution suggested an origin of the genus in southern South America (S), and diversification with three major dispersal events (Fig. 1). The first one involves migration from the south into the tropical Andes (T), in the ancestor of the large-headed, hummingbird-pollinated, northern clade, resulting in an important evolutionary radiation in the tropics. The second dispersal would have been into the southern Andes(S) in the ancestor of one of the species nested high within this northern group (T). The third dispersal appears from the south (S) into the tropical Andes (T), in the ancestor of a small clade of Puna species found in a terminal position within the small-headed southern clade. The first dispersal from south to north was probably associated with the major elevation of the tropical High Andes only achieved in late Tertiary (Taylor, 1991), the second dispersal from north to south could be related to the great climatic fluctuations of Pleistocene and Holocene times, and the third dispersal from the south to the Puna was probably associated with the hyper-aridization of Quaternary times (Ortiz Jaureguizar and Cladera 2006). The second analysis suggests an origin of the group in areas comprising cold-temperate regions (C, CW), and an unambiguous origin of Chuquiraga in cold areas (C), with later dispersals to warmer climates (W). These results support an origin of the whole group in cold or temperate areas of the Andes, Patagonia and/or the Pampas, and later dispersals to the warmer hyperarid Pacific and Monte deserts. All these biogeographic reconstructions using DIVA analyses generally point to a southern origin of Chuquiraga and allied genera in the austral region of South America, and later migrations to the northern Tropical Andes as has been previously hypothesized (Ezcurra, 1985; Devore & Stuessy 1995, Gustafsson et al., 2001; Ezcurra, 2002; Funk et al. 2005). These unique dispersals between different latitudes and climatic regions along the Andes that we inferred in Chuquiraga and allied genera show another example of the complex characteristics of the assemblage of the Andean flora, to which several genera of southern origin have contributed, together with the more numerous tropical elements of lower latitudes and the many holarctic elements from the northern hemisphere (Simpson & Todzia, 1990). They also show an important amount of niche conservatism (Wiens and Graham 2005) within this mostly microthermic clade. This characteristic has probably helped not only the Barandesioideae, but also the large Asteraceae family in general, to conquer the mountains and open temperate regions of the whole world from their common high-latitude austral origin.