59
In southern South America, the greatest registered glaciation occurred in the
Early Pleistocene, at about 1.2–0.7 My BP (Kodama et al. 1986), with a maximum
expansion of ice in extra-Andean Patagonia (Flint and Fidalgo 1964). Last glacial
maximum occurred about 20,000 years BP (Porter 1981), and the glacier complex
that developed over the Andes was largely confined to the mountains in the region
north of 41° S (i.e. the distribution range of raulí), both in Chile and Argentina
(Glasser et al. 2008). The scarceness and discontinuity of paleoecological records in
Patagonia (Iglesias et al. 2014), and the inability to distinguish between tree species
with similar pollen morphology (Heusser 1984), complicate detailed reconstructions of past species distributions. In this sense, intraspecific molecular phylogeographies introduced a powerful tool to make inferences about the location of putative
refugia (Petit et al. 1997) by studying patterns of genetic variation in a geographical
context through gene trees.
In long-leaved species, like trees, the current genetic structure can still be
imprinted by postglacial migration (Newton et al. 1999). Since migration occurs via
seeds, maternal inherited plastids are the most suitable markers to describe past
recolonization routes, in a way unaffected by posterior pollen movements (Petit
et al. 2003). The low mutation rates of the chloroplast genome (i.e. about 10
−9
substitutions/site/year; Clegg et al. 1991), together with its uniparental inheritance (i.e.
reduced gene flow), promote that differences in the chloroplast sequence can persist
allowing for population differentiation and the reconstruction of post-glacial migration routes. The predictions indicate that populations surviving in or near refugia
should be highly divergent because of prolonged isolation and that intraspecific
diversity should decline away from refugia because of successive founder events
(Petit et al. 2003).
In order to unravel the evolutionary processes undergone by the populations of
N. alpina during and after the glacial period, the intraspecific genetic variation at the
chloroplast DNA level was evaluated (Marchelli et al. 1998; Marchelli and Gallo
2006). Five haplotypes were detected between 26 populations distributed along the
complete natural range in Chile and Argentina (Fig. 3.3a). One of the main features
of this phylogeographic study was the confirmation of the location of glacial refugia
along the Coastal Range, as suggested by palynological records (Villagran 1991)
evidenced by the presence of exclusive haplotypes (Fig. 3.3a). Moreover, Andean
refugia were suggested, and even cryptic refugia located towards the eastern side of
the Andes were proposed after analysing the distribution of haplotypes. The eastern
cryptic refugia were supported later on by ecological niche modelling (Marchelli
et al. 2017) and recently confirmed by pollen records (Moreno et al. 2019). As in
other tree species (e.g. Premoli et al. 2000; Bekessy et al. 2002; Azpilicueta et al.
2009; Mathiasen and Premoli 2010; Soliani et al. 2012), the existence of multiple
refugia in raulí was suggested by the distribution of the cpDNA variation. Also, as
in other Patagonian species (reviewed by Sérsic et al. 2011), phylogeographic
breaks shared by different species indicate a common history and a strong latitudinal division between populations, probably related to the different glaciation patterns (Flint and Fidalgo 1964; Glasser et al. 2008). Contrary to other species where
admixture of colonization routes was detected (e.g. in Nothofagus pumilio; Soliani
3 Raulí (Nothofagus alpina = N. nervosa): The Best Quality Hardwood in Patagonia
In southern South America, the greatest registered glaciation occurred in the
Early Pleistocene, at about 1.2–0.7 My BP (Kodama et al. 1986), with a maximum
expansion of ice in extra-Andean Patagonia (Flint and Fidalgo 1964). Last glacial
maximum occurred about 20,000 years BP (Porter 1981), and the glacier complex
that developed over the Andes was largely confined to the mountains in the region
north of 41° S (i.e. the distribution range of raulí), both in Chile and Argentina
(Glasser et al. 2008). The scarceness and discontinuity of paleoecological records in
Patagonia (Iglesias et al. 2014), and the inability to distinguish between tree species
with similar pollen morphology (Heusser 1984), complicate detailed reconstructions of past species distributions. In this sense, intraspecific molecular phylogeographies introduced a powerful tool to make inferences about the location of putative
refugia (Petit et al. 1997) by studying patterns of genetic variation in a geographical
context through gene trees.
In long-leaved species, like trees, the current genetic structure can still be
imprinted by postglacial migration (Newton et al. 1999). Since migration occurs via
seeds, maternal inherited plastids are the most suitable markers to describe past
recolonization routes, in a way unaffected by posterior pollen movements (Petit
et al. 2003). The low mutation rates of the chloroplast genome (i.e. about 10
−9
substitutions/site/year; Clegg et al. 1991), together with its uniparental inheritance (i.e.
reduced gene flow), promote that differences in the chloroplast sequence can persist
allowing for population differentiation and the reconstruction of post-glacial migration routes. The predictions indicate that populations surviving in or near refugia
should be highly divergent because of prolonged isolation and that intraspecific
diversity should decline away from refugia because of successive founder events
(Petit et al. 2003).
In order to unravel the evolutionary processes undergone by the populations of
N. alpina during and after the glacial period, the intraspecific genetic variation at the
chloroplast DNA level was evaluated (Marchelli et al. 1998; Marchelli and Gallo
2006). Five haplotypes were detected between 26 populations distributed along the
complete natural range in Chile and Argentina (Fig. 3.3a). One of the main features
of this phylogeographic study was the confirmation of the location of glacial refugia
along the Coastal Range, as suggested by palynological records (Villagran 1991)
evidenced by the presence of exclusive haplotypes (Fig. 3.3a). Moreover, Andean
refugia were suggested, and even cryptic refugia located towards the eastern side of
the Andes were proposed after analysing the distribution of haplotypes. The eastern
cryptic refugia were supported later on by ecological niche modelling (Marchelli
et al. 2017) and recently confirmed by pollen records (Moreno et al. 2019). As in
other tree species (e.g. Premoli et al. 2000; Bekessy et al. 2002; Azpilicueta et al.
2009; Mathiasen and Premoli 2010; Soliani et al. 2012), the existence of multiple
refugia in raulí was suggested by the distribution of the cpDNA variation. Also, as
in other Patagonian species (reviewed by Sérsic et al. 2011), phylogeographic
breaks shared by different species indicate a common history and a strong latitudinal division between populations, probably related to the different glaciation patterns (Flint and Fidalgo 1964; Glasser et al. 2008). Contrary to other species where
admixture of colonization routes was detected (e.g. in Nothofagus pumilio; Soliani
3 Raulí (Nothofagus alpina = N. nervosa): The Best Quality Hardwood in Patagonia