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

Abstract

Climatic oscillations during the Quaternary strongly affected the distribution of warm-temperate tree species, which experienced local restrictions into ice-free areas and posterior expansions. To evaluate the impact of these range movements on the genetic structure of populations, we performed a phylogeographical analysis of the species Nothofagus obliqua with chloroplast DNA markers. A total of 27 populations covering the whole natural distribution range were analyzed using polymerase chain reaction-restriction fragment length polymorphism. Diversity (h T , h S ), allelic richness (r g ), and differentiation among populations for unordered (G ST ) and ordered alleles (N ST ) were calculated. The relationships among haplotypes were evaluated by the construction of a minimum spanning network. The spatial distribution of the genetic variation was analyzed through a Mantel test and with a nested analysis of molecular variance to differentiate between geographic regions. The screening of 11 non-coding regions allowed the identification of 14 haplotypes. A high genetic differentiation was detected (N ST =0.875 and G ST = 0.824) with the existence of phylogeographic structure (p< 0.05). The distribution of the genetic variation was partially explained by the topography of the region when the populations were divided longitudinally into Coastal Mountains, Central Valley, and Andes Mountains ( RT = 0.093, p=0.001). In agreement with pollen records, our results support the hypothesis of Coastal refuges since the region harbors high diversity together with older and private haplotypes. Long-lasting persistence of some Coastal populations without contribution to recolonization is proposed. Additional refuges are also postulated along the Andes and Longitudinal Valley. Survival in multiple glacial refuges is discussed together with the possible migratory routes.

Robles in Lagunas de Epulauquen, Argentina: previous and recent evidence of their distinctive character

“…One of these haplotypes was found in two Chilean populations from similar latitudes (Altos de Vilches at 35°34′ S and Embalse Bulilleo at 36°22′ S), supporting the connection postulated by Markgraf (1987). The other cpDNA haplotype found at Lagunas de Epulauquen was fixed in all the Argentinean populations of N. obliqua growing north of Lanin volcano (39°30′ S) (Azpilicueta et al 2009). …”

“…Accordingly, species-specific isozyme markers revealed a very high proportion of N. alpina alleles in the robles of Lagunas de Epulauquen. Adh locus (alcohol dehydrogenase, E.C.1.1.1.1) showed the highest frequency for Adh-2 allele -up to then considered as species-specific for N. alpina (Gallo et al 1997;Marchelli and Gallo 2000) -suggesting the hybrid origin of trees in this population (Azpilicueta and Gallo 2009). This allele had a frequency of 25%, in contrast with frequencies of <14% in sympatric populations where hybrids are more likely to occur (Azpilicueta and Gallo 2009).…”

“…Adh locus (alcohol dehydrogenase, E.C.1.1.1.1) showed the highest frequency for Adh-2 allele -up to then considered as species-specific for N. alpina (Gallo et al 1997;Marchelli and Gallo 2000) -suggesting the hybrid origin of trees in this population (Azpilicueta and Gallo 2009). This allele had a frequency of 25%, in contrast with frequencies of <14% in sympatric populations where hybrids are more likely to occur (Azpilicueta and Gallo 2009). This result was unexpected given the absence of N. alpina New evidence supporting the distinctiveness of robles from Lagunas de Epulauquen Biochemical markers: isozymes As mentioned, N. obliqua also potentially hybridise with N. macrocarpa (Vázquez and Rodríguez 1999).…”

“…Accordingly, many species could have survived in multiple glacial refugia (Markgraf et al 1995;Veit and Garleff 1995) and gone on to recolonise the area in post-glacial times. Genetic studies in N. obliqua forests (Azpilicueta et al 2009) and other South American temperate tree species (e.g. Marchelli et al 1998;Premoli et al 2000;Bekessy et al 2002;Pastorino and Gallo 2002;Allnut et al 2003;Azpilicueta et al 2009;Marchelli et al 2010) give support to this multiple refugia hypothesis.…”

“…Furthermore, the low mutation rate of the chloroplast (Wolfe et al 1987), which determines its highly conservative nature, helps in the inference of glacial refugia and post-glacial migration routes of glaciation-affected species. Azpilicueta et al (2009) identified two different cpDNA haplotypes in the Lagunas de Epulauquen population. One of these haplotypes was found in two Chilean populations from similar latitudes (Altos de Vilches at 35°34′ S and Embalse Bulilleo at 36°22′ S), supporting the connection postulated by Markgraf (1987).…”