The effect of different glaciation patterns over the current genetic structure of the southern beech Nothofagus antarctica

Abstract

Different regional patterns of glaciation are expected to have brought about a differential effect on the present genetic structure of natural tree populations in the temperate regions. The aim of the present study is to test this hypothesis in Nothofagus antarctica, a key tree species of the temperate forests of southern South America. An almost continuous ice layer characterized the region of the Andes south of 41 degrees S, while towards northern latitudes the pattern was more fragmented. Therefore, a higher chance for the location of larger or more numerous glacial refuges in the north of the Argentinean range, leads us to predict a higher genetic diversity in this region. Twelve natural populations of N. antarctica were sampled along the northern half of its Argentinean range, including six above 41 degrees S and six below that latitude. Sampled populations were genetically characterized through cpDNA and isozyme gene markers. Both groups of populations were compared by means of several diversity and differentiation parameters. A genetic structure analysis was conducted with isozyme data through clustering and Bayesian approaches. Based on three polymorphic chloroplast regions, only two haplotypes were distinguished, one corresponding to the nine northernmost sampled populations and the other to the two southernmost ones. Only the population located between those two groups resulted polymorphic. AMOVA analyses also revealed a latitudinal genetic structure for the populations surveyed, and higher levels of genetic variation were recognized in the northern populations.

Out in the cold: genetic variation of Nothofagus pumilio (Nothofagaceae) provides evidence for latitudinally distinct evolutionary histories in austral South America

“…In contrast, two genetically distinct groups of populations by means of PCR‐RFLP of cpDNA markers on 12 populations, and thus a reduced portion of the range of the widespread Nothofagus antarctica , was interpreted as a long lasting isolation in at least two different glacial refuges north and south c . 43°S (Pastorino et al. 2009).…”

“…Also, other genetic studies including isozymes and/or PCR‐RFLP chloroplast DNA (cpDNA) have provided evidence of the multiple refugia hypothesis (Marchelli & Gallo 2006; Azpilicueta et al. 2009; Pastorino et al. 2009).…”

Variación genética en Nothofagus (subgénero Nothofagus).

“…Otra divergencia antigua de unos 20 Ma fue encontrada más hacia el norte a los 40° S. Similares divergencias en regiones del ADNc analizadas mediante RFLP-PCR fueron reportadas en N. nervosa (Phil.) Krasser (raulí) al norte (Marchelli et al 1998) y en N. antarctica y N. pumilio al sur (Pastorino et al 2009, Soliani et al 2011) que fueron interpretadas como producto del aislamiento en distintos refugios glaciarios. Si bien las glaciaciones pueden haber afectado la estructura genética de las poblaciones, se requiere el uso de secuencias de ADN conservado, análisis filogeográficos y la combinación con marcadores nucleares para poder desentrañar la señal contemporánea (i.e., glaciaciones) de la antigua (i.e., rasgos paleogeográficos del paisaje) (Mathiasen y Premoli 2010).…”

The effects of Quaternary glaciations in Patagonia as evidenced by chloroplast DNA phylogeography of Southern beech Nothofagus obliqua

“…The scattered pollen records suggested the persistence of Nothofagus forests mainly at the Pacific Coastal Mountains, in the Central Valley of Chile and along the foothills of the Andes Mountains north of the Lake District (42°S; Heusser 1983Heusser , 1984Villagrán 1991). Moreover, some recent studies based on molecular and biochemical markers in native tree species of the region gave complementary insights into the Quaternary history of South American temperate forests also suggesting multiple and additional refugia (e.g., Marchelli et al 1998;Premoli et al 2000;Bekessy et al 2002;Pastorino and Gallo 2002;Allnut et al 2003;Gallo 2004, 2006;Pastorino et al 2008). After deglaciation, forest expansion occurred synchronously at both sides of the Andes Mountains about 14,000 years BP (Moreno 1997), but the current floristic structure was established only about 3,000 years BP (Villagrán 1991).…”